Shaving prop diameter and transom lift
 

I'm about to do some prop tweaking, and I'd like to understand what shaving some diameter off my props will do for me.

I've recently tested 5 sets of props on my 10-Meter, and I've determined I need to be somewhere between a Bravo and a Hydro with transom lift.

The two sets of Bravo's I've tried (30 stock and 28 labbed) performed well with planing and mid-range accelleration, but the top end wasn't there, and they tended to carry the bow a bit high, unless I reduced trim, thus scrubbing off speed.

Two more sets of Hydro's (28 & 29 stock QIV's) carried the boat at the angle I'm used to, but need LOTS of trim for good speed. I could also use 200 or so more rpm to get into my power band better.

Ok, so the question... what effect does shaving off 1/4"(or more?) of overall diameter do for (or against) the transom lifting abilities of the Hydro QIV? And how will it effect slip numbers, and the related top end? With my aggressive trim angles, I'm calculating 16% slip, a pretty high number.

My theory, which may be off :rolleyes: is: if I can keep the revs up with less diameter and less transom lift, and with less trim angle that's necessary to force the bow up, more thrust energy will be spent moving me forward, gaining speed.

Anyone shaved a Hydro lately for a 33/35 straight-bottom Fountain?

Thanks in advance,
Brian

Re: Shaving prop diameter and transom lift
 

If the B1 had good top speed why trim it down? Was the bow kiting? if you keep trimming and gaining speed, don't stop unless you can't drive it due to danger.

We have cut the diameter of both props down. We have had better success with the B1. That's our experience and may not be others same experience.

I think your theory is correct to some degree but may not be realistic. The least amount of wefted surface area with prop shaft parallel to the surface and the highest pitch possible will give the best speed. Your exact set up may not have a perfect prop. There are very few boats that do.

I think your situation needs a discussion via phone. I have some other thoughts.

Re: Shaving prop diameter and transom lift
 

Brett, when I trim out the Bravo props for speed, the nose is all over the place. Porposes, and gets real squirrely. The only way to get a handle on it is to trim in a couple of ticks, and then speed drops off.

The "feel" I'm used to is a flat running attitude with a bunch of trim. My Fountain carries the bow well on it's own, and the stern lifting abilities of the Hydro prop simply sits the boat up on top of the water and goes.

What I'm trying to understand is whether shaving diameter will allow me to keep the rpm's up while running with less trim angle, more forward thrust, better speed. I believe what may be happening is with such severe trim angles, I'm effectively turning my Konrads into surface drives to break the props free on the top end of the rotation, and I don't think the Bravo prop is suited well for surface applications.

Hmmm... if only Konrad had a "shorty" lower. :cool: :D

Thanks,
Brian