Is my top speed right?

[kenohus85]

I have a 1973 MFG super gypsy and a 125 horsepower evinrude starflite. The boat,I hear, weighs 1325 pounds. At WOT my speedo says I am doing about 28 MPH. I heard that I should be hitting higher speeds than that.

 

[tashasdaddy]

Re: Is my top speed right?

i would think so, you need a tach, to see if you are turning the correct rpms. the engine height set correctly, also is the boat holding water in the foam. also speedo's are a pressure guage, pressure is put on the pitot opening, as the boat moves thru the water, they applies pressure to the air in the hose, and is registered on the speedo, a small air leak will effect the reading. also the higher the speed the less accurate that type speedo is.

 

[luckyinkentucky]

Re: Is my top speed right?

The 1325 lbs. is just your boat's weight. You have to take into consideration your engine along with any other weight such as fuel, gear, etc ...

You never said what year your engine is. Just because it's a 125hp doesn't mean it will keep up with a new 125hp engine. Also, you have to take into consideration the efficiency of your boat.

 

[tashasdaddy]

Re: Is my top speed right?

is it a cuddy, bowrider, closed bow?

 

[Chris1956]

Re: Is my top speed right?

Keno, You should check the speed with a GPS for accuracy. Your speedo could show any speed.

I would think that boat would go at least 35MPH. if you do not have a tachometer, you can enter prop pitch, gear ratio and GPS Speed plus a reasonable slip value into one of the prop calculators and get an idea of the RPM.

Also make sure you are running on all cylinders, and the ignition timing is correct, and check the compression. 28MPH sounds like either an incorrect reading on the speedo, low compression on one or more cylinders, or a grossly overpropped motor.

 

[kenohus85]

Re: Is my top speed right?

The boat is an open bow and tri-hull. The motor is a 1971 4 cylinder 2 stroke.

 

[angus63]

Re: Is my top speed right?

If you can provide wot rpms, mph, and prop pitch, we can calculate how efficient your setup is.

 

[kenohus85]

Re: Is my top speed right?

The boat has a tach but it does not work. The motor runs great with no hesitations or misses, but it sometimes is very hard to start.