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RE: [campernicholson] Props

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  • Colin Campbell-Dunlop
    I am no expert on this area but I have just re-propped Trutz. We had the two bladed prop with the Perkins 4-108. Seemed to push her along fine in moderate
    Message 1 of 5 , May 1, 2006
      Message

      I am no expert on this area but I have just re-propped Trutz.

       

      We had the two bladed prop with the Perkins 4-108.  Seemed to push her along fine in moderate conditions at around the 2500 rev mark.  Would get around 5.5-6 knots which was ok. 

       

      We chose to replace with a three bladed autoprop.  It is a great piece of equipment and works very well.  However, we still get knocked back when motoring in to steep head seas and head winds.  I can recall a trip across Lyme Bay last summer when the waves were very steep and we were occasionally down to 2 knots.  It was a long day. 

       

      I can only assume that with such a heavy boat this is something we have to live with. 

       

      On the prop walk issue.  We still get a kick to port but nothing like as pronounced as with the 2 bladed set up. 

       

      Rgds

       

      Colin Campbell-Dunlop

       

      -----Original Message-----
      From: campernicholson@yahoogroups.com [mailto:campernicholson@yahoogroups.com] On Behalf Of Graham Norbury
      Sent: 01 May 2006 12:20
      To: campernicholson@yahoogroups.com
      Subject: RE: [campernicholson] Props

       

      Early in our ownership of Luna Azul, we replaced the 2 blade fixed prop with a 3 blade MaxProp.  With calm seas and everything set up correctly, the VW engine would push her along at 6.8 knots max, but throw in any significant headwind or choppy conditions and she'd be down around 5kts or worse.   Our most efficient cruise speed was somewhere around 5.0kts @ 2300rpm for 0.5 USgal/hr.

       

      Sorry, can't remember the dimensions of the MaxProp, but I recall it was largish dia (maybe 19") with quite low pitch setting.  Experimentation definitely required!

       

      Graham

       

    • tom1us2001
      Simon, I replaced the original 2 blade (19x13) prop on Dream three years ago with an Autostream 3 blade (18X12). I have not checked the fuel consumption since
      Message 2 of 5 , May 1, 2006
        Simon,

        I replaced the original 2 blade (19x13) prop on Dream three years ago
        with an Autostream 3 blade (18X12). I have not checked the fuel
        consumption since changing props. The 3 blade has improved forward and
        reserve thrust although the forward speed at a set RPM did not seem to
        change. I usually plunk along at just over 5 knots at 2100 RPM.
        Reverse with the three blade has almost twice the thrust from that of
        the 2 blade. Prop walk in reverse is a little less than the 2 blade
        but still evident. I've been planning on adjusting one degree of
        pitch out of reverse to see how the prop walk is then. My reverse Max
        RPM is also pretty low which tells me I have too much pitch. I may
        take about one half degree off the forward pitch also. I think my max
        RPM during a speed run test was 2800 RPM with just a little black soot
        from the exhaust. While maneuvering at the dock max forward RPM is
        about 2400 and about 2000 in reverse. I usually don't floor it at the
        dock but I had a 25 knot wind I was trying to turn into with very
        little room to move. I just happen to glance at the gauge when I
        pushed the throttle to the floor.

        Speed into head seas seems a little better with the three blade but
        not too noticable. Normal inland water chop into say 20 knot winds
        I'll get 3 to 4 knots. While motoring into heavier seas (bow under
        every third wave) I only get 1 to 2 knots at 2100 RPM. Once clear of a
        channel I don't steer straight into the sea which helps with speed.

        I was going to put a 19" 3 blade on but autostream sujested the 18" do
        to how close the tip of the blade is the the hull. I think a 19" blade
        put the tip within a couple of inched. There consern was you can get a
        slapping (ticking)sound from the prop wash of a prop running too close
        to the hull. Having an extra 1/2" of clearance would help eliminate
        that. The three blade does run quieter than two blade. although it is
        louder when shifting from forward to reverse since the blades had to
        rotate.

        I have the VW engine with V-drive. Rated at 35HP at 3800RPM. Overall
        I'm happy with the prop. All it requires is an aniod and some grease
        once a year. It is a feathering prop but will not feather until I put
        the transmission in reserve. Once feathered then I put the
        transmission back to neutral. It has added about half knot to one knot
        to speed under sail depending on wind speed.


        Hope this info helps,

        Tom
        CN35-199 Dream


        --- In campernicholson@yahoogroups.com, "Katie and Simon"
        <katieandsimon@...> wrote:
        >
        > All,
        >
        > Since we seem to back on the subject of props I'd also like to tap
        into the
        > group's combined wisdom. We have a 2-bladed Max-prop on Gin Rummy,
        which is
        > at least 15 years old and is heavily pitted from cavitation (I
        think). It's
        > a 19" prop, set at 19" pitch, 2-bladed. My concerns are:
        >
        > - The pitch is so high that the boat has a tremendous prop walk in
        reverse;
        > - In good weather we can easily achieve 6 knots at 3,000rpm, but
        motoring in
        > head seas the performance falls off rapidly as if the prop is not
        able to
        > deliver any real punch;
        > - the heavy pitting makes me think the prop is often cavitating.
        >
        > I have the drawings for our boat, and they show that the design prop
        for the
        > 4-108 engine is 19" dia x 14" pitch 2-bladed. However, my feeling is
        that
        > there is simply not enough blade area to deliver the ample (excessive?)
        > power of the 4-108 engine to the water. When I push the throttle up in
        > forward gear the engine easily spins up to 4,000 rpm, and would
        probably go
        > higher if I had the nerve.
        >
        > As the Max-Prop is getting old and new ones are extremely expensive,
        I'd
        > like to experiment first by buying a used 3-bladed prop to see what
        happens.
        > My objective is to load the engine more so that we get 5-6 knots at
        lower
        > revs and can push the revs up to maintain speed as the seas build.
        I'd also
        > like to reduce the prop walk in reverse.
        >
        > I'd be really interested in any advice or comments, especially from
        those
        > with experience of 3-bladed props. If I go for a 19" 3-bladed prop,
        what
        > sort of pitch should I go for?
        >
        > I know, I know... if the head winds do pipe up we really should
        simply turn
        > off the engine and tack to windward!!
        >
        > Looking forward to your thoughts,
        >
        > Simon
        > Gin Rummy CN35-202
        >
      • Graham Norbury
        Tom, You might want to check those specs on the VW engine - from what I recall, you should get 35HP (continuous) at 3000rpm. I believe there are also specs
        Message 3 of 5 , May 1, 2006
          Message
          Tom,
           
          You might want to check those specs on the VW engine - from what I recall, you should get 35HP (continuous) at 3000rpm.  I believe there are also specs for intermittent ~40(ish)HP at some higher rpm, but mine never showed much desire to run above 3000-3200 even when out of gear.
           
          Graham
          -----Original Message-----
          From: campernicholson@yahoogroups.com [mailto:campernicholson@yahoogroups.com] On Behalf Of tom1us2001
          Sent: Monday, May 01, 2006 10:11 AM
          To: campernicholson@yahoogroups.com
          Subject: [campernicholson] Re: Props

          Simon,

          I replaced the original 2 blade (19x13) prop on Dream three years ago
          with an Autostream 3 blade (18X12). I have not checked the fuel
          consumption since changing props. The 3 blade has improved forward and
          reserve thrust although the forward speed at a set RPM did not seem to
          change. I usually plunk along at just over 5 knots at 2100 RPM.
          Reverse with the three blade has almost twice the thrust from that of
          the 2 blade. Prop walk in reverse is a little less than the 2 blade
          but still evident.  I've been planning on adjusting one degree of
          pitch out of reverse to see how the prop walk is then. My reverse Max
          RPM is also pretty low which tells me I have too much pitch. I may
          take about one half degree off the forward pitch also. I think my max
          RPM during a speed run test was 2800 RPM with just a little black soot
          from the exhaust. While maneuvering at the dock max forward RPM is
          about 2400 and about 2000 in reverse. I usually don't floor it at the
          dock but I had a 25 knot wind I was trying to turn into with very
          little room to move. I just happen to glance at the gauge when I
          pushed the throttle to the floor.

          Speed into head seas seems a little better with the three blade but
          not too noticable. Normal inland water chop into say 20 knot winds
          I'll get 3 to 4 knots. While motoring into heavier seas (bow under
          every third wave) I only get 1 to 2 knots at 2100 RPM. Once clear of a
          channel I don't steer straight into the sea which helps with speed.

          I was going to put a 19" 3 blade on but autostream sujested the 18" do
          to how close the tip of the blade is the the hull. I think a 19" blade
          put the tip within a couple of inched. There consern was you can get a
          slapping (ticking)sound from the prop wash of a prop running too close
          to the hull. Having an extra 1/2" of clearance would help eliminate
          that. The three blade does run quieter than two blade. although it is
          louder when shifting from forward to reverse since the blades had to
          rotate.

          I have the VW engine with V-drive. Rated at 35HP at 3800RPM. Overall
          I'm happy with the prop. All it requires is an aniod and some grease
          once a year. It is a feathering prop but will not feather until I put
          the transmission in reserve. Once feathered then I put the
          transmission back to neutral. It has added about half knot to one knot
          to speed under sail depending on wind speed.


          Hope this info helps,

          Tom
          CN35-199 Dream
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