Prop selection help

[Fr3AkAzOiD]

Ok, I'm trying to squeeze more top end out of my tiny boat and am hoping a new SS prop will get me what I'm looking for.


I have a 2000 Mercury WaterMouse thats 10 ft 6 inches long, 4ft 4 inches wide, Vee hull, weighs about 325 lbs give or take 50 lbs.
It's a single person boat (150 lbs), 4 gallons of gas (stored in bow tank), and I just like racing around the lake at WOT.

My engine is a 2000 Mercury, 2 cycle outboard, Model 15 hp, 5,000 - 6,000 RPM WOT range, motor weights 75 lbs and has a 2.0:1 gear ratio

Anti-Ventilation Plate is one inch above the keel.

Theoretical top speed with no prop slip would be 25.2 mpg, I currently run 23.3 mph giving me a prop slip of 7.5%
WOT is 5920 rpms.

Got a stock 9 X 9 aluminum prop.


Ok, I think that handles the part where I give you all my info.
Now for my question....

1. What pitch would you recommend considering I'll be going from aluminum to SS and 9" to 9.25" diameter?


I was told that the 200 rpms per pitch wasn't accurate in low hp engines so going from a 9 pitch to 10 pitch is an 11% increase and would lower rpms 11%.
Also that going from aluminum to SS would lower my rpms by 100.


Thanks in advance

 

[74john50]

Re: Prop selection help

check out boats.net they have a list of oem props that might help it worked for me but like you havent made up my mind on what i want speed or power

 

[Fr3AkAzOiD]

Re: Prop selection help

Edited the huge wall of txt, still need help with what prop size to get.

 

[steelespike]

Re: Prop selection help

Whether the double or triple ss cost is worth it is up to to you ??
Your al prop is doing pretty well that would seem to indicate the ss improvement may be marginal.
If your not having any venting(cavitation) you may be able to raise the motor more.
Adjust trim if one hole is not enough and the next is too much you can buy or make wedges to make half a hole.
Raise it to a point just before venting becomes a problem.The ss will allow maximum height.
Changing from al to ss can be unpredictable You not only have a design that may load the motor more you have a higher tech design that has less drag then you have a prop that may affect the hull more.Some times rpm goes up other times down.I think I would go with a 9" pitch don't worry about slight differences in diameter.
While I'm not crazy about the Turning Point Rascal prop (unpredictable) Some have had close
to ss performance at al cost.