Race Cat running 86mph With 25p Hydromotive Props ???

Ok, I took my cat out Sunday for the first time with all the new gauges and Computer system but was unable to “barrow” some props. So I took a set Of 25p Hydromotive’s I had in the garage figuring I would hit around 75mph but still be able to run the motors pretty hard.

Well the boat jumped on plane and ran up to 80/83 (gps) and 86 going into the wind while only turning 6700/6800rpm..

That’s not right.. I would have a negative prop slip at those rpm’s. Is the tach wrong? Or do cats have a different ratio to figure out prop slip?


Motors (2) 2.5/260
Gear 2:1
Weight 4000lbs
Boat 30ft race.

Either your tachs are off, they're not really 25P props (tweeked), or your gear ratio is not 2.1

At zero prop slip, the theoretical speed with 25p props at 3238 rpms (6800/2.1), you should see 76mph.

Ok, I'm starting to think that my new Tachometers are set on the wrong dial (ie: 4/6/8 oe A/B)

If I was turing 7700/7800rpm with a 6% slip would put me at 83/85mph..

Looks like I solved my problem.