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Prop change for my old pontoon boat

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  • Prop change for my old pontoon boat

    Here's what I now have:
    • Old two log 24' pontoon boat with outboard
    • Use it mostly for family outings on a medium size lake (tubing at WOT, cruising a mid-throttle)
    • Engine is 2015 Mercury 115HP 4-stroke with Command Thrust gear box
    • Current prop is 4-blade aluminum 14.8" diameter with 15" pitch
    • Max rated RPM is 6000
    • WOT with just me yields 24 MPH (GPS) at 5300 RPM
      • Slip calculator says that is 27% slip
    • WOT with 1,000 pounds of people and gear is 20 MPH at 5000 RPM
      • Slip calculator says that is 33% slip
    My goal is to get higher in the RPM range with a 1,000 pound load while gaining a little top speed as well. (I would expect the slip to come down some as well.) My guess is I need less pitch and maybe a change in diameter. The reasonably priced propeller choices don't offer many options without a big change in pitch. The two that caught my eye are both aluminum 3-blade props. One is 14x14 and the other is 14x16. Here are my questions:
    1. When looking to gain RPM and decrease slip, which if either is more important, pitch or diameter?
    2. Between the 14x14 and the 14x16, which would you recommend to meet my goal and why?
    3. Are there other reasonably priced propellers you'd recoommend over the two I mentioned.
    Thanks in advance for the opinions and advice.

  • #2
    Are there 4 blade props with less pitch available. say 11-13 pitch props to pull wot revs up towards middle wot rpm as max loaded. When less loaded wot rpm will increase accordingly.

    Happy Boating

    Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers


    • #3
      Seems we are in the same boat, pun intended! Trying to get prop slip down and move a heavy toon up the river. Best advice I got so far is to find the biggest diameter prop you can then adjust pitch to get your rpm where they need to be. My 05 tritoon with a Honda 150 seems happy with a 16 x 13 3 blade black max prop. Less slip and I can pull a tube without
      blowing out in a turn. Props are not cheap I can tell you that, so if you can find a place that will let you try a few out would be most helpful. I would not go up in pitch, you need to go down.


      • #4
        Well, the season is pretty much done around here. If that were my boat, I would go with an option you didn't suggest. I'd send the prop you have out for some professional massaging during the off season. With your current performance, and your target performance in mind, I would think that very "do-able". A good repair shop could easily re-pitch that prop you have to a 14". You could discuss cupping with them while you're at it, to get their thoughts on how they feel about more or less for your application. The guys I used to work with frequently would offer to take a second crack at it if they're off by much. I never had to take them up on it.....

        Going with a 16" pitch prop is going to load the engine more than it is now - taking you the wrong way, leaving you with less rpm (at WOT) than you have now.

        When talking diameter you really don't have a lot of options. If selecting from 2 otherwise similar props, I would likely go with the larger diameter for your application (which is nearly identical to mine). Think tug boat vs. a blown fuel nitro boat, and the differences you might see in those 2 props. Both able to absorb a thousand horsepower, with very different purposes in mind.

        Last, I have no experience in the 3 blade vs. 4 blade theater with a 'toon and this kind of power. Being from the old school, I'd likely go with a 3 blade as I've seen no overwhelming logical arguments that have sold me on the 4 blade plan - when considering a boat this size with an engine this size. -Al


        • #5
          Scott, nice to hear you have that boat sorted out! -Al


          • #6
            I decided to take Al's advice and found a prop shop about an hour away. I spoke with the owner and he can turn my 14.8" prop down to 14". I'll give that a try next spring and see how it works out.


            • #7
              Tommy, you don't want that prop turned down. Any half baked repair shop can do that. You want it re-pitched! The original diameter will help maintain your original thrust, the re-pitching allow a few hundred extra rpm on top. (My opinion)


              • #8
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                OK. Turning it down was my idea, not theirs. I'll ask about changing the pitch.