Hydro Lock Exhaust Problem
 

Has anyone ever heard of a boat "Hydro Locking" in the exhaust?
Basically I understand that when the boat comes off plain it is possible for water to back up throught the thru-hull exhaust and get into the engines and blow the motor. This is most common on boats where the thru-hull exits under the swim platform.
Now there is supposed to be a butterfly in the exhaust that prevents this, but in some cases, if the conditions are right, it can still happen.
What precautions can one take to ensure that this never happens again?
Get rid of the thru hull with a Quick and Quiet?
Some type of riser?
Any information?

Sometimes coming off plane with the throttles closed and the engines at a high RPM will cause the exhaust to scavenge water up the exhaust pipes...This can happen if there is a big overlap in the cam timing. I'd suggest getting and installing the rubber flaps on the ends of the through hull exhaust pipes and being careful coming off plane... it seems that with some boats .. just as it is coming to a stop... there is a huge wave from behind that will swamp the stern. I've seen this on a 30' Scarab.The trick to not getting the stern swamped was to throttle up just as the wave was coming and the stern wouldn't get covered with water.Then you can proceed at a wakeless speed and not worry about water scavenging into the exhaust. Good Luck.

What about at the dock. The exhaust is only 1 # from the water line. The rubber flap probably wouldn't stop a small surge of water at the dock (not running) then the water can still get in the engines, right? Someone told me to get some risers? Is that logical, nearly $1200 for parts that I am not sure are necessary.

It happened to my 30 Scarab. I was running hard when I looked down to see one temp gauge at 240. I shut down the throttles and switched off the hot engine before the boat had a chance to settle. My theory is the water starts up the tailpipe and as it cools, the exaust creates its own suction and draws the water right into the engine. A few minutes later, I tried to start the engine but it wouldn't turn over. I thought the engine was seized. By the time the marine repair guys looked at it the engine was rusted, ruined.

The same thing happened to a friend with a Baja 240 Sport. He was running at high speed when his throttle linkage jammed wide open. Thinking calmly he switched off the key. Sure enough his engine lockd up too. Since I had just had my experience, we decided to pull the spark plugs. Sure enough, water! After we got the water out, the engine started up and ran fine. Wish I had known about this sooner.

So what I am gathering, so far, is that it's not necessary to spend big bucks to stop this from ever happening as long as you are aware that it can happen, and how to prevent it, or fix it if it ever does happen.

These types of thing make me glad that I didn't have thru-hull on my last boat.

Let me ask you this, if the boat needed to be shut off immediately while it was running at high speed, and it was equiped with Quick and Quiet exhaust, could the thru-hull have been closed to prevent problems?

Probably but I'm not certain. When a emergency happens will you remember to shut it? I carry a sparkplug wrench in my toolkit always now.:rolleyes:

If your exhaust is so close to the water line... put the rubber flaps on for sure.. and be careful backing up that you don't swamp the stern.

ive seen it happen twice, both times when the enigne was shut off while running mid-high rpms, drained the water out and was "ok", not my boat, hell this even had exhaust from the outdrive, not thru-hall

Call Dino At Teague Custom Marine he can fix you up.

http://www.teaguecustommarine.com

Fightclub

What are they going to fix me up with?
I called BAM and they said that I better have an Mercruiser mechanic check it out because there must be some kind of leak or problem that can't be resolved over the phone.
Fact is, I will fix it myself, or sink it before I call a mechanic.

I had Merc exhaust on a 502 mpi and it leaked and hydro locked the motor which caused two teeth to break of the flywheel and soon after the the main bearings kicked out and Kaboom........I put a new motor and stainless marine exhaust on it.

Rubber Flaps
 

The flap pictures from Teague posted above will close when you come off plane and the water breaches the swim platform or tips.

This keeps water from entering the exhaust. If you are unable to use the external flap style you can get tips with closure units built in.

Any HP shop can get them I would think every tip MFG. has a method to keep the water out.

see the attached pic. these are the old ones, I just put new 4" tips with mufflers and odered new flaps from Teague.

fightclub