496 water inversion
 

Here is a strange one. Customer put her twin 496 Bravo sport cruiser on her Hydrohoist Sunday nite,trimmed drives all the way up to check props,left drives up. Now her lift will only raise the boat about half way up, transom plate maybe just at waterline, she has stored boat like this for a year,but never left the drives up. Monday morning one engine was locked up from water inversion,apparently from backwash of boats going by and entered the engine. Bravos don't have an exhaust bellows except for a short sleeve that seals with drive down, and 496's don't have flappers in the y-pipe cause Merc says the new dry joint exhaust manifolds don't need them. We will dry out her motor and get her going,but this is a new one on me. I never realized that could happen. Any comments?

Re: 496 water inversion
 

I think maybe when the bravo drives are up the two exhaust bypass holes at the bottom of the the transom plate are totally exposed and wakes slaming against the back of the transom could shove water up the y-pipes to the motor. although I have never heard of this its about the only thing I could suppose. Also, was the front of the boat lower on the lift aiding the water entry in the exhaust manifolds?
Raylar

Re: 496 water inversion
 

Raylar,I am of the same opinion,but like you,never seen it happen in 35+ years as a dealer,but it is the only explanation we can come up with. Boat sits fairly level on the lift but water gets fairly rough there. Doubt it will happen again as I will caution the customer to not leave drives up. I have a call into Mercruiser tech service,it will be interesting to hear what they say. I don't really understand why there are no internal flappers in the y-pipe of a 496,most other models have them. Robert

Re: 496 water inversion
 

I was thinking along the same lines as the bow being lower than the stern.

Re: 496 water inversion
 

drives up or down, that's still alot of "rise" for water to (be pushed) up over the exhaust risers. From intermittent action of boat wakes? I don't buy it. You would need a steadier push of water (gravitationally) to get up and over. Are you sure there isn't more than one variable in this event?

Re: 496 water inversion
 

Have you got an answer from Merc about this issue?

I also have a boat lift and a 496HO and I'd like to know what to do or not to do...

Thanks

Re: 496 water inversion
 

What about a high tide?

Re: 496 water inversion
 

The 496's that I have worked on have the flappers. I don't see how the dry joint exhaust could be a factor in needing or not needing the flappers, since one has nothing to do with the other.

Do you have a picture of the boat on the lift? Sure would like to see how it sits on there.

Dave

Re: 496 water inversion
 

The theory would mean you couldn't trailer the drive in the water due to displacement pressure. I'm thinking along the same lines as Rippem. There's got to be a different explanation from a different source/problem.