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Old 09-13-2015, 05:18 PM   #61
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Originally Posted by O C Diver View Post
Simple answer is that the external screen prevents most of the junk, but whatever goes through goes until it hangs up somewhere else. The internal strainer basket often holds some solids that fell out do to gravity. Have both on my charter boat, and often find some hard bits in the bottom of the strainer at the end of the season. While they likely go right on through, I'm happy that there not getting between the pump impeller and the housing. While the internal one isn't absolutely necessary, I certainly wouldn't remove it if you were adding the pin hole style external one. Now have both on my trawler.

Ted
Ted - Per bold sentences in your above, again quoted below... how/what falls out do to gravity, and from what... engine rust??

"The internal strainer basket often holds some solids that fell out do to gravity."

"... often find some hard bits in the bottom of the strainer at the end of the season"
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Old 09-13-2015, 05:20 PM   #62
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Seems you must have wide open hole in bottom for water draw. We don't. Our water hole has cover of many 1/4" slat openings about 5" long. Total width of this slated external strainer is about 4". What you found in your inside strainer would get past our external strainer.
Art, this is the ultimate external strainer. Only little bits get by. They are available in 2 sizes. Think this one is good for up to 3" intakes.

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Old 09-13-2015, 05:30 PM   #63
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Ted - Per bold sentences in your above, again quoted below... how/what falls out do to gravity, and from what... engine rust??

"The internal strainer basket often holds some solids that fell out do to gravity."

"... often find some hard bits in the bottom of the strainer at the end of the season"
This isn't a gas engine. Nothing that touches raw water is steel or iron. Strainer is before the engine anyway. They are particles from the ocean that found they're way through the external strainer. I go out through a stone jetty inlet with a current that can be 3 knots. All sorts of stuff can get stirred up with that kind of flow. Could be bits of stone, sand, shell, or who knows what. Just happy it's getting filtered out.

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Old 09-13-2015, 05:30 PM   #64
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Art, this is the ultimate external strainer. Only little bits get by. They are available in 2 sizes. Think this one is good for up to 3" intakes.

Attachment 44486

Ted
Nice one! However, I feel the holes are so small they could plug via growths or seaweed. I often swim under our boat to check the slated strainers. About twice per year I pull a knife-point through the slats just to make sure they allow full water-draw. Although I previously mentioned 1/4" opening between slats... I think it's actually 3/16" openings.
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Old 09-13-2015, 05:31 PM   #65
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Depending on where one boats the water can be muddy with suspended solids in it. For example the Fraser River dumps tons of mud and debris into the Strait of Georgia turning the water into a bit of a milkshake. This stuff easily gets through external strainers and the internal sea strainer, too. But on engine shutdown the muddy water in the strainer stops moving through it and instead just sits. At that point the suspended muck starts settling out to the bottom of the strainer where it can compact itself into a layer.

And depending on where one boats, operating in shallow water can stir up stuff some of which can be little solid bits and they, too, can end up being caught and held by the sea strainer.
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Old 09-13-2015, 05:40 PM   #66
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Depending on where one boats the water can be muddy with suspended solids in it. For example the Fraser River dumps tons of mud and debris into the Strait of Georgia turning the water into a bit of a milkshake. This stuff easily gets through external strainers and the internal sea strainer, too. But on engine shutdown the muddy water in the strainer stops moving through it and instead just sits. At that point the suspended muck starts settling out to the bottom of the strainer where it can compact itself into a layer.

And depending on where one boats, operating in shallow water can stir up stuff some of which can be little solid bits and they, too, can end up being caught and held by the sea strainer.
True! i.e. "Depending on where one boats..."
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Old 09-13-2015, 05:48 PM   #67
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Nice one! However, I feel the holes are so small they could plug via growths or seaweed. I often swim under our boat to check the slated strainers. About twice per year I pull a knife-point through the slats just to make sure they allow full water-draw. Although I previously mentioned 1/4" opening between slats... I think it's actually 3/16" openings.
Never had to clean mine during the season, but if I did, you remove the two 1/4" 20 screws and slide the screen out. You could power wash it, sand blast it, or the simple approach would be to wet it with muriatic acid and it will be spotless in 5 minutes. Stuff dissolves marine growth right before your eyes. Clean mine every year during haul out. They also sell spare screens so you could just swap it and clean it later. Note to self, add spare screen to trawler spares.

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Old 09-13-2015, 05:54 PM   #68
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Never had to clean mine during the season, but if I did, you remove the two 1/4" 20 screws and slide the screen out. You could power wash it, sand blast it, or the simple approach would be to wet it with muriatic acid and it will be spotless in 5 minutes. Stuff dissolves marine growth right before your eyes. Clean mine every year during haul out. They also sell spare screens so you could just swap it and clean it later. Note to self, add spare screen to trawler spares.

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In Florida if those screens are left unpainted they'd get covered in barnacles and such in a matter of weeks. But when painted they do work very well.
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Old 09-13-2015, 06:04 PM   #69
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When I bought my trawler, it hadn't been run much in the preceding years. Both the engine and generator had external slot strainers on them. Oyster spat had gotten inside each and there were oysters growing inside. Ended up busting then up with a screw driver and hammer during the survey short haul. Both had internal strainers, so I wasn't particularly worried about any shell getting to a pump. Thought about removing the external strainers to do a proper cleaning, but decided not during a short haul and not until it was my boat.

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Old 09-13-2015, 06:05 PM   #70
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In Florida if those screens are left unpainted they'd get covered in barnacles and such in a matter of weeks. But when painted they do work very well.
Yup, my gets prop speed.

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Old 09-13-2015, 08:47 PM   #71
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Yup, my gets prop speed.

Ted
Ah, I get now. Based on you how to clean post I got the mistaken impression that you didn't paint you grate.
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Old 09-13-2015, 10:47 PM   #72
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About two years ago I installed a Groco APHS strainer on my engine intake.


It replaced the common slotted external strainer. Prior to installing the APHS I had to clean the basket of my internal sea strainer fairly often. Since installing the APHS fine screen external strainer I haven't found anything in the internal strainer.


I decided to talk to Don Gross, the owner of Groco, about it with the idea of removing my internal sea strainer. Don likes the idea of having both. I was going to ignore his advise and remove the internal strainer anyway, then I looked into the internal strainer. There were about a dozen pea sized oysters in it! If they had gotten to the pump they would have ruined the impeller right now. There was no way they got through the external strainer. They must have grown inside the thru-hull, broken loose and been caught by the internal strainer. I also have a set up that allows me to pump my bilge with the engine raw water pump. I guess I'll keep the internal sea strainer as well as the fine screen external strainer.
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Old 09-13-2015, 11:46 PM   #73
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Looks like electrolysis ate your strainer basket. Need to add a small zinc or I'm trying their plastic one and will see how it holds up.

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Old 09-14-2015, 12:07 AM   #74
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Hi Ted, yes switching to plastic. Renewing my bonding system as well.
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Old 09-14-2015, 12:20 AM   #75
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I have been boating in the waters of Southwestern BC for 40 years. I have always had strainers. Very occasionally I anchor where there is a lot of weed, but even then, I have never had any show up in my strainers.
The only time I have ever had an obstruction in the water intake was when an oyster grew inside the intake cover, one of the slotted kind, and occluded 95% of the flow.
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