prop questions

[cleve]

i have a yamaha 60(2.33 gear) with an aluminum yamaha 19 pitch on an aluminum bass boat. i have raised engine and the prop vents a little. wot rpms @5500-5600. i tried a stiletto ss 21 pitch and it did not vent but rpms at wot were @4500, i guess because of cupping on th prop. should i have went with a 17 stiletto? there is a yamaha ss pro series 18 pitch on ebay. would anyone recommend either of these options? with a cupped prop i need to drop an inch or 2 of pitch, right?

 

[boat1010]

Re: prop questions

I don't have a clue what you are talking about when you say you raised the vent. But any way. The pitch of the props. If you are at the manufactures RPM at WOT there isn't much you can do with the pitch of the prop unless you are looking for something specific. Your motor just doesn't have enough HP to push that big a pitch prop. So if you are looking for a little better hole shot or a little higher top in you can play a little with the pitch. The cupping of the prop does play a little on things but it is mostly the pitch that is making the difference with the RPM at WOT. Hope this helped you.

 

[bowman316]

Re: prop questions

I would stick with a 19, maybe lower, Going higher will reduce hole shot, but it will give you better gas mileage. Was it hard to get on plane with the 21 pitch?

and with more weight on board, it will be harder to get on plane.

 

[Silvertip]

Re: prop questions

Sounds to me like you raised the engine a tad too much. The problem with changing prop materials, prop designs, prop pitch and going to a cup from a non-cup throws too many variables into the mix to accurately predict the outcome. The Steletto is a good prop but at 21P it severely overpowered the engine. In other words the engine simply does not have enough power to twist a prop with that much pitch. With a 19P prop, 5600 RPM, 2.33 gears and using 13% slip factor that produces a theoretical speed of 37 MPH. It would help to know what boat you have and what the observed WOT speed is but I'm thinking those numbers are pretty close to optimum. While a 17P would provide a good boost getting out of the hole, it would raise engine rpm about 400 (to the 6000 range) but there would be no increase in speed. I think you have a good prop now but if you want a little better hole shot or frequently run heavily loaded then the 17P from the same manufacturer as the 19 might be a benefit.

 

[cleve]

Re: prop questions

you are right silvertip, my top speed is @37-38. i am looking for a little more topend because my holeshot and midrange is awesome. i did get 40 with the 21 but rpms were way low. i can't trim out very much with the 19 aluminum bfore it vents. maybe i should just lower motor back down where it was and be satisfied. i just thought with all that power on the bottom end, that a ss prop would give me a little more on topend but i need to stay at least over 5000 rpms. i guess i'm getting all i'm gonna get, like you said. thanks for the reply.

 

[Silvertip]

Re: prop questions

Tinkering with props at this point would probably get you a tad more speed but not enough to justify an expensive prop in my view. But if you have a thick wallet, go for it. But what you MUST do is keep the engine rpm at the upper end of the band to get the most out of it. You saw the effect of too much pitch. Lugging an engine will eventually kill it and propping for the low end of the band is not recommended.