Prop help
 

I have a 2002 Baja 302 with a pair of built 383's putting out 352 HP at the prop shafts. I have a set of Rev 4 23's that run well, but are costing me a little top end, about 2 MPH. My boat has Bravo 1's, with ratio's of 1.5. I also have a set of Mirage Plus 23's that give me a GPS of 68.5 at 5000-5100 rpm's. Its 95 degrees here, and its still running well, however I really would like to see 70 in the heat. She's heavy, about 7800#'s and I am more than pleased with my performance, but again, I am sooo close to 70. Would I be better to lab the mirages or the Rev 4's? The mirages tend to blow out, not easily, but I have to baby it a little more. If I labbed the 3 blades and changed the pitch to 24, would that help? Brent, Julie?????????? HELP!:signs069:

At what RPM is your peak HP produced?
What drive and gear ratio?

Julie

Bravo one drives, 1.5 ratio

from 5200-5400 there is 1.5 HP difference, so anywhere in there should be good I would think.

will 24p hydro QIV's work for you ??? I have a set for sale.

Well I have calculated your slip at 6% with the 3B Mirage Plus...which I don't have to tell you is very very unlikely! I would verify all recording devices and baseline again. If they all hold true I would recommend that you don't touch / modify that propeller. It just isn't gonna get any better than 6% on a Vee Bottom, non-stepped hull.

Julie

Julie, I was looking at that too, and thought that was off, but I hooked up a tach to verify the rpm's not long ago. The GPS is brand new, and I verified it with my airplanes gps Ground speed readout, what else could be off? The drives say 1.5 on them. I switched over to the 4 blades and will be taking it to the lake today. They are the rev 4's. WHat type of slip should I expect from that one?

The range of a 4B, on a Vee Bottom is 10-14%.

Julie

Not to disagree with you Julie but we have seen many true V's under 10%.. However, higher slips on true V's often produce better top speeds. Slip % can be over rated. If the 3 blade runs 6%, the 4 blade will be close too. It could actually be higher than the 3 blade for various reasons

I think what Julie may have meant was, anywhere under 15% is acceptable on a hull such as your's.

My thoughts are, Lab the Mirage Plus props. You have rpm room to grow and 1.5 mph is definately in reach.

Thanks Brent, remember, its 95+ degrees here too. I think when it cools down, she will scream. LOL

I switched to the Rev 4 23's for the weekend, and filled it with 150 gallons of fuel, and still ran 65.1, thats an extra 700 pounds of fuel over what I normally carry. The boat still turned 5000 rpm's, and it was 95 degrees, and very humid. I used the prop slip calculator, and it said 11% for those props, so at a lower weight, I would think 67 MPH would be attainable. How is my crappy old BAJA's props running so efficient? Does that mean I don't have much to gain from labbing?