nordic95

Ok prop gods,

I need advice on what props to run this spring on my Winter project.I have a 1991 32 Fountain Fever no steps.Twin 502 I just had built and dynoed.I am currently running bravo ones with 1:36 ratio.I need to upgrade drives,should I go with 1:36 or 1:50 ratio in the new drive?I am looking for mid range cruising and some top end.I don't know exact weight of boat but I think its about 7500 lbs.Any advice would be greatly appreciated.Here are the dyno sheets for both motors.

Thanks Nordic95

throttleup

First of all, I would go with the 1.5 gear set.

As far as props go, something in the true 28 pitch range (30 Bravo 1's) should get you in the ball park WOT rpm of 5800. Depending on many factors I would expect to see about 90-93 with the boat.

Matt

nordic95

[QUOTE=throttleup]First of all, I would go with the 1.5 gear set.

As far as props go, something in the true 28 pitch range (30 Bravo 1's) should get you in the ball park WOT rpm of 5800. Depending on many factors I would expect to see about 90-93 with the boat.

Matt[/QUO
Thanks for the advice.I was thinking of trying to run these engines on the conservative side,say around 5200-5400 at wot.I want to set my rev limit at 5600 rpms.What pitch prop should I run with these numbers factored in?I would like to have a good cruise speed running 3000 rpms.

Thanks Nordic95

throttleup

You may run into some potential problems if you prop the boat to run at 5200. It's important to get as far away from the torque peak as possible.

Of course you can always try different props and see how the boat responds. Figure about a 200 rpm reduction for each inch of pitch increase. So a 31 pitch prop, 32 Bravo 1, should get the rpm down to the 5200 range.

A good starting point may be to try a set of both 32 and 30 Bravo 1's. See what results you get and go from there.

Some potential problems by over propping the boat down to 5200 may be, excessive slip, difficulty getting on plane, potential handling problems, etc. The only way to know for sure is to try different props and see how the boat reacts.

Needless to say if you run at 5200 at WOT you will lose some speed compared to running at 5800.

Matt

bbladesprops

I agree to go with the 1.5 gear ratio. With this, the throttle response will be better.

As far as propping, 5500-5600 will be fine. I wouldn't go much lower than that, but it's not a necessity to go to 5800 either.

nordic95

I am ordering my drives with the 1:5 ratio based on your recommendations.I think the 5400-5600 rpm range is also about right.So with this info narrowed down I would think a 30 bravo one or a 28 bravo one would be the right choice?Does any body do a test program on there props?How much fine tuning can be done by labing a prop?Does any one do in house labing or do they get sent out to Merc. for this?

Sorry so many questions
Thanks Nordic95

bbladesprops

nordic95,

Although we are Mercury Racing alumni, we do all our Lab Finishing in house. We don't send anything outside.

We do offer a test program to the general public. It is easy to get involved.

Fine tuning can be done to the Bravo 1 propellers. Because the propellers come in 2 inch increments, we prefer to only go 1 inch in either direction. True geometry is always better. Choosing whether to work a prop up or down is made for having experience with the particular casting and the hull, drive combo.

throttleup

We have had a test prop program for quite a while. It includes every Bravo 1 from 22-36 as well as 4 and 5 blade Hydromotive props. For the upcoming season we will have a new program for test props and will announce the details when we get closer to the season.

Matt

nordic95

Please let me know any details when they become available.I am assembling my project now and I should be ready for prop testing in a few weeks.

Thanks
Nordic95
Anthony R.

bbladesprops

The loaner programs you would need for "Bravo drive" propellers are already in place.

We have a minimal processing fee and you pay the shipping. That's all there is to it. We would be happy to help you as the testing time approaches.