Blowing outdrives - Why???
 

My buddy has a 30' Sleek Craft with a blown 560 motor pushing 800 HP. He is running a B-Max outdrive. The drive has broke a total of 4 times. I have been in the boat the last 2 times his B-Max outdrive broke, and both times has been this year (a total of 3 times this year) and within 2 hours run time of the "re-build".

First let me say that I am NOT dogging the B-Max. My experience is with Bravo drives and I don't know squat about the B-Max. I am only looking for some expert advice from the board as to possible causes of these failures. He never "dropped the hammer" on it. The first time I saw it fail, we were coming off plane when the engine spun up to the rev limiter. The second time we were just leaving the dock and put it in gear and felt the vibration. Total time on it before any failure was 3 hours. Is there an "X" dimension issue or something like that?

He has run a 5 blade 28 pitch and had a failure. This last time he had a 4 Blade 22 P on it. Both prop set-ups were recommended by Dererbury Marine. In either case, he was never at WOT or hitting anything above 4 lbs boost.

Thanks for your help,
Bruce...

What is breaking inside the drives?

I gotta ask...
 

How can any boat run with a 5 blade 28p and then have a 4 blade 22p be anywhere in the ball park with regard to speed and RPM? Something else had to change - about 300hp worth of something.

Yeah...whats failing in there?

The gears in the lower end have been ground up.

As for the props, the 28P 5 blade wouldn't spin up past 4800 RPM. Couldn't develop enough boost at that RPM. They then went to the 22P in hopes of getting the rpm up and developing boost. I think it was under propped because it would spin up to 6000 with only 4 PSI boost. To me, it wasn't loading the motor enough. Thoughts?

How long of a breakin period did he give the drives? I am a firm believer in running them very easy till things settle inside, five hours or more and a lube change! He may have overloaded the "new drive" with that big prop and then over revved it with the small one!!

You said lower gears are dieing.. I have seen some pretty big power go thru lower gears in a Bravo and hold up for some time.. They shouldnt be failing that quick.. Just my .02

Dick

Good luck I hope you get it figured out..

Find someone else to recommend propellers for you...

Your first problem, obviously, is to find out why your drives are breaking. Then, make incremental changes in pitch staying with a single blade configuration until you get where you need to be. You're dealing with too many variable to be able to make informed decisions.

My friend has a new 38 Sonic the has gone through 3 Bmax drives in 2 months of light use. He has taken the boat back to Sonic to have the drives removed and I think he's going to move the engines and go w/VI's.

That change is very costly and difficult in the 30 foot boat.

What kind of power is his Sonic putting out? Does he get "good" service from the folks at Bmax?

I have a very good friend who is putting over 1300 hp through a B-max and has not had any drive failure. He has been running this combination for 2 seasons on a 24 Elminator Cat. There must be something else wrong to be seeing this kind of problem with only 800hp. Dean at the Bravo Shop has been very helpful with this particular setup.

check300,

there you go. you should be able to figure out the problem with what check said.


bottom line is your boat is to heavey. you are pushing to much weight. a 24 eliminater cat wieghs a 1/4 of a 30 sonic. do all you want. you will always blow drives. all the money you spent on drives could of gone to a set of speedmaster threea's. and you would of still had some money in the bank. and if you don't want the transmision then use a crash box.

Treadwell

mr treadwell a rookie question what the heck is a crashbox?

The lowers!? Very interesting...I'll let you know what I find out.

Carreraboat:

A crashbox is a type of tranmission that is unable to shift under power, i.e. the engine must be shut off when shifting. A crashbox is simpler and stronger than a "normal" transmission.

vtec

thanks vtec but why the name

My personal opinion why its called a crashbox.....cause when you are comming up to the dock and you can't get the dang thing into the gear you need ......well the rest is self explanitory. You see .....these are not the most user friendly of trannys.

thanks big dog makes since