With all the talk about blown couplers lately, I thought I would join the club (almost). I feel kind of boneheaded but I think sharing my bone headedness might save some of you guys some trouble.

While cruising along Saturday at about 3500rpm I suddenly heard one of the engines rev way up without my consent. I was off the throttles so fast I wasn’t even sure which engine it was. Thought for sure I spun a coupler or spun a prop since this is the classic symptom. Both engines still worked and went in and out of gear so I idled back to the ramp. Just before pulling into the ramp, I tried to put it on plane just to see which engine was at fault. As expected the boat did not come on plane and the port side did not hook up – it just revved up.

Today the repair shop looked at it, water tested it, and found no problem at all. The boat came on plane and worked fine.

My theory is as follows:

Upon putting the boat on the trailer, I noticed I had hit a submerged object on the port side. It was obvious due to a scuff on the drive that had not been there previously. Well, we all know that the hydraulic trim system on Bravos is designed to give way and trim up when hitting a submerged object in order to protect itself. I’ve concluded that whatever I hit caused that drive to trim itself up far enough to cause the prop to blowout. The drive must still not have been in the full-down position when trying to come on plane later.

Having it on the trailer and moving the drive in and out of trailer mode a couple times, must have bleed the hydraulic trim allowing it to go down all the way by the time the repair shop water tested it.

A while back OSO member Baja Bopp posted a tread describing a scenario identical to mine. Folks were quick to remind him that spun couplers and spun props don’t just fix themselves overnight. I have to wonder it he had the same issue as me.

Very interesting scenario. I never would have thought of that. You didn feel the impact? Usually if it's enough to move the drive up, you're going to feel something.

Question: The Bravo drives will cushion a blow and deflect upwards, won't they rebound to the original position...or is it some sort of one-way relief valve?

BD,

Nope, I did not feel any impact but I was also in water with tight chop and was kind of bouncing around to begin with.

At any rate, check your 496HO owners manual on page 39. There is a paragraph titled "Drive Unit Impact Protection". It discusses the "break-away" (trim up) feature of the drive when you hit something.

Are you shure you didn't catch
a piece of floating debris, like an
ice bag, or small tree limb ?
This can cause water disruption
in front of the prop, and cause the
symptoms you discribed.

Then it probably dropped off when
you loaded the boat on the trailer.

Couplers and prop hubs don't grow back

jt

jt,

Thanks for the idea but I would have to rule that out. I idled back to the ramp for about 4 miles with both engines and drives running forward without any odd handling characteristics. When I got back to the ramp and went to go on plane, still major prop slip. I would have to think that if something were clinging to the drive or the prop it would have fallen off by then or it would have manifest itself thru odd handling, shifting, vibration, etc prior to reaching the ramp. Bottom line - who knows. All I know is I wacked something Saturday as evidenced by the scuff on the drive.

never thought about that, thats one to remember for sure, hope they did not charge you some big money for a water test.
Mark

Well, since I am super paranoid and super anal, I told the repair shop to check the torque of all the motor mounts and if they found any that were not in spec they were to pull the associated drive and check alignment. Heck – there’s no way I can make it out of a repair shop without spending money.