Prop slip help...whats good?
 

I have a sunsation 288, 1.5 Bravo XR and im spinning a 4 blade bravo 1 30 pitch. The prop has had work done to it by the previous owner but im not exactly sure what but the blades have been thinned. Im running 81 at 5200 rpms which calculates about 18% slip. This sounds a little high to me? Whats good for that boat, I was thinking about 12%? Also it slips a little when just getting up on plane with a heavy load and I have trouble keeping it at a low planing speed without first going faster and then slowing down. Any ideas a different prop that might work??? By the way the rpms are right in the range I want to be in for the motor.

Re: Prop slip help...whats good?
 

There are many factors that influence slip.

In your case from what you are describing it sounds as if your prop has been lab finished. The other possibility is that your drive is too high.

It's hard to say for sure without some baseline numbers with a stock prop. Those are generally the most consistent as each lab prop will be a little different than the next depending on it's application.

You may want to consider a stock 28 Bravo 1. It may address your complaints. If not the performance numbers from the stock 28 can be used to diagnose what the exact problem is with your boat.

Matt

Re: Prop slip help...whats good?
 

I believe you guys are the ones that did the prop, would you have a record of what was done if I give you the previous owners name? I do have access to a stock Bravo 1 28 to try next week.

Re: Prop slip help...whats good?
 

Yes, we should have the info. Shoot me a PM if you liek and I can look it up.

Julie

Re: Prop slip help...whats good?
 

Looks like to me, your slip percentage is closer to 16%.

Re: Prop slip help...whats good?
 

You are just under 16%. Not great, not terrible. You are in a balancing act mode with your hull. Decreasing slip now may require losing a small amount of rpm or going down in pitch to get the rpm back. That means the speed may stay the same. As stated before, see what has been done to the propeller first.

Re: Prop slip help...whats good?
 

Hummmm, I used this on-line calculator, is it wrong? Whats the formula that you guys use? I want to make sure im doing it right or its a wate of time....

http://www.rbbi.com/folders/prop/propcalc.htm

Re: Prop slip help...whats good?
 

Bravo 1 props vary from .7 to 1.3 inches below the stamped pitch. They are all different from prop to prop and working them changes things too. Use 1 inch to .75 inches under the pitch when calculating.

Re: Prop slip help...whats good?
 

Interesting......, I guess its not as simple as I though. Thanks.

Re: Prop slip help...whats good?
 

Is this the correct formula?

1 - {(MPH/60) / [(rpm / ratio x pitch)/12/5280]} = prop slip percentage