Prop Question

[Streffpilot]

Hi, I have a 17'starcraft with a 115hp mercury outboard, the tower of power type. the boat is probably a little on the heavy side. it is fiberglass with 3/4 treated flooring. i was wondering what size prop would be good for this? id like the motor to top out around 5300-5500 rpm. any suggestions are highly appreciated!!!

 

[steelespike]

Re: Prop Question

If you answer the questions in the stickys at the top of the prop forum we can help you out.

 

[Bamaman1]

Re: Prop Question

You didn't say what rpm's you're maxing out at already. I would imagine you're looking for a 21 pitch, however.

 

[jestor68]

Re: Prop Question

It would be helpful to know what rpm the motor is turning at full throttle, combined with the current size prop.

My educated guess would be a 17" pitch as a starting point.

 

[Streffpilot]

Re: Prop Question

Well, I last ran it in early summer (the stator went out, and the engine is now being rebuilt) so I dont remember specifics, but I do remember only getting maybe 35 mph out of the non gps spedo. The rpms were maybe around 4000-4500. I have the oportunity to buy a nice stainless prop that is 13 1/4 x21 or i can get one in 19.

The motor is a 1972 Mercury thunderbolt tower of power 115 hp.
The current prop is a mercury aluminum 12 3/4 x21.
The boat is a 1988 Starcraft Select 170

I know i should be getting more rpms out of the motor, im just not sure if the low rpms was due to a weak motor or a over piched prop.

 

[Georgesalmon]

Re: Prop Question

IMHO you should wait until you get your motor back and run it with the prop you have. Doing anything else may just be a waste of money. The bare minimum info is needed (WOT rpm) to determine the correct pitch so your motor will run in the recommended rpm range is critical.

 

[jestor68]

Re: Prop Question

For testing purposes, your motor's WOT rpm range is 4800-5300 rpm.

 

[Chris1956]

Re: Prop Question

Streff, I think the 21P prop is a stretch for your boat/motor combo. The only way to know for sure is to check the WOT speed and RPM. Where are you located? I have several props for that motor, including 19 and 21 SS ones.