Heavy V, old Cigarette 10-14% slip
Stepped V, light hull, 8-10% slip
Cat 6-9% slip
Race Cat 4-7% slip

Hope this helps

These are pretty conservative estimates. Most modern cats that I have seen will run 7-12% depending on rotation

Thanks, yes that gives me some good starting numbers for rough calcs.

If tachs are correct, run your boat and record top speed on a gps.

Then use following formula and play with % efficiency to get to gps recorded mph and you have your % slip.

rpm divided by drive ratio times pitch divided by 1056 times % efficiency.

5600/1.5x25/1056x.90 = 79.54 mph.

This would be 10% slip. Keep changing % efficiency up or down until you get your gps speed and your are done.

If you are turning the props in, I would bet you are at about .88 efficiency.

What kind of power do you have in that Formula that turns the 25s 5600rpm?

I am having my HP500's built into some 600-625's as we speak. If what the previous owner tells me is correct, I may need to jump to some 27's. He said he was turning the 25's at almost 5600, with basically stock HP 500's?

Keep your 25s until you complete the rebuild. Break in the engines and make sure Tachs are correct. Then you can get a baseline gps speed/rpm and have an idea of what prop will be needed.

Something is not right. There is no way twin 470 horse engines are going to turn 25 pitch props through 1.5 drives 5600 rpm on a very heavy deep v like your 357 Formula.

That's kinda what I thought also. I plan on doing just as you suggested, if I ended up hitting 80 all dialed in I would be stoked. Not sure if I will get there, but that's the goal. Then I have to start saving for konrads, so I can bolt Blowers on my new power!

TRS drives?:eek:

First post says 1.5 drives, does TRS make a difference?

Trs drives are 1.5 ratio. He is concerned with the power I will be putting through them. Which from what I understand they are stronger than the xr's, so I am not to concerned cause I will be easy on the sticks. When I go Blowers, I will be upgrading drives for sure!!!