prop slip of 20
 

even after having 30 Bravo-1's labbed I still have 20% slip.
5200rpm 1.65 Bravos running 72. WTF gives on that kind of slip.Life would be great if I was down to 13-15%ike they should be..Any thoughts

My guess is that your gear ratio is too low for the application. 1.65 is fairly uncommon, and would probably work well if you had a motor spinning closer to 6000. The small diameter bravo prop isn't getting the blade speed you need to support the blade loading. Your 5200 rpm is turning the prop the same speed as a 1.5:1 drive would at 4700, and that's not where the top end was intended to be.

If you are going to stay with the gears, I'd try some 5-bladers. Otherwise, you'd have better slip numbers with 1.5:1 gears and a 26 or maybe 28 prop if the motors can pull them.

A question. When you had the lab done, did they lab it to be an actual 30" prop? Remember that in stock form, it's more of a 28.75" - 29" prop.

I'll agree that you are lacking rpms to get the prop at its efficient rpm range, but this would normally be something you could change somewhat by labbing. Who did the lab job?

I had a prop slip of 23% when I first took the boat out and made a run. I contacted a prop pro and he said that I clearly was running with the B3 drive trimmed out too far.

I'm getting back to boating after many years and I realized after he said that that he was right. I was trimmed out too far and the amount of tab I was using proved it. In my case it was operator error. Live and learn.

That said, I don't know if trim was having an effect in your situation.

Many things can cause excessive slip numbers.
More often than I'd like these days, it is due to manufacturer "X" dimension set up. (I can get a little conservative here) The drive may be too high.
Standard Labbing procedures can cause additional slip. Adjusting the Lab recipe can definitely help.
I calculate your slip at 17.5% using 29.3 inches of pitch. Obviously it will go up or down depending on the actual pitch of the props and the cup heights and locations.

I really don't find the gear ratio to be involved here. Turning 15x30's at 5200 is a good combo Spinning the props at a higher or lower rpm may adjust the slip number due to the angle of attack from the water as the boat attitude changes a touch. But the blades being loaded better do to ratio (prop shaft speed) isn't the issue here. Adjusting the Lab recipe, rotatio or prop depth will be more effective (and a lot cheaper) than changing gears.

5 blades most likely will decrease slip but may also decrease speed due to rpm depletion, drag and boat attitude changes.

I need more information to help. If we have worked together in the past I'm sure we have history of pre and post. Either way, call us if you desire and we can cover a ton of ground over the phone.

Brett

Silent, is that a 292 Fastech you have? What power? I'm setting mine up with new props as well...be nice to compare numbers...

Bret you did the lab on these twice. Where you are saying the slip is at or about 17.5 is what I thought..too, in past you had thought it was 13-15...after lab per past e-mails.
I'll call and we can talk about and see what we can come up with.

Howdy,

What are the serial numbers so I can look at the recipe.

It would be rare for me to state 13-15% slip. It is always a hard core number since that is what the slip equation gives me. The variable would only be if the pitch was unknown.

If we thought the slip was lower before, I should have the numbers we used prior in your file.

Let me know.

Brett