Engine height or prop?

S

Scotty P.

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I've got a 20' cc with a 99 150 Johnson hanging on a transom bracket. The bracket extends out 22". The prop is 15x17 stainless. With motor trimmed down my cavitation plate is around an 1 1/2" above keel. I've read that for every 12" of set back it should be raised an 1". It takes a while to get on a plane. Didn't know if I have a lot of drag from motor or pitch just not working for me. At WOT I'm running around 4500-4700 rpm's. Any information would be greatly appreciated. Thanks!!!
 
metriccrescentwrench

metriccrescentwrench

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Re: Engine height or prop?

I'm leery of those generalized 'rules', what really matters is how high the engine is in relation to the water's surface when you're running at speed. Check to see if the AV plate is a bit above the surface, that's what you're looking for.

Do you know what the maximum rpm range of your engine is supposed to be? Off the top of my head 4700 rpm's sounds low, which would indicate that you need a lower pitched prop (and that would help your hole shot).
 
JB

JB

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Re: Engine height or prop?

^^ Exactly.
 
S

Scotty P.

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Re: Engine height or prop?

I was curious about the prop but was not exactly sure about that. But I will definately try it this week and if I'm not mistakin my rpm's should max out 5600. And I will also look at my cavitation plate on the run this week as well. Just got to tie off so I can walk out on bracket that runs across the entire width of boat. I do appreciate it!!
 
S

Scotty P.

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Re: Engine height or prop?

I also was considering adding some of the hydro fins! Do these actually help?
 
metriccrescentwrench

metriccrescentwrench

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Re: Engine height or prop?

I'd first get the engine height correct as mentioned, and once you're good there find the correct pitch prop to get your rpms at WOT with a light load up as close as possible to 5600.

And yes, those fins can help hole shot in some circumstances. First though I'd get the engine height and prop pitch worked out. After all of that, if you're still not happy with hole-shot I'd try a fin and see if it does what you want and doesn't induce any unwanted handling characteristics. I have one on a 15 ft fisn-n-ski and it works great, but I don't have any reason to put one on the Checkmate because it's a fairly light boat with plenty of power.
 
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