Thread: Prop dilemma

Originally Posted by SeaRay

Help me understand the mechanics here guys:
I have a 20 HP Tohatsu on a light Gheenoe type skiff. It is a center console rig. The factory prop is a 10 pitch aluminum which red lines(6100 RPMs) at about 3/4 throttle.
I put a SS 11 pitch on which does fine but will only pull 5200 RPMs.Top speed is about 23MPH with just me on board, 20 with a passenger.

Obviously with a small engine I'd like to get peak performance. Prop selection in that size motor is very limited so I considered putting a CMC tilt and trim on it. In addition to giving me trim ability it would set the engine back 5" and also allow me to place the motor higher off the transom.

My question is would those changes likely give me any more RPMs(or speed) from the SS prop?
Thanks for any thoughts or suggestions.

On my boat trimming up will increase RPMs by 2-300.

I have seen the same thing, with 13p aluminum I would get 6200 RPM. 13p stainless brought it down to 5300. 14p aluminum 4 blade is right at 5500 trimmed up all the way.

The aluminum flexes. The stainless maintains its pitch

Ray, I know you are pretty limited on that transom, but if you could raise the motor one notch with that stainless prop I think you would see a difference. If not the CMC would defiantly help. Just got to be careful on the extra stresses it will place on the transom.

i dont no all that much just fish all the the time,i have 14ft allu wide boat 25hp i put a cmc on it cause i dont want to lift motor.was best money i spent,boat gets on plane good i trim up or down according to load ,for a small boat it makes it travel so much better,i have used cmc 3 years in stumps,shallow water ,have abused it leave boat in water an that thing works like new.good luck

Originally Posted by Cray

Ray, I know you are pretty limited on that transom, but if you could raise the motor one notch with that stainless prop I think you would see a difference. If not the CMC would defiantly help. Just got to be careful on the extra stresses it will place on the transom.

It porpoises if I go up a notch.

Originally Posted by SeaRay

It porpoises if I go up a notch.

What about going up one notch with motor and then adjust your motor trim in one hole ? try that and see how it does

Are you talking about a 3 blade or a 4 blade prop?

I always recommend a 4 blade, especially with a smaller engine. A 4 blade actually lifts the stern more than a 3 blade, giving you less chance of porpoising, gets you on plane faster, and allows you to stay on plane at slower speeds.

If you raise the motor on the transom you can run a SS prop with some cup in it as those can be run only partially submerged. It's possible your current prop needs to run closer to the surface too.