Shaving diameter on Hydro props

[p4-33]

I just posted this in the prop section, but it's more of a Fountain-specific question...

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 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

[chief fever]

What is your power band?how much trim 4.5-5.5?,i would call Bret at bblades he is very knowledgable and will steer you in the right direction.Irun a 32 labbed B1 on my 29 Fever with a Imco extreme sc and a Chief 825SC i see 93.8 on gps with more left Hydro 30 pf-x 89 Maximus labbed 28 91,I would highly recommend Bret.I'am originally from Livonia Mi. don't miss that could weather i now live in Naples Fl. good luck Ray.

[p4-33]

Hello Ray,

Peak hp is at 5500, tq at 4800. 4.5-5.5??? Try 7... or more. This is all the way out on my Fountain indicators, and 7 out of 9 on my Livorsi's at the throttleman's seat. Like I said, a LOT of trim.

Bravo props aren't going to work for me, they just suck down the transom way too much and I have to run at 4.5-5 to keep the nose down. This also scrubs off more than a whole MPH.

My 29 Hydro's are enroute to Julie and Matt at Throttle-Up for some dyno-tuning. Just trying to understand what shaving the diameter will do for me. I'd like to run with less trim, more parallel thrust angle. But what can I say, runs the fastest with more trim.

I went to school in Livonia. Next time you're back up in Lake Erie, look me up.

Thanks,
Brian

[chief fever]

Hey Brian,I think you ought to go on the prop forum,those guys know there sh-- seems like a awful lot of trim.But i;am no expert.Though i no my boat very well i've tryed three diff. engines and seven props,i think it's pretty close to being dialed in at this point.I went to Bentley class of 80,My nephew just grad, from Clarenceville my wife and i are going up in July for a grad. party.Been 5 yrs. since i've been up North.Julie is great at throttle up she helped me also.My boat likes the B1.Who built your motors?What drives are you running?HP of your bullets?Good luck speed is so much fun!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!

[p4-33]

Yeah, this has been in the prop forum for a few days, 40 views, no replies.

I hear you on the trim, that's what I'm trying to solve, and pick up some speed along with it. Motors were done at Flow Technologies in Plymouth, MI, and I run the Konrad 540 drive package, 1.52:1 ratio, with the high performance lower gear cases. Everything is strong now, so just going for the fine-tune. Shooting for a solid 85.

I graduated from Churchill, class of 78. There's a couple of races going on up here in July, plus the LEOPA summer poker run out of Put-In-Bay... check out my website for dates and locations.

Oh, and welcome to the Fountain Forum!

Brian