25hp 4 stroke motor height

[targetpanic]

I just purchased a Merc 25hp 4 stroke long shaft powere tilt and trim. I went through the break in procedure yesterday according to the owners manual.
The boat is a heavy 16' sylvan Expedition. At WOT the motor only gets to 4900 rpm and top speed is 11.6 gps. It currently has a 10X8P prop. The anti-ventilation plate is 2-3" below the lowest point of the keel and the water line is about 8" up from the bottom of the keel. The motor was mounted in the top holes. If I raise it up 1 or 2 holes what will this do to performance???? where should the ventilation plate be in relation to the keel?? Max rpm for the motor is 6K. I know it's not a performance boat but the reservoir has hp restrictions and I'm trying to get whatever I can out of it.

 

[Martian]

Re: 25hp 4 stroke motor height

Sounds like you need a different prop.
Do you checked the motor/prop/boat weight combo to see what speeds you should be getting?

check the merc site for the prop selector app.

Martian

 

[targetpanic]

Re: 25hp 4 stroke motor height

That's the lowest pitch they make for that motor. If I increase pitch I will drop even farther out of the rpm range correct???????

 

[Martian]

Re: 25hp 4 stroke motor height

Drop the pitch to increase RPM. Increasing the pitch would be bad.
Check with Mercury about prop choices or other options. You are pressing the limits of the motor.

martian