Mirage vs Bravo
 

I'm running a 25p mirage with 9% slip. would a 24p bravo give more slip or less

Single or twin? If a single I would think a 4 blade prop wood give better performance on a 29' boat. I'd try both a Merc Bravo and a Merc Rev 4...

Pondering this myself...I keep blowing out my 3 blades at speed now with the new engines.

Hey Capt, whats your setup. Boat, hp, props, how deep is your prop shaft

Hey Pat,,, running twin SB makin 400hp 425tq. spin a 23p mirage+ 5400, a 25p mirage 5000.... prop shaft is 7 3/8 deep... looking to put -2 Imco.

More blade surface area usually means less slip. From 3 to 4 blades of the same diameter should be less slip.

If switching to a Bravo 1, go up in size one pitch. They tend to be over-rated. A 26p Bravo should keep you in the same rpm range as the 25p Mirage. I had to find this out the hard way. I'm running a 30p Bravo 1 with 1.5 gears and I doubt I could pull a 30p in any other prop. I think you should try one. The shorty worked great on my boat and if you do that you will almost certainly need four blades. I don't know how the shorty will work on a 29' boat though as you will lose bow lift due to less leverage (higher prop).

I have twin 400 HP 383s, Mirage Plus 23s. Not sure on X dimension. Keep getting over speed on port when I start to trim out.

Thanks thirdchild, I will try a pair of 26,s. I have a friend with some. The boat does ride nice in the water. Did your -3 Imco bolt up to a Bravo1

Yes it bolts right up. Mine is -2".

I believe we have the same dyno guy, Full Throttle Marine. What boat do you have ? can you measure your propshaft height ? I think we can trade a lot of information.

I always thought that was the opposite.... since 4 blades have more bight they take more to turn so if you have a 25 3 blade you would need a 24 4 blade...

Yes, what he said!

hey if you are getting 9% slip on a big V-bottom that sounds pretty darn good.

Bravo props do measure about 1" smaller actual pitch than their rating; how they hook up (slip at various RPMs) can be different for every boat.

Yeah we do, we have talked before. I'll have to measure next time I'm with my boat. Maybe someone knows stock 6.2 prop height.

Agreed. Every application desires certain propeller geometry for certain performance goals. One prop design will propel a boat but specific goals can improve by changing props.
I also agree the reported 9% slip can potentially be left alone unless you are desiring better cruise speeds or planning.

Brett

My desire is getting the most out of what I have. I'm 7 3/8 deep and wondering if I install -2 Imco's what prop would be looking for. In a somewhat perfect world... And will a -3 Imco bolt to a Bravo1?

As you raise X dimensions, additional blades can be required to get the best planning and trim reaction. Especially on V bottom boats.
The -3 should work. Contact IMCO with questions.

Brett

For a -3 lower, you either need an Imco upper designed for it or you need to have a stock Bravo upper cut and modified.

http://www.imcomarine.com/cal_store/...e-3-black.html

Raising the propshaft 3" is a ton. I'd go -2's max.

On single 29 Scarab what would be the best choice for a 80 + mph with standart lower an standart prop shaft height, what would be the best -1 or -2 in single aplication?

Big single engine boats generally need help carrying the bow.
It really depends on how deep the stock propshaft height is and how much power you have.
With more power, you can go a little higher on the prop.
You could always go with -2 and test spacers to find the optimal.

To hit 80 in a 29 single, I'm guessing you'll need 600-650hp.

The engine is a 468ci with BDS 871 at near 8lbs boost 2x quick fuel marine 850 carb, edelbrock performer rpm marine ported head, hyd roller cam by Bob Madara, daytona sensor 3d map ignition, timing at full boost 33 deg. I have never put it on dyno but with my old 525sc engine the speed was 68-69 mph and max 70 mph in good day. Now it ran 80mph all day and in good day good condition i it 82mph. i am guessing the i am at arond 800hp but it is just a guess.
Prop shaft height with the standard bravo lower is at 7.375 inch below the hull.

You should easily be able to go with -2 lower. The Imco lower design should also help. I wouldn't be surprised if you gained up to 5 mph.