prop question

[dirtpapa]

Have a 1990 Bayliner 1800 capri with 3.0 mercrusier. Has a 15 inch 17 degrees prop that needs replace. My question is 17 or 19 degrees for overall good preformance

 

[Scott Danforth]

did you have any performance issues with the 17P? what was your WOT RPM?

since your new, not sure if you know of the stickies at the top of the forums. here is one on prop questions http://forums.iboats.com/forum/gene...p-questions-and-topics/295058-read-this-first

 

[steelespike]

Any prop change needs to be based on your present performance. wot rpm and gps speed.
Just to avoid confusion prop size is given in inches. Usually a healthy 3.0 with a 17" prop would likely over rev
Typically a 17" prop would be selected for heavy loads or water sports or a combination of those.
Get us your lightly loaded performance numbers.

 

[dirtpapa]

My 15 inch 17 degree was good out of the hole but was lacking on top end. Will the 19 degree give me more speed. It's an old motor and I hold her around 3700 RPMs.

 

[steelespike]

The motor needs to be propped so it can reach the max rated rpm.(4800)You don't have to run it there.
If the motor can reach or exceed max rpm with the 17" pitch then a 19 may add a little speed with a slower hole shot.
Going to the 19 could lower wot rpm up to 400.IOf we assume the 17 makes 4800 rpm guessing a 2.00 gear ratio and 13% slip gets about 33 mph.
If we assume 4400 with a 19, 13% slip nets about 34 mph.Thats a lot of guessing So results could be different.
By the way 4400 is at the bottom of the rpm rating. As you add weight it moves below the rating lugging the motor.
Once the motor is forced below the rating it is lugging whether you reduce the throttle or not.
The motor needs to rev freely within its range 4400 t0 4800. Again once propped correctly you can run any rpm you choose.