How do I tell which prop I need !

[cub48]

New to the larger outboard motors just wanting to make sure everything is correct. 1998 Stratos 273, 150 Faststrike Johnson, 18' Boat. Prop 13X25, 4 Blade stainless. Have not ran a wot. How is the correct way to do a wot. Is this from a stop go wot and see what the rpm high is. My RPM and MPH are almost matched as in 20 MPH - 2000 RPM , 40 MPH -4000 RPM The boat comes out of the hole and plains off good. Is there a chart that gives you a ball park figure for engine size. Cub48

 

[Dhadley]

Re: Need Prop Information

Re: Need Prop Information

Your prop probably is more than a 13" diameter. If it's a 4 blade it's probably a 13 3/4". If it's a 3 blade it's probably 14 1/4 or more. At any rate thats a great motor and boat. We've had really good luck with a Turbo Lightning on that combo. If you need help finding one just let me know.

 

[torbjorn]

Re: How do I tell which prop I need !

New to the larger outboard motors just wanting to make sure everything is correct. 1998 Stratos 273, 150 Faststrike Johnson, 18' Boat. Prop 13X25, 4 Blade stainless. Have not ran a wot. How is the correct way to do a wot. Is this from a stop go wot and see what the rpm high is. My RPM and MPH are almost matched as in 20 MPH - 2000 RPM , 40 MPH -4000 RPM The boat comes out of the hole and plains off good. Is there a chart that gives you a ball park figure for engine size. Cub48

RPM vs. speed depends on several factors including gear ratio and prop pitch. It's an insignificant accident that 2000 RPM yields 20 mph. Just open the throttle wide open and read RPM and speed, same as with a car. RPM should be in the upper range of what Johnson advertised for the motor.

 

[SingleShot]

Re: How do I tell which prop I need !

Basicaly already stated, but I will add my 1$ worth. Run in a straight line wide open and trim your motor up until your speed is as high as it will go. Look at your rpms. As you start to trim up you will see your rpms rise and at some point your speed will go down as your prop starts slipping or slipping more. You realy are trying to find the top speed for a trim setting that keeps your wot within its range.

JK