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-   -   Is a prop slip of 7-8% realistic? (https://www.offshoreonly.com/forums/prop-talk/350144-prop-slip-7-8%25-realistic.html)

Sonic24 10-04-2017 02:44 PM

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

TxHawk 10-04-2017 03:57 PM

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

5400 RPM
1.5 Gear
28P
87 MPH

Dave M 10-05-2017 05:32 AM

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

t500hps 10-05-2017 06:42 AM

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 :(

veloc410 10-05-2017 07:04 AM

Quote:

Originally Posted by Sonic24 (Post 4586174)
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

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.

veloc410 10-05-2017 07:09 AM

Quote:

Originally Posted by t500hps (Post 4586277)
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 :(

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

SB 10-05-2017 07:25 AM

Quote:

Originally Posted by t500hps (Post 4586277)
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 agree.

t500hps 10-05-2017 08:17 AM

Quote:

Originally Posted by veloc410 (Post 4586284)
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

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.

Warship2k15 10-05-2017 01:38 PM

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.

veloc410 10-05-2017 05:23 PM

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


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