Yamaha f250 cobra 755 Prop choice

[trickyrich]

Ive got a cobra 755 with a 2008 yam 250 and am having prop choice issues.

We need to change the prop due to some issue with the bushing causing the vibration i mentioned in my other thread.

My issue is, we have a 15.25x19 on currently, and the boat seems to hit 6100WOT with ease. Yam specs are 5000-6000WOT rpm, the boat tops out at 44 knts mid trim. it feels like the engine peaks far to soon, and we just run out of steam 3/4 throttle and up.

What would your recommendations be regarding prop size or does anything have any experience with this combo.

Thanks
rich

[beamishken]

It's possible the engine is hitting the rev limiter which is usually set just over the recommended max rpm in which case you could try a 21"which would increase top speed and in theory reduce rpm to around 5800rpm which is still within the correct range.
Prop selection is a bit of trial and error so often the best way is to try and borrow a trial prop from a dealer on the assurance that when you find the correct set up you will purchase the new prop from the dealer

[trickyrich]

So the boat yard we got it from is replacing the prop and has suggested a 13.75 x21. We have at the moment 15.25x19 now, this seems in my lesser knowledge to be a smaller prop which is going to cause more of an issue with our over rpm ..