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What would happen with these props?

What would happen with these props?

Old 09-29-2006, 09:14 AM
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Default What would happen with these props?

My boat is not an offshore racer but is based on a cigarrette 42 hull, kevlar glass/foam sadndwich from mid 80s and weighs around 15,000 lbs and has arneson ASD8.

Having difficulty finding props to replace the 19x19 3-blade round eared, low rake props that are on it. I get very little slip with these but cant pull rpms past 4000 with twin 502 420 hp motors and 1.5:1 reduction trannies.

What would happen if I went down to 16.5/17-inch diameter cleavered merc props and upped the pitch to 26 or 27?

Would I get more slip but more rpms? Would I still get out of the hole? Top speed is not the goal - getting the motors into the right rpm is and I'm not sure how diameter effects the equasion with arnesons.

Thanks Yodas
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Old 09-29-2006, 09:48 AM
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Default Re: What would happen with these props?

What would happen if you keep knocking a quater of an inch off the diameter of your existing props until you got where you want the boat to run?
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Old 09-29-2006, 12:16 PM
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Default Re: What would happen with these props?

I've told you several times, you need to contact Ellis Propellers in FL. Ask for John Rose. 904-354-8233 and tell him your setup. The old Harley boats run well but they are not rocket ships. 15,000 lbs is on the light side for weight on its best day.

First a 3 bladed propeller with no slip is rare.
Second if you want more speed you will need different propellers. You can up the rpm just by removing cup or diameter or a combination of the two. The slippage will go up accordingly.
Third, you have a square propeller, going under square is not a good idea so you should not go to a smaller pitch propeller.
Fourth, you might need more power.
Fifth, you might need a different reduction ratio in your transmission. This will make one of the largest differences as it will get you away from a square propeller, improve your mid range cruise, top speed and getting on plane.
Sixth, if you cannot pull a 19" pitch there is no way you can pull a 26-27" cleaver with more blades without changing the reduction ratio and HP.
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Old 09-29-2006, 12:23 PM
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Default Re: What would happen with these props?

I doubt if the cleaver will carry the bow as well as a round ear.
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