Your Opinions On Prop Pitch And RPM

[rutcutter]

I am rather new to boating. My boat has a 2005 50HP Mercury and was only turning 4800 rpm at WOT when I got it. The range is 5000 to 5500. My question for you guys is this. Is anywhere in that 500 rpm range OK? A friend loaned me his spare prop and it got 5200. His other one was a little over at 5700. Is there an ideal spot in that range that I need to shoot for and will that extra 200 rpm over 5500 harm the motor? My friend has been a boater for a long time and he says the company is very consevative with the max rpm and that the 200 over will not hurt anything. I would like some opinions from the forum.
Thanks.

 

[lncoop]

Re: Your Opinions On Prop Pitch And RPM

Your friend is probably right, but why take the risk and possibly shorten the life of your motor based on his opinion? Those specs are there for a reason. The best prop is the one that maxes out your RPMs at WOT. It does sound like you need to make an adjustment to get them up a little. You don't want to lug your motor. Does the prop conform to the factory recommendation? If not, your best bet is to start there.

 

[steelespike]

Re: Your Opinions On Prop Pitch And RPM

You can fine tune your setup to improve your rpm and speed.
The antivent plate (just above the prop) should be visable on plane.
Usually there are holes in the mounting bracket that will allow you to raise the motor.In the extreme this could net 2 to 3 mph.and some rpm.Generally this will slightly improve hole shot and handling.If you get back to us with your prop size and material,max rpm and speed
it will help tell if your setup is working.

 

[Silvertip]

Re: Your Opinions On Prop Pitch And RPM

One way to look at this is that with WOT at 5700 RPM you can throttle back to 5500 but can hammer down to get terrific hole shot. Add a load or tow a skier or water toys and you will appreciate the extra grunt that prop provides. If you install a prop that gets you to only 5200 for example, you cannot throttle up any more and towing a skier would be a struggle and very likely pull WOT rpm below 5000. No -- 5700 won't hurt the engine if the extra rpm is used wisely. But 5200 will harm the motor if you lug it to the point where it cannot reach that rpm. I had a 40 HP Evinrude that was propped for 6000 on the money and it ran there a lot. Great hole shot yet you could cruise at whatever rpm you wanted without strain. Just because you have some extra RPM on tap doesn't mean you need to use it all the time.

 

[RicMic]

Re: Your Opinions On Prop Pitch And RPM

It depends on what load you are going to carry. Was it an average load, light or heavy? Also to consider, how and when you use your boat. Testing on a hot dry summer day, the rpms can be 200 lower than on a cool damp autumn day. I wouldn't worry much about the 200 rpms, if thats the way you go, how often are you going to run WOT?

 

[Tig]

Re: Your Opinions On Prop Pitch And RPM

My boat can run as much as 500 RPM past redline with a light load, but I rarely do exceed redline at all. I like to be able to reach the upper end of the RPM range to maintain a reasonable holeshot with a heavier load. I generally cruise at 1000RPM below redline. I think 200 over at WOT is reasonable. Just back off and cruise like you would in a car.

 

[rutcutter]

Re: Your Opinions On Prop Pitch And RPM

I want to thank you guys for your comments as they were very insightful.