Is a prop slip of 7-8% realistic?
 

Is a prop slip of 7-8% realistic?

We recently tried a new prop and got significantly better performance.
Our previous props were producing 16-19% slip (24 and 26 Bravo I props. 24, 26, and 27 Hydro props)

Then we tested a 21 Pitch Revolution 4 prop, 7% slip!
It is such a dramatic difference, I have to question the results.

Boat details:
1993 26' Velocity
Bravo XR 1.5:1
new 21 Pitch Revolution 4 (LH)
new tach 5700 rpm
2 independent gps showing 70 mph

It is realistic but maybe rare. I am at 8% as well.

5400 RPM
1.5 Gear
28P
87 MPH

When I calculated the slip at WOT on the 24 Superboat I owned, I was getting 9-10%. That was under ideal circumstances.

After prop experiments I went from 18-19% to 10.5% in a 382 Formula......and 10 hours later trashed an outdrive. Slip isn't always a bad thing :(

I had a 25 revolution on a Baja a few years back. It was like I put 27 pitch prop on. They definitely grab some water.

Im getting quite a bit of slip on my props now and was worried about the same thing if I went to 5 blade. Twin 572's 30 pitch 4 blades sl4 and bravo one outdrives . After what you said I think I'll stick with the 4 blades .I get a lot of slip at cruise speed say 40 mph

I agree.

Yep, twin 540's/700 ft/lbs TQ. 32P bravos, 18-19%.........28P full size (15 5/8) maximus were 10.5%. Cruise speed increase was great (WOT speed dropped), but the drives didn't survive.

Sometimes slip numbers are wrong.

example:
I switch from one 25 to another.
my slip numbers go down from say 13 percent to 9 percent.Looks good on paper but if my new prop actually has 26 instead of 25.Or my old one was actually 24 instead of the 25 it said then my slip numbers are almost identical to my old prop.

T500 .Is that a fountain. I see step transom. How far below the deadrise are your propshafts??