Prop Question 1988 80 HP Mercury

[Starman]

I have a 16' Starcraft aluminum boat with a 80 HP Mercury. It has a 21P prop. This seems high. Don't have a tach. Boat runs 35 mph at wot. Doesn't sound like its getting all the rpm's. Any help appreciated.

 

[Chris1956]

Re: Prop Question 1988 80 HP Mercury

Ok, How accurate is the speedometer? You can use the prop calculator to see what the RPM is predicted to be given a likely slip factor.

Realistically, to fine tune this application, you will neeed a tach. Does the motor have PTT? If not, you will have a real hard time to get top RPM.