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  • Prop Setup

    I have a '79 23' Mako. Approx. 2500 lbs with a Johnson 235 outboard with a 1.86 gear ratio on it. I'm running close to 6000 rpm WOT! Seems High?

    WOT should be between 5000-6000. The dealer said top RPM shouldn't go over 5600?

    My top speed on the GPS is only about 40-44mph and she seems to really spin hard on takeoff with out going anywhere. I think my pitch or my prop is totally wrong. Anyone know what I should get or what I need.

  • #2
    You didn't say if you were running a SS prop or an Aluminum or the size (dia) and pitch. SS makes a big difference. From the info you gave, I would say that you could go up another 1 or 2 pitches if your running SS. The spinning on the start could be that your giving it to much gas but then again the higher the pitch on the prop the more chances you will get a blow out (of the water) on the prop. This is the old double edge: Usually - the lower the pitch you get more power and a better hole shot but loose top end speed and some MPG. A higher pitch gives you more speed and MPG but you loose on the hole shot and stability on takeoff. ALSO, the weight of the boat has a lot to do with it - you don't prop a boat with one person and half a tank of fuel and no gear and expect it to perform well when you go offshore with extra gas and 3 people and the fishing equipment for tuna. Your best bet is to find someone that will let you try another prop and then you decide by the way the boat handels and the WOT RPM's with the weight in the boat that you do most all of your boating with. Sometimes a dealer will let you try a prop if there is a good chance that your going to buy it. But be careful with a try prop, as SS props run from the low end of $350 to up over $500 ++. And don't worry about how fast your going on the GPS - as long as the boat is handeling the way you want it to.

    Hope this helps -

    Mike
    1973 22 CC Milford, CT USA[br]

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    • #3
      I checked last night, the prop is an aluminum and it's a 15X17 someone said I should try a 4 blade? what's everyones opinions on that? Should I move to a 19 pitch? I had a tank and a half of fuel in the boat and 4 people, just still seems that the RPM'S are too high? Close to 6000!

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      • #4
        Well, again, as stated in the above post, you prop a boat to your normal, or at least expected load. I'm a pretty firm believer in propping to the max RPM, and I believe on your engine it is indeed 6K. Not that you are going to run there, but it makes life for the engine much easier throughout the RPM range. Less heat, less torque. And, I know that when we load to go fishing, after ice, bodies, gear, (tunafish!) etc we're running alot heavier than when running around on the bay. Keep it at 6K, but you have other things to think about here:

        Forget the 4 blade wheel. You only need that if A)your a flats guy and need to get the boat up, out and going FAST, or B)you have cavitation problems. A 4 blader is less efficient than a three blade wheel, and while you may not notice much at your cruise, you will lose top end. Flip side is you will probably plane at a lower and more consistent speed. And, they do hang on better in rough water, particularly when you're loaded so if thats a concern maybe...

        The other thing I'd say is that alum wheels suck. Unless your in a rocky area, or prone to finding bottom elsewhere, s/s is the way to go. They are more efficient (faster, which ultimately = better economically) b/c of thinner blades...and also, this may go towards your current RPM and hole shot issues, but alum wheels will wear, as well as distort with load. You may be running less wheel now than you think, depending on the age.

        Long story short, I'd try a 17p s/s wheel, a stiletto or rapture type, something with rake that will let you fly that hull. Both these wheels will do that, dollar for dollar they are awesome, I've been very very happy with my stilettos. (I replaced 19p stock Yam s/s wheels with 17p stilettos, things are so damn efficient my speeds pretty much stayed the same across the board, except top end where I gained and got my RPMs to where they need to be) Try one and see where you're at - just make sure its returnable if for some reason you dont like it! I know Overtons will let you return a wheel, amarket.com (where I got the best price on mine) may as well. But do try to keep the RPMS towards the upper limit, unless you're testing as normally loaded. In that case, Mid-5's would be the lowest I'd accept. I'm betting you'll see a tremendous change in performance going to a stiletto over the alum prop.
        1990 261 T/2001 200 HPDIs[br]Basking Ridge/Mantoloking NJ[br]

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        • #5
          Makorider kinda said it all in his post - Get a SS prop and then start making decisions about proping the boat. Al props are so inefficient it doesn't pay to even have one on the boat (except for a spare get home prop).

          Mike
          1973 22 CC Milford, CT USA[br]

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