thayes11

Just installed a bravo 1 drive 1:32 ratio, 31' V bottom boat. Prop shaft is 2" below bottom of boat. powered by a 598 CI BBC. (( Proplem: I tryed many diif props, some I cannot plane off cleavers, others sound like they slip at high RPM Mirage, Mirage Plus)) ANY Ideas what the problem may be ?

throttleup

Give us some more details about your set-up.

Make, year and model of boat (Assume it is a superboat)
At what RPM is the peak HP produced on the 598 ci motor?
What props have you tried and post performance numbers with them.

Julie

thayes11

Boat is a 1990 31' V bottom Corsa, light weight but most weight in front of boat. Looks just like the 30' Superboat. (( Last year stock 454/365 with OMC King cobra drive 51 MPH top speed at 5000 RPM )) Removes the package and put a 598 BBC, 750 HP at 5500 RPM, Bravo 1 outdrive 1:32 ratio. Tried a hydromotive 4 blade, 24" 61 MPH @ 5300 RPM lost of high rpm slip in the prop. Tried a 3 blade 25" cleaver NG would would not palne off, tried a 26 4 blade cleaver NG boat would not plane off. Tried a 3 blade Mirage Plus 23" OK 61 MPH 5300 RPM Lots of prop slip @ high RPM, Tried a Rapture 23" 3 blade cupped 5100 RPM 61 MPH lots of slip again.

Pure Energy

How about a 5 blade?

bbladesprops

We have run all kinds of props and drives on Superboats. We usually end up with 3bl props to carry the bow. They don't seem to be working here

I didn't see that you tried any Bravo 1 props. What rpm do you want to turn the motors? We may have something you can test with. Also, this may require lowering the gear case and running a customized propeller to get the best efficiency.

throttleup

You need to get the boat running close to where it should be before dialing in a prop.

Are you sure about the gear ratio? You slip is very high. Is it possible you have a 1.5 gear ratio?

Does the boat have a rooster tail at top speed when properly trimmed?
How much drive trim do you have to put in the drive to achieve top speed?
What's the attitude of the boat at top speed?

You may need a spacer from 1"-2" to get the boat running properly. After the boat is running close to where it should be then start dialing in a prop to your boat.

Matt

thayes11

MATT, with the trim down all the way, just tap it up a few times and it has have a rooster tail, the nose of the boat is down and does not come up with all the props I use. I think maybe your right about the spacer, I may not be getting enough water. I looked on the drive and it sayd 1:32 for the radio, I do have a 1:50 Bravo as a back up.

throttleup

I would check the ratio of the drive. Put the drive in gear, rotate the engine by hand and count how many engine revolutions are required for each propshaft revolution. If your current drive isn't a 1.5 I would consider putting on the 1.5 back up drive. I think the 1.5 ratio will work better for your application.

The rooster tail and the fact that you can't get the nose up is an indication the drive is too high. I think with the proper spacer you will find some speed as well as a better mannered boat.

Matt

thayes11

Matt, we tryed a 28 pitch 4 blade Bravo 1 propeller, No slip. 4700 RPM 61 MPH. Lots of mid range speed. The bow is lifting up now with this propeller. Not the top MPH that we were looking for with a 598 Ci Motor.

Pat McPherson

If your running a 1.5 drive, your at 25+% slip; with a 1.3 drive, much worse...
I would say the prop needs to be a lot deeper.