Changing from a Bravo I to a Bravo III

[Putinbaybum]

Does anyone know if it is possible to bolt a Bravo III outdrive up to a Bravo I gimbal assembly? I have a heavy single engine cruiser that could benefit from the Bravo III.

 

[Don S]

Re: Changing from a Bravo I to a Bravo III

Not only will the outdrive bolt to the bell housing, all you really need is the lower unit. The upper is the same for Bravo I, II, and III.

 

[Putinbaybum]

Re: Changing from a Bravo I to a Bravo III

Ok then my question would be is it worth changing to the Bravo III lower unit? I have a 1988 Formula 26pc with the single 454 Bravo I set up. I have a 16x16 propeller that I am spinning. It does get up on plane decently BUT to keep it out of the water at a good speed I have to put the trim tabs down substantionally. When it does seem to be at a good planing speed I am starting to get into the 4barrels. I'm not really worried about the speed, but I would like the engine to not struggle as much.

 

[TilliamWe]

Re: Changing from a Bravo I to a Bravo III

A Bravo three would help with what you are describing.

 

[Putinbaybum]

Re: Changing from a Bravo I to a Bravo III

ok, next question. Lower unit for a Bravo III that i can buy is 2k. A whole reman. Bravo I drive, is 2200. The Bravo III worth it? I appreciate all of your answers / suggestions...

 

[Putinbaybum]

Re: Changing from a Bravo I to a Bravo III

Also how do I know which ratio to go with on the Bravo III and which pitch I should go with on the propeller set up? I have never experimented with the duo props at all..

 

[HT32BSX115]

Re: Changing from a Bravo I to a Bravo III

Also how do I know which ratio to go with on the Bravo III and which pitch I should go with on the propeller set up? I have never experimented with the duo props at all..

Howdy,


Your 26ft boat is fairly heavy.

I have a 21ft boat that weighs around 4200 lbs.

I installed a 97 454 (stock & carbureted) engine with a 1.81:1 Bravo III drive.

With 26p Props, and with only 2 people and 1/2 fuel(44 gal tank), it will turn 4600 RPM and run about 57 MPH.

Your boat probably weighs considerably more. I am thinking that you would probably need a 2.00:1 drive or a 2.20:1 drive.

With a stock 454, and a 2.20:1 drive and 24P props it might go 45 MPH at WOT.


I am guestimating what it might do considering the length and approx weight of that boat.

Your best bet will be to talk to someone with a similar boat that has a Bravo III installed and ask them about performance before you go out and and get another lower.

I did a little searching around an immediately found one with a 454 and a Bravo III on the back.

You could call them and simply ask them about the drive ratio, prop pitch and performance.

Don't they still make Formula Boats? Call a dealer that sells them and ask them how they were set up with the 454/Bravo III.

Once you get some info, you can find a set of props on ebay easily. 24p props seem to be the most plentiful.

I had a 340 (crank) HP OMC 460 King Cobra installed in the boat I got from my brother (who bought it new).......... It ran 60 mph at 5000 RPM (400 RPM over recommended) with a 19p (cupped to 20) 3 blade prop but it was a REAL DOG out of the hole!

With the (330 crank hp) 454 and Bravo III, It's slightly slower, but it just ROCKETS out of the hole better than it EVER did even when it was new!! (My brothers words!!)



Good luck,



Rick

 

[TilliamWe]

Re: Changing from a Bravo I to a Bravo III

If you are buying froma Mercruiser dealer, give him your B1's serial number. He'll know your ratio, and which lower unit from the B3 to sell you. B3s readily come in 1.81, 2.0, and 2.2. There are other ratios available, but they are not really for gasoline engines. Propsets are only available in 2" pitch increments from 20 to 30. Propsets are only available from Mercruiser, so they are EXPENSIVE when new. (Think $1200 at least) But you can get used propsets on Ebay for half that, usually.

The advantages of a dual prop drive have been discussed on here MANY times, but I'll give you the highlights:
1) Faster time to plane
2) Able to hold plane at lower speeds
3) Better low speed turn, especially in reverse
4) Better cruising rpms at planing speeds

Disadvantages of a dual prop design:
1) Propsets are EXPENSIVE
2) LImited propsets pitches
3) Increased chance of corrosion (All that Stainless Steel in the props does not help the aluminum case and rear bearing carrier)
4) Bravo 3s move FAST at idle speeds. Much faster than what your single prop drive does. So you have to put them in and out of gear more often, or you run into things much harder.

 

[26aftcab454]

Re: Changing from a Bravo I to a Bravo III

The above posts nailed it on the head.
My boat is the exact floor plan as yours and has exrta weight -genset-hotwater-lot of extras- just not nearly as nice:redface:
1996 7.4Merc BravoIII
I get on plane quickly-and can stay on plane at 3000rpm--but usually cruise 3500-3700 rpm . WOT 4600rpm is 40mph-43mph for me.
I have the 22p props but not sure of drive ratio.
The Drive # OF264580 if someone can tell from it.

also Idle speed in reverse is fast when trying to back into a slip.:facepalm:
.

 

[HT32BSX115]

Re: Changing from a Bravo I to a Bravo III

I have the 22p props but not sure of drive ratio.

You can use a prop-slip calculator calculate your actual prop "slip" (using accurate RPM, GPS-speed, drive ratio and prop pitch)

The following site has a really good discussion on what slip actually is etc.

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

http://www.go-fast.com/Prop_Slip_Calculator.htm

Using their prop slip calculator and approx 8% slip (for a dual counter-rotating prop drive) Your drive ratio estimates at 2.00:1.......(Slip might be more with a heavier boat....Use 12-15 for a single prop drive on the back of most planing hulls)......

Your drive should also have the ratio indicated on a sticker on the side if it's unmodified and the sticker hasn't fallen off! Other wise you can easily find your drive ratio by removing your spark plugs, putting it in gear (while turning the engine over) and count engine turns vs prop turns.

If you had a 2.20:1 drive with 24p props it would probably have similar performance.


ALL this stuff is approximate.......the heavier a boat is, the more slip it will have.

Chain the boat to the dock and put it in gear and you'll have 100% slip!! It's also not fixed. It will change with speed since the drag increases dramatically as speed increases above planing speeds.....