Need advice on props
 

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

Re: Need advice on props
 

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

Re: Need advice on props
 

[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

Re: Need advice on props
 

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

Re: Need advice on props
 

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.

Re: Need advice on props
 

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

Re: Need advice on props
 

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.

Re: Need advice on props
 

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

Re: Need advice on props
 

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.

Re: Need advice on props
 

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.

Re: Need advice on props
 

Will do Anthony, call us when you are ready to test.

Matt

Re: Need advice on props
 

As far as ideal propping for best prop from the HP/Torque/RPM factors....

Even though say best RPM is at 5800, but a customer prefers 5200 as his WOT, do you still ideally prop for the 5800 factor and just not use the full potential?

Re: Need advice on props
 

Yeah what he asked. :evilb: :evilb: :evilb:

Re: Need advice on props
 

One of the things that you need to keep in mind is at what RPM the peak torque is produced. You DO NOT want to run at or near your peak torque as this can lead to early drive failure and behavioral issues that can be associated with torque loading. So in nordic95's case you don't want to run at 4800 RPM or near it according to the dyno sheet posted, in post #1. In my opinion running at 5200 is to low, and you are not utilizing all that HP you just purchased!

Julie

Julie

Re: Need advice on props
 

Like I stated earlier, 55-5600 will be fine. You do not need to prop at the highest hp # on the dyno sheet. In fact, in some instances this will hurt the overall performance. Especially when the last few hp come over a 3-500 rpm increment. You do need to get close to the max and the dyno sheet tells me where that point is. To answer your question, If you over prop and keep the rpm too low, you risk engine failure from detonation. It's like running your SUV around town all day in overdrive.There is a window to keep the rpm max at. It depends on the customers boating habits and desires and the design of the engine. Once the engine is propped correctly, you can run at any rpm you wish.

Re: Need advice on props
 

OK,


I am finally ready to start testing some props.I have posted my dyno sheets and since my last post I have added new XR drives with the 1:50 ratio and with Imco prop shafts.Pictured is the hub system that came with the drives.I will need props to fit this hub,please make sure its not too much pitch as to kill my planing time with four or five people aboard.I am not to concerned about getting every last MPH out of it.Let me know what kind of loaner programs are available also.I would like to also keep my old props for spares but this hub does not fit them.Can they be machined to accept the hubs or no?

Re: Need advice on props
 

ttt

Re: Need advice on props
 

Your old props have rubber bushings in them. A large shaft hub can be welded into the old props which will allow you to use the old props with the new drives.


You will not be able to use the old props on a standard prop shaft once the larger hub is welded in.

Re: Need advice on props
 

You can contact us at the phone number below when you are ready to test propellers.

Re: Need advice on props
 

OK Here are some preliminary test results.I have broken in the motors and drives the last couple of weekends.Since I have installed new motors,drives with different ratios,and new transoms its like a completely different boat.I ran stock power 415 hp 502 with 1:36 ratio bravo one and a 23 pitch 3 blade Mirage.5200 rpm gps at 75 MPH in stock configuration.Now running 600 hp per side,1:50 bravo XRs and 30 pitch 4 blade Bravo ones.Mid range 3600 rpm 60 mph and could only turn to 5000 rpm at 80 mph gps.Boat has a ton of stern lift.I am trimmed almost double as the stock set up and it still feels like it is running to flat,nose down.I'm not sure if its where I have the celery stick located on the new drives or if its the prop,but I should be able to spin to at least 5600 rpms with this set up I would think.Where should I start with a different prop or what should I look to do with the set up I have?I love the hole shot and mid range but I feel like I am dragging the bow through the water.Is there a happy medium prop I should try?

Thanks
Nordic95

Re: Need advice on props
 

ttt

Re: Need advice on props
 

ttt