should I change prop size?

[flyguy767]

I recently purchased a Lowe 20 ft pontoon with Mercury 50hp ELPTO and a 10 3/4 x 12 prop. The mechanic suggested that should change to a 15" prop. Boat weights 1900lbs and normal carry 4 to 5 adults, maybe be interested in pulling a tube once and awhile. WOT I'm indicating around 5250 rpm, max is 5500 rpm
Wondering if I would benefit changing to a different prop.

 

[Maclin]

Re: should I change prop size?

In my opinion the prop you have now is close to ideal based on the RPM's you are attaining at WOT. Going to a 15 pitch would not be a good thing. If anything you need the next size samaller pitch, like 11.5 or 11 to get to the top 5500 rpm range at WOT.

Did the mechanic give any reasoning or supporting facts for his recommendation to go to a 15p?

 

[Outsider]

Re: should I change prop size?

In theory, going to a 15" will lower your RPMs by 4-600. You might see improved tube performance without danger to the motor. Might ... :facepalm:

 

[jestor68]

Re: should I change prop size?

I agree that you are pretty close to perfect now.

Putting a 13 pitch on there should lower your rpm to about 5100 and pick up 1 mph.

Since your motor's hp is rated at 5000 rpm, running it faster only uses more gas.