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17' w115 opti question, umachine, cgmiller?

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  • #1

    17' w115 opti question, umachine, cgmiller?

    I have a '77 17' like you guys. I just bought a 2010 115 opti and am looking for advice on prop pitch.

    The prop that came with the motor is a 20p stainless and only turns 5100 rpms or so.

    Ryan I see you have a very similar boat and motor and went through a number of props. Which gave you the best performance. I'm interested in fuel economy and lower rpm planing ability. No tabs yet.

    Thanks

    John
    1977 22\' Mako sold[br]1975 24\' Blackfin Fisherman sold[br]1973 19\' Mako sold[br]1974 19\' Mako sold[br]1987 Wellcraft 180 Fisherman Sold[br]1988 Rampage 24 Express (New Ride)[br]1977 17\' Mako Standard[br]1989 17\' Mako 171 Just added
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  • #2
    John..if you are only turning 5100 rpms your wheel is too big. That motor should wind up to at least 5500 rpms. Dropping to a 19P will pick up 200 rpms at the same diameter. A little less diameter should get you there. When I ran a 1991 115 Merc, I was spinning a 13x19 and was right in the range for that motor, which was a little over 5500 rpms and I could touch 40 mph. Also by dropping the pitch you will lower your fuel burn a little as it will be easier for the motor to spin the prop.
    Chris Miller[br]Mystic Islands, NJ[br]1974 17 Classic[br]1988 211 Classic (sold)[br]1990 Grady White 230 Gulfstream (sold)[br][img][br]

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    • #3
      I have a 1979 182 Backcountry...same hull, gunnels cut down and sponsons added...that has a 1999 Mercury 115 ELPTO on it. I put a Power Tec 4 blade 13"x16" prop on it and it seems close...will know next week as still breaking in fresh power head. I would think you need a 17" pitch prop with some cup. Also, is the motor height correct...ie the cavitation plate is on the surface of the water when running?

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      • #4
        Chris, thanks for getting back to me. I didn't think about the diameter of the prop. Were you able to plane at a low rpm, like 26-2800, with the 13x19?
        1977 22\' Mako sold[br]1975 24\' Blackfin Fisherman sold[br]1973 19\' Mako sold[br]1974 19\' Mako sold[br]1987 Wellcraft 180 Fisherman Sold[br]1988 Rampage 24 Express (New Ride)[br]1977 17\' Mako Standard[br]1989 17\' Mako 171 Just added

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        • #5
          BW, the cavitation plate is right where it should be, just on top.

          What advantage is the 4 blade prop?

          I've read it gives bow lift.

          Was that the reason?

          Please post numbers when you break in the motor.

          Thanks

          John
          1977 22\' Mako sold[br]1975 24\' Blackfin Fisherman sold[br]1973 19\' Mako sold[br]1974 19\' Mako sold[br]1987 Wellcraft 180 Fisherman Sold[br]1988 Rampage 24 Express (New Ride)[br]1977 17\' Mako Standard[br]1989 17\' Mako 171 Just added

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          • #6
            John,

            I cant say about the planning rpms. I am not one that beats on my engine to get my boat on plane immediately. it takes some forward speed and momentum to climb over the bow wave..granted the 17's hop up pretty quick with the shallow deadrise hull...I'll watch it in the morning for grins and giggles and let you know.
            Chris Miller[br]Mystic Islands, NJ[br]1974 17 Classic[br]1988 211 Classic (sold)[br]1990 Grady White 230 Gulfstream (sold)[br][img][br]

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            • #7
              My boat is a lot heavier with the full stringer grid. A 16deg pitch works best for me. If I had a 16.5 it would be perfect. 17deg Im a couple hundred short. I hit a cut piling at low tide and bent my 16. I'm using a cheapo 17 aluminum prop right now. Here are my numbers.

              I cruise at 25-30 3700-4100 RPMs 4.5-5gph.

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              • #8
                Thanks for all the replies. I found a new Silverado prop 13x18 I installed and it seems to work nicely. So this is what I have found out.

                My wot is 5450, 42 mph per gps and fuel burn is lower. I can stay on plane at a lower rpm, about 3000. I can also trim the motor higher without cavitation.

                Alone with 20 gals of fuel and "flat", I can get close to 7 mpg at 4200 rpms and 29-30 mph. Any wave action or current running cuts that down though. I can average about 5.5-6 mpg per trip.

                You guys were a great help. The only thing I am going to change right now is the flo torq II that is on the prop. After I installed the prop and put it in gear for the first time I thought something was wrong. A lot of noise was coming from the motor at low rpms. From what I've read I need the flo torq III hub kit and it should quiet that noise.

                John
                1977 22\' Mako sold[br]1975 24\' Blackfin Fisherman sold[br]1973 19\' Mako sold[br]1974 19\' Mako sold[br]1987 Wellcraft 180 Fisherman Sold[br]1988 Rampage 24 Express (New Ride)[br]1977 17\' Mako Standard[br]1989 17\' Mako 171 Just added

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                • #9
                  Installed the flo torq III and what a difference.

                  Quiet and steering is easier.
                  1977 22\' Mako sold[br]1975 24\' Blackfin Fisherman sold[br]1973 19\' Mako sold[br]1974 19\' Mako sold[br]1987 Wellcraft 180 Fisherman Sold[br]1988 Rampage 24 Express (New Ride)[br]1977 17\' Mako Standard[br]1989 17\' Mako 171 Just added

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                  • #10
                    1981 17 mako standard, 2005 115 Mercury Optimax, 13x17 Mercury Vengence prop 40-41mph 2 people on the boat flat calm no wind.
                    1981 17 mako[br]115 Optimax[br][br]

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                    • #11
                      Sorry it is actually 13x18 prop. Here is the pic

                      https://1drv.ms/u/s!ApCfwTOj86P_htJj2gbkYY7-6GQmOw
                      1981 17 mako[br]115 Optimax[br][br]

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                      • #12
                        quote:

                        Originally posted by dayjtradr


                        BW, the cavitation plate is right where it should be, just on top.

                        What advantage is the 4 blade prop?

                        I've read it gives bow lift.

                        Was that the reason?

                        Please post numbers when you break in the motor.

                        Thanks

                        John

                        Actually it's the opposite...it gives stern lift which is better for hole shot and shallow water performance and staying on plane at lower speeds. Best I can tell...haven't taken the motor up to wot...but ran the numbers for prop slip and it's at 6%.

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