New to outboard boating rpm questions???yamaha 55

[Ccctakacs]

I bought a 94 Harris sunliner 24ft pontoon from some people that had it sitting for 4 years. Bought it, cleaned it and got the Yamaha 55hp 2 stroke running again. Ran all last year and it was super slow rpms only made it to 3500 but controller seems to have a lot of throttle past that. Figured it was my prop it had some dings. When I pulled it I found no numbers left just corrosion all I know is it's 12 inch. Took it Yamaha dealer he gave me a prop after looking at mine and telling him my problem. I left with a 11 1/4 inch x 10 pitch. Tried it and got up to 3900 rpms at top side again a lot of room left on top side of controller. But this time my 24 ft dock was actually moving noticeably faster, front end rose right up and I usually have to trim it to do so and it was all the way down. Also realized I cruise a lower rpm threw wake zone too. But when I look at specs I find rpm rang to be 4500-5500 on motor. Will this prop work or are low rpms gonna make some thing happen to motor? If I do run prop can I run 3900 rpm down the lake or should I back off a little?

 

[Scott Danforth]

low RPM is lugging the motor which is bad.

at WOT (Wide Open Throttle), what is the motor RPM?

on a pontoon, the first thing you do is raise or lower your motor, then optimize your prop.

if your motor is too low, it will plow and the motor wont come up on RPM. under way at WOT, your anti-cav plate should be 1-2" below the surface

if your motor is optimized for height you may need to drop down to a 9 pitch

 

[Ccctakacs]

3900 is wot right now. Only ran in once for a short trip but when at wot if I raise trim over a 1/4 of what's on gauge it's spins out ( not sure of proper term for this). Old prop would go up half way threw gauge befor doing it.

 

[Scott Danforth]

where is your anti-cav plate with respect to the water when running?

3900 is way too low of RPM