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Re: [bolger] Re: engines; jet drives

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  • Don Tyson
    Jeff, I could be wrong but I think Dave Gerr ( Well known east coast designer/author) did some designs with this concept which is essentially the same as the
    Message 1 of 13 , Jan 4, 2004
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      Jeff, I could be wrong but I think Dave Gerr ( Well known east coast designer/author) did some designs with this concept which is essentially the same as the historic Seabright Skiff. The seabright skiff is uniqe in that it was launched from unprotected sand beaches directly into the rough Atlantic off the NJ coast. Having the prop up in like that alowed the hulls to be dragged up the beach at the end of the day. As long as the two bladed prop was horizontal dragging the hulls didn't cause any damage. I havent seen anyone enploy a stern drive to this bottom but it sounds inexpensive as there are many used 3.0 units out there for a song.
      Keep me posted.
      Don Tyson

      Jeff Blunck <boatbuilding@...> wrote:
      Actually I have adapted the Wyo to something similar though it's untested
      yet. I put a 28" inch wide by 5" deep tunnel running 42 inches long at the
      stern. You can just see it on some of my pictures showing me move the stern
      section with a trailer.

      The key here is that the tunnel is still under the designed water line so
      there should be no problems with reversing or cooling. It was not installed
      to get into shallows with a stern drive but it does reduce the overall
      operating depth by 5 inches. Theory here is to have a tunnel allowing me to
      raise the Sterndrive high enough that it's mostly out of the water for
      corrosion problems plus it can be removed with out shipping water into the
      engine compartment so repairs can be made without pulling the 50 foot boat.

      This tunnel will not be very effective at the top end speeds of the Wyo and
      in fact may cause some cavitations, that's still to be determined.

      Jeff

      http://www.4dw.net/cosailor/


      ----- Original Message -----
      From:
      To:
      Sent: Saturday, January 03, 2004 11:14 PM
      Subject: Re: [bolger] Re: engines; jet drives


      > For a low-speed boat you might consider a tunnel stern, which is
      essentially
      > a high-volume, low-velocity jet drive. In ascending order of construction
      > complexity and propulsion efficiency, here are some examples from Chester
      > Nedwidek and the Atkin catalog:
      >
      > http://www.boat-links.com/images/Skeeter.gif
      >
      > http://www.boat-links.com/Atkinco/Utilities/Twinkle.html
      >
      > http://www.boat-links.com/Atkinco/Utilities/RescueMinor.html
      >
      > On Sat, 3 Jan 2004 09:31:28 -0700, Jeff wrote:
      > > ...
      > > They also expressed that the efficiency of jet drives are not realized
      > until
      > > the boat exceeds planing speeds so if I was to travel at hull speeds
      most
      > of
      > > the time, my fuel consumption would be excessive compared to a
      propeller.
      > > ...
      >
      > --
      > John
      > http://www.boat-links.com/
      > Distrust any enterprise that requires new clothes.
      >
      >
      >
      >
      >
      > Bolger rules!!!
      > - no cursing, flaming, trolling, spamming, or flogging dead horses
      > - stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
      > - Pls add your comments at the TOP, SIGN your posts, and snip away
      > - Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax:
      (978) 282-1349
      > - Unsubscribe: bolger-unsubscribe@yahoogroups.com
      > - Open discussion: bolger_coffee_lounge-subscribe@yahoogroups.com
      >
      > Yahoo! Groups Links
      >
      > To visit your group on the web, go to:
      > http://groups.yahoo.com/group/bolger/
      >
      > To unsubscribe from this group, send an email to:
      > bolger-unsubscribe@yahoogroups.com
      >
      > Your use of Yahoo! Groups is subject to:
      > http://docs.yahoo.com/info/terms/
      >
      >


      Bolger rules!!!
      - no cursing, flaming, trolling, spamming, or flogging dead horses
      - stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
      - Pls add your comments at the TOP, SIGN your posts, and snip away
      - Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax: (978) 282-1349
      - Unsubscribe: bolger-unsubscribe@yahoogroups.com
      - Open discussion: bolger_coffee_lounge-subscribe@yahoogroups.com


      Yahoo! Groups Links

      To visit your group on the web, go to:
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      [Non-text portions of this message have been removed]
    • Jeff Blunck
      The prop I intend to use is a 15 prop and with the cavitation plate about an inch below the top of the tunnel at rest, I would estimate that only the top
      Message 2 of 13 , Jan 4, 2004
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        The prop I intend to use is a 15" prop and with the cavitation plate about
        an inch below the top of the tunnel at rest, I would estimate that only the
        top three inches of the prop will actually be running in the tunnel itself.
        Without a drive to test fit, I can only estimate that even in the full up
        position, the bottom of the fin may still drag in the mud but the prop
        should be clear. Either way I was only after the ability to have the drive
        lift clear of the water and to remove the drive unit without pulling the
        boat. I don't plan on motoring the Wyo in real shallows except to nose up
        to a beach.

        Jeff

        ----- Original Message -----
        From: "Don Tyson" <tysond99@...>
        To: <bolger@yahoogroups.com>
        Sent: Sunday, January 04, 2004 1:51 PM
        Subject: Re: [bolger] Re: engines; jet drives


        > Jeff, I could be wrong but I think Dave Gerr ( Well known east coast
        designer/author) did some designs with this concept which is essentially the
        same as the historic Seabright Skiff. The seabright skiff is uniqe in that
        it was launched from unprotected sand beaches directly into the rough
        Atlantic off the NJ coast. Having the prop up in like that alowed the hulls
        to be dragged up the beach at the end of the day. As long as the two bladed
        prop was horizontal dragging the hulls didn't cause any damage. I havent
        seen anyone enploy a stern drive to this bottom but it sounds inexpensive as
        there are many used 3.0 units out there for a song.
        > Keep me posted.
        > Don Tyson
        >
        > Jeff Blunck <boatbuilding@...> wrote:
        > Actually I have adapted the Wyo to something similar though it's untested
        > yet. I put a 28" inch wide by 5" deep tunnel running 42 inches long at the
        > stern. You can just see it on some of my pictures showing me move the
        stern
        > section with a trailer.
        >
        > The key here is that the tunnel is still under the designed water line so
        > there should be no problems with reversing or cooling. It was not
        installed
        > to get into shallows with a stern drive but it does reduce the overall
        > operating depth by 5 inches. Theory here is to have a tunnel allowing me
        to
        > raise the Sterndrive high enough that it's mostly out of the water for
        > corrosion problems plus it can be removed with out shipping water into the
        > engine compartment so repairs can be made without pulling the 50 foot
        boat.
        >
        > This tunnel will not be very effective at the top end speeds of the Wyo
        and
        > in fact may cause some cavitations, that's still to be determined.
        >
        > Jeff
        >
        > http://www.4dw.net/cosailor/
        >
        >
        > ----- Original Message -----
        > From:
        > To:
        > Sent: Saturday, January 03, 2004 11:14 PM
        > Subject: Re: [bolger] Re: engines; jet drives
        >
        >
        > > For a low-speed boat you might consider a tunnel stern, which is
        > essentially
        > > a high-volume, low-velocity jet drive. In ascending order of
        construction
        > > complexity and propulsion efficiency, here are some examples from
        Chester
        > > Nedwidek and the Atkin catalog:
        > >
        > > http://www.boat-links.com/images/Skeeter.gif
        > >
        > > http://www.boat-links.com/Atkinco/Utilities/Twinkle.html
        > >
        > > http://www.boat-links.com/Atkinco/Utilities/RescueMinor.html
        > >
        > > On Sat, 3 Jan 2004 09:31:28 -0700, Jeff wrote:
        > > > ...
        > > > They also expressed that the efficiency of jet drives are not realized
        > > until
        > > > the boat exceeds planing speeds so if I was to travel at hull speeds
        > most
        > > of
        > > > the time, my fuel consumption would be excessive compared to a
        > propeller.
        > > > ...
        > >
        > > --
        > > John
        > > http://www.boat-links.com/
        > > Distrust any enterprise that requires new clothes.
        > >
        > >
        > >
        > >
        > >
        > > Bolger rules!!!
        > > - no cursing, flaming, trolling, spamming, or flogging dead horses
        > > - stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
        > > - Pls add your comments at the TOP, SIGN your posts, and snip away
        > > - Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930,
        Fax:
        > (978) 282-1349
        > > - Unsubscribe: bolger-unsubscribe@yahoogroups.com
        > > - Open discussion: bolger_coffee_lounge-subscribe@yahoogroups.com
        > >
        > > Yahoo! Groups Links
        > >
        > > To visit your group on the web, go to:
        > > http://groups.yahoo.com/group/bolger/
        > >
        > > To unsubscribe from this group, send an email to:
        > > bolger-unsubscribe@yahoogroups.com
        > >
        > > Your use of Yahoo! Groups is subject to:
        > > http://docs.yahoo.com/info/terms/
        > >
        > >
        >
        >
        > Bolger rules!!!
        > - no cursing, flaming, trolling, spamming, or flogging dead horses
        > - stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
        > - Pls add your comments at the TOP, SIGN your posts, and snip away
        > - Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax:
        (978) 282-1349
        > - Unsubscribe: bolger-unsubscribe@yahoogroups.com
        > - Open discussion: bolger_coffee_lounge-subscribe@yahoogroups.com
        >
        >
        > Yahoo! Groups Links
        >
        > To visit your group on the web, go to:
        > http://groups.yahoo.com/group/bolger/
        >
        > To unsubscribe from this group, send an email to:
        > bolger-unsubscribe@yahoogroups.com
        >
        > Your use of Yahoo! Groups is subject to:
        > http://docs.yahoo.com/info/terms/
        >
        >
        >
        > [Non-text portions of this message have been removed]
        >
        >
        > Bolger rules!!!
        > - no cursing, flaming, trolling, spamming, or flogging dead horses
        > - stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
        > - Pls add your comments at the TOP, SIGN your posts, and snip away
        > - Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax:
        (978) 282-1349
        > - Unsubscribe: bolger-unsubscribe@yahoogroups.com
        > - Open discussion: bolger_coffee_lounge-subscribe@yahoogroups.com
        >
        > Yahoo! Groups Links
        >
        > To visit your group on the web, go to:
        > http://groups.yahoo.com/group/bolger/
        >
        > To unsubscribe from this group, send an email to:
        > bolger-unsubscribe@yahoogroups.com
        >
        > Your use of Yahoo! Groups is subject to:
        > http://docs.yahoo.com/info/terms/
        >
        >
        >
      • jhkohnen@boat-links.com
        It was William Atkin who first modified the Seabright skiff with reverse deadrise aft, forming a tunnel. He also mated the Seabright skiff box deadwood with a
        Message 3 of 13 , Jan 5, 2004
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          It was William Atkin who first modified the Seabright skiff with reverse
          deadrise aft, forming a tunnel. He also mated the Seabright skiff box
          deadwood with a V-bottom, both with tunnel sterns and without. Most of us
          think of Billy Atkin as a designer of Good Boats, but not as much of an
          innovator, but his V-bottom and tunnel stern Seabright skiffs were truly
          innovative. His gift to the boat design world, as he put it. Dave Gerr has
          done some tunnel-stern boats, but I don't recall if he was inspired by the
          Atkin designs. Here are some Atkin tunnel-stern Seabrights:

          http://www.boat-links.com/Atkinco/Utilities/Everhope.html

          http://www.boat-links.com/Atkinco/Utilities/ShoalsRunner.html

          http://www.boat-links.com/Atkinco/Cruisers/NanukIII.html

          And a non-tunnel-stern V-bottom Seabright skiff:

          http://www.boat-links.com/Atkinco/Cruisers/NanukIII.html

          On Sun, 4 Jan 2004 12:51:27 -0800 (PST), Don Tyson wrote:
          > Jeff, I could be wrong but I think Dave Gerr ( Well known east coast
          designer/author) did some designs with this concept which is essentially the
          same as the historic Seabright Skiff. The seabright skiff is uniqe in that
          it was launched from unprotected sand beaches directly into the rough
          Atlantic off the NJ coast. Having the prop up in like that alowed the hulls
          to be dragged up the beach at the end of the day. As long as the two bladed
          prop was horizontal dragging the hulls didn't cause any damage.
          > ...

          --
          John <jkohnen@...>
          http://www.boat-links.com/
          In this world of sin and sorrow there is always something to be thankful
          for; as for me, I rejoice that I am not a Republican. <H. L. Mencken>
        • hal
          ... The efficiency of a jet drive is related to the diameter of the nozzle, among other things. A high speed jet will have a -small- diameter nozzle to
          Message 4 of 13 , Jan 5, 2004
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            On Jan 3, 2004, at 4:49 PM, Hugo Tyson wrote:

            > Jet drives are best at speeds above 25 Knots where they are more
            > efficient than propellers. Speeds under 25 Kts the're really
            > inefficient as the motor is still working relatively hard to drive
            > them.

            The efficiency of a jet drive is related to the diameter
            of the nozzle, among other things. A high speed jet
            will have a -small- diameter nozzle to increase the
            velocity of the stream, and will be inefficient at low
            speeds because not much water will be flowing. A low
            speed jet will have a -large- diameter nozzle so a lot
            of water will flow at low speeds, but it won't go fast.

            Most commercial jet makers allow you to choose nozzle
            diameter based partly on the weight of the boat and
            desired speed. And of course the power of the engine.

            hal
          • hal
            ... I believe the inefficiencies of outboard jets are due to the type of pump used. Outboards us a centrifugal pump, where inboard jets such as berkeley,
            Message 5 of 13 , Jan 5, 2004
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              On Jan 3, 2004, at 4:35 PM, someone wrote:
              >
              > Seriously, how much power do you need? From what I've read about
              > outboard jets, they are really inefficient... as I remember, they are
              > about as effective as a screw-driven outbaard one-third the size. Max,
              > correct me please if I'm misremembering. Of course, with that goes 3X
              > the fuel consumption for a given thrust, Compared to a prop.

              I believe the inefficiencies of outboard jets are due
              to the type of pump used. Outboards us a centrifugal
              pump, where inboard jets such as berkeley, Panther, and
              jetski/wave runners use axial flow pumps.

              hal
            • Sal's Dad
              I know of two Atkins tunnel drives built recently, both documented extensively in MAIB: Robb White s Rescue Minor, which IIRC is about 20 x5 , with a small
              Message 6 of 13 , Jan 5, 2004
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                I know of two Atkins tunnel drives built recently, both documented
                extensively in MAIB: Robb White's Rescue Minor, which IIRC is about 20'x5',
                with a small deisel, and a 34' deisel cruiser built by Alex Hadden - took
                more than 2 years, in a professional shop with 2-3 guys working. Both are
                reported to be remarkable . But don't try to design one yourself, or to
                modify a Sneakeasy to this shape.

                The JetJon site is a bunch of guys who are actively experimenting with old
                jetski drives, stuck into various hull shapes. I suspect that the Sneakeasy
                would be perfect for this, perhaps with some slight modifications, or using
                the "step sharpie" variation to limit ventilation (NOT 'cavitation'). Draft
                might increase a couple inches, but still, a boat that would plane at 20mph
                in less than 6".... For low speed, consider a pair of trolling motors,
                foreward and aft, as "thrusters"

                One of the big jet mfrs used to make a small unit, for up to 20hp, iirc. It
                was inexpensive, for toys and projects. I seem to remember they sold it
                with no warranty.

                To get a couple inches less draft in my Diablo, I cut a notch, or "tunnel"
                2-3" up into the transom. The transom was 20", now it's effectively 17",
                which works fine with a short shaft 25. Doing it again, I'd cut much more
                out, and raise the transom...

                Best regards
                Curtis
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