You may want to do some research on that. Quickly off hand i read about a stock 28 sunsation and a 29 laveycraft that blew bravos with UNDER 100 hours.

Also research the past when bravo gears used to be able to handle extra power and/last longer. Then merc changed who forged the gears.

500hp and up just plain wear out the gears faster then they should with or without hole shots.

I agree with c-spray that some damage has started before the failure occurs and just hammering the throttle from a standstill causes it get to a point of failure.

I also believe, well best guess

With a holeshot the prop burns (boils) a hole in the water (like spinning tires) because it is turning too fast with no forward movement (the water boils as we all know which is cavation) as the boat starts to leap forward from water starting to move away from the prop it's goes from almost zero loading (when in a full cavation mode the load is almost nothing) to full loading in an instant and that shock is what causes stuff to twist or teeth to shear off.

Like has been expressed by others it is like reving the engine and dumping the clutch, stuff will get over stressed

mine is a real ass dragger i thought maybe i had bad clutches or something.. i feel slightly better but im going to install some tabs to help it out

Ok How many people on here have a boat 10 yrs or older with original drives??Let's see how they come on plane WOT or easy????That will be the correct answer truth pills before posting!!Thanks!!

I think most drives fail because of the slip when getting on plane. The prop is biting and slipping thousands of times a min. Boats with the drives in deep are less likely to blow then ones with a higher X. There is also a lot of side load at speed if you have your prop starting to surface that can cause your drive to start to deflect. This changes the gear lash... On my pontoon boat I roll on the gas fairly fast. It is the only fun you can have on the thing because it accelerates like a rocket. Once it hits it's top speed... Not like I can roll on slow if towing a person water skiing.

'88-Fountain 8.8 330's and TRS, drives are DEEP, but even then if I tried to push the sticks too far forward in 95 degree aerated water (trying to plane in the spot where another boat just climbed out), it would spin the props, no forward motion. So, come up slow to keep them biting. When the props are cavitating, it is easy to detect that there is little load on the drives because it stops climbing up and actually settles back some.

But what I do believe a lot are missing here is that the load on the drive while cruising at 4600 rpm is NOT full motor torque output, it is less, perhaps a lot less than full load. At WOT, when the boat is no longer accelerating but at steady state speed then the torque at that time is what the engine can produce at that specific engine speed.

If the torque output of the engine at 4600 rpm was matched by the torque required to push the boat 4600 rpm, then when you "mashed" the throttles forward from that point there would be little or no acceleration, it is the differential between what the engine can produce and what the boat requires at that specific speed that determines acceleration rate.

Therefore, the starting torque load on the drive is determined by what the engine can deliver at the rpm's as they increase only when the prop is hooked up and pulling, It could be suffering slippage and what not but it can't be fully cavitating. So, besides WOT, climbing to plane may actually be the most load on the drive components. If WOT is far beyond torque peak rpm, actual torque at lower rpm may actually exceed WOT torque output as well.

If you're trying to plane coming out of a spot where a boat just took off on your going to cavitate the props regardless because that is dirty/airated water

Motor torque on a dyno is totally different than the torque on the drive, post motor, in the water, spinning the wheel...

You don't dyno in neutral.....your torque and hp would be zero...or close enough to make you cry....

What no one is pointing at is the combined load of the vessel, passengers, and prop pitch + bite and diameter creating the load.

Your motor has a torque "potential"....and for all of the obvious reasons, this number should be well below the maximum load the drive is DESGNED for.....forgetting about prior use/abuse....

Not hypothetically, but in reality, your drive requires a tremendous amount of torque applied to move slowly at the fuel dock, or to you local mooring spot. Not because you are using available hp, but because you are counteracting the inertia created by movement.

Force to loading surfaces changes exponentially as the tourqe required to move the vessel ( weight, current, wind, x dim/slip, prop pitch and diam, fresh or salt) in any direction.

So...

Considering that the main shaft and prop shaft are connected to a torque potential on one side, and a load unknown on the other, why spend money for being dumb?

mine is 12 years old with 500 efi's and bravo x drives. not share if they came on the boat i just got it at the beginning of this year. but like i said in my other post i dont slam them down but role them pretty quickly or my boat stands up and burns out. now my boat is in the shop getting top ends and the drives will be gone over as well. so we will see and will let people know if i was just f-in my self all summer lol

My boat has a high X. When getting on plane, the big cleavers cavitate a lot. 4000RPM on the tachs is common before she even begins to lay over. However, at 4000RPM, Im at about half throttle, and the engines are still in vacuum on the gauge (supercharged). Im less worried about the drives in that scenario, as my engines spinning 4000RPM with cold oil in them still.

Shock loads breaks stuff. Take a piece of glass, like a car window. You can stand on it and not break it. However tap it with a ball peen hammer gently and watch it shatter. When a street car bolts some slicks on and heads to the track and dumps the clutch at the line, he snaps the axles, u-joint, etc. It doesn't normally snap things when the engine is pulling hard say in 3rd gear making gobs of torque in high boost.

Same goes for my Semi truck. The engines in the trucks put out say 1500 ft lbs of torque. Day in and day out the truck weighs 80,000lbs. From standing starts to uphills. Light turns green let off the clutch, and its full throttle 35lbs of boost, until I get thru the gears up to speed. You know when the u-joints snap, or rear axles snap?? Its when the wheels lose traction and hop (mud/sand), or you dump the clutch at full throttle. Hence the hammering effect.

So, in my opinion, what eats up drives, isn't the planning aggressively(not suggesting go from idle to WOT planning), its the unloading and loading them (airing out) and what not. Race boats with mild power eat up #6's, because the drives are always being pushed hard in rough water. Of course this doesn't apply to the guy running 1000's in front of his XR's. The only way not to break the drive would be leave it on the trailer.