Bravo 1
 

What can you do to break or blow up a Bravo 1 drive? And what can be done to prevent it? Thanks, Mach 1

Bravos' tend to break when you apply to much power when coming onto plane or when you re-enter the water after a good launch. The best you can do is take it easy when pulling up onto plane and make sure you back off when you are in the air. Try to get the prop to re-enter the water at the speed that your hull is going to minimize the hit on the drive. Changing your drive oil every 20 hours or so helps. Of course, any big power motor will break drive parts sooner than later. Also spinning larger props associated with bigger power motors puts more of a strain on drive parts.

Well I do take it easy getting on to plane, and if I leave the water, I do back off the throttle. But I do have a big prop with a 500 hp 454 so would a drive upgrade be necessary for reliablity? If so which drive?

how big and what type of hull,whats it weigh,what make,how big a wheel are you spinnin,turnin it right or left,what brand wheel,it all makes the difference.....

Here is a good link

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

Offshore Addiction, to answer your questions:
27'
Deep V
4800 lbs
Mach 1
15 1/4 4 blade 22p
Right turn
type? It says Bravo one engraved in the prop

Raypanic, Thanks for the link, very infomative

Hey Offshore Addiction, ANSWERS
 

The answers you asked for

from bam marine
 

Why do my Bravo Drives keep blowing up?

The Bravo drive as supplied by Mercury Marine was originally designed for about 375 HP. In its current production form it is pretty good up to 500 horsepower or so. You are probably asking the drive to do something it was never intended to do. Do to the physical size of the drive, there is only so much that can be done to strengthen it. Having said that, I will try and give you some insight as to what is breaking, why and what you can do to help.

First, a short explanation of the various types of failure that apply to the parts in your drive. Just so you know, there are people with doctorates in the part of engineering called "Strength of Materials" I don’t have one of those, and this won’t give you one, but it is a start.

Fatigue is caused by repeatedly applying enough load to a part to cause it to deform (bend or twist). As long as the strain caused by the load is below the part’s elastic limit the part will return to its original shape once the load is removed. The amount of fatigue is related to the amount of deformation (how far the part twists or bends). For the same load, a bigger shaft (or gear tooth or other part) will twist less and be subject to less fatigue and stress. In this case, bigger is better! The exception is when you want part of a shaft to act as a shock absorber. Softer or more ductile materials will deform permanently (plastic deformation) and some will work harden. Extremely hard materials such as high carbon steel (like your gear teeth) do not deform very much when overloaded, but break do to brittle fracture or fatigue. After enough load cycles and the resulting bending or twisting a crack will start at some weak point on the part (usually on the surface) and grow with each repetition of the cycle. Shot peening and other surface treatments can help prevent fatigue cracks from starting on gears and other parts that are breaking from fatigue but won't do anything for brittle fracture or yield failure.

Twisted prop shafts are an example of plastic deformation. A hardened shaft will not twist, but is more likely to break from fatigue. However, there is a whole family of fatigue resistant steel alloys that make great shafts. These are currently available as aftermarket parts and are highly recommended. A billet lower bearing carrier adds additional support and helps eliminate fatigue from the bending caused by the prop. A bigger shaft is the best answer, and Mercury now has one available in the new XR and XZ drives.

The problem is that the weak areas on Bravo gears just aren't big enough.

Shifting in the Bravo is accomplished by the use of cone clutch. This ingenious mechanism uses the engine rotation and torque to engage the forward and reverse gears. As more torque is applied, the force applied to engage the clutch increases. Unfortunately, this force pulls on the floor of the gears in the Bravo drive.

part2
 

Many repeated stress's, including the impact of each blade as the prop rotates (usually do to catching a little air) subjects this area to fatigue failure. Of course there is always that one giant wave that sends you to the moon when all you can think about is holding on to the wheel and BAM - broken gear - that is a yield failure. The same applies to the vertical and prop shaft. Repeated loading below the yield point will result in fatigue.

How you drive your boat has a lot to do with the longevity of the drive (along with the engine and the rest of you expensive parts). The single biggest cause of drive failure is poor throttling. To put it in perspective, a factory stock boat today can run in the 90 MPH range. This is faster than a world champion Open class boat of the 70's and 80's. Boats in Offshore competition today (and for the last 30 years) have at least a two man crew. With very few exceptions one of them is responsible for throttling.

Proper control of engine RPM when leaving and entering the water will do a lot to make your parts live. Timing is everything. The goal is to keep the engine RPM constant, regardless of whether the prop is in the water or not. This means that just as the props leave the water the throttles should be pulled back enough to keep the rpm from surging. It is not humanly possible to react quickly enough once the boat is up, and the tachs lag as much as 1500 RPM behind the engines.

Ideally what really happens is that you learn to anticipate and pull back just enough to maintain rpm. If you pull back too early the boat will trip (pull the nose down). Too late and you will over rev. All the way back to idle is not a good idea either. Even though that is ok for the engines, the props should really be turning close to the same speed as when they left the water.

Think of the tires on an airliner when it first hits the runway. As far as the prop and rest of the boat is concerned the water is non compressible, and the impact on water is as bad (or worse) as if it were concrete. The key to a graceful reentry is the perfectly timed application of the throttles to keep the engines at a constant speed. Too little or too many RPM can both damage the drive.

Most failures in the Bravo are prop shaft, floor of forward gear, tower in upper gear case, vertical drive shaft, or upper gear tooth failure. Mercury has finally addressed all these problems with the new X drives

The parts described above will break from either fatigue, brittle or yield failure assuming the drive is assembled properly

An RPM limiter is a must have. No matter how good you are, there is always that one time when you sneeze or are distracted. If your drive does blow, it could save your engine from total destruction

my idea: your boat is not very heavy.if you rebuild the drive correctly or if it is new there should be no problem with your drive as long as you keep one hand on the throotle on a wavy water.Cause as I know beside all other factors ;props coming out of water and going back with much higher rpm(no throttle down) damages drives

OK so what I have learned so far.......


Change the oil regularly.
don't jump on it out of the hole,
And keep it in the water


Thanks, all 88 Mach 1

Keep it cool-- Add a drive shower!
Keep it stable-- Add external steering!
Keep it lubed-- Use synthetic lube, Amsoil, Royal Purple.
Keep your prop under 30" pitch.

Thanks cobra marty, anything I can do to keep the boat in one piece is good. Was down with an unrelated problem for 6 out of a 9 day vacation, the wife wasn't happy. Thanks again

"Of course, any big power motor will break drive parts sooner than later. Also spinning larger props associated with bigger power motors puts more of a strain on drive parts."

":27'
Deep V
4800 lbs
Mach 1
15 1/4 4 blade 22p "

You sound like you are pretty safe. 22pitch is a small prop. I would assume your engine is quite a bit less than 500HP also if this is all the prop you have. I have rarely heard of Bravo's breaking with mild to moderate prop and HP. Mercury rates them for up to 500HP I believe.

I've got a boat that weighs about the same and has the same power and am running pretty much the same prop. I've never had an issue with my Bravo drive that I didn't cause myself (leave the top vent plug out once and see how long it will run full of water!! :mad: ) But I do NOT do hole shots, and I do NOT over rev it when leaving the water off a swell or boat wake. I also have a drive shower and use Merc. High Performance Gear Lube, changing it about every 20-30 hours.

Oh, and don't hit the bottom either.....stainless props are so strong (oh wait.....Michigan scores AGAIN!!!! Go Blue....42-13)...where was I....Oh yeah...if you hit the bottom hard enough you will break or at least bend the prop shaft, or spin the splines. This is especially true if you have a solid hub prop. Stay off the bottom.

Mike

One thing has been overlooked. If you have separate throttle and shifter, do not shift into gear above 1000 rpm. I lost the upper gears and Merc. would not warrenty saying it was "A high speed shifting error"

Okie Tunnel
 

Okie, Still working on the prop size. Not sure which one to run. As for the HP, it was dynoed at 5200 rpm, 502.35 hp. was running a 3 blade 19 p and turned 5800 rpm now with the 4 blade 22 p can only turn 4200-4400 rpm. Still trying to get the right size prop. May try a 3 blade 25 p. any suggestion?

here is the complete list:

Change the oil regularly.
don't jump on it out of the hole,
And keep it in the water
Keep it cool-- Add a drive shower!
Keep it stable-- Add external steering!
Keep it lubed-- Use synthetic lube, Amsoil, Royal Purple.
Keep your prop under 30" pitch.
do not shift into gear above 1000 rpm


;)

88Mach1, Every 2" prop pitch change is equal to about 400 rpm. So your 19" and 5800prm try a 23" and 5000rpm, A 25" might work if you have the power.

cobra marty
 

I have to power, just need to know, 3 or 4 blade? What I have learned so far is a 4 blade is better out of the hole. Which I don't really need. If I wanna ski, I'll just change the prop. So which one? 3 or 4 blade? Thanks, Mach 1

88Mach1
 

How is it in the turns? Does the prop lose bite and how is it fully loaded-fuel, guests-Easy to get on plane? Generally go 1" smaller if using a 4 blade. 3 blade wil run faster if it keeps its bite in the turns and it planes easily.

Like I said, I run a boat with about the same displacement and similar hull design......I will never go back to a 3 blade. Handling is much better on my boat with a 4 blade prop. Handles better in rough water (better bight in churned up water), handles better around the dock (small steering inputs and small throttle inputs do more than with a 3 blade), and I can get on plane with 6 people and a full tank MUCH easier than with a 3 blade. I don't know about you, but I don't do a LOT of boating without some people with me and a fairly full fuel tank (not to mention all the gear, food, and beverages people bring with them). For my money the 4 blade is without question the better choice. I'll give up the 1-2 mph on the top end to have a better all around prop. You'll find that your cruising speed and efficiency will also increase with a 4 blade wheel.

Does your boat have trim tabs?? If not, a relatively inexpensive set of Bennet or similar brand of dual ram tabs will help a lot too with your planing when loaded. Not to mention their benifit when the water gets snotty or the load needs to be leveled.

Just some thoughts.....

Yes on the trim tabs. Sometimes I have people with me sometimes not. With the turning I usually put the drive down when turning to prevent cupping. I didn't the first time out and it was not good so trim down on the turns.

As for the prop I guess I'll try a 23 and a 25 3 blade and see which one works better. Thanks, 88 Mach 1

Pics of my boat are in the photo area, User name 88 Mach 1

Something doesn't sound right, you have 500 HP and can only turn a 22P 4 blade to 4,200 - 4,400?

I have a hundred HP less and turn a 24 pitch 4 blade to 5,100 and a 25P to 4,900
You may have HP but what were your TQ numbers?

Apache 22
 

Don't remember, the Dyno was last December. I was turning a 3 blade 19 p at 5800 I have been told that figuring props is all trial and error so still trying.......lol

Running the 4 blade I don't have to trim down much if any in turns....and I have a raised x dimension on my boat from stock.

Waterfowl
 

I started trimming down with the 3 blade, I haven't tried the 4 blade. Kinda new to the I/O set up. Used to run an inboard.

I have also been trying a different prop. My boat came with a 23 pitch mirage 3 blade and I have just installed a 24 pitch 4 blade Bravo 1. I really really like the way my boat performs with the 4 blade prop. I, like an earlier poster, will not go back to the 3 blade. My boat is a 23 foot SeaRay with a 385 hp 454 MAG and Bravo 1 outdrive. It turns about 4700 rpm with the 4 blade prop. I have thought about dropping down to the 22 pitch Bravo One, but I'm not sure I need to . Boat is not a go-fast boat like a lot of them here, but it does run gps 63MPH with the 3 blade and 62 with the 4 blade. It feels a lot more stable with the 4 blade, even at WOT. The boat feels really loose with the 3 blade at WOT.The engine would bump the rev limiter with the 3 blade.

Hudson
 

Wanna sell your 23 p 3 blade? Let me know

88 I am running about the same. A 29' vee with a 502mag mpi and a 23 pitch 3 blade. If you are having any blow out or cavatation I would agree with waterfoul on the 4 blade vs the 3. Try a smany props as you can in the range you think you need before buying is all I can say. Oh yea carefull on the trim in those turns. To much trim while turning is not a good thing.

sorry,been working on another project this week in the barn at home,what kind of punishment do you plan on giving this thing,lakes,rivers,offshore pounding,sounds like you just may need to keep a close eye on the oil in the drive,it'll usually tell the story,a stock used drive should be torn down and magnafluxed,reaasembled and use some redline shockproof oil and keep an eye on the magnets....Imco does make some nice high perf parts if you can afford them,shafts,gears,etc....for the most part I would reccomend only propping to the point wher you can still almost touch your rev limiter,and make sure the motor and drive can still freewheel,you can also try a larger wheel and have it labbed to your needs and keep your slippage correct allowing the setup not to be to tight,most drive problems come from either driver error,or just propping to tight not allowing the drive to have its proper slippage........and of course a drive shower does always need to be there.....

Offshore Addiction
 

Punishment? Nah. The boat is kept in LOTO. Just want to know this info so I don't blow the drive. It is about a 500 mile drive for me to get to LOTO so when I drive down I'd like to be able to use the boat without any problems. The drive and engine were rebuilt at the same time. Thanks for your reply, 88 Mach 1

88 MACH 1

I wouldn't mind selling the 23 pitch Mirage. What is it worth to you?

Hudson
 

You have mail...

Alot of good advice in this thread except for oil advice. ALWAYS run the Mercury recommended lube NOT after market! For warranty mostly, the High Perf is good stuff. Beware there is alot of "snake oil" out there. ;)

rhino
 

Thanks for the info but as you can tell by my user name it's an 88. I guess warranty is not a concern..........lol........