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  • #1

    Advice on prop for new boat

    Hello all,

    I just purchased a new (2015) Alumacraft Crappie Deluxe, 16' jon boat. It came with a Yamaha F20 (20 HP) motor. Love the boat. My concern is that I am having trouble getting it up on plane. I am a big guy (270). When I'm by myself, it gets up on plane fine and tops out at 20 mpg - all that I want. However, if I add one person (150 pounds) I can't get the boat on plane so top speed drops to 10 mph.

    The prop is a 9 1/4 x 10 - J1. I have no idea what the J1 designation is but I understand the other numbers to indicate it is a 9 1/4 diameter prop with a 10 pitch.

    Based on what I have seen on the Yamaha site and the Boats.net site, it is obvious that I can purchased a new prop with anywhere from 7 to 12 pitch. As I understand things (based on reading about props) if I change props I should go to a lesser number to better handle a heavy load.

    So my questions:
    1) Am I on the right track. Would a 7, 8, or 9 pitch prop help me get on plane with another person in the boat?

    2) I understand the lower pitch number would increase the rpm of the engine at full throttle and that care must be taken not to overrev the motor. Does it make more sense to go with the 7, 8, or 9?

    Thanks for any advice. I tried to call the customer service number on Boats.net but never got through (the music was nice).
    Tags: prop pitch
  • #2
    You are on the right track. I would try the 7 pitch.

    Would be nice to have a tachometer but the motor has a rev limiter to save itself in the unlikely event the motor could over speed with you in the boat by itself.

    Maybe let your lighter friend drive the boat with you up front to help it plane.

    Comment

    • #3
      Thanks

      I appreciate the advice on moving my fat butt forward - although you were much more tactful.

      I have ordered a small tachometer/hour meter to check the rpm's while on the lake.

      My plan is to wait and check the rpm's and then, assuming the reading is low, order the 7 pitch prop. Good to know about the rev limiter on this motor - I had no idea.

      Thanks again for your help.

      Comment

      • #4
        you need to read RPMs at WOT with only you in the boat and also with your friend in there and report back before getting a different prop.

        You may end up having to switch back and forth between different props depending on the load. But see how it reads first to make sure what prop to get.

        How wide is that boat?
        I have seen a 16' deep and wide flat bottom boat with 4 adults plane well with a 25 Evenruide .
        narrow boats do not do as well though

        Comment

        • #5
          I have a similar boat with the same motor. My boat is a 1648T Lowe Jon with a factory aluminum floor, with plywood carpeted floor on top so not a lightweight. I bought a used Yamaha F20 which has the 9 1/4 x 12 prop. Its been perfect. Im a big guy too...300lbs and with my son who is 60lbs and rigged light we will hit 22 mph (gps). Thats with a couple anchors and deep cycle battery too. When my wife and daughter go and I have more gear I can still hit 17mph. I dont know what my rpms are but I did just buy a tiny tach but havent installed yet. It seems the consenus is to go smaller on the prop but I have the biggest prop you can put on that motor and it seems perfect. Quick to plane good top speed.

          Dave
          Attached Files
          Last edited by DSmith1178; 03-18-2016, 03:37 PM.

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          • #6
            The height of your motor on the stern is correct?

            Comment

            • #7
              DSmith1178 - thanks for the encouraging news - but also a little discouraging since it sounds like we have very similar arrangements. I do have a deep cycle battery in the back of the boat, with the engine battery in the back on the opposite side. 6 gallon fuel tank as well. The boat itself has the usual gear, three life jackets, plastic oar, and some rope for tying to the dock. All this to say that I don't feel like it is overloaded.

              I have ordered a tach/hour meter and will check the rpms at wot under load ("load" being me and one other adult in the 160 pound range). I suspect the rpm's will be low. The next question will be what to do about that.

              I have ordered a 9 1/4 x 7 pitch prop and will put it on (after my rpm check) to see if that helps.

              Boscoe 99 mentioned a rev limiter. The motor is brand new (less than 20 hours) so it seems doubtful anything could be wrong with it. I'm going to do some checking to see if it is an adjustable device - assuming my rpm and prop experiment does not work.

              Thanks again for all the help. I'm probably overthinking all of this but it does concern me being a new boat and motor. I'm retiring June 1 (man that sounds weird after all these years) and plan on fishing quite a bit. Leave it to me to already figure out a way to worry about something.

              Jim

              Comment

              • #8
                As it has been asked but you did not reply to it, is the lower unit too low?

                What shaft motor do you have?
                and what does the boat need?
                All you have said so far is F20.
                There is more info on the stickers

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