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snoozebutton

Do I have the right prop on my boat?

7 posts in this topic

What I have on came from the manufacturer. It's a 90 hp 4 stroke Johnson and on the prop it has 3X14X17. I'm guessing this mean 3 blade, 14 inch diameter, 17 pitch. It's seems good out of the hole, a little disappointed in the top end (38 mph with just me), and I'm getting some porpoising. I'm running 5,800 RPM's WOT and the manufacturer recommends 5,500 RPMs at WOT.

Would I get more porpoising with a 19 pitch? I think a 19 would give me a better top end at lower RPMs wouldn't it?

Appreciate any advice!!!

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The 19 would get you more top end and lower rpms ---- also less hole shot.

I don't know about the porpoising - I wouldn't think you'd get more. Redistributing the weight in the boat might help. Also a stainless prop might take care of the porpoising by giving you more stern lift, it's one of those things where you'd have to try some props to see what works best. It's always a trade-off, every time you gain something in one area you're going to be giving up something else in a different area.

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I would try a 19 pitch 4-blade stainless renegade prop. That should keep your holeshot up to par, and also give you better top end whle eliminating most of your porpoising problems. For each pitch you to up, typically you drop about 200rmps. I would guess it should also bring down your rpms close to 5400. The only other solution to your porposing problem (besides prop) is to change the engine height or go with an ugly whale tail. You will also like a stainless 4-blade much better if you have any blow-out problems on tight turns, or if you like to pull any skiiers or tubes.

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The 14" diameter sounds a little large to me. I'm running a13 1/4" x 20 stainless prop on a 130 Yamaha. If your running an aluminum prop I would recommend going with a stainless 17P 3-blade prop. The stainless prop is more aggresive than the aluminum prop due to the cupping and rake and should lower your rpm some while at the same time maintaining good holeshot and top speed. A 19P 4 blade stainless prop will be too much prop IMO. 4 blade props of the same pitch tend to reduce rpm a couple hundred rpm over an identical 3 blade. My $.02.

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what do you expect out of a 90 horse power that sounds good to me.

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I have a 75hp mariner and use a 13/19 and a 13/21t the 19 gets me going on plane faster than the 21t. but the 21t gets me a few more miles and hour both gat me to the buzzer @ 5500 rpms these props are not stainless. 1 have a 17ft lund Mr. Pike.I have got it to 41 by myself with the 21t and getter to go 38 with the 19. my buddy tried stainless on his 75 and only gained two miles and hour with the same pitch, he also tried a 13/17 and that thing freakin rocked just no top end it jumped out the hole really good tho.

Depends on how far you travel on water I only use the 21t up north and millac.

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Thanks for all the replies. I'm going to head to the dealer this week and talk it over with them but now I have some info so I won't sound like a total one-who-thinks-I-am-silly. grin

what do you expect out of a 90 horse power that sounds good to me.

I said a "little" disappointed. Just thought that with a 16' Alumacraft I'd be getting a little over 40 with that motor which I still think is possible with the right prop but first I have to deal with the porpoising issue.

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