CONTINUOUSWAVE

I recently acquired a 1988 Super Sport 13 with a 1999 Evinrude 40-HP four-stroke-power-cycle engine--the "Suzirude" made by Suzuki. The propeller is 11-1/2-inch with a 13-pitch. Top speed with only me in the boat is 30-MPH in the Great South Bay in low wind, mild conditions but far from a glassy smooth inland lake.

I just bought a tachometer so I can see exactly how fast the engine is turning at WOT. My gut is that [the Evinrude 40-HP four-stroke engine] might be turning too fast at wide open throttle.

Should I expect more [boat] speed [than the 30-MPH attained now]?

Propellers are available up to a 17-pitch.

I guess I'll have more information once I run with the tachometer.

Love the boat so far. My other boat is a tiny MFG 12 footer. It's a fun lake boat but taking it in the bay during small craft warnings is a bit sketchy.

How are you measuring boat speed?

Yes, you must have engine speed measurement to know what's going on.

Once you have engine speed, you then need gear ratio. With engine speed and gear ratio you can calculate propeller shaft speed. Then multiply by pitch to find the target boat speed. Now compare that calculated speed to actual measured speed to find slip.

The best propeller will let the engine reach the very top of its recommended engine speed range when at full throttle. The propeller slip should be about 10-percent. That's when you'll achieve optimum boat speed.

But you have to have accurate measurements of boat speed and engine speed to make these assessments.

Use a propeller calculator to help make these calculations.

Thank you. I am using a Garmin Forerunner which is a sport GPS and running a straight course in the channel to determine speed.