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Old 10-06-2012, 12:41 AM   #1
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Your raw-water intake

This is the Coot's raw-water intake. What does yours look like?

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Old 10-06-2012, 01:32 AM   #2
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Don't have a shot of them but they are round bronze plates about six inches in diameter that are dished out a bit like the top of a tennis ball. The plates are perforated with holes.

There are eleven holes in the bottom of our boat. Eight of them are intakes and they all have the perforated bronze plates over them. Three are discharges and so have no perforated plate over them.
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Old 10-06-2012, 06:27 AM   #3
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Many strainers are removable so barnacales can be removed from the inside and then painted with anti-fouling .
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Old 10-06-2012, 07:01 AM   #4
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no screens...REALLY easy to clean now from the inside...

I'll let you know how it works out after my trip to Fla this winter but my summer at the dock experience has been I may have had to manually clean the strainers a few times but my dockmates had to use divers a few times....
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Old 10-06-2012, 07:42 AM   #5
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I have a scoop strainer like Coot's and a Groco 1 1/2 inch strainer inside.
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Old 10-06-2012, 08:32 AM   #6
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My engine water scoop is the same style as the Coots, the genset"and others are mushroom style.
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Old 10-06-2012, 08:37 AM   #7
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Can't really tell in Mark's picture, but is the strainer facing fore or aft? Does it make a difference?

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Old 10-06-2012, 08:53 AM   #8
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Can't really tell in Mark's picture, but is the strainer facing fore or aft? Does it make a difference?

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Absolutely... and the speed of the boat determines what kind/size of scoop or not should be used.
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Old 10-06-2012, 10:17 AM   #9
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Can't really tell in Mark's picture, but is the strainer facing fore or aft? Does it make a difference?
The bow is to the right of the picture of the intake.

Strainer is accessible from the engine compartment.

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Old 10-06-2012, 11:06 AM   #10
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Right of picture is main engine (forward facing) and left of picture is gen-set (aft facing).
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Old 10-06-2012, 12:42 PM   #11
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Can't really tell in Mark's picture, but is the strainer facing fore or aft? Does it make a difference?

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Yes it does make a difference, the engine scoop should be facing forward and the same for AC units. You should not have a scoop for the generator. The reason, particularly on semi-planing or planing hulls, is if the gen-set is not running, you can potentialy push water through the system and backfill the exhaust while underway.
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Old 10-06-2012, 02:12 PM   #12
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no screens...REALLY easy to clean now from the inside...
Intake screens are pretty important to have up here. It is quite common to have eelgrass mats or individual strands in the water, particularly along the tide sheers. These sheers also collect and hold other debris--- kelp, sticks, pieces of driftwood, etc. The debris lines are often hundreds of feet long or longer. So you pick the clearest spot to cross them but there will still be stuff in the water where you go through.

Eelgrass strands are thin and tough enough to go up a raw water intake, snake through the big sea strainer in the engine room, and get into the raw water pump where they can clog the pump and even-- rarely--- break the impeller.

The first line of defense is the intake screen or perforated plate over the through-hull. When Carey had a new engine installed in his lobsterboat boat some years ago the raw water through-hull was installed without a screen. The other year we were boating together in the San Juans and he ended up with a huge clog of eelgrass in the hose between the through-hull and the sea strainer. Fortunately they had just gotten underway so the engine overheat was not serious and they were able to get back to a dock where Carey spent the next hour clearing the clog, which was packed amazingly tight into several feet of hose.

Our boat had perforated plates over all the intake through-hulls when we bought it but it had no sea strainers inside. This was surprising but perhaps stuff like eelgrass is not an issue in SFO Bay where the boat had spent the first 25 years of its life. The first thing we had done when the boat came off the truck was to have a big Groco sea strainer installed for each engine.
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Old 10-06-2012, 05:24 PM   #13
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There's just as much stuff around here to get sucked up......and a LOT shallower water to suck it from.

There's 2 schools of thought and I lived with both of them and prefer not diving under the boat to clean out screens or anything else. Compass marine has a section of pics on strainers....pretty self explanitory.

I'll really know after my trip south this winter...if they are more of a problem than easy to clear...then I can always screw covers back on in a few minutes on the next haulout.
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Old 10-06-2012, 05:55 PM   #14
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Right of picture is main engine (forward facing) and left of picture is gen-set (aft facing).
SteveH: I missed your post. That's a good install on the gen-set. That's the first one that I've seen that is aft facing. You have the benefits of the screen with out the issue of pushing water through the system while underway when the gen-set is off.
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Old 10-06-2012, 06:16 PM   #15
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Thanks..., can't take credit though it's how it was installed by the yard during manufacture. As a rule, I don't operate the gen-set while underway anyway and always close the outlet cooling water seacock when the gen-set is off. I do this to avoid the possibility of sea water going above the loop and back filling through the exhaust with large waves.

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Old 10-06-2012, 10:03 PM   #16
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....nd prefer not diving under the boat to clean out screens or anything else.
We've never had to have anyone dive on our intakes and covers but once. And that was not to clean them out but to scrape off barnacles that had partially covered the perforated plate over the port engine raw water intake because we'd gone too long between bottom jobs. Engine started to run warm so we shut it down and finished the last bit of the run to an island on one. A friend on the island dove on the boat and cleaned off the barnacles.

I can see how the scoop-type covers could get clogged and require a diver to clear or a haulout. And I agree, that would be a pain either way. But our simple convex bronze plates won't trap anything or scoop it in. But they do a good job because we've so far never gotten anything in the filter cages of the big sea strainers we had installed when we got the boat.
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Old 10-06-2012, 10:11 PM   #17
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We've never had to have anyone dive on our intakes and covers but once. And that was not to clean them out but to scrape off barnacles that had partially covered the perforated plate over the port engine raw water intake because we'd gone too long between bottom jobs. Engine started to run warm so we shut it down and finished the last bit of the run to an island on one. A friend on the island dove on the boat and cleaned off the barnacles.

I can see how the scoop-type covers could get clogged and require a diver to clear or a haulout. And I agree, that would be a pain either way. But our simple convex bronze plates won't trap anything or scoop it in. But they do a good job because we've so far never gotten anything in the filter cages of the big sea strainers we had installed when we got the boat.
I prefer them too for our slower boats...If I wind up thinking I need something...they are what I would use.

Where we are..especially with running Air Conditioning 24/7 for months...when the barnacles and growth nearly clog off the hull strainers...every little floating thing gets sucked into the mini beaver dam thus closing it off completely and now you have to dive...mine never does that and when a slug of eel grass comes in...I just pick it out of the internal strainer and shove a broom handle down the hose and through the sea cock...whole procedure to completely clean takes less than 5 minutes. But as I said ...the jury is still out till I log a couple thousand miles with them off.
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Old 10-06-2012, 10:20 PM   #18
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I prefer them too for our slower boats...If I wind up thinking I need something...they are what I would use.
Yes, a Lehman 120 is not exactly generating a ton of heat so there seems be no need for the "ram assist" of a scoop.

The one thing you have to be mindful of with the perforated plates is to clear out the holes every time you haul out for bottom point. The paint can start to fill them in when it's rolled on. So before the boat goes back in the water I clear out the holes with a short length of brass rod.
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Old 10-06-2012, 10:51 PM   #19
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Not sure why, but as the diver of my boat I can say I have never seen any hard growth on the inside of the raw water screen plates mounted on the hull exterior. If there's enough light (sunny day) I can see past the screen bars and see directly in the hole. My theory is that there just isn't enough plankton available inside these crevices (except maybe when then engine is running) to allow the mussels and barnacles to grow. Just a thought.

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Old 10-07-2012, 07:33 AM   #20
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you were just lucky....many boat here on the East Coast wind up with tube worms in their inside strainers...let alone their external hull screens.
External Strainers - OMG Phhe external hull screens.oto Gallery by Compass Marine at pbase.com
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