O.K. I just bought a GPS and now have some good figures to run off to get a little more speed out of my current setup. Power wise I've got a 454mag EFI, Bravo 1 drive spinning a 23 Mirage Plus at 4800 rpm and seeing 57 on GPS with about 3/4 tank of gas. Boat wise is a 26' 1997 Powerquest Legend .
How do I figure my slippage ,what should it be and what can be done to the prop to minimize the slippage to gain some speed?? I did just purchase a 21 Mirage Plus but won't have time to test till the weekend weather permit.

try this:
http://www.go-fast.com/prop_slip.htm

i think youll find itll answer most your questions. check out some other useful things at that site.

Here's the prop slip calculator.http://www.go-fast.com/Prop_Slip_Calculator.htm


Yours is pretty high at 19%

19% is what I came up with as well. So what needs to be done to the prop to reduce the slippage and what can I expect in a gain?

At 19% we need to look at your set-up. However, knowing that you are going to try a 21P this weekend, lets take a look at the slip with the 21P and go from there. I would take the time while you are, with the boat, to measure the prop shaft in relation to the hull. Take a straight edge from the lowest point of the hull (at the transom) and then measure the distance to the centerline of the prop shaft, in other words how many inches from the centerline of the prop shaft to the straight edge coming off of the hull. Reporting the distance above or below the hull.

Julie

Julie, Just had a chance to get over to the boat to take that measurement. It came in at 5.75" from the bottom of the V to the centerline of the prop shaft. That's 5.75" below the lowest part of the hull. So next question is that considered high , low or average?? And whats the relationship?

Well I had one last chance to get the boat wet and see how the 21 Mirage Plus performed. With nearly everything out of the boat , half tank of gas and just me on board. Only problem the water condition did not allow me to let it top out. Plane time was fantastic, cruise speed was good 4,000 rpm I ran 46 mph on GPS, at 4900 rpm gps showed 58mph and still climbing (but slowly). Seemed about the time I had everything set some large wakes would come in and I'd have to pull back on the throttles. My guess is I may have seen 61-62mph as the 58mph mark came pretty easy. Now I'll have to wait till spring as our weather well be changing and it's time to winterize. Still wondering as to any thought to the drive height posted above??

Thanks for the help.

What happened to my prop guys and gals for help?? I'm figuring my data is of no use unless I can hit the top speed mark??
I may try to get out Saturday again for one last shot before I winterize.

We need to look at your propellers. Not knowing what the motor would spool up to, since you had to back out, will not allow you to run any solid numbers. So looking at the 23P running the same as the 21P in so far as the RPM is concerned, we know it probably did not spool up. There should be 400 RPM difference between the 2 propellers.

Has the 23P ever been reworked by a propeller shop? This may hold the key to some of the answers we are looking for. With your prop shaft being at 5.75" below the hull I would not consider this to be excessive either way.

Julie