need help figuring speed
 

I have a 02 29' fountain fever. I have a bravo1 xr 1.5 drive with a mercury bravo 1 lab 31p , the motor is running 5500 rpm . My speedo does not work and I do not have a gps. Can any calculate my speed appx? Thanks Chris.

Due to the fact that props have slip,, it's very difficult ( next to impossible) to get an accurate number. My guess is that someone here will have a similar set up, and give you a ballpark number.


Darrell.

Just for ****s and giggles, i ran these numbers:

5500 rpm/ 1.5 gears/ 31pitch/ 15% slip = 91mph.

5500rpm/ 1.5 gears/ 31pitch/ 20% slip = 86mph.


I have no idea what the slip would be, but you can get an idea of how much it affects speed.


Darrell.

Try this, I have .10 prop slip in a Baja, a Fountain may may be .08 or .09 http://www.rbbi.com/folders/prop/propcalc.htm

Borrow a handheld GPS and take it for a ride

That's the only accurate way to do it.


Darrell.

elise..

pitch x rpm / 1584 = 100% for 1.5:1 ratio

31x5500/1584= 107.63mph x .90 (10% slip)= 96.8mph.. go from there.. more or less slip. then get the GPS and see how you made out.

I have a customer with a 29 Fountain that I did the engine in. He's running a labbed 32 Bravo at about 5800 rpm with speeds in the low 90's on gps. Lots of prop slip.