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Old 07-06-2022, 01:24 PM   #1
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Generator Sea Strainer packed with seaweed

Last week, while cruising in the BC Gulf Islands, I had an odd occurrence. My generator shut down on its own. Starting it up again had the same result, with a flashing message that translated to “insufficient cooling flow.”

A quick visit to the generator sea strainer and I found that it was packed tightly with a fine sea grass, the kind that is like filaments.

I dug it out - there was about a softball sized amount when I finished, maybe 3/4 of a pound. I have never had this happen before! Thank goodness the generator has built in sensors….by the way, the boat had very recently been serviced, including inspection/cleaning of the sea strainers.

Has anyone else had this occur in the BC Gulf Islands??
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Old 07-06-2022, 02:00 PM   #2
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When we were up in Desolation Sound in 2019, we had it happen at Prideaux Haven. It clogged up the intake screen on our Onan 9kw. It also plugged up the intake below the valve and had to rooter it out. We have also had it clog with the milfoil grass here on the Columbia river. We do like the Onan raw water pressure switch. It is an impeller saver!
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Old 07-06-2022, 02:03 PM   #3
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It happens but not often. Happened to Todd on the Uniflite 25 years ago.
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Old 07-06-2022, 02:32 PM   #4
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Some interesting things can end up in strainers. A few years ago we were free diving offshore San Diego about 10 miles out. While in the water there were large amounts of big jelly fish, a type I have never seen before. They probably came up from the southern Mex waters with the currents. They got sucked into several of the strainers, including the main engine. Good reminder to check the strainers often.
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Old 07-06-2022, 06:02 PM   #5
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We had the same thing happen to one of our main engines enroute from Hood Canal to Anacortes some years bak. The high temp alarm went off. Cleaning the strainer was easy enough but I had to use ? a dowel or something similar to push the seaweed blockage out of the thru-hull. Very fine hair-like, bright green.
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Old 07-06-2022, 07:12 PM   #6
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There's a fix for that. The surface area is large enough that nothing gets sucked to the screen.

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Ted
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Old 07-06-2022, 08:57 PM   #7
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Sue, I suspect you crossed over a tide line and did not notice the fine seaweed. It is thick & wide sometimes.
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Old 07-07-2022, 10:12 AM   #8
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Quote:
Originally Posted by Fletcher500 View Post
Some interesting things can end up in strainers.
I remember doing a running engine check and saw two small fish going round and round in the strainer! After shutdown they swam out the intake to where they came from.
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Old 07-07-2022, 12:25 PM   #9
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There's a fix for that. The surface area is large enough that nothing gets sucked to the screen.

Attachment 130184

Ted

A lot of grass gets pushed through one of our favorite Bahamas anchorages on an incoming tide. Our gen set intake is right next to our keel, and it somehow creates a swirling effect that concentrates the grass right under the intake. It gets is so bad in that anchorage that it would shut down the genset every 30 minutes to an hour, packing the strainer full and sometimes the inlet hose as well.


I installed a hinged "mushroom head" strainer from groco over the intake. Haven't had the issue since.
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Old 07-07-2022, 12:36 PM   #10
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Sue:
Anchoring at Sidney Spit, years ago. The depth at low tide put the engine intake lower than the height of the eel grass. Lesson learned.
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Old 07-07-2022, 12:52 PM   #11
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Thanks everyone for the suggestions! I don’t recall crossing a tide line that contained this very fine stuff, but who knows!! I will add “check sea strainer” to list of things to do….
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Old 07-11-2022, 04:38 PM   #12
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I'm just going to leave this here... strainer was clear, so I removed the inlet hose to to figure out what was obstructing it. Time for a strainer on the hull!
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eel1.jpg   eel2.jpg  
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Old 07-11-2022, 07:40 PM   #13
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I got tired of my intakes clogging for the mains and built these:

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I stepped the forward face to ensure water would flow into rather than over the cover.
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Old 07-11-2022, 07:47 PM   #14
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I got tired of my intakes clogging for the mains and built these:

Attachment 130339

Attachment 130340
I stepped the forward face to ensure water would flow into rather than over the cover.
Pete, If the inlet is facing forward it will vacuum up everything in its path, facing aft only some.
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Old 07-11-2022, 09:06 PM   #15
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There's a fix for that. The surface area is large enough that nothing gets sucked to the screen.

Attachment 130184

Ted
All my boats have always had external strainers and I've never had one clog up. Several friends with internal strainers have had problems, one every time he went out. Backing out of his slip through the weed patch that grew there would plug up his strainer every time. He switched to external, no more problems. Note this was in Michigan where all nearly boats get hauled for the winter so underwater things get maintained better. In warmer waters where you might not get hauled for several years, external strainers might get clogged.
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Old 07-11-2022, 09:13 PM   #16
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Pete, If the inlet is facing forward it will vacuum up everything in its path, facing aft only some.
That is correct. A scoop shaped strainer, especially on a generator in a powerboat or main engine in a sailboat, should be facing aft. The boat's motion through the water when that engine is not running can force water up through the system and hydrolock the engine. And if you pick up a plastic bag or jellyfish with the engine running, the flow of water past the strainer will help dislodge it. The installation manual for the engine in my sailboat was very specific about that.
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Old 07-11-2022, 10:57 PM   #17
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Thanks! I am fairly certain there is an external strainer but this stuff was really fine!!
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Old 07-13-2022, 10:48 AM   #18
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Us Too—flush the hoses too

Interesting to see this thread as we had the same thing happen at the same time and location. I had been commenting on the inordinate amount of seaweed floating on the surface of Sansum Narrows and north. In my case I lost the impeller before shut down occurred. I cleared the strainer and replaced the impeller. We have a tap and and garden hose in the engine room and following my mechanics recommendation I screwed the pump hose (while off) onto the end of the hose using the same hose clamp and first flushed with fresh water (60 psi does a good job) back through the cleaned raw water strainer to clear the hose and then reclaimed the outlet pump hose and flushed through the heat exchanger and could verify I had flow that direction. As an aside, this last part was after I lost a second impeller because the heat exchanger was blocked up and it wasn’t with impeller bits as none were visible in the end cap. I carry a spare heat exchanger thanks to the previous owner who was highly organized and a long time central coat boater. So second time was the charm but the flushing helped clear hoses and made it possible to verify there was flow. Lesson learned. According to my mechanic he sees this happen several times a year usually in the eel grass anchorages like Sidney Spit.
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Old 07-13-2022, 11:30 AM   #19
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I appreciate the suggestion!!
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Old 07-13-2022, 11:30 AM   #20
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That is correct. A scoop shaped strainer, especially on a generator in a powerboat or main engine in a sailboat, should be facing aft. The boat's motion through the water when that engine is not running can force water up through the system and hydrolock the engine. And if you pick up a plastic bag or jellyfish with the engine running, the flow of water past the strainer will help dislodge it. The installation manual for the engine in my sailboat was very specific about that.
Inlet water breaks eliminate that problem. The raw water line goes well above sea level (ideally to the engine room ceiling) and then comes down to the engine. A vacuum break is at the peak, lowering the water to sea level. A stern facing scoop generating a venturi vacuum just seems less than optimal. This assumes a boat traveling at displacement speed.

My strainer faces forward with all water inlets in a single sea chest type system with exhaust mixing elbows well above sea level.

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