1. ## Boat Horsepower Calculator

http://www.go-fast.com/boat_speed_predictions.htm

You have to figure out what the constant is for your setup is based on stock numbers. Then you can get an idea how much HP you have to add to get to your MPH goal MPH. I wound up guessing 140 for my 2012 RXPX.

Way cool stuff

Andy

2. This really puts into perspective what it takes to run 90 when stock the boat ran 68.

Keep in mind that you have to double fuel to support twice as much HP.

3. How do you know what the constant is for our hull?

4. WAG...

5. I used 260 HP will get you about 68 MPH with a total weight of 1100 with rider. Then hit the <calculate> below Constant.

I get 140 for the 2012 - 14 RXPX hull

6. Too many variables in skis though. For example change the rideplate and you pick up speed with no added power.

7. ## +1 by:

8. water drag is huge
then the sucking in the water pulls the boat down more with the extra HP
jet powered is a bad way to go fast, too much drag
a 250hp out board on a boat the size of a pwc would/should crack 100 easy

9. I'd bet a na155 with a prop would run 100. Without pump tunnel losses, 155hp would get that thing movin'.

10. Originally Posted by Mothman
I'd bet a na155 with a prop would run 100. Without pump tunnel losses, 155hp would get that thing movin'.
Someone did just that, modding their NA ski for a surfacing prop, did 90+MPH, but was sketchy as hell, lol. Riding the prop isn't fun at all, gets squirly.

11. 106mph with a 1300GPR motor.