Propeller question

[Lectrick]

I just bought a 1979 16' Sylvan pontoon with a 1974 Johnson 25hp outboard. Never owned a pontoon before. The thing is, the propeller is pretty chewed up. I've done a fair amount of googling and searching, and I don't know what the recommended top RPM range is... or if I even need to worry about it? For a boat this size, should I just get the lowest pitch propeller available? Thanks in advance for any help.

 

[Jeep Man]

I have a 60 hp and have an 11p. Not sure what your 25 will need but for sure the pitch will be low. You want the biggest diameter prop the motor will take. Doing things like having the prop cupped will help. As to your RPMs, It is very important. Find out what your wide open RPM is suppose to be and gauge your prop to it. Almost assuredly, your motor needs to be a 20 inch shaft.

 

[Silvertip]

At this point I would not experiment. Buy the same prop that is on the motor. There should be a part number or diameter and pitch info stamped either on the hub or behind the prop nut. Without a tach, withoujt speed data, you have no idea what prop pitch you need. Whatever was on the engine when you acquired the boat was probably relatively close.

 

[steelespike]

Your 25 is a small displacement 22 cube 69-76 are rated at 5000-6000 rpm.
I think you should have at least an induction tach(Tiny Tach) to verify your rpm.
​Explain to them about its an outboard on a pontoon may need a long wire.
I think the 22 cube may suffer if operated below 5000 rpm at wot.