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Old 05-29-2020, 04:27 AM   #1
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Angry salt water strainer

We are installing a new engine and are fitting an internal strainer instead of the "scoop" type that was fitted before on the outside of the hull covering the intake flange. As the new strainer will be above the waterline I should be able to clean the intake if I don't put a new "scoop" over the intake flange by poking a round brush all the way through the strainer, valve and flange without having to get wet by diving under the boat periodically. Is that an accepted strategy or should I still install a "scoop" strainer on the outside to deflect possible rubbish being sucked in?
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Old 05-29-2020, 06:27 AM   #2
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Unless you need the scoop to force water into that intake, you should be fine with the internal strainer only. It'll need cleaning more often, but it's also easier to clean or un-clog, so in my mind, it's better. If you do need a scoop to force water in, you could always find or make a non-strainer scoop.
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Old 05-29-2020, 08:32 AM   #3
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I much prefer the external screen / scoop as it keeps almost everything out of the strainer. Where I summer, we have sea nettles (jelly fish). Without the external screen, I would have to deal with a basket full of jelly fish periodically.

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Old 05-29-2020, 10:25 AM   #4
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Ted,
Do you ever have to "go over the side" to clean that screen? Or is it just a clean up at haul out?
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Old 05-29-2020, 10:38 AM   #5
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Quote:
Where I summer, we have sea nettles (jelly fish).
Sometimes they seem concentrated enough to walk on them.

I have a scoop strainer with the slots, and an inside Groco strainer basket. It's rare that I ever have to remove anything from the basket. If I do it's usually just a couple of pieces of eel grass.
But I have oversized thru hulls and strainers. My generator would clog up with jellyfish (nowhere near the amount in the Chesapeake) until I installed the larger thru hull, strainer basket and a scoop strainer, installed facing aft for the generator.
It hasn't clogged up up since.
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Old 05-29-2020, 11:14 AM   #6
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Originally Posted by firehoser75 View Post
Ted,
Do you ever have to "go over the side" to clean that screen? Or is it just a clean up at haul out?
I've never had to clean it because of flow reduction. But then I have a diver scrub the bottom every 1 to 3 months depending on where I am. This particular one has enough surface area to supply a 3" through hull. In my OCD style, I bought perforated 316 stainless sheet metal with slightly larger holes and less metal between holes. The holes are over 60% of the area. My through hull is like a sea chest in that everything (engine, generator, 3 air conditioners, and saltwater washdown pump) is fed through that one 2" seacock. It easily handles 45 GPM. While my inside strainer still traps some small stuff, nothing has ever stopped the flow of water. Have had the same setup on my charter boat for 15+ years.

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Old 05-29-2020, 11:41 AM   #7
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I installed a Groco perforated exterior strainer similar to what a Ted installed. I never had to clean the internal sea strainer again.

The Groco one that I used has a hinged door that can be opened for cleaning. I used a plastic pin to hold it closed on the theory that I could punch it open from inside the boat if I had to.
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Old 05-30-2020, 06:45 AM   #8
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Thanks for all the replies. I am inclined to install a strainer on the outside of the hull as we also can have a decent population of jelly fish in the Swan river at times. I suppose I can always ask one of my sons to dive over and scrub it now and then? Theo
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Old 05-30-2020, 07:09 AM   #9
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I have no strainers on the outside.

I have 1 1/2 thru hulls for a very low flow Lehman engine and A/C intakes. Because they dont "pull" a lot of water in, only once in 9 years and 20,000 miles from NJ to the Keys have I had a clogging issue. That was from 3 small fish swimming in and clogging at the filter basket on the inside.

I figured if I had issues, I would add the kind Ted pictured at my next haulout. Never felt I needed them.

The 2 years I lived on the Chesapeake, seemed to me people had issues with Air Conditioner intakes no matter what method they chose because of Nettles.

On the assistance towing vessel I ran.....I had 2 water inlets. One with an external strainer, one without. After shallow water operations, the external strainer would often plug up. So I would open the uncovered one, run a long rod through it to make sure it was clear and swap over the engine intake hose. After running a bit, I would check the covered intake to see if it was clear, and then swap back. This was my lesson in having nothing on the bottom to clear thru hulls...but I dont thinks it's a clear winner, just a slightly different option.
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Old 05-30-2020, 10:12 AM   #10
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Another variation.
I have a single engine with two intakes, close by but on opposite sides of the keel joined inside by a large curl of hose. THen to the single internal strainer, Perko.

I have never , yet of course, had anything clog the intakes even though I plowed through lots of stuff. over 30+ years.

The two intakes do have a coarse slot screen outside but the saving part I think is that the suction at each is so low that there is virtually no pull at the mouth of each through hull. I think it was a variation driven by the hull builders experience of building most of these things for the commercial fishing industry.
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Old 05-30-2020, 10:30 PM   #11
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Quote:
Originally Posted by Theo1 View Post
We are installing a new engine and are fitting an internal strainer instead of the "scoop" type that was fitted before on the outside of the hull covering the intake flange. As the new strainer will be above the waterline I should be able to clean the intake if I don't put a new "scoop" over the intake flange by poking a round brush all the way through the strainer, valve and flange without having to get wet by diving under the boat periodically. Is that an accepted strategy or should I still install a "scoop" strainer on the outside to deflect possible rubbish being sucked in?
Thatís intelligent installation technique. The ability to clean Right through is a great safety feature.
I install them so the top of the strainer is just above the waterline, no priming necessary, just open the seacock and it fills without overflowing.
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Old 05-31-2020, 07:52 AM   #12
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Thatís intelligent installation technique. The ability to clean Right through is a great safety feature.
I install them so the top of the strainer is just above the waterline, no priming necessary, just open the seacock and it fills without overflowing.
Priming is the same on mine, although the tops of mine are about 3 inches below waterline so some overflow happens.
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