Prop Slip
 

Hi All, All the info from ya'll on props and 5-6 test props.I ended up with a hydromotive 24. My Rpms are now 4700 running 60 gps. I need to have it re worked to get the last 300.
My slip ratio is 25.What does it take to get the slip down, does it take more cup or what to have less slip. I will be sending to BBlades during the winter.
THanks for all the help.

25% slip is a LOT. Sounds to me like the prop is too high and you need a drive spacer

What gear ratio did you finally settle with? You were swapping gearing around in your Drives.
What's the diameter of the props and how many blade?
What speed are you getting the 25% prop slip? WOT?

Hmmm....how do you come up with 25%? This chart shows more like 16%, assuming a 1.50:1 outdrive ratio...

https://cimg2.ibsrv.net/gimg/www.off...c347105ccb.jpg

My bad, I'm running 4700 amd 56 mph. I had a 1.62 drive running a 26 bravo one until I blew the upper gears. Now I have 1.50 gears.

I had a 1.62 drive running a 26 bravo one at 5000 and 62 gps, until I blew the upper gears. Now I have 1.50 gears. I'm running 4700 and 56 mph.

My bad the gps is 56 at 4700rpms

I have family in Omaha,three sisters... I have an aplha gen 2 1.5 now until I have the $ for a bravo swap. The centerline is about 5 off the bottom.
I can measure next week.

Yeah...you are a little over 21% which indicates you are giving up a lot of performance...somewhere. My 208 Baja was incredibly efficient at around 8% slip (with 17 degree deadrise), my 252 Baja is right at 10%

Have you ever seen what your prop wash looks like? It IS hard to tell whilst underway but if it appears highly 'aerated' then it could mean the drive is not the right height. I am assuming your boat is what is in your name...? Is this a new boat for you or have you had it a while and are now just seeing this issue? Do you have any sort of items that could cause a disturbance in the flow to your outdrive/prop? I've seen some badly placed transducers that cause JUST enough disturbance that it affects performance, for example. I am going to ask how experienced you are with trimming, as a poorly trimmed boat is going to slip a lot, too...no offense intended, just trying to cover the bases. Are you sure of your engine rpm? The Hydromotive prop you mention...3, 4, or 5 blade? And what diameter? I think your outdrive is limited to about a 15.75" max diameter.
Props can be 'black magic' and all too often take tremendous time and effort to get figured out. Are there any Donzi specific groups you can inquire of to see what those owners are using?

It is a Donzi Z22 open bow that has a step hull. I just had a stroker 383 with 397hp and 430lbs of torque fully dressed put in a few months ago. With this motor the boat now gets up on the pad,before
it really never got aired out. The prop is a hydromotive 4 blade. I have tried bravo ones, tempest plus. both different sizes and pitch. Some would hit the rev limiter and others would only get 4500 rpms.
The hydro is the best I can find. Maybe other props out there ? I do have a transducer that is just off center line to the left and level with the bottom of the hull. You may be on to something.
I'm still learning where the boat likes the trim with this motor. I have asked on Donzi forums but this hull was only made 3 years.

Hmmm...looking at the Hydromotive site, their 5 blade might work even better than the four...based on the descriptions.

agreed. Hydromotive tend to have very low slip %