I'm in Canada, and our prop labbing resources are limited compared to the experts that participate on this board in the USA. Shipping and exchange and down time make it just too difficult to send props to the USA for work.
That said, I'm working with a local prop shop to help dial in my 25P Mirage Plus for my 1999 Baja 232 with a 502 MAG MPI 415hp motor. Bravo 1.5 ratio drive

Spinning a stock 25P Mirage Plus, I run about 4900 rpm at 69.5-69.9mph GPS. I had a brand new 25P Mirage plus labbed. Work done, was thinning the blades, sharpening the leading edges and cleaning the trailing edge into a good clean edge. Some cupping was dialed into the trailing edge and tip. The prop work looked really nice to the eye. I ran 4800rpm and 69-69.5, with a bit more working trim to get the best numbers, versus the stock prop that seemed to have a better window of trim to dial in the speed. I ran back to back testing and got the same results.
The cupping on the props look similar to the eye, with the stock prop probably running the cup over broader area down the trailing edge towards the hub. This is just by eye, and feel to describe it. Compared to the stock prop you can really see the blade thickness change.
Any ideas on how to steer my local shop to get more MPH and RPM out of this prop?
Is cutting the diffuser ring a good idea? I have zero issue getting on plane and run silent choice thru hull.
Thanks for any feedback

I'll try to break it down in parts. Thinning the blades (and sometimes barrel) will help in reduced rotational drag and increased rpm, and usually, but not always, an increase in WOT speed. The downside of thinning the blades is limited or less holding power (hence your reduce trim range) and in extreme cases weakened blades. I would not necessarily worry about the latter in your case.

The problem is you have removed blade thickness and that can't be replaced. The other item to look at is make a cardboard template of the original blade (if you have one for comparison) and lay it over your new labbed blade. Often the leading edge is drawn back and total blade area is reduced some what in addition to increasing prop sweep angle (not rake).

So where do you go from here? I would likely try taking out just a little of the trailing edge cup but leave the tip cup and see what happens. Your midrange might suffer a bit but I'd wager WOT rpm goes up.

The diffuser ring helps with stern lift. Removing it would further limit trim response and reduce drive lift. Not sure if that would help in your case.

BTW, I've had a Laser II fully labbed and it didn't do anything for me except make my wallet $480 lighter and gave the prop reduced holding power and a narrower trim range.

I highly recommend taking GPS speed vs rpm data at 200 rpm increments from idle to WOT for each and every prop you have. You can also then calculate slip at each data point. Take this information and graph it. This will give you a bigger and better picture of what the prop is doing and which direction you can go.

Best of luck.

windsurnut,

Before I comment on the quote attached, I can tell you it is hard to determine the exact amount of work that has been done to your propeller via description. Having the propeller in the shop to actually measure the propeller via mechanical and computer aided tools is the only way to know for sure what is done and if it is done correctly.

Now to address the comments above. We do not thin barrel walls. We may remove parting lines or shell crack lines during Lab work, but never thin the barrels as they are so close to the rotating center line, they don't prove to increase performance when reduced in thickness.
Thinning blades however is a integral part of the Lab/blueprint process. This is artwork and is done to exacting specs determined by the future usage of the propeller.
The comment of thinning blade creates less holding power and less trim range is completely false. Thinning blades has no bearing on blade area, pitch progression, rake, cup ect. All of these other things are dealt with on their own merit.
Thinning of your blades is not you problem unless blade area was removed. Then, again we would need to see the propeller to determine the degree and the options.
It is rare for us to decrease the cord length of blades by removing LE material. As mentioned above, it was suggested it is done often. In over 90% of Lab jobs we do, we will not remove LE material. I don't know what sweep angle is.

It was suggested above you remove some TE cup height. I caution you on this as it is a science within itself. We take a bunch of pride in and have decades of practice in this art. Many, many prop shops don't understand the heights and radius's as well as the locations.
Lastly, the diffuser ring "can" create stern lift. Removing does not decrease trim and actually can increase trim as removing diff rings decrease stern lift which allows the transom to be leveraged more when adding positive trim. This too should be done by proffesionals after discussing the boats current personality.

My guess is the prop was thinned a bit and the LE's sharpened and it was balanced. I can only assume the this was a standard procedure and not a Lab specific to your boat.
Call us anytime and we can help you to the best of our ability.

Brett