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Old 01-11-2021, 02:03 PM   #1
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Hydrolock Prevention

On two occasions while on a mooring the seas kicked up and were hitting on the starboard aft quarter and hydrolocked my engine. Our 350 is a 2002 model with a single Yanmar 6LYASTP.


The first time was nearly catastrophic, with sea water in the cylinders, crankcase and intake manifold. Quick action after being towed 25 miles to my slip removed the water and saved an overhaul, but I'm still seeing traces of sodium in the oil analysis.


The second time happened when I was ashore and didn't think it was that rough. I returned to the boat and caught it before more than a cylinder of two flooded. Just had to pull the injectors.


This also happened to a friend with a Ranger Tug with this engine.


I now pop a 2.5qt plastic paint bucket in the exhaust outlet when not in a totally protected area.


I'd like a more permanent solution that doesn't include require spending a couple of boat units and redesigning the exhaust to add more rise.


Am I the only Mainshpper who's had this happen?


Prevention suggestions? I've considered adding a flap, but undeway the exhaust outlet orientation might make a flap problematic.
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Old 01-11-2021, 02:18 PM   #2
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I have two inflatable green rubber balls with a place to attach a line I got at West Marine that fit into our exhaust outlets. Our owner's manual (Bertram) specifically says to take care to avoid water intrusion in the exhausts when anchored, with a danger of a following sea. They fit inside perfectly, are easy to pull out, and would probably blow out if I ever cranked the engines without remembering to remove them.
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Old 01-11-2021, 02:28 PM   #3
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Here are some things that have been tried (and some worked):

A flapper on the exhaust exit at the transom. Centek makes them. Probably the cheapest and easiest thing you can do.

A surge tube in the exhaust. This tube absorbs surges and doesn't let the water get up into the turbo or exhaust manifold.

A redesigned exhaust system that adds to the height above water. Expensive, yes. I did this on my Pilot 34 and it cost me less than a grand for parts and welding. I designed and installed it myself.

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Old 01-11-2021, 02:33 PM   #4
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My old boat had a seacock on the generator's exhaust. That was nice.

On my new boat, I don't have that. But, when I bought the boat, the person who did some initial work recommended moving the muffler and exhaust far forward, actually forward of the genset, in order that the exhaust pipe could be raised higher above the water line before it drops in.

It cost a good b it because the exhaust hose ain't cheap. And, it was less convenient having it come forward into a busy part of the engine room. But, it did raise it about a foot, which I imagine is good.
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Old 01-11-2021, 03:04 PM   #5
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Does your exhaust have a large up loop?
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Old 01-11-2021, 03:05 PM   #6
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There should be enough room on a 350/390 to raise the elbow above the waterline enough to prevent hydrolock.
A surge tube will also help prevent it.

Another suggestion would be to give a call to Seaboard Marine in Oxnard and talk with Tony Athens. He is familiar with this problem on that style Mainship.
He'll have a solution that will work.
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Old 01-11-2021, 03:54 PM   #7
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If I'm not mistaken you have a lift muffler, and on 390 models I have seen there is an "overflow port" near the top of the muffler for when water reaches that high it is directed through this port to overboard. This is specifically for hydrolock protection.
If you have this set up is the drain open to overboard? The "overflow port" is near the top of the muffler on the side and well below the exhaust elbow and should protect from hydrolock
I believe they also did something similar on the Polit 34's

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Old 01-11-2021, 04:17 PM   #8
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Sounds like you have dodged a bullet twice and I'll bet your insurance company would expect you to take action.
As a temp. measure the balls with strings seem like a good idea.
The external flaps I see alot but anchored in a seaway, when the transom plunges the flap opens so N/G
The Centec internal check valves are another option that don't suffer from that shortcoming but I would not trust them as a complete solution either.
Installing a properly designed system is the only complete answer. This could even involve waterlift mufflers and goosenecks at the transom b/4 you could safely anchor in the tradewinds. Without goosenecks, water will roll up the exhaust as you "hobbyhorse" at anchor, the waterlifts will fill and then fill the engine.
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Old 01-11-2021, 05:35 PM   #9
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While I didn't have this happen, I was worried it could. Sole of my main deck is about 12-inches above waterline and getting the exhaust high enough was impossible without heroic measures.

I pinged this forum a couple times, and also pinged "Ask Steve [d'Antonio]". I didn't get an absolute "here's the right answer" response, but best I could figure, best solution for me was a gooseneck before exhaust exits the hull. Now, my boat (like Brooksie
s) has a raised bench at the fantail so there's room to raise the exhaust.

https://www.vetus.com/en/exhaust-systems/gooseneck.html

But as Brooksie states, you have dodged a bullet. You have a relatively common boat so I'd wager something has been changed or there's be a ton of MS 390's with blown engines.

Peter
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Old 01-11-2021, 05:50 PM   #10
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Peter. I'm assuming then that Weebles already had a waterlift behind the engine allowing you to add a gooseneck? Seeker did not so one needed to be added. I made my gooseneck from hose and f/g elbows wasn't crazy about the plastic goosenecks.
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Old 01-11-2021, 06:05 PM   #11
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This just sounds like poor exhaust design and engine installation. Get that exhaust raised and redesigned.
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Old 01-12-2021, 02:19 PM   #12
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Quote:
Originally Posted by Arc View Post
This just sounds like poor exhaust design and engine installation. Get that exhaust raised and redesigned.
An exhaust redesign is a great idea, but A LOT more expensive than a 2 1/2 quart paint bucket!
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Old 01-12-2021, 02:35 PM   #13
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Quote:
Originally Posted by Brooksie View Post
Peter. I'm assuming then that Weebles already had a waterlift behind the engine allowing you to add a gooseneck? Seeker did not so one needed to be added. I made my gooseneck from hose and f/g elbows wasn't crazy about the plastic goosenecks.
Quote:
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Peter. I'm assuming then that Weebles already had a waterlift behind the engine allowing you to add a gooseneck? Seeker did not so one needed to be added. I made my gooseneck from hose and f/g elbows wasn't crazy about the plastic goosenecks.
I struggled with my exhaust system. When I got the boat it had just a plain water injector elbow off the engine exhaust manifold. 45 degree bend down, no loop, to a lift muffler. Then up along the sole to the back where it raised up and exited the hull higher than the sole - exit was the highest point of the exhaust system.

Several years ago I added an exhaust elbow that looped as high as possible, but the exhaust outlet through the hull was still the high point (I also added a rubber flap on the exhaust pipe).

I talked to a lot of people and never really came up with a good design that I liked a lot, just less bad than others. The plastic gooseneck is that "least bad" solution.

I forget if it was you or Island Cessna that put a loop above the cabin sole. This is a very sound design, the best from an exhaust design perspective. But would seriously interrupt my interior layout. And I had to ask myself "it's worked for 50 years...."

The biggest problem with small cruising boats is simply finding the space for stuff. The W36 is plenty big for moving along oceans, but space fills up quickly. Fuel tanks line the outboard sides of the engine room, water tanks behind. No way to run the exhaust out the side, probably the other best solution.

One of the few items I feel like I resolved, but never solved.

Peter
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Old 01-12-2021, 02:36 PM   #14
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An exhaust redesign is a great idea, but A LOT more expensive than a 2 1/2 quart paint bucket!
...... But not nearly as expensive as a failed exhaust system.

Seriously, you dodged a couple bullets. "you gotta ask yourself.......do you feel lucky today? Do ya?"
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Old 01-12-2021, 02:39 PM   #15
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Quote:
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A redesigned exhaust system that adds to the height above water. Expensive, yes. I did this on my Pilot 34 and it cost me less than a grand for parts and welding. I designed and installed it myself. David
David
Aren't some Mainship install and designs problematic in this regard and require a re-design as you mention?

Water getting into an engine from the exhaust side is the cause of many engine issues and failures. The OP may want to visit boatdiesel and sbar websites for information on this all too common type of problem. It may be worthwhile to pull the turbo and have a good look to assess any damage to-date
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Old 01-12-2021, 02:48 PM   #16
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Following.

Our new-to-us generator is being rebuilt and I believe a similar phenomena was the problem. We were considering a pvc test plug sized to the exhaust for when it's not in use
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Old 01-12-2021, 02:52 PM   #17
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Hard to recommend a solution without knowing the levels and space available in a boat.

I'm lucky enough to have plenty of vertical space at the stern (up to the top of the wide gunwales) allowing a high loop with the exhaust hose before exiting.
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Old 01-12-2021, 04:21 PM   #18
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Quote:
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David
Aren't some Mainship install and designs problematic in this regard and require a re-design as you mention?
Yes the 390s were very problematic. I know of several owners who hydrolocked their CATs and two who lost the engines and one who was lucky and only lost a turbocharger. They were all 3126 engines.
Seems the 3116s were fine.
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Old 01-12-2021, 04:52 PM   #19
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Yanmar makes a dry 90deg dry cast iron elbow that can be added between the turbo outlet and mixer inlet. With a little finagling, you can get some more height for not too much money.
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Old 01-12-2021, 06:41 PM   #20
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I had a new custom mixer made for the purpose of PM . I could not afford a complete failure of a $50k engine, when it could be prevented.
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