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Old 16 May 2013, 05:52   #11
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Country: UK - England
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Boat name: WhiteNoise/Dominator
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Quote:
Originally Posted by mick View Post
I only have one its the one Chris Caton had spare
You'll have to get another then.

Lemme put it this way, it's the equivalent to putting a 19" wheels on one side of the car and 17" wheels on the other.
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Old 16 May 2013, 05:55   #12
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Fair does will wait for another to come along
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Old 16 May 2013, 09:22   #13
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Originally Posted by Nos4r2 View Post
It will, but it'll reduce your top speed.

A 19p 5 blade will do less rpm than a 19p 3 blade. You're better off doing the comparison on like for like props and only changing one variable at a time.
Thanks for all the advise but I have given up , I took the boat out for a test today with the outboard raised so the cav plate is 1" above the bottom of the boat and a smaller prop ( 15p ) but the revs are still only reaching 4400 when they should be getting 5600.
I have now just taken the boat to Advance Marine to see if the rev counter is telling lies or if anything else is wrong
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Old 16 May 2013, 12:50   #14
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Country: UK - England
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FWIW, I think a stainless 19p 3 blade on a 75 is probably overpropped by about 4 inches.

However, what you just said sounds like something's not right apart from the prop.
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Old 19 May 2013, 06:17   #15
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To Teamplonker

You don't say what pitch your present 3 blade prop is ! Nor your present "low" RPM ! Is it really 4400 with a 15" prop, extremely low indeed.


You said nothing about speed, did you measure it with a GPS.
Knowing it, and the gear ratio, and the prop pitch, you could approximate the RPM and know if your tachometer is lying.

I would suspect that your engine doesn't deliver the 75hp it should, or that your hull is very dirty, or ...
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