how far above range can you before being worried

[jbalestr]

Hi,

I have a 115hp yamaha with a 17" prop. It is probably an original yamaha prop. The range for my engine is 4500-5500. What I am finding WOT is 37knots at 5700rpm.
I hardly ever cruise at WOT and prefer to sit around 3500-4000 range. Is this a case where I go to a 4blade prop of the same size to get better low speed performance ? or do I just not worry about it. Currently it gets onto plane pretty easy so I could probably go up in pitch ?

Thanks

James.

 

[Crownie2]

Re: how far above range can you before being worried

Personally, I wouldn't worry about it. How much time do you spend at WOT anyway??

I have read that some Yamaha's actually perform better at slightly higher RPM's as far as top speed goes.

If you were thinking about dropping cruising RPM's then you could go with a (three blade) SS prop or try to find one one or two inches higher in pitch...

Bob

 

[walleyehed]

Re: how far above range can you before being worried

You're setting at the perfect RPM now, with real good speed. No reason to change anything that I see...
Your 2-stroke is nothing but an air-pump running on needle bearings, and ball and roller at either end.
The intake system will keep it from going high enough to do any damage anyway.

 

[jbalestr]

Re: how far above range can you before being worried

Cool. Thanks for the answers.

James.

 

[Texasmark]

Re: how far above range can you before being worried

I bought this '02 boat in '06. WOT rating was 5500. Person I bought it from was running a 17" prop; dealer he bought it from propped it that way (Ok fine if gearbox was 2:1, but it was 2.3 to 1....usual sloppy service you get out of your dealer; just like the last new Ranger I bought from Barber Boats, Dallas, Texas.....had a 24p on my boat and the right prop turned out to be a 19p).

(Current boat data) On my first hole shot punch I got whiplash; the rpm's hit 7500 before I could blink.

Now here is a boat that has been used for 4 years and you aren't going to tell me that the owner didn't hit the WOT and haul buttox more than once.

I bought and retroftted a 21P and it brought the rpm's down to 6250 and spent another $250 and bought a 24 P which brought them down to 5600. Both props, she purred like a kitten, sang rather.

So you can talk to dhadley, but as far as my Merc 3 cyl 90 is concerned, the sky's the limit.

Mark