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Cowl Vents - 4" with a little extra work?

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  • JohnF
    The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks
    Message 1 of 27 , Jan 1, 2012
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      The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.

      Has anyone gone to the effort to slightly modify the dorade box to install 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.

      It's tempting -- the 4" vents are only an inch taller (so I don't think they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).

      I don't see any references to this approach, so am suspecting that there is a hidden 'gotcha !!!'.

      Thanks -
    • Dave Evans
      Just for ideas, we switched to the 3 ABI vents using a spacer of 1/4 starboard on our 34-II: http://images.sailonset.com/DSCN2346x750.jpg
      Message 2 of 27 , Jan 1, 2012
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        Just for ideas, we switched to the 3" ABI vents using a spacer of 1/4" starboard on our 34-II:
        http://images.sailonset.com/DSCN2346x750.jpg


        On 1/1/2012 9:12 AM, JohnF wrote:
         

        The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.

        Has anyone gone to the effort to slightly modify the dorade box to install 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.

        It's tempting -- the 4" vents are only an inch taller (so I don't think they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).

        I don't see any references to this approach, so am suspecting that there is a hidden 'gotcha !!!'.

        Thanks -


      • Ken Jenkins
        John, As a side question, did you have much trouble getting the mounting plate for the Martec vent off? I also have a 34 MkII andI had unscrewed one earlier
        Message 3 of 27 , Jan 1, 2012
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          John,

          As a side question, did you have much trouble getting the mounting plate for the Martec vent off? I also have a 34 MkII andI had unscrewed one earlier this Fall to check hole size, but could not seem to pull out the mounting plate. I thought maybe it had been bedded with an adhesive. Having limited time, I decided to put off really working on the problem.

          Thanks for any insight, Ken

           


          From: Sabresailboat@yahoogroups.com [mailto: Sabresailboat@yahoogroups.com ] On Behalf Of JohnF
          Sent: Sunday, January 01, 2012 6:13 AM
          To: Sabresailboat@yahoogroups.com
          Subject: [SabreSailboat] Cowl Vents - 4" with a little extra work?

           

           

          The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.

          Has anyone gone to the effort to slightly modify the dorade box to install 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.

          It's tempting -- the 4" vents are only an inch taller (so I don't think they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).

          I don't see any references to this approach, so am suspecting that there is a hidden 'gotcha !!!'.

          Thanks -

        • JohnF
          Ken, The old deck plates were bedded, they didn t budge by just yanking on them. I drove a sharp putty knife under the flange all the way around. I used a
          Message 4 of 27 , Jan 1, 2012
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            Ken,

            The old deck plates were bedded, they didn't budge by just yanking on them. I drove a sharp putty knife under the flange all the way around. I used a short pry bar to reach down inside the box in order to get some leverage from underneath the throat of the vent. That seemed to help break the grip of the adhesive. Only one of the deck plates came out whole. The old plastic was very brittle and easily split up with the putty knife and some gentle tapping. It was easier to get out once broken up into pieces.

            Once the deck plate was out, it was easy to scrape off the old adhesive and clean it up with some acetone.

            The first one took about 20 minutes, then the other three took about 20 minutes total once I figured out how to do it!





            --- In Sabresailboat@yahoogroups.com, "Ken Jenkins" <kjenk3@...> wrote:
            >
            > John,
            >
            > As a side question, did you have much trouble getting the mounting plate for
            > the Martec vent off? I also have a 34 MkII andI had unscrewed one earlier
            > this Fall to check hole size, but could not seem to pull out the mounting
            > plate. I thought maybe it had been bedded with an adhesive. Having limited
            > time, I decided to put off really working on the problem.
            >
            > Thanks for any insight, Ken
            >
            >
            >
            > _____
            >
            > From: Sabresailboat@yahoogroups.com [mailto:Sabresailboat@yahoogroups.com]
            > On Behalf Of JohnF
            > Sent: Sunday, January 01, 2012 6:13 AM
            > To: Sabresailboat@yahoogroups.com
            > Subject: [SabreSailboat] Cowl Vents - 4" with a little extra work?
            >
            >
            >
            >
            >
            > The old original Martec cowl vents were removed yesterday on our 1987 34
            > MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it
            > looks like most people have replaced with 3" cowl vents, often requiring a
            > teak or starboard 'pad' to accommodate a smaller deck ring.
            >
            > Has anyone gone to the effort to slightly modify the dorade box to install
            > 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is
            > needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
            >
            > It's tempting -- the 4" vents are only an inch taller (so I don't think they
            > would look out of scale), but have 40% more air flow capacity (based on
            > Vetus catalog).
            >
            > I don't see any references to this approach, so am suspecting that there is
            > a hidden 'gotcha !!!'.
            >
            > Thanks -
            >
          • JOHN CALLIS
            I removed all 4 of my dorade deck plates without damaging them. They were bedded in butyl tape on my 88 S34, and I used a putty knife and pulled up with my
            Message 5 of 27 , Jan 2, 2012
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              I removed all 4 of my dorade deck plates without damaging them.  They were bedded in butyl tape on my 88 S34, and I used a putty knife and pulled up with my hand from the inside.  Maybe John's were installed with a stronger adhesive, but mine pulled out very easily.  I think this is another argument for using butyl tape as a sealant when things may need to be uninstalled in the future.

              John
              S34 MKII


              On Sun, Jan 1, 2012 at 6:21 PM, JohnF wrote:

                 Ken,

              The old deck plates were bedded, they didn't budge by just yanking on them.  I drove a sharp putty knife under the flange all the way around.  I used a short pry bar to reach down inside the box in order to get some leverage from underneath the throat of the vent.  That seemed to help break the grip of the adhesive.   Only one of the deck plates came out whole.  The old plastic was very brittle and easily split up with the putty knife and some gentle tapping.  It was easier to get out once broken up into pieces.

              Once the deck plate was out, it was easy to scrape off the old adhesive and clean it up with some acetone.

              The first one took about 20 minutes,  then the other three took about 20 minutes total once I figured out how to do it!

              --- In Sabresailboat@yahoogroups.com, "Ken Jenkins" <kjenk3@...> wrote:
              >
              > John,
              >
              > As a side question, did you have much trouble getting the mounting plate for
              > the Martec vent off? I also have a 34 MkII andI had unscrewed one earlier
              > this Fall to check hole size, but could not seem to pull out the mounting
              > plate. I thought maybe it had been bedded with an adhesive. Having limited
              > time, I decided to put off really working on the problem.
              >
              > Thanks for any insight, Ken
              >
              >
              >
              >   _____
              >
              > On Behalf Of JohnF
              > Sent: Sunday, January 01, 2012 6:13 AM
              > Subject: [SabreSailboat] Cowl Vents - 4" with a little extra work?
              >
              >
              >
              >
              >
              > The old original Martec cowl vents were removed yesterday on our 1987 34
              > MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it
              > looks like most people have replaced with 3" cowl vents, often requiring a
              > teak or starboard 'pad' to accommodate a smaller deck ring.
              >
              > Has anyone gone to the effort to slightly modify the dorade box to install
              > 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is
              > needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
              >
              > It's tempting -- the 4" vents are only an inch taller (so I don't think they
              > would look out of scale), but have 40% more air flow capacity (based on
              > Vetus catalog).
              >
              > I don't see any references to this approach, so am suspecting that there is
              > a hidden 'gotcha !!!'.
              >
              > Thanks -
              >

            • Ken Jenkins
              John, Thanks for the input. I was pretty sure if I started doing much work, I d break the old plates as you mentioned. Good luck with the vents. I m leaning
              Message 6 of 27 , Jan 2, 2012
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                John,

                Thanks for the input. I was pretty sure if I started doing much work, I’d break the old plates as you mentioned. Good luck with the vents. I’m leaning toward staying with 3” vents as I like a low profile on the cabin top. In fact I am considering the Vetus low profile 3” SS vent as I tend to step on things up around the mast when I’m rushing around. However the price is sort of hanging me up.

                Regards, Ken

                 


                From: Sabresailboat@yahoogroups.com [mailto: Sabresailboat@yahoogroups.com ] On Behalf Of JohnF
                Sent: Sunday, January 01, 2012 3:22 PM
                To: Sabresailboat@yahoogroups.com
                Subject: [SabreSailboat] Re: Cowl Vents - 4" with a little extra work?

                 

                 

                Ken,

                The old deck plates were bedded, they didn't budge by just yanking on them. I drove a sharp putty knife under the flange all the way around. I used a short pry bar to reach down inside the box in order to get some leverage from underneath the throat of the vent. That seemed to help break the grip of the adhesive. Only one of the deck plates came out whole. The old plastic was very brittle and easily split up with the putty knife and some gentle tapping. It was easier to get out once broken up into pieces.

                Once the deck plate was out, it was easy to scrape off the old adhesive and clean it up with some acetone.

                The first one took about 20 minutes, then the other three took about 20 minutes total once I figured out how to do it!

                --- In Sabresailboat@yahoogroups.com, "Ken Jenkins" <kjenk3@...> wrote:

                >
                > John,
                >
                > As a side question, did you have much trouble getting the mounting plate
                for
                > the Martec vent off? I also have a 34 MkII andI had unscrewed one earlier
                > this Fall to check hole size, but could not seem to pull out the mounting
                > plate. I thought maybe it had been bedded with an adhesive. Having limited
                > time, I decided to put off really working on the problem.
                >
                > Thanks for any insight, Ken
                >
                >
                >
                > _____
                >
                > From: Sabresailboat@yahoogroups.com
                [mailto:Sabresailboat@yahoogroups.com]
                > On Behalf Of JohnF
                > Sent: Sunday, January 01, 2012 6:13 AM
                > To: Sabresailboat@yahoogroups.com
                > Subject: [SabreSailboat] Cowl Vents - 4" with a little extra work?
                >
                >
                >
                >
                >
                > The old original Martec cowl vents were removed yesterday on our 1987 34
                > MkII (thank you 55 degree Maryland
                weather!). In reviewing the archives, it
                > looks like most people have replaced with 3" cowl vents, often
                requiring a
                > teak or starboard 'pad' to accommodate a smaller deck ring.
                >
                > Has anyone gone to the effort to slightly modify the dorade box to install
                > 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger
                than is
                > needed for a 3" vent, and slightly smaller than is needed for a
                4" vent.
                >
                > It's tempting -- the 4" vents are only an inch taller (so I don't
                think they
                > would look out of scale), but have 40% more air flow capacity (based on
                > Vetus catalog).
                >
                > I don't see any references to this approach, so am suspecting that there
                is
                > a hidden 'gotcha !!!'.
                >
                > Thanks -
                >

              • Peter Tollini
                Mine ( 88) came off easily with a thin putty knife. Since then I ve foun that an incredible tool for removing caulk, etc, and freeing bedded flanges is a
                Message 7 of 27 , Jan 2, 2012
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                  Mine ('88) came off easily with a thin putty knife.  Since then I've foun that an incredible tool for removing caulk, etc, and freeing bedded flanges is a reciprocating tool (Fein, Dremel, Rockwell) with a thin, flexible scraper blade.  I removed a through hull bedded with 5200 in a matter of minutes with no damage.  I think the high frequency vibration softens the material and allows easy removal.
                  Pete

                  On Sun, Jan 1, 2012 at 6:21 PM, JohnF <jl_folk@...> wrote:
                   

                  Ken,

                  The old deck plates were bedded, they didn't budge by just yanking on them. I drove a sharp putty knife under the flange all the way around. I used a short pry bar to reach down inside the box in order to get some leverage from underneath the throat of the vent. That seemed to help break the grip of the adhesive. Only one of the deck plates came out whole. The old plastic was very brittle and easily split up with the putty knife and some gentle tapping. It was easier to get out once broken up into pieces.

                  Once the deck plate was out, it was easy to scrape off the old adhesive and clean it up with some acetone.

                  The first one took about 20 minutes, then the other three took about 20 minutes total once I figured out how to do it!



                  --- In Sabresailboat@yahoogroups.com, "Ken Jenkins" <kjenk3@...> wrote:
                  >
                  > John,
                  >
                  > As a side question, did you have much trouble getting the mounting plate for
                  > the Martec vent off? I also have a 34 MkII andI had unscrewed one earlier
                  > this Fall to check hole size, but could not seem to pull out the mounting
                  > plate. I thought maybe it had been bedded with an adhesive. Having limited
                  > time, I decided to put off really working on the problem.
                  >
                  > Thanks for any insight, Ken
                  >
                  >
                  >
                  > _____
                  >
                  > From: Sabresailboat@yahoogroups.com [mailto:Sabresailboat@yahoogroups.com]
                  > On Behalf Of JohnF
                  > Sent: Sunday, January 01, 2012 6:13 AM
                  > To: Sabresailboat@yahoogroups.com
                  > Subject: [SabreSailboat] Cowl Vents - 4" with a little extra work?
                  >
                  >
                  >
                  >
                  >
                  > The old original Martec cowl vents were removed yesterday on our 1987 34
                  > MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it
                  > looks like most people have replaced with 3" cowl vents, often requiring a
                  > teak or starboard 'pad' to accommodate a smaller deck ring.
                  >
                  > Has anyone gone to the effort to slightly modify the dorade box to install
                  > 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is
                  > needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
                  >
                  > It's tempting -- the 4" vents are only an inch taller (so I don't think they
                  > would look out of scale), but have 40% more air flow capacity (based on
                  > Vetus catalog).
                  >
                  > I don't see any references to this approach, so am suspecting that there is
                  > a hidden 'gotcha !!!'.
                  >
                  > Thanks -
                  >


                • JohnF
                  Peter and John - Did you go with a 3 or 4 vent as your replacement? If you went with 3 , did you consider trying a 4 ? Just trying to understand others
                  Message 8 of 27 , Jan 2, 2012
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                    Peter and John - Did you go with a 3" or 4" vent as your replacement? If you went with 3", did you consider trying a 4" ? Just trying to understand others' thought process on this one...

                    --- In Sabresailboat@yahoogroups.com, "JohnF" <jl_folk@...> wrote:
                    >
                    > The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.
                    >
                    > Has anyone gone to the effort to slightly modify the dorade box to install 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
                    >
                    > It's tempting -- the 4" vents are only an inch taller (so I don't think they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).
                    >
                    > I don't see any references to this approach, so am suspecting that there is a hidden 'gotcha !!!'.
                    >
                    > Thanks -
                    >
                  • cr_folk
                    Lovely!
                    Message 9 of 27 , Jan 2, 2012
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                      Lovely!
                    • Peter Tollini
                      I just went with Manship stainless 3 low profile. If I recall, the 4 mounting rings may not fit on the molded Dorade boxes. See attached picture. Pete
                      Message 10 of 27 , Jan 2, 2012
                      • 1 Attachment
                      • 1.3 MB
                      I just went with Manship stainless 3" low profile.  If I recall, the 4" mounting rings may not fit on the molded Dorade boxes. See attached picture.
                      Pete

                      On Mon, Jan 2, 2012 at 11:03 AM, JohnF <jl_folk@...> wrote:
                       

                      Peter and John - Did you go with a 3" or 4" vent as your replacement? If you went with 3", did you consider trying a 4" ? Just trying to understand others' thought process on this one...



                      --- In Sabresailboat@yahoogroups.com, "JohnF" <jl_folk@...> wrote:
                      >
                      > The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.
                      >
                      > Has anyone gone to the effort to slightly modify the dorade box to install 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
                      >
                      > It's tempting -- the 4" vents are only an inch taller (so I don't think they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).
                      >
                      > I don't see any references to this approach, so am suspecting that there is a hidden 'gotcha !!!'.
                      >
                      > Thanks -
                      >


                    • vanbeckump
                      I am thinking that the restrictions of the dorade and particularly the tiny vent into the boat s interior may limit the air flow to the point that the larger
                      Message 11 of 27 , Jan 3, 2012
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                        I am thinking that the restrictions of the dorade and particularly the tiny vent into the boat's interior may limit the air flow to the point that the larger cowl may not be worth it. One also has to worry about the exterior size of the cowl. You don't want to fall against it and pry it loose or bend it. Big cowls usually have a stainless tubing cage around them for protection.

                        Just sayin'

                        Peter

                        --- In Sabresailboat@yahoogroups.com, "JohnF" <jl_folk@...> wrote:
                        >
                        > The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.
                        >
                        > Has anyone gone to the effort to slightly modify the dorade box to install 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
                        >
                        > It's tempting -- the 4" vents are only an inch taller (so I don't think they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).
                        >
                        > I don't see any references to this approach, so am suspecting that there is a hidden 'gotcha !!!'.
                        >
                        > Thanks -
                        >
                      • Ken Jenkins
                        Peter, Those look very nice, Where did you get them? A quick Google search didn t turn up any Manship low profile vents. Also, I agree with vanbeckump that the
                        Message 12 of 27 , Jan 3, 2012
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                          Peter,

                          Those look very nice, Where did you get them? A quick Google search didn’t turn up any Manship low profile vents.

                          Also, I agree with vanbeckump that the size restrictions on the opening into the cabin are probably going to make the 4” vents not much better at airflow than the 3”.

                          Regards, Ken

                           


                          From: Sabresailboat@yahoogroups.com [mailto: Sabresailboat@yahoogroups.com ] On Behalf Of Peter Tollini
                          Sent: Monday, January 02, 2012 2:57 PM
                          To: Sabresailboat@yahoogroups.com
                          Subject: Re: [SabreSailboat] Re: Cowl Vents - 4" with a little extra work? [1 Attachment]

                           

                           

                          I just went with Manship stainless 3" low profile.  If I recall, the 4" mounting rings may not fit on the molded Dorade boxes. See attached picture.

                          Pete

                          On Mon, Jan 2, 2012 at 11:03 AM, JohnF <jl_folk@...> wrote:

                           

                          Peter and John - Did you go with a 3" or 4" vent as your replacement? If you went with 3", did you consider trying a 4" ? Just trying to understand others' thought process on this one...



                          --- In Sabresailboat@yahoogroups.com, "JohnF" <jl_folk@...> wrote:

                          >
                          > The old original Martec cowl vents were removed yesterday on our 1987 34 MkII
                          (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.
                          >
                          > Has anyone gone to the effort to slightly modify the dorade box to install
                          4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
                          >
                          > It's tempting -- the 4" vents are only an inch taller (so I don't think
                          they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).
                          >
                          > I don't see any references to this approach, so am suspecting that there
                          is a hidden 'gotcha !!!'.
                          >
                          > Thanks -
                          >

                           

                        • Jim Starkey
                          ... No, the cage is to keep lines from snagging the cowls leading to strong language and/or expensive splashes if not properly screwed in. The round style
                          Message 13 of 27 , Jan 3, 2012
                          • 0 Attachment
                            On 1/3/2012 10:39 AM, vanbeckump wrote:
                             

                            I am thinking that the restrictions of the dorade and particularly the tiny vent into the boat's interior may limit the air flow to the point that the larger cowl may not be worth it. One also has to worry about the exterior size of the cowl. You don't want to fall against it and pry it loose or bend it. Big cowls usually have a stainless tubing cage around them for protection.


                            No, the cage is to keep lines from snagging the cowls leading to strong language and/or expensive splashes if not properly screwed in.  The round style cowls, at least, are near infinitely strong.  Bend them, not a chance.


                            Just sayin'

                            Peter

                            --- In Sabresailboat@yahoogroups.com, "JohnF" <jl_folk@...> wrote:
                            >
                            > The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.
                            >
                            > Has anyone gone to the effort to slightly modify the dorade box to install 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
                            >
                            > It's tempting -- the 4" vents are only an inch taller (so I don't think they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).
                            >
                            > I don't see any references to this approach, so am suspecting that there is a hidden 'gotcha !!!'.
                            >
                            > Thanks -
                            >



                            -- 
                            Jim Starkey
                            Founder and CTO
                            NuoDB, Inc.
                          • Peter Tollini
                            I got them from the now defunct Mariners Hardware, but I found this site which has the same products. They are made by Manship in Taiwan as are the stainless
                            Message 14 of 27 , Jan 3, 2012
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                              I got them from the now defunct Mariners Hardware, but I found this site which has the same products.  They are made by Manship in Taiwan as are the stainless hatches and ports Sabre now uses.  Given the the state of the world for small maritime businesses, you should make contact with them before ordering anything. Another nice touch is choosing the inside color.
                               
                               
                              Pete

                              On Tue, Jan 3, 2012 at 11:26 AM, Ken Jenkins <kjenk3@...> wrote:
                               

                              Peter,

                              Those look very nice, Where did you get them? A quick Google search didn’t turn up any Manship low profile vents.

                              Also, I agree with vanbeckump that the size restrictions on the opening into the cabin are probably going to make the 4” vents not much better at airflow than the 3”.

                              Regards, Ken

                               


                              From: Sabresailboat@yahoogroups.com [mailto:Sabresailboat@yahoogroups.com] On Behalf Of Peter Tollini
                              Sent: Monday, January 02, 2012 2:57 PM
                              To: Sabresailboat@yahoogroups.com
                              Subject: Re: [SabreSailboat] Re: Cowl Vents - 4" with a little extra work? [1 Attachment]

                               

                               

                              I just went with Manship stainless 3" low profile.  If I recall, the 4" mounting rings may not fit on the molded Dorade boxes. See attached picture.

                              Pete

                              On Mon, Jan 2, 2012 at 11:03 AM, JohnF <jl_folk@...> wrote:

                               

                              Peter and John - Did you go with a 3" or 4" vent as your replacement? If you went with 3", did you consider trying a 4" ? Just trying to understand others' thought process on this one...



                              --- In Sabresailboat@yahoogroups.com, "JohnF" <jl_folk@...> wrote:
                              >
                              > The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.
                              >
                              > Has anyone gone to the effort to slightly modify the dorade box to install 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
                              >
                              > It's tempting -- the 4" vents are only an inch taller (so I don't think they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).
                              >
                              > I don't see any references to this approach, so am suspecting that there is a hidden 'gotcha !!!'.
                              >
                              > Thanks -
                              >

                               


                            • Scott
                              I remember reports that Mariners Hardware was often noted for being a poor operation. Late and non-deliveries, hard to contact, etc. So, I thought I should
                              Message 15 of 27 , Jan 3, 2012
                              • 0 Attachment
                                I remember reports that Mariners Hardware was often noted for being a poor operation. Late and non-deliveries, hard to contact, etc. 
                                So, I thought I should google Blue Water Hardware and bbb to see what I get. The results were not good. Is Blue Water just a new name? Too bad, I like the product selection/ prices. 

                                Scott


                                On Jan 3, 2012, at 12:49 PM, Peter Tollini <pete@...> wrote:

                                 

                                I got them from the now defunct Mariners Hardware, but I found this site which has the same products.  They are made by Manship in Taiwan as are the stainless hatches and ports Sabre now uses.  Given the the state of the world for small maritime businesses, you should make contact with them before ordering anything. Another nice touch is choosing the inside color.
                                 
                                 
                                Pete

                                On Tue, Jan 3, 2012 at 11:26 AM, Ken Jenkins <kjenk3@...> wrote:
                                 

                                Peter,

                                Those look very nice, Where did you get them? A quick Google search didn’t turn up any Manship low profile vents.

                                Also, I agree with vanbeckump that the size restrictions on the opening into the cabin are probably going to make the 4” vents not much better at airflow than the 3”.

                                Regards, Ken

                                 


                                From: Sabresailboat@yahoogroups.com [mailto:Sabresailboat@yahoogroups.com] On Behalf Of Peter Tollini
                                Sent: Monday, January 02, 2012 2:57 PM
                                To: Sabresailboat@yahoogroups.com
                                Subject: Re: [SabreSailboat] Re: Cowl Vents - 4" with a little extra work? [1 Attachment]

                                 

                                 

                                I just went with Manship stainless 3" low profile.  If I recall, the 4" mounting rings may not fit on the molded Dorade boxes. See attached picture.

                                Pete

                                On Mon, Jan 2, 2012 at 11:03 AM, JohnF <jl_folk@...> wrote:

                                 

                                Peter and John - Did you go with a 3" or 4" vent as your replacement? If you went with 3", did you consider trying a 4" ? Just trying to understand others' thought process on this one...



                                --- In Sabresailboat@yahoogroups.com, "JohnF" <jl_folk@...> wrote:
                                >
                                > The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.
                                >
                                > Has anyone gone to the effort to slightly modify the dorade box to install 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
                                >
                                > It's tempting -- the 4" vents are only an inch taller (so I don't think they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).
                                >
                                > I don't see any references to this approach, so am suspecting that there is a hidden 'gotcha !!!'.
                                >
                                > Thanks -
                                >

                                 


                              • carter.brey@gmail.com
                                I have the sheet stainless round cowl vent from Bluewater. The experience was not good. It looked to me like a guy in over his head. He finally got it right
                                Message 16 of 27 , Jan 3, 2012
                                • 0 Attachment
                                  I have the sheet stainless round cowl vent from Bluewater. The experience was not good. It looked to me like a guy in over his head. He finally got it right after weeks of misdirected or incorrect orders.

                                  -------- Original message -------- Subject: Re: [SabreSailboat] Re: Cowl Vents - 4" with a little extra work? From: Scott To: Sabresailboat@yahoogroups.com CC:

                                   

                                  I remember reports that Mariners Hardware was often noted for being a poor operation. Late and non-deliveries, hard to contact, etc. 
                                  So, I thought I should google Blue Water Hardware and bbb to see what I get. The results were not good. Is Blue Water just a new name? Too bad, I like the product selection/ prices. 

                                  Scott


                                  On Jan 3, 2012, at 12:49 PM, Peter Tollini <pete@...> wrote:

                                   

                                  I got them from the now defunct Mariners Hardware, but I found this site which has the same products.  They are made by Manship in Taiwan as are the stainless hatches and ports Sabre now uses.  Given the the state of the world for small maritime businesses, you should make contact with them before ordering anything. Another nice touch is choosing the inside color.
                                   
                                   
                                  Pete

                                  On Tue, Jan 3, 2012 at 11:26 AM, Ken Jenkins <kjenk3@...> wrote:
                                   

                                  Peter,

                                  Those look very nice, Where did you get them? A quick Google search didn’t turn up any Manship low profile vents.

                                  Also, I agree with vanbeckump that the size restrictions on the opening into the cabin are probably going to make the 4” vents not much better at airflow than the 3”.

                                  Regards, Ken

                                   


                                  From: Sabresailboat@yahoogroups.com [mailto:Sabresailboat@yahoogroups.com] On Behalf Of Peter Tollini
                                  Sent: Monday, January 02, 2012 2:57 PM
                                  To: Sabresailboat@yahoogroups.com
                                  Subject: Re: [SabreSailboat] Re: Cowl Vents - 4" with a little extra work? [1 Attachment]

                                   

                                   

                                  I just went with Manship stainless 3" low profile.  If I recall, the 4" mounting rings may not fit on the molded Dorade boxes. See attached picture.

                                  Pete

                                  On Mon, Jan 2, 2012 at 11:03 AM, JohnF <jl_folk@...> wrote:

                                   

                                  Peter and John - Did you go with a 3" or 4" vent as your replacement? If you went with 3", did you consider trying a 4" ? Just trying to understand others' thought process on this one...



                                  --- In Sabresailboat@yahoogroups.com, "JohnF" <jl_folk@...> wrote:
                                  >
                                  > The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.
                                  >
                                  > Has anyone gone to the effort to slightly modify the dorade box to install 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
                                  >
                                  > It's tempting -- the 4" vents are only an inch taller (so I don't think they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).
                                  >
                                  > I don't see any references to this approach, so am suspecting that there is a hidden 'gotcha !!!'.
                                  >
                                  > Thanks -
                                  >

                                   


                                • Peter Tollini
                                  I did a little research and Marine Depot, Inc www.marinedepot.us is an authorized Manship distributor. They are/were Mariners Hardware and Bluewater
                                  Message 17 of 27 , Jan 3, 2012
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                                    I did a little research and Marine Depot, Inc  www.marinedepot.us is an authorized Manship distributor.  They are/were Mariners Hardware and Bluewater Hardware's supplier.  They sell retail as well and seem to have a better rep for reliability.  Unfortunately, I don't see the low profile stainless vents on their site.  Maybe available with an inquiry.
                                    No endorsement here, as I haven't deallt with them, but before things went bad, MH was a pleasure to deal with.
                                    Pete

                                    On Tue, Jan 3, 2012 at 3:47 PM, carter.brey@... <carter.brey@...> wrote:
                                     

                                    I have the sheet stainless round cowl vent from Bluewater. The experience was not good. It looked to me like a guy in over his head. He finally got it right after weeks of misdirected or incorrect orders.

                                    -------- Original message -------- Subject: Re: [SabreSailboat] Re: Cowl Vents - 4" with a little extra work? From: Scott To: Sabresailboat@yahoogroups.com CC:


                                     

                                    I remember reports that Mariners Hardware was often noted for being a poor operation. Late and non-deliveries, hard to contact, etc. 
                                    So, I thought I should google Blue Water Hardware and bbb to see what I get. The results were not good. Is Blue Water just a new name? Too bad, I like the product selection/ prices. 

                                    Scott


                                    On Jan 3, 2012, at 12:49 PM, Peter Tollini <pete@...> wrote:

                                     

                                    I got them from the now defunct Mariners Hardware, but I found this site which has the same products.  They are made by Manship in Taiwan as are the stainless hatches and ports Sabre now uses.  Given the the state of the world for small maritime businesses, you should make contact with them before ordering anything. Another nice touch is choosing the inside color.
                                     
                                     
                                    Pete

                                    On Tue, Jan 3, 2012 at 11:26 AM, Ken Jenkins <kjenk3@...> wrote:
                                     

                                    Peter,

                                    Those look very nice, Where did you get them? A quick Google search didn’t turn up any Manship low profile vents.

                                    Also, I agree with vanbeckump that the size restrictions on the opening into the cabin are probably going to make the 4” vents not much better at airflow than the 3”.

                                    Regards, Ken

                                     


                                    From: Sabresailboat@yahoogroups.com [mailto:Sabresailboat@yahoogroups.com] On Behalf Of Peter Tollini
                                    Sent: Monday, January 02, 2012 2:57 PM
                                    To: Sabresailboat@yahoogroups.com
                                    Subject: Re: [SabreSailboat] Re: Cowl Vents - 4" with a little extra work? [1 Attachment]

                                     

                                     

                                    I just went with Manship stainless 3" low profile.  If I recall, the 4" mounting rings may not fit on the molded Dorade boxes. See attached picture.

                                    Pete

                                    On Mon, Jan 2, 2012 at 11:03 AM, JohnF <jl_folk@...> wrote:

                                     

                                    Peter and John - Did you go with a 3" or 4" vent as your replacement? If you went with 3", did you consider trying a 4" ? Just trying to understand others' thought process on this one...



                                    --- In Sabresailboat@yahoogroups.com, "JohnF" <jl_folk@...> wrote:
                                    >
                                    > The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.
                                    >
                                    > Has anyone gone to the effort to slightly modify the dorade box to install 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
                                    >
                                    > It's tempting -- the 4" vents are only an inch taller (so I don't think they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).
                                    >
                                    > I don't see any references to this approach, so am suspecting that there is a hidden 'gotcha !!!'.
                                    >
                                    > Thanks -
                                    >

                                     



                                  • JohnF
                                    Peter - that s a great thought. The actual vents into the cabin are tiny. More air through a bigger cowl probably isn t going to make a difference.
                                    Message 18 of 27 , Jan 3, 2012
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                                      Peter - that's a great thought. The actual vents into the cabin are tiny. More air through a bigger cowl probably isn't going to make a difference.

                                      --- In Sabresailboat@yahoogroups.com, "vanbeckump" <vanbeckump@...> wrote:
                                      >
                                      > I am thinking that the restrictions of the dorade and particularly the tiny vent into the boat's interior may limit the air flow to the point that the larger cowl may not be worth it. One also has to worry about the exterior size of the cowl. You don't want to fall against it and pry it loose or bend it. Big cowls usually have a stainless tubing cage around them for protection.
                                      >
                                      > Just sayin'
                                      >
                                      > Peter
                                      >
                                      > --- In Sabresailboat@yahoogroups.com, "JohnF" <jl_folk@> wrote:
                                      > >
                                      > > The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.
                                      > >
                                      > > Has anyone gone to the effort to slightly modify the dorade box to install 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
                                      > >
                                      > > It's tempting -- the 4" vents are only an inch taller (so I don't think they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).
                                      > >
                                      > > I don't see any references to this approach, so am suspecting that there is a hidden 'gotcha !!!'.
                                      > >
                                      > > Thanks -
                                      > >
                                      >
                                    • Jim Starkey
                                      Perhaps some analysis might help. A round 3 cowl has a frontal section of 4.7 square inches. A round 4 cowl has a frontal section of 12.5 square inches.
                                      Message 19 of 27 , Jan 3, 2012
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                                        Perhaps some analysis might help.  A round 3" cowl has a frontal section of 4.7 square inches.  A round 4" cowl has a frontal section of 12.5 square inches.  The internal orifice is probably only 1.5" wide or  2.35", the pressure from the large cowl will be 2.65 times the pressure of the 3" cowl.  Somebody else can take it from here, but the amount of air circulating through the cabin will be substantially greater with a 4" cowl than a 3" cowl.

                                        My current (manufacturer problematic) boat has 4" cowls and approximate 2" vents.  In a modest breeze, we need to close the vents (a feature unknown to Sabres) so the dinner candles don't blow out.

                                        If you like mildew and cherish the wet boat smell, by all means go for the smallest cowls possible.  Sabre was a production boat builder and $.75 per boat saved was $.75 in the stockholders pocket, market share not withstanding.

                                        So I guess the question is whether you want a dungeon or a castle.  Dungeons are a little cheaper, but...


                                        On 1/3/2012 7:45 PM, JohnF wrote:
                                         

                                        Peter - that's a great thought. The actual vents into the cabin are tiny. More air through a bigger cowl probably isn't going to make a difference.

                                        --- In Sabresailboat@yahoogroups.com, "vanbeckump" <vanbeckump@...> wrote:
                                        >
                                        > I am thinking that the restrictions of the dorade and particularly the tiny vent into the boat's interior may limit the air flow to the point that the larger cowl may not be worth it. One also has to worry about the exterior size of the cowl. You don't want to fall against it and pry it loose or bend it. Big cowls usually have a stainless tubing cage around them for protection.
                                        >
                                        > Just sayin'
                                        >
                                        > Peter
                                        >
                                        > --- In Sabresailboat@yahoogroups.com, "JohnF" <jl_folk@> wrote:
                                        > >
                                        > > The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.
                                        > >
                                        > > Has anyone gone to the effort to slightly modify the dorade box to install 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
                                        > >
                                        > > It's tempting -- the 4" vents are only an inch taller (so I don't think they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).
                                        > >
                                        > > I don't see any references to this approach, so am suspecting that there is a hidden 'gotcha !!!'.
                                        > >
                                        > > Thanks -
                                        > >
                                        >


                                      • Ken Jenkins
                                        Jim, If your analysis is correct then you d better not use airplanes because you have just overturned Bernoulli s principle and the related venturi effect, not
                                        Message 20 of 27 , Jan 4, 2012
                                        • 0 Attachment

                                          Jim,

                                          If your analysis is correct then you’d better not use airplanes because you have just overturned Bernoulli’s principle and the related venturi effect, not to metion all the fluid flow measurements that are done using orifice plates. Basically as the velocity of a fluid increases due to a restriction in a pipe the static pressure decreases. Furthermore the total pressure of the air at the cowl inlet is not primarily a function of cowl area. A larger cowl would probably draw in more air because its opening is, on average, higher off the deck where the air velocity is higher resulting in higher average dynamic pressure. In the case of Sabre dorades there is not only the area reduction to 1.5” but the baffle inside the box which would producie a pressure drop due to frictional loss. So, in this case I would guess that air flow is primarily controlled by the dorade baffle and the 1.5” exit diameter.

                                           

                                          As a small matter, the frontal section of the 3” cowl is 7.07 square inches, not 4.7. In the interest of science, why don’t you try using masking tape to block off the bottom third of your vents sometime to appoximate a 3” cowl and see what you get? In the meantime I’m currently sailing my dungeon with no vents, but living in California we can get away with thatJ

                                          Regards, Ken


                                          From: Sabresailboat@yahoogroups.com [mailto: Sabresailboat@yahoogroups.com ] On Behalf Of Jim Starkey
                                          Sent: Tuesday, January 03, 2012 7:05 PM
                                          To: Sabresailboat@yahoogroups.com
                                          Subject: Re: [SabreSailboat] Re: Cowl Vents - 4" with a little extra work?

                                           

                                           

                                          Perhaps some analysis might help.  A round 3" cowl has a frontal section of 4.7 square inches.  A round 4" cowl has a frontal section of 12.5 square inches.  The internal orifice is probably only 1.5" wide or  2.35", the pressure from the large cowl will be 2.65 times the pressure of the 3" cowl.  Somebody else can take it from here, but the amount of air circulating through the cabin will be substantially greater with a 4" cowl than a 3" cowl.

                                          My current (manufacturer problematic) boat has 4" cowls and approximate 2" vents.  In a modest breeze, we need to close the vents (a feature unknown to Sabres) so the dinner candles don't blow out.

                                          If you like mildew and cherish the wet boat smell, by all means go for the smallest cowls possible.  Sabre was a production boat builder and $.75 per boat saved was $.75 in the stockholders pocket, market share not withstanding.

                                          So I guess the question is whether you want a dungeon or a castle.  Dungeons are a little cheaper, but...


                                          On 1/3/2012 7:45 PM, JohnF wrote:

                                           

                                          Peter - that's a great thought. The actual vents into the cabin are tiny. More air through a bigger cowl probably isn't going to make a difference.

                                          --- In Sabresailboat@yahoogroups.com, "vanbeckump" <vanbeckump@...> wrote:
                                          >
                                          > I am thinking that the restrictions of the dorade and particularly the tiny vent into the boat's interior may limit the air flow to the point that the larger cowl may not be worth it. One also has to worry about the exterior size of the cowl. You don't want to fall against it and pry it loose or bend it. Big cowls usually have a stainless tubing cage around them for protection.
                                          >
                                          > Just sayin'
                                          >
                                          > Peter
                                          >
                                          > --- In Sabresailboat@yahoogroups.com, "JohnF" <jl_folk@> wrote:
                                          > >
                                          > > The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.
                                          > >
                                          > > Has anyone gone to the effort to slightly modify the dorade box to install 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
                                          > >
                                          > > It's tempting -- the 4" vents are only an inch taller (so I don't think they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).
                                          > >
                                          > > I don't see any references to this approach, so am suspecting that there is a hidden 'gotcha !!!'.
                                          > >
                                          > > Thanks -
                                          > >
                                          >

                                           

                                        • Peter Tollini
                                          I checked with Marine Depot and they are the real thing. I asked if the 3 low profile vents were still available, and the checked with Manship, responding
                                          Message 21 of 27 , Jan 4, 2012
                                          • 0 Attachment
                                            I checked with Marine Depot and they are the real thing.  I asked if the 3" low profile vents were still available, and the checked with Manship, responding back within 24 hours. Unfortunately the low profile vents are not available, but the round and teardrop vents are. They come with stainless mounting rings and stainless cover plates with a winch handle socket.
                                            Also, Marine Depot also carries its own set of cowl vents which can be found on page 75: http://dl.dropbox.com/u/6258237/Marine%20Depot%20Catalog%202011.pdf
                                            The lady that I spoke with is :
                                            Victoria Ma
                                            Marine Depot, Inc.
                                            14716 Central Ave.
                                            Chino, CA 91710
                                            Tel: (909) 393 - 6100 Fax: (909) 393 - 2009

                                             
                                            On Wed, Jan 4, 2012 at 11:56 AM, Ken Jenkins <kjenk3@...> wrote:
                                             

                                            Jim,

                                            If your analysis is correct then you’d better not use airplanes because you have just overturned Bernoulli’s principle and the related venturi effect, not to metion all the fluid flow measurements that are done using orifice plates. Basically as the velocity of a fluid increases due to a restriction in a pipe the static pressure decreases. Furthermore the total pressure of the air at the cowl inlet is not primarily a function of cowl area. A larger cowl would probably draw in more air because its opening is, on average, higher off the deck where the air velocity is higher resulting in higher average dynamic pressure. In the case of Sabre dorades there is not only the area reduction to 1.5” but the baffle inside the box which would producie a pressure drop due to frictional loss. So, in this case I would guess that air flow is primarily controlled by the dorade baffle and the 1.5” exit diameter.

                                             

                                            As a small matter, the frontal section of the 3” cowl is 7.07 square inches, not 4.7. In the interest of science, why don’t you try using masking tape to block off the bottom third of your vents sometime to appoximate a 3” cowl and see what you get? In the meantime I’m currently sailing my dungeon with no vents, but living in California we can get away with thatJ

                                            Regards, Ken


                                            From: Sabresailboat@yahoogroups.com [mailto:Sabresailboat@yahoogroups.com] On Behalf Of Jim Starkey
                                            Sent: Tuesday, January 03, 2012 7:05 PM


                                            To: Sabresailboat@yahoogroups.com
                                            Subject: Re: [SabreSailboat] Re: Cowl Vents - 4" with a little extra work?

                                             

                                             

                                            Perhaps some analysis might help.  A round 3" cowl has a frontal section of 4.7 square inches.  A round 4" cowl has a frontal section of 12.5 square inches.  The internal orifice is probably only 1.5" wide or  2.35", the pressure from the large cowl will be 2.65 times the pressure of the 3" cowl.  Somebody else can take it from here, but the amount of air circulating through the cabin will be substantially greater with a 4" cowl than a 3" cowl.



                                            My current (manufacturer problematic) boat has 4" cowls and approximate 2" vents.  In a modest breeze, we need to close the vents (a feature unknown to Sabres) so the dinner candles don't blow out.

                                            If you like mildew and cherish the wet boat smell, by all means go for the smallest cowls possible.  Sabre was a production boat builder and $.75 per boat saved was $.75 in the stockholders pocket, market share not withstanding.

                                            So I guess the question is whether you want a dungeon or a castle.  Dungeons are a little cheaper, but...


                                            On 1/3/2012 7:45 PM, JohnF wrote:

                                             

                                            Peter - that's a great thought. The actual vents into the cabin are tiny. More air through a bigger cowl probably isn't going to make a difference.

                                            --- In Sabresailboat@yahoogroups.com, "vanbeckump" <vanbeckump@...> wrote:
                                            >
                                            > I am thinking that the restrictions of the dorade and particularly the tiny vent into the boat's interior may limit the air flow to the point that the larger cowl may not be worth it. One also has to worry about the exterior size of the cowl. You don't want to fall against it and pry it loose or bend it. Big cowls usually have a stainless tubing cage around them for protection.
                                            >
                                            > Just sayin'
                                            >
                                            > Peter
                                            >
                                            > --- In Sabresailboat@yahoogroups.com, "JohnF" <jl_folk@> wrote:
                                            > >
                                            > > The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.
                                            > >
                                            > > Has anyone gone to the effort to slightly modify the dorade box to install 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
                                            > >
                                            > > It's tempting -- the 4" vents are only an inch taller (so I don't think they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).
                                            > >
                                            > > I don't see any references to this approach, so am suspecting that there is a hidden 'gotcha !!!'.
                                            > >
                                            > > Thanks -
                                            > >
                                            >

                                             


                                          • Jim Starkey
                                            OK, let s work this through. The venturi that sucks air through the gyros on your rustic Cessna 170 has one funnel facing into the airstream connected to
                                            Message 22 of 27 , Jan 4, 2012
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                                              OK, let's work this through.  The venturi that sucks air through the gyros on your rustic Cessna 170 has one funnel facing into the airstream connected to another smaller funnel facing downstream, and a hole in the middle connected by cracked Tygon to a dying directional gyro.  The constriction of the forward facing funnel increases the air pressure in turn accelerating the air through the constriction.  The pressure measured in the constriction relative to cabin pressure (assuming neither your instructor or your passenger is yelling at you) is lower, drawing air (not vacuum, ladies and gentlemen) through the gyro cause the rotor to spin sufficiently to keep the dirty side down, even in the clouds.

                                              I submit that a) a Sabre isn't a Cessna 170,  b) the cowl / dorade / interior vent is not a venturi, and c) Mr. Bernoulli has as little to do with it as he has to do with keeping your Cessna 170 in the air (which, technically, is held up by the declining balance in your checking account).  I further submit that the pressure inside the dorade is higher than cabin pressure, for if it were not, air would flow from the cabin to the dorade causing it to explode or morph into a black hole.

                                              Perhaps we might agree on a simpler analysis, if not arithmetic.  Air comes in the cowl, through the dorade box, through the internal vent, and into the cabin.  I hope this is self-evident.  The amount of air passing through this system is a function of a) the frontal section of the cowl, b) the speed of the air relative to the cowl, c) the obstruction of the interior of the dorade box, and d) the size of the interior vent.  Increase the frontal section of the cowl, the speed of the cowl relative to the outside air, lower the air resistance of the dorade box, or increase the size of the interior vent and you get more air passing through the cabin, the ultimate goal of this exercise.

                                              Of these options, the only feasible on is increasing the frontal section of the cowl.  I have no doubt that Roy Lopresti could design a more efficient cowl/dorade/vent system, though doing it postmortem would be a trick.  That said, his famously efficient cowls were round, which is where we started.

                                               I graciously concede the 7.07 square inches.  You are of course correct.

                                              (Note: no comparisons between sail and wings were tortured by this post.)


                                              On 1/4/2012 11:56 AM, Ken Jenkins wrote:
                                               

                                              Jim,

                                              If your analysis is correct then you’d better not use airplanes because you have just overturned Bernoulli’s principle and the related venturi effect, not to metion all the fluid flow measurements that are done using orifice plates. Basically as the velocity of a fluid increases due to a restriction in a pipe the static pressure decreases. Furthermore the total pressure of the air at the cowl inlet is not primarily a function of cowl area. A larger cowl would probably draw in more air because its opening is, on average, higher off the deck where the air velocity is higher resulting in higher average dynamic pressure. In the case of Sabre dorades there is not only the area reduction to 1.5” but the baffle inside the box which would producie a pressure drop due to frictional loss. So, in this case I would guess that air flow is primarily controlled by the dorade baffle and the 1.5” exit diameter.

                                               

                                              As a small matter, the frontal section of the 3” cowl is 7.07 square inches, not 4.7. In the interest of science, why don’t you try using masking tape to block off the bottom third of your vents sometime to appoximate a 3” cowl and see what you get? In the meantime I’m currently sailing my dungeon with no vents, but living in California we can get away with thatJ

                                              Regards, Ken


                                              From: Sabresailboat@yahoogroups.com [mailto:Sabresailboat@yahoogroups.com ] On Behalf Of Jim Starkey
                                              Sent: Tuesday, January 03, 2012 7:05 PM
                                              To: Sabresailboat@yahoogroups.com
                                              Subject: Re: [SabreSailboat] Re: Cowl Vents - 4" with a little extra work?

                                               

                                               

                                              Perhaps some analysis might help.  A round 3" cowl has a frontal section of 4.7 square inches.  A round 4" cowl has a frontal section of 12.5 square inches.  The internal orifice is probably only 1.5" wide or  2.35", the pressure from the large cowl will be 2.65 times the pressure of the 3" cowl.  Somebody else can take it from here, but the amount of air circulating through the cabin will be substantially greater with a 4" cowl than a 3" cowl.

                                              My current (manufacturer problematic) boat has 4" cowls and approximate 2" vents.  In a modest breeze, we need to close the vents (a feature unknown to Sabres) so the dinner candles don't blow out.

                                              If you like mildew and cherish the wet boat smell, by all means go for the smallest cowls possible.  Sabre was a production boat builder and $.75 per boat saved was $.75 in the stockholders pocket, market share not withstanding.

                                              So I guess the question is whether you want a dungeon or a castle.  Dungeons are a little cheaper, but...


                                              On 1/3/2012 7:45 PM, JohnF wrote:

                                               

                                              Peter - that's a great thought. The actual vents into the cabin are tiny. More air through a bigger cowl probably isn't going to make a difference.

                                              --- In Sabresailboat@yahoogroups.com, "vanbeckump" <vanbeckump@...> wrote:
                                              >
                                              > I am thinking that the restrictions of the dorade and particularly the tiny vent into the boat's interior may limit the air flow to the point that the larger cowl may not be worth it. One also has to worry about the exterior size of the cowl. You don't want to fall against it and pry it loose or bend it. Big cowls usually have a stainless tubing cage around them for protection.
                                              >
                                              > Just sayin'
                                              >
                                              > Peter
                                              >
                                              > --- In Sabresailboat@yahoogroups.com, "JohnF" <jl_folk@> wrote:
                                              > >
                                              > > The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.
                                              > >
                                              > > Has anyone gone to the effort to slightly modify the dorade box to install 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
                                              > >
                                              > > It's tempting -- the 4" vents are only an inch taller (so I don't think they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).
                                              > >
                                              > > I don't see any references to this approach, so am suspecting that there is a hidden 'gotcha !!!'.
                                              > >
                                              > > Thanks -
                                              > >
                                              >

                                               



                                              -- 
                                              Jim Starkey
                                              Founder and CTO
                                              NuoDB, Inc.
                                            • Peter Tollini
                                              Jim - A simpler analysis. If your assertion was incorrect, no one would have or buy a Windscoop. We d spend July nights at anchor sweating like pigs, but
                                              Message 23 of 27 , Jan 4, 2012
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                                                Jim -
                                                A simpler analysis.  If your assertion was incorrect, no one would have or buy a Windscoop.  We'd spend July nights at anchor sweating like pigs, but secure in our knowledge.
                                                Pete
                                              • vanbeckump
                                                While we re at it let s consider where the air trying to enter the boat goes and how does the air it displaces leave the cabin. I would submit that two cowls
                                                Message 24 of 27 , Jan 4, 2012
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                                                  While we're at it let's consider where the air trying to enter the boat goes and how does the air it displaces leave the cabin. I would submit that two cowls should face aft and two forward. This will create a pressure differential that will both push and pull (thank you Dr. Doolittle) air through the boat giving us the ventilation I assume we all want.

                                                  Having said that, even with all four cowls facing forward, I have had to tape my tiny cabin vents shut to keep warm while on the hook in October so apparently there are some exits that I am not aware of.

                                                  Practice vs theory, hmmm.

                                                  Peter


                                                  --- In Sabresailboat@yahoogroups.com, Jim Starkey <jstarkey@...> wrote:
                                                  >
                                                  > Perhaps some analysis might help. A round 3" cowl has a frontal section
                                                  > of 4.7 square inches. A round 4" cowl has a frontal section of 12.5
                                                  > square inches. The internal orifice is probably only 1.5" wide or
                                                  > 2.35", the pressure from the large cowl will be 2.65 times the pressure
                                                  > of the 3" cowl. Somebody else can take it from here, but the amount of
                                                  > air circulating through the cabin will be substantially greater with a
                                                  > 4" cowl than a 3" cowl.
                                                  >
                                                  > My current (manufacturer problematic) boat has 4" cowls and approximate
                                                  > 2" vents. In a modest breeze, we need to close the vents (a feature
                                                  > unknown to Sabres) so the dinner candles don't blow out.
                                                  >
                                                  > If you like mildew and cherish the wet boat smell, by all means go for
                                                  > the smallest cowls possible. Sabre was a production boat builder and
                                                  > $.75 per boat saved was $.75 in the stockholders pocket, market share
                                                  > not withstanding.
                                                  >
                                                  > So I guess the question is whether you want a dungeon or a castle.
                                                  > Dungeons are a little cheaper, but...
                                                  >
                                                  >
                                                  > On 1/3/2012 7:45 PM, JohnF wrote:
                                                  > >
                                                  > > Peter - that's a great thought. The actual vents into the cabin are
                                                  > > tiny. More air through a bigger cowl probably isn't going to make a
                                                  > > difference.
                                                  > >
                                                  > > --- In Sabresailboat@yahoogroups.com
                                                  > > <mailto:Sabresailboat%40yahoogroups.com>, "vanbeckump"
                                                  > > <vanbeckump@> wrote:
                                                  > > >
                                                  > > > I am thinking that the restrictions of the dorade and particularly
                                                  > > the tiny vent into the boat's interior may limit the air flow to the
                                                  > > point that the larger cowl may not be worth it. One also has to worry
                                                  > > about the exterior size of the cowl. You don't want to fall against it
                                                  > > and pry it loose or bend it. Big cowls usually have a stainless tubing
                                                  > > cage around them for protection.
                                                  > > >
                                                  > > > Just sayin'
                                                  > > >
                                                  > > > Peter
                                                  > > >
                                                  > > > --- In Sabresailboat@yahoogroups.com
                                                  > > <mailto:Sabresailboat%40yahoogroups.com>, "JohnF" <jl_folk@> wrote:
                                                  > > > >
                                                  > > > > The old original Martec cowl vents were removed yesterday on our
                                                  > > 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the
                                                  > > archives, it looks like most people have replaced with 3" cowl vents,
                                                  > > often requiring a teak or starboard 'pad' to accommodate a smaller
                                                  > > deck ring.
                                                  > > > >
                                                  > > > > Has anyone gone to the effort to slightly modify the dorade box to
                                                  > > install 4" vents? The holes in my deck are 3 11/16 inches, somewhat
                                                  > > bigger than is needed for a 3" vent, and slightly smaller than is
                                                  > > needed for a 4" vent.
                                                  > > > >
                                                  > > > > It's tempting -- the 4" vents are only an inch taller (so I don't
                                                  > > think they would look out of scale), but have 40% more air flow
                                                  > > capacity (based on Vetus catalog).
                                                  > > > >
                                                  > > > > I don't see any references to this approach, so am suspecting that
                                                  > > there is a hidden 'gotcha !!!'.
                                                  > > > >
                                                  > > > > Thanks -
                                                  > > > >
                                                  > > >
                                                  > >
                                                  > >
                                                  >
                                                • JohnF
                                                  We made a decision - At the end of the day aesthetics trumps fluid dynamics. On a piece of paper we laid out the footprint of the original deck flange, a 3
                                                  Message 25 of 27 , Jan 5, 2012
                                                  • 0 Attachment
                                                    We made a decision - At the end of the day aesthetics trumps fluid dynamics. On a piece of paper we laid out the footprint of the original deck flange, a 3" flange, and a 4" flange (based on Vetus measurements). It's pretty clear that the 4" flange will barely fit on top of the dorade box. It will go right up to the edge, and that it wouldn't look "right". We are going with the 3" ...

                                                    JLF

                                                    --- In Sabresailboat@yahoogroups.com, "JohnF" <jl_folk@...> wrote:
                                                    >
                                                    > The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.
                                                    >
                                                    > Has anyone gone to the effort to slightly modify the dorade box to install 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
                                                    >
                                                    > It's tempting -- the 4" vents are only an inch taller (so I don't think they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).
                                                    >
                                                    > I don't see any references to this approach, so am suspecting that there is a hidden 'gotcha !!!'.
                                                    >
                                                    > Thanks -
                                                    >
                                                  • Bill Blalock
                                                    There s an old saying among fluid dynamicists: If it looks right, it is right.
                                                    Message 26 of 27 , Jan 5, 2012
                                                    • 0 Attachment
                                                      There's an old saying among fluid dynamicists: If it looks right, it is right.

                                                      On Thu, Jan 5, 2012 at 9:55 AM, JohnF <jl_folk@...> wrote:
                                                       

                                                      We made a decision - At the end of the day aesthetics trumps fluid dynamics. On a piece of paper we laid out the footprint of the original deck flange, a 3" flange, and a 4" flange (based on Vetus measurements). It's pretty clear that the 4" flange will barely fit on top of the dorade box. It will go right up to the edge, and that it wouldn't look "right". We are going with the 3" ...

                                                      JLF

                                                      --- In Sabresailboat@yahoogroups.com, "JohnF" <jl_folk@...> wrote:
                                                      >
                                                      > The old original Martec cowl vents were removed yesterday on our 1987 34 MkII (thank you 55 degree Maryland weather!). In reviewing the archives, it looks like most people have replaced with 3" cowl vents, often requiring a teak or starboard 'pad' to accommodate a smaller deck ring.
                                                      >
                                                      > Has anyone gone to the effort to slightly modify the dorade box to install 4" vents? The holes in my deck are 3 11/16 inches, somewhat bigger than is needed for a 3" vent, and slightly smaller than is needed for a 4" vent.
                                                      >
                                                      > It's tempting -- the 4" vents are only an inch taller (so I don't think they would look out of scale), but have 40% more air flow capacity (based on Vetus catalog).
                                                      >
                                                      > I don't see any references to this approach, so am suspecting that there is a hidden 'gotcha !!!'.
                                                      >
                                                      > Thanks -
                                                      >


                                                    • Ken Jenkins
                                                      OK, let s try a thought experiment. First, choose as big a dorade cowl as you like. To simplify matters, instead of the baffle assume the dorade just funnels
                                                      Message 27 of 27 , Jan 5, 2012
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                                                        OK, let’s try a thought experiment. First, choose as big a dorade cowl as you like. To simplify matters, instead of the baffle assume the dorade just funnels down into the cabin. Now, put a plate across the opening into the cabin, sealing it. What you now have is a giant pitot tube. The pressure at the dorade side of the plate is the stagnation pressure for the opening of the cowl. Assuming uniform flow outside the boat, it doesn’t matter what size the cowl is the pressure is still the stagnation pressure. The pressure on the other side of the plate is the static pressure in the cabin. Now drill a small hole in the plate (and be sure the companionway is open so the cabin remains at static pressureJ). The flow is going to be controlled by the hole size and can be calculated as flow thru a hole with the stagnation pressure on one side and static pressure on the other. As you enlarge the hole more air flows, and the static pressure on the upstream side of the plate drops, but continuity says the static plus dynamic pressure are constant. If we look at the cowl inlet when we put a small hole in the plate, most of the cowl frontal area is still nearly stagnant air. That is why you can’t assume that greater cowl area equals greater flow. The cowl is positioned like a probe in a free air flow. With a restriction further downsteam inside the cowl some of the free air flow impinging on the cowl flows outside of it so the flow into the cowl entrance is not the free air velocity times the cowl cross sectional area. The limiting case is where the opening is closed and all air impinging on the cowl flows around it.

                                                        I hope this helps. No Cessnas were crashed in the preparation of this e-mail.

                                                        Ken

                                                         


                                                        From: Sabresailboat@yahoogroups.com [mailto: Sabresailboat@yahoogroups.com ] On Behalf Of Jim Starkey
                                                        Sent: Wednesday, January 04, 2012 3:29 PM
                                                        To: Sabresailboat@yahoogroups.com
                                                        Subject: Re: [SabreSailboat] Re: Cowl Vents - 4" with a little extra work?

                                                         

                                                         

                                                        OK, let's work this through.  The venturi that sucks air through the gyros on your rustic Cessna 170 has one funnel facing into the airstream connected to another smaller funnel facing downstream, and a hole in the middle connected by cracked Tygon to a dying directional gyro.  The constriction of the forward facing funnel increases the air pressure in turn accelerating the air through the constriction.  The pressure measured in the constriction relative to cabin pressure (assuming neither your instructor or your passenger is yelling at you) is lower, drawing air (not vacuum, ladies and gentlemen) through the gyro cause the rotor to spin sufficiently to keep the dirty side down, even in the clouds.

                                                        I submit that a) a Sabre isn't a Cessna 170,  b) the cowl / dorade / interior vent is not a venturi, and c) Mr. Bernoulli has as little to do with it as he has to do with keeping your Cessna 170 in the air (which, technically, is held up by the declining balance in your checking account).  I further submit that the pressure inside the dorade is higher than cabin pressure, for if it were not, air would flow from the cabin to the dorade causing it to explode or morph into a black hole.

                                                        Perhaps we might agree on a simpler analysis, if not arithmetic.  Air comes in the cowl, through the dorade box, through the internal vent, and into the cabin.  I hope this is self-evident.  The amount of air passing through this system is a function of a) the frontal section of the cowl, b) the speed of the air relative to the cowl, c) the obstruction of the interior of the dorade box, and d) the size of the interior vent.  Increase the frontal section of the cowl, the speed of the cowl relative to the outside air, lower the air resistance of the dorade box, or increase the size of the interior vent and you get more air passing through the cabin, the ultimate goal of this exercise.

                                                        Of these options, the only feasible on is increasing the frontal section of the cowl.  I have no doubt that Roy Lopresti could design a more efficient cowl/dorade/vent system, though doing it postmortem would be a trick.  That said, his famously efficient cowls were round, which is where we started.

                                                         I graciously concede the 7.07 square inches.  You are of course correct.

                                                        (Note: no comparisons between sail and wings were tortured by this post.)


                                                        Founder and CTO
                                                        NuoDB, Inc.
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