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I have a pontoon boat with a Mercury 90 engine a prop pitch with a 17 pitch. The RPM at full throttle is 5000 and the MPH is about 23. 8 have read that if drop to to a 15 pitch, I will get an 500-800 RPM increase. I don't know what these means as for a MPH increase. Should my next prop be a 15?

You will get a better holeshot with the lower pitch. You RPMs will increase also. It will probably be slower on the top end

Your top end mph will drop with the 15, but your hole shot will be better. Generally speaking, you should run whichever prop puts you in the recommended max rpm range for your motor. You don't want to bog the motor with too much prop, nor over-rev it with too little.

- Steve Stinson

Thanks for the replies. My objective was ton increase speed. My thought is that increasing the RPM would increase the speed. It looks like I was and have been saved from aggrevation and wasting money.

Might be worth your time to do some reading.

http://www.mercurymarine.com/propellers/about/overview/

I'm running a 15 pitch on my toon with a 90hp Yammy 4-stroke and have seen speeds as high as 27 and my RPM's are 5300. 15 definitely does well for me but your mileage may vary. What size are your pontoons? That makes a difference in the top end speed you will see. You said your objective was a ton increase in speed, I'd say the answer to that is buy a boat that isn't a pontoon...

Rob, if your WOT is 5300, you need to drop your pitch down to around 13 your yammy is desighned to run at 6000 WOT and you are putting a good bit of strain on the motor at 5300 WOT. You could probably drop to a 12 pitch for that matter, but going to 13 will increase the motors life span

wevans wrote:Rob, if your WOT is 5300, you need to drop your pitch down to around 13 your yammy is desighned to run at 6000 WOT and you are putting a good bit of strain on the motor at 5300 WOT. You could probably drop to a 12 pitch for that matter, but going to 13 will increase the motors life span

From what I have read 5300 is within spec. The manual on my engine says its designed to run between 5000-6000 on the RPM's. I've also done some of the prop pitch tools on the web where you plugin RPM's, speed, boat type, prop pitch and they are saying I'm good on the pitch. I get great hole shot and what I consider good top end. I'm not going to mess with it but I'll definitely keep what you said in mind. Thanks bud.