Avoiding water coming in through exhaust (hydrolock)

[Fluer de Mer]

Waves driving up the back of the boat when the engine is off can fill the exhaust system to the point where it backs up into the engine and causes $$$ damage. To prevent this make sure the exhaust hose is looped up as far above the waterline as possible and then down to the thru-hull exit so as to create a vented loop (many boats don't have this but all should) If you have a low freeboard then fit the exhaust pipe with a seacock valve of the same diameter as the hose.

[jsc7]

Originally Posted by wingless

The Mercruiser engines in my boat have raw water cooled exhaust manifolds, risers and elbows. When these are used in a salt water environment and they are not periodically inspected and then replaced once deteriorated, the result is engine failure.

My exhaust was redesigned by me from no fresh water flush possible and the bottom half of those expensive cast iron parts filled w/ salt water 24/7/365, to now flushed w/ fresh water, soapy water and Salt Away after each use. Then I drain the exhaust bone dry, ready for the next use.

Additionally, Sea Ray had built prior model years of my boat w/ a water lift muffler. In 2000 they switched to the lower cost log muffler, until many boats suffered hydrolock when quickly coming off throttle and getting whacked in the rear by the boat's wake. Sea Ray reworked my boat and many others to remove the log muffler and to install the water lift muffler, to restore protection from that failure mode.

That is interesting. What was the design you made? Can you post a diagram?

[slowpoker]

Have noticed that on a few inboard diesels, that the exhaust elbow's raw water cooling line is bolted right off the manifold and very close to the engine valves. The angle pitching down on the engine is basically what keeps the levels of the water inlet and the top of the head where the valves are, separated by a few inches, but it's close. A spacer could be added there to make those levels further apart.
Another thing is that most boats have their exhaust at the stern very close to the waterline to maybe make it more quiet or to minimize staining from the drippings. I believe the exhaust water should be more than 14" above the waterline but this makes the exhaust line loop smaller.
Another idea is to put a drain valve at the bottom of the waterlift muffler to open easily if accessible, when long cranking.

[Three Sisters]

Originally Posted by wingless

Additionally, Sea Ray had built prior model years of my boat w/ a water lift muffler. In 2000 they switched to the lower cost log muffler, until many boats suffered hydrolock when quickly coming off throttle and getting whacked in the rear by the boat's wake. Sea Ray reworked my boat and many others to remove the log muffler and to install the water lift muffler, to restore protection from that failure mode.

Searay used oval thru hull exhaust exiting on the port and starboard quarters, not the transom.


Have they changed back to the transom location ?

Did Searay include flappers built into the oval exhaust ?

Just curious if the side exhausts alleviated the backflow of water when slowing.

[valhalla360]

My inboard boat had a rubber flap. If a wave came up behind, I forced the flap down unless there was enough exhaust pressure to keep it open and then the exhaust kept the water out.

I believe on sailboats, the typical issue is the engine fails to start and the water pump keeps sending water to the water lift muffler. BUT since the engine doesn't start, there isn't enough exhaust pressure to clear the water out of the muffler and eventually, it backs up into the engine. A flapper valve or similar solutions won't solve this as the water is not entering via the exhaust outlet.

The solution is if the engine doesn't start relatively quickly, turn off the water source until you get it started. Key Point: Make sure to quickly open the valve as soon as it does start, so the running engine gets cooling water.

[wingless]

Originally Posted by wingless

Additionally, Sea Ray had built prior model years of my boat w/ a water lift muffler. In 2000 they switched to the lower cost log muffler, until many boats suffered hydrolock when quickly coming off throttle and getting whacked in the rear by the boat's wake. Sea Ray reworked my boat and many others to remove the log muffler and to install the water lift muffler, to restore protection from that failure mode.

Originally Posted by Three Sisters

Searay used oval thru hull exhaust exiting on the port and starboard quarters, not the transom.


Have they changed back to the transom location ?

Did Searay include flappers built into the oval exhaust ?

Just curious if the side exhausts alleviated the backflow of water when slowing.

The factory installed exhaust on my boat includes both side exhaust outlets and underwater "torpedo" shaped venturi outlets.

Both exhaust designs used both outlet locations.

None of the designs include flappers or anything other than an elevated or convoluted path to prevent the trailing wake hitting the back of the boat from hydrolocking the engines. There was never an issue w/ the lift mufflers used through 1999 and later restored in 2001.



This shows the lower cost log exhaust that Sea Ray used for a short period.




This show the underwater "torpedo" venturi exhaust outlet.




The lowest opening shows the port side exhaust opening.

[wingless]

This parts diagram image also shows the log muffler system, going to the bottom venturi port and to the side port.

[chris95040]

Originally Posted by Fluer de Mer

Waves driving up the back of the boat when the engine is off can fill the exhaust system to the point where it backs up into the engine and causes $$$ damage. To prevent this make sure the exhaust hose is looped up as far above the waterline as possible and then down to the thru-hull exit so as to create a vented loop (many boats don't have this but all should) If you have a low freeboard then fit the exhaust pipe with a seacock valve of the same diameter as the hose.

What you describe is not a 'vented' loop.

A vented loop has a check valve (or a lift of tiny diameter hose) at the high point such that its 'closed' when there is pressure (normal operation) and 'open' when there is suction (an unwanted siphon has started.). Having an opening there allows air in to break a siphon.

A rise in your exhaust before exiting the boat is certainly good practice to minimize the chance of water making it back to the rest of your exhaust system, its just not called a 'vented loop', which is an entirely different concept.

This needs to be well thought out, however, to verify that when the engine is shut down the remaining water on the engine side isnt enough volume to overcome the capacity of the waterlift muffler and flow into the engine!

[barnakiel]

We have sailed hundreds of days before the seas and some of those days were very rough - comparable or beyond the North Sea in the winter. We never had water come into the engine thru the exhaust.

I think some of us have poorly / badly designed exhausts and that's that.

On our boat this is what we have:

- the exhaust exit is about 10'' above the waterline, no flap,
- then the hose loops up to the highest point in the hull (some 2'),
- then the hose goes very low to a watertrap placed well below the elbow,
- then it travels up to the elbow (some 2' again),
- raw water injects on the elbow,
- raw water loops thru a siphon some 2' above the elbow.

Our boat is minute, the waves were extreme at times. We never had any water come into the engine thru this set up. We had one full wipe out and one time mast in the water (about 135 degrees, I think), we had waves coming over the stern and flooding the cockpit to the rim maybe half a dozen times.

If you can't have an equivalent or BETTER set up in a bigger boat, then you are either lazy or ignorant or else there is some other challenge.

Things like this can get sorted before heading offshore.

Sort of like this except our watertrap seems lower related to the rest of the components.

http://i1121.photobucket.com/albums/...er/boatexh.jpg

b.

[zeehag]

you need an exhaust riser or a flapper cap over your exhaust thru hull fitting.
i have riser. works great.

[Fluer de Mer]

Good catch. I stand corrected.

[DeepFrz]

There can be many reasons that an engine gets hydrolocked. One of them is not paying attention to the anti siphon valve on a regular basis. These need to be attended to on a preventative maintenance schedule. One way around the anti siphon valve problem is to have a small tube at the top of the loop that drains a small amount of the cooling water water either overboard or into a cockpit drain. This was shown in barnakiel's post.

Another problem is over cranking the engine and not paying attention to the water backing up into the exhaust manifold. This is quite common to newbies and could go under the heading of RTFM.

I think another problem that destroys engines is not flushing the engine/exhaust system with fresh water on a regular basis. This comes back to PM schedule again.

Another problem area; an engine should be laid up properly when being left inactive for a while. I think this should include a fresh water flush and then draining the exhaust system. Along with this I feel that the impeller should be removed and stored in a container so that it is not left sitting with the vanes all bent up. This is especially important, IMO, when a boat is being left over the winter.

I think these measures will cover the majority of maintenance issues.

Then again there may be design issues that need to be taken care of to keep your engine running reliably.

[sailcrazy]

We have "enjoyed" a waterlogged eng-but did not discover it until 3 months later.....got to completely rebuild the engine!!! Pistons were rusted so tight to the cylinder sleeves we had to take out the sleeves only after the con rods were disconnected. Tried a rubber flapper valve over the exhaust....complete waste of time and money! They do not seal, and do not stop water ingress. Just get your exh sys properly designed, and maintain your exh elbow!!

[Squanderbucks]

I see no downside of a "flapper" in the exhaust tube between the exhaust exit and the Elbow riser. Mine has one in the exhaust tube midway and has never been a problem in the 20 years or so since its installation. I certainly would not want to hassle with putting plastic bags on and off my exhaust and shudder at the thought of just letting them blow off when the engine is started. The poor guy that sucks one of them up his intake will pay the price.

[wvfamily]

There is a good article in Sail magazine with diagrams for running an anti-siphon loop.

Hydrolock Headache - Sail Magazine