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Old 03-10-2012, 09:49 PM   #1
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do you need a strainer

I am rebuilding a 1971 GB 50' and it doesn't have sea strainers on it. I also for the boat yard am tearing down/spashing other old wood boats for them and have noticed lots of them don't have sea strainer. the threw hull outside has small holes say 1/8 bit size maybe a touch bigger but nothing after that. so do I need to spend the 300$ x 2 for sea strainer I am wounder how many people have them
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Old 03-10-2012, 10:03 PM   #2
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RE: do you need a strainer

olesouth,
It is a good idea to have a sea strainer on your inlet.
A good bronze or s/s cased unit with a basket with approx 1/4" holes would suffice for say a 1 1/2" inlet.
A good bronze gate v/v (top quality) or a top quality s/s ball v/v as a sea cock.
You could run a larger thru hull with a bigger sea strainer with multiple outlets to cut down on the number of holes you actually have.
This will minimise the amount of rubbish/weed that can be pushed into your engine (main/aux) coolers.
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Old 03-10-2012, 10:57 PM   #3
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RE: do you need a strainer

Would something like this work?
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Old 03-11-2012, 04:19 AM   #4
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RE: do you need a strainer

Mark, I think that would qualify as a rhetorical question - also know here is Aus, as a Dorothy Dixer....in other words, a question to which you know the answer...skite....ooops....this comment maybe should been on OTDE...maybe....but it's not there...yet
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Old 03-11-2012, 05:01 AM   #5
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RE: do you need a strainer

SIZE counts , the surface area will get plugged , plastic bag , jellyfish or dead leaves in the water.

More surface area the longer it may take , till zero flow .

Also the large filters can move the water a bit slower , allowing sand and silt to drop, requiring fewer rubber impeller changes .
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Old 03-11-2012, 06:44 AM   #6
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RE: do you need a strainer

In our part of the world I think a SS will also serve to keep sand out. I have soft grounded a couple of times over the years and am pretty certain this was the source of a nice load of sand in my strainers.
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Old 03-11-2012, 07:49 AM   #7
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RE: do you need a strainer

The slower speed and deeper draft of a trawler help keep a lot of floating stuff out of the strainers.

In theory the outside perferated setup should be fine. However strainers are still a good idea.

I have seen some used ones on Ebay, and sometimes even pairs.

Bought a small one for my genny all it needed was a new drain plug.

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Old 03-12-2012, 06:51 AM   #8
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RE: do you need a strainer

http://72land-n-sea.blogspot.com/201...ainer.html?m=1
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Old 03-12-2012, 07:47 AM   #9
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RE: do you need a strainer

My boat has the external covers over the thru hull with the 1/8" holes. The engine has no seperate strainer except the one that's on the engine. The AC does have a seperate strainer inside the boat. It never clogs because nothing larger than 1/8" can get in unles it grows in there.

The disadvantage of the external screen is that you can't clean it without hauling the boat or having a diver clean it. Under certain conditions, those 1/8" hole can plug up. There's another version with wider slots and I think that, plus a strainer inside the boat would be a better plan..
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Old 03-12-2012, 08:07 AM   #10
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RE: do you need a strainer

is the strainer size the same size as the threw hull size meaning 1 1/2 valve is the same size as the strainer.
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Old 03-12-2012, 08:08 AM   #11
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RE: do you need a strainer

I don't have a strainer other than the slotted scoop on the outside of the hull.

The boat has never had one and I have never had an issue with anything clogging things up.

It must be the area I live in or that there is plenty of space for things to* move thru the heat exchanger.

It may also be that the scoop is about 3 ft below the surface so the floating stuff doesn't get down that deep. Just a guess.

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Old 03-12-2012, 09:23 AM   #12
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RE: do you need a strainer

having helped a friend trouble shoot his engine overheating, leading to cleaning vegetation out of his strainer (this was*after running through a shallow area)...**I see*strainers as a good thing to have.* Not as convinced about the "screen" on the outside but I guess that would help with jellyfish as FF pointed out.* I don't go places where there are jellyfish.
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Old 03-12-2012, 12:13 PM   #13
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do you need a strainer

Quote:
olesouth wrote:
I am rebuilding a 1971 GB 50' and it doesn't have sea strainers on it. ... I am wounder how many people have them
Our GB36 did not have them when we bought the boat and they were the first thing we told the yard we had the boat trucked to from California to install before the boat went back into the water.* Up here there is a fair amount of debris in the water including individual floating sections up to huge mats of eelgrass.* If eelgrass gets into your raw water pump it can clog it, or worse, damage the impeller, and I have heard of one case where the tough eelgrass strands so knotted and balled up in the pump chamber and locked up the pump so hard and suddenly that the pump driveshaft sheared as improbable as that sounds.* So I would say that for these waters, at least, a properly sized sea strainer on the engine raw water intakes is almost mandatory.* Ours are large bronze and glass Groco units.

By the same token a screen or perforated plate on the outside of every intake throughull is a good idea here, too.* Even with a proper sea strainer our diesel shop told us that individual strands of eelgrass can work their way past the strainer and get into the pump. A screen or perf plate on the outside of a raw water intake throughull is a good first line of defense.


-- Edited by Marin on Monday 12th of March 2012 12:25:23 PM
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Old 03-12-2012, 06:03 PM   #14
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RE: do you need a strainer

I saw a neat setup one time. Straight mushroom through-hull, then a piece of pipe on the inside. There was a tee in the pipe. A short piece of pipe sticking straight up with a cap on it, then the tee went to a strainer, then on to the engine. That way, if anything got hung up ouside, you could just open the cap and ram a dowell or somehing down there to clear it. Work quick and you won't have too much water on board.
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Old 03-12-2012, 06:29 PM   #15
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RE: do you need a strainer

As long as we're on the topic, let me relate a story from last summers cruising with Marin.

We were drifting and putting around deciding what to do near Center Island in the Washington, San Juans, when my temp alarm went off. A quick check of the guage proved that we were just leaving the safe temp zone. No problem says I as I shut down the engine. Immediately I went to my rather large strainer in the engine room, expecting to dump a small basket of eel grass. What I found however was a well packed basket, followed by a well packed inlet. No tool seemed to work, to get around the elbow preceding the strainier, until upon further thought toward available tools brought me to the life-saver. I have this flexible pincher tool used for retrieving small objects which may have fallen in otherwise inaccessible locations. You push the plunger, and three little prongs with triangular tips come out of the tube and separate. This process allowed the tool to take about half inch bites of eel grass, and then drag that material and a few more strands out at a time. After clearing as much as I could, I would then start the engine for mere seconds, but long enough to bring forth another harvest of this otherwise delectable bounty from the sea. I think we went through that process a half dozen or more times, and then while running, slipped into a dock to complete the process. By the time we were done, my thumb was raw from pushing the plunger on the tool.

There are two things to take from this incident. One is that you MUST have some sort of strainer, and then a plan to remove the stuff packed in front of it. I am going tomorrow to purchase another tool such as the one I have, just in case I ever break that one. I am still considering whether to put a strainer on the outside of my mushroom through hull as a first line of defense.*

I am somewhat reluctant to add the outer strainer, as I would have a much bigger problem trying to clear that strainer. It would involve me in a wetsuit, and a hull possibly pounding down on my head. My do me some good actually.
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Old 03-12-2012, 06:57 PM   #16
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RE: do you need a strainer

ok so follow my thought, I have attached to pic's I have installed a pool inground before and the pool pump hit me. get a pool strainer there plastic for chemichals and has a quick access top and clear so you can see what you go inthere most are 1 1/2 in and our or 2"** or you can get the pump with it and if you put a t on the top going to the engine and a valve you can use the top for a fire hose or a great washdown or you can pump it back down to blow out the clog. on the other engine I have twin engines.
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Old 03-12-2012, 06:59 PM   #17
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RE: do you need a strainer

o for got on ebay strainer is 40.00 $ and with the motor is 140.00 If you impellor goes out and you don't have a spare the pump can pump engough to keep the engine cool and you can addjust the flow coming out of the pump but not in.
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Old 03-13-2012, 06:09 AM   #18
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RE: do you need a strainer

Quote:
Keith wrote:
I saw a neat setup one time. Straight mushroom through-hull, then a piece of pipe on the inside. There was a tee in the pipe. A short piece of pipe sticking straight up with a cap on it, then the tee went to a strainer, then on to the engine. That way, if anything got hung up ouside, you could just open the cap and ram a dowell or somehing down there to clear it. Work quick and you won't have too much water on board.

No seacock?
*
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Old 03-13-2012, 06:13 AM   #19
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RE: do you need a strainer

Quote:
olesouth wrote:
ok so follow my thought, I have attached to pic's I have installed a pool inground before and the pool pump hit me. get a pool strainer there plastic for chemichals and has a quick access top and clear so you can see what you go inthere most are 1 1/2 in and our or 2"** or you can get the pump with it and if you put a t on the top going to the engine and a valve you can use the top for a fire hose or a great washdown or you can pump it back down to blow out the clog. on the other engine I have twin engines.

I don't think I would trust a swimming pool strainer or pump for my underwater plumbing.* There are many styles of approved marine strainers available that will do the job.
*
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Old 03-13-2012, 09:15 AM   #20
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RE: do you need a strainer

On my first sailboat, I had eelgrass in the strainer a couple of times, but didn't have an external screen. On my next sailboat and on my present trawler, I have the external screen and have never seen anything in the strainers. So if you have the external strainer, your internal strainer will get anything small enough to get that far up the system. Where you travel, if that is necessary to be strained out, you need a strainer.
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