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1984 Contessa 2850 Flybridge duo prop size

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    1984 Contessa 2850 Flybridge duo prop size

    Hello all,

    I tried to social distance this weekend and looked forward to seeing how my new props would increase performance. At the recommnedation of my mechanic and posts on this forum, I just changed my duo prop from a set of B3's to B2's, First run was yesterday out of Bellingham Bay. Fully loaded, fuel, water, kids etc. I could reach 4200 rpm not 4400 rpm WOT. On the B3's I could also reach 4200. I cruised at my usual 3600 rpm and was at 14 to 15 knots on the GPS, with the B3's I would be at 19-20 knots. Is the change in props showing a different issue with my engine? I had to run at 3800 to maintain 18 knots, to keep Admiral happy entertaining 3 boys under the age of 11 years old. Also fuel consumption was high, I usually burn about 60 gallons, I am guessing I burned 75 gallons. I will know more tomorrow when I fill up. Hull was reasonably clean per normal use.

    Specs
    AQ260A with 280 duo prop
    Marine Electronic Distributor (old prestolite 65-190)

    Any thoughts? On the bright side we saw a pod of orcas in San Juan Channel on our way to Roche.

    Thank you,
    1984 Contessa Command Bridge
    AQ260a
    VP 280 duo prop
    North Puget Sound
    Squalicum Harbor

    #2
    The difference of the props is absolutely a problem. The original set was more correct for your boat because it’s reaching the proper wide open throttle rpm that it should.
    I’ll admit right off that I don’t know the difference, and the sellers on line that I found in a quick search don’t tell me the pitches in each kit, but what you are describing is an over prop, meaning the prop has too much travel in each rotation so the engine is working harder to spin the prop. With your normal cruise rpm and the b2’s I think you are getting a lot of slip because the push from the prop wash isn’t enough to get the boat into the correct planing configuration. I’m guessing that you were stern heavy at 14kn. This is where the wizards and mystics earn their money. The information you've obtained from all of the sources is gold. You have something peculiar going on with your boat. It could be loading and storage, where and how things are stowed, or the runoff from the creek from Lake Watcom.
    That higher fuel burn means you were probably opening the secondary on the carb. Kinda like going into passing gear. Btdt
    P/C Pete
    Edmonds Yacht Club (Commodore 1993)
    1988 3818 "GLAUBEN”
    Hino EH700 175 Onan MDKD Genset
    MMSI 367770440

    Comment


      #3
      I ran B3 on my 85 Contessa Command bridge and would get about 20kn at 3500. Never really got to 4500 like it should when loaded up. I watched for B2 set but never found one to try.
      1999 Sandpiper Pilothouse - Current
      1989 3888 - 2011-2019, 1985 Contessa - 2005-2011, 1986 21' Trophy 1998-2005
      Nobody gets out alive.

      Comment


      • NWEricson
        NWEricson commented
        Editing a comment
        Yes this what I get with the B3s.

      #4
      I have B2 which I found to be better than B3 that I am able at get 4400 rmp. Attached is my boat speed (blue) and fuel usage (pink) chart.

      Joe
      1986 2850 with duo prop


      Click image for larger version  Name:	image002.gif Views:	0 Size:	7.2 KB ID:	566669
      Attached Files
      1986 2850 Commend Bridge on hydrohoist
      A260 and AQ280 with DP lower unit

      Comment


      • NWEricson
        NWEricson commented
        Editing a comment
        This is what I was expecting!

      #5
      Something is wrong!
      The Duo Prop drive ( with a healthy and well tune engine, hull clean, and of the correct reduction) will offer a 25% to 35% performance gain.

      Have you verified the following:

      .... 1.95:1 reduction
      .... fuel delivery system working as it should
      .... good cylinder pressure readings
      .... ignition advance at/ near 28* @ 3,200 RPM
      .... location of set pin
      .... is the hull stern heavy


      .
      Rick E. Gresham, Oregon
      2850 Bounty Sedan Flybridge model
      Twin 280 HP 5.7's w/ Closed Cooling
      Volvo Penta DuoProp Drives
      Kohler 4 CZ Gen Set

      Comment


        #6
        Originally posted by 2850Bounty View Post
        Something is wrong!
        The Duo Prop drive ( with a healthy and well tune engine, hull clean, and of the correct reduction) will offer a 25% to 35% performance gain.

        Have you verified the following:

        .... 1.95:1 reduction
        .... fuel delivery system working as it should
        .... good cylinder pressure readings
        .... ignition advance at/ near 28* @ 3,200 RPM
        .... location of set pin
        .... is the hull stern heavy


        .
        Bounty,

        This was not a swap from single to duo, I only changed the props from b3 to b2. As a scientist I wanted to limit the change in variables to one, the prop, all other variables were kept the same, weight, fuel amount, water tank amount, empty holding tank, number of batteries, oops I did change a second variable I had the three kids total 200 pounds extra.

        1. The casing is stamped with 1.95:1 on the lower unit. Is there a way to test this?
        2. I will check fuel system. It is a mechanical pump. I can hear the rod taping. Fuel filter changed last year.
        3. I will check cylinder pressure. When I purchased the boat the mechanic told me the engine pressure was good. Did not give me numbers.
        4. I will check advance. I have not given the engine a proper tune up since I purchased the boat two years ago.
        5. I have not changed the set the pin since replacing the transom shield three years ago. Would I need to change the setting with B2's?
        6. I was not anymore stern heavy than usual, we carry the inflatable on the swim step weaver davits. I could run without the inflatable?

        Thank for everyone for your help, as I work through the diagnosis.
        1984 Contessa Command Bridge
        AQ260a
        VP 280 duo prop
        North Puget Sound
        Squalicum Harbor

        Comment


          #7
          Elaborate on #2 You hear the rod tapping?
          Dave
          Edmonds, WA
          "THE FIX"
          '93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
          (.030 over-Vortec top end-part closed cooled)
          The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
          Misc. projects thread
          https://www.baylinerownersclub.org/f...56-gctid789773

          Comment


            #8
            Originally posted by builderdude View Post
            Elaborate on #2 You hear the rod tapping?
            Scares you doesn’t it after you blew a hole in a piston? Should not be any tapping noises.
            1997 Maxum 2400 SCR 5.7LX Bravo II

            Mike

            Comment


              #9
              Originally posted by Nauti_Mike View Post

              Scares you doesn’t it after you blew a hole in a piston? Should not be any tapping noises.
              I’d assumed the pushrod for his mechanical pump is making the noise. Yea don’t think that’s normal😳
              Dave
              Edmonds, WA
              "THE FIX"
              '93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
              (.030 over-Vortec top end-part closed cooled)
              The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
              Misc. projects thread
              https://www.baylinerownersclub.org/f...56-gctid789773

              Comment


                #10
                Originally posted by builderdude View Post
                Elaborate on #2 You hear the rod tapping?
                I am sorry I should have been more clear, the fuel pump connect rod or push rod to the cam.

                This sound started over the winter for the first few minutes after startup I could hear a tapping sound, it would then go away or become to faint to hear. I used my stethoscope and located the sound was coming from the fuel pump connect rod and not through the valve cover, exhaust or stern drive. I could hear the tap through the intake manifold and the loudest at the fuel pump.

                Kind Regards,
                1984 Contessa Command Bridge
                AQ260a
                VP 280 duo prop
                North Puget Sound
                Squalicum Harbor

                Comment


                  #11
                  ................
                  Originally posted by NWEricson View Post

                  Bounty,

                  This was not a swap from single to duo, I only changed the props from b3 to b2. As a scientist I wanted to limit the change in variables to one, the prop, all other variables were kept the same, weight, fuel amount, water tank amount, empty holding tank, number of batteries, oops I did change a second variable I had the three kids total 200 pounds extra.
                  Are you running the B or C series props? Are they a matched set? The two must be a matched pair.

                  1. The casing is stamped with 1.95:1 on the lower unit. Is there a way to test this?
                  Yes. With the transmission's sliding sleeve locked into the gear cup, the engine will rotate 1.95 times to 1 prop revolution.
                  Once you begin this test/check, you cannot let up..... you must keep the sliding sleeve and gear cup engaged.


                  2. I will check fuel system. It is a mechanical pump. I can hear the rod taping. Fuel filter changed last year.
                  By "fuel delivery system" I was referring to the carburetor.

                  3. I will check cylinder pressure. When I purchased the boat the mechanic told me the engine pressure was good. Did not give me numbers.
                  4. I will check advance. I have not given the engine a proper tune up since I purchased the boat two years ago.
                  This will be important.

                  5. I have not changed the set the pin since replacing the transom shield three years ago. Would I need to change the setting with B2's?
                  No! Center hole works best.

                  6. I was not anymore stern heavy than usual, we carry the inflatable on the swim step weaver davits. I could run without the inflatable?
                  Are you using large plane trim tabs?

                  Thank for everyone for your help, as I work through the diagnosis.
                  Rick E. Gresham, Oregon
                  2850 Bounty Sedan Flybridge model
                  Twin 280 HP 5.7's w/ Closed Cooling
                  Volvo Penta DuoProp Drives
                  Kohler 4 CZ Gen Set

                  Comment


                  • NWEricson
                    NWEricson commented
                    Editing a comment
                    If they are not a match set, is there a way fix this or do I need to buy a new set?

                  #12
                  Originally posted by 2850Bounty View Post
                  ................
                  #1. Running B series. They are not a matched set. I purchased from the Prop Shop Mukilteo, WA ; FWD prop is used as they did not have the rear pair so they sold me a new rear. Shouldn't they have known they need to be match?

                  # 2, 3, 4 - I will be getting down to the boat and will check on all three.

                  #5 - We will be pulling the boat in two weeks and I will check.

                  #6 - I believe they are the 12x12. I never had a problem getting up plane until last weekend, I only use the tabs for port/stb trim.

                  Again thanks for the assistance.
                  1984 Contessa Command Bridge
                  AQ260a
                  VP 280 duo prop
                  North Puget Sound
                  Squalicum Harbor

                  Comment

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