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I have 2 friends who have the same boats 19 1/2 seapro bay boats, both have 115 4-stroke yammys, one boat has a solas 13x19 prop and he runs 32mph (by gps) at 6000 rpm at wot. The other boat has a 13 1/4x 17 prop and he runs 39mph (gps) at 5200 rpm at wot. I would have thought the higher pitch prop should run less rpm's and faster mph than the other boat. I am confused by this situation as well as the guy with 13x19 prop. He wants more speed out of the boat, but not sure why he has such a drastic difference in rpm and speed than other boats. For what it is worth i have a kw 196 bayreef with 115 4-stroke yammy and a 13 1/4 x17 prop and run 5200 rpm and 40 mph at wot. If any body has any thought on this situation, or how my friend can get more speed out of his boat let me know. My thinking is go to a 21 pitch prop but that seems very large for his boat.

Thanks for the help

Well for one, the 17 pitch prop has a 1/4" larger diameter.

will a 1/4 make that big of a difference ? I can see where the 1/4 could acount for the rpms being higher but would have thought the 19 pitch prop would still be the faster boat? I am not sure i understand the effects of diameter to pitch.

Diameter, pitch and CUP make a huge difference in the way a prop preforms

what's the other kind of prop? the solas is a budget prop. it's the kind i run...

I have a couple of solas props. I am not real impressed. I have been told what they deliver in the way of price they take away in the area of performance.
Cup plays a big part in the performance of a prop as well as diameter and pitch. Smaller diameter props are able to turn faster with the same or greater pitch. But that does not mean they will push the boat faster.
The difference between your friends with identical boats might also be the material the prop is made of. A stainless prop will push a boat faster than an identical aluminum prop. This is due to less flex in the steel prop.
Tell your buddy to send his solas to one of the local prop re-finishers to have some cup added. This should give him the added top end he wants as well as slowing down his wot rpm a little by increasing the load on the engine.
The following link should give you all the information you need to completely fry your brain with all the combinations and adjustments available. http://www.boatfix.com/how/props.html
FF

My issue with the solas is I can't get my rpm's up where I want them. I'm thinking of going to stainless when the budget permits...

i will say i don't feel as bad about chewing up the solas from time to time.

Weight and balance have a lot to do with performance as well. The slower boat may have more "stuff" in the boat.

As FishinFool pointed out, the flex difference between stainless steel and aluminum can be huge. So can the quality of the prop. A top brand will be forged truer than a cheap one. Check with your dealer to see if they have loaner props and try comparison tests under the same conditions (weight, rpm, fuel, sea conditions, etc.). That's the best way to dial in the right prop for your particular hull.

It's late so I wont go into it but this is a very useful link that can help you see what your boat should be doing.
http://go-fast.com/Prop_Slip_Calculator.htm

Your prop, in combination with motor setup, determines the performance of any boat.

Spot on, it could be a number of things. It could be a bent prop, a bent prop shaft, motor height, trim angle, or the lack of, a spun hub, or a combination of several things. If your buddy is turning a 19 pitch prop 6000 RPM and only running 32 mph something is wrong with the prop. I'm wondering if the prop hub is slipping and he's hitting the rev limiter.

Why dont they swap props to see if their numbers change? That will give them a starting point.

I swear by these props "never at em"
http://www.propcopropellers.com/yamaha_Propellers.htm