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Old 17-03-2013, 11:16   #1
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Raw water intake to multiple pumps?

Im replacing the seackock for my raw water intake to the engine. Im also adding a washdown pump. Is there any reason not to install a larger seacock (the old one was 3/4") and split it after the strainer to feed both the engine pump and the washdown pump? The alternative would be to install separate 3/4" seacocks for each. I'd rather have less holes in the bottom of my boat but wasn't sure if it was ill advised to share the engine intake with another system. Also, how much larger of a seacock would I need to use to allow adequate flow to each pump?

Thanks.
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Old 17-03-2013, 12:04   #2
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Re: Raw water intake to multiple pumps?

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Originally Posted by Captndan714 View Post
Im replacing the seackock for my raw water intake to the engine. Im also adding a washdown pump. Is there any reason not to install a larger seacock (the old one was 3/4") and split it after the strainer to feed both the engine pump and the washdown pump? The alternative would be to install separate 3/4" seacocks for each. I'd rather have less holes in the bottom of my boat but wasn't sure if it was ill advised to share the engine intake with another system. Also, how much larger of a seacock would I need to use to allow adequate flow to each pump?

Thanks.
It won't matter at all if you are not using both at once. My gut feeling is don't change it. What other users are on the sea water? If you have AC and refrigerators, it would make the best sense to keep th engine isolated.

Ours is main engine alone (lower left Groco strainer). Two smaller strainers from two seperate through-hulls feed the manifold with the yellow valves. Refrigeration, two AC units, Generator, deck wash, watermaker, galley foot pump. The logic is to keep the engine alone so that problems in other places have no influence.
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Old 17-03-2013, 12:11   #3
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Re: Raw water intake to multiple pumps?

I've doubled up before, but I wouldnt on an engine intake. I did have some issues with sucking air when I used one thru hull for two two pumps. If you do it, I would put a check valve in the non engine line.
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Old 17-03-2013, 12:21   #4
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Re: Raw water intake to multiple pumps?

Captndan,
I have been running multiple pumps on a single thru-hull for years. I feed seawater to the 1" hoses to the main engine and generator pumps via a 1-1/2" seacock. I also feed the 3/4" hoses for the frig and A/C pumps via another 1-1/2 seacock. This system also provide seawater to a manual pump at the galley sink and a spare valve that was used for the head before I converted to a composting toilet. In both cases the separate systems are split from the main input via a manifold down stream of a raw water strainer. Each system has a ball valve to allow the pump to be serviced without shutting off water to the other systems.
I'm no engineer, but I just figured that if the cross-sectional area of the input was greater than the sum of the cross-sectional area of all of separate system all of the separate systems could maintain their full flow. I used the ID of smallest hose barbs to determine the cross-sectional area. So the 1-1/2" feed systems are actually 1-1/4" ID because of the hose barbs. Simiilarly the 1" engine/generator hoses actually have a cross-sectional area of 3/4".

I was able eliminate three seacocks from the original configuration by using manifolds and larger intakes.

Here is a pic of the two manifolds.
http://www.svsarah.com/Sarah/Images/ManifoldNew2.JPG
http://www.svsarah.com/Sarah/Images/...nifold%201.JPG

John
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Old 17-03-2013, 12:45   #5
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Re: Raw water intake to multiple pumps?

I did a manifold like that once. In the end, I felt the weight and stress of all that stuff, as well as the hose runs to reach the various appliances was probably less safe than a seacock for each. I figured there were as many hose clamps , if not more and a lot of fittings. For each T to collet another thing you have 4 fittings instead of 1. (T and 3 barbs) and 3-6 clamps. I never did it again. Nice job though, and I see you have the manifold secured which is good.
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Old 17-03-2013, 12:51   #6
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The only other system I have on raw water besides the engine is the washdown pump Ive added, which feeds the hose on deck and the galley sink. No fridge, ac, head, etc.

Also, Im having a hell of a time finding fiberglass backing plates for the seacock, aside from making my own. What have you used here and where can I find them?
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Old 17-03-2013, 13:46   #7
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Re: Raw water intake to multiple pumps?

If your hull is thick, I 've thought that a rigid backing plate like fiberglass is not the best thing. Having something that has a bit of "squeeze" to conform to the hull etc would be a good thing I would think. I've used epoxied mahoghany marine ply before, although ply scares me a bit. Or with flanged seacocks, just went with a lot of 5200; snugged down the first day and snugged fully tight a day or two later.
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Old 17-03-2013, 22:37   #8
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Re: Raw water intake to multiple pumps?

Groco makes a manifold to do just what you've suggested.
Here is a link to their website that will help you decide how big a thru-hull fitting you would need to supply enough water for both users.
GROCO-FITTINGS

They start off by saying they don't recommend doing it but since everyone does it anyway, they made a manifold.
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Old 26-03-2013, 09:20   #9
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Re: Raw water intake to multiple pumps?

Depends. Want to run both or multiple pumps at the same time? If yes, Then I say no, especially if one is the engine cooling. If no, then install a y valve to shut off the unused pump and it will work. I still won't do a spilt on the engine cooling source, Too important. The head intake, yes.
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Old 26-03-2013, 21:06   #10
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Re: Raw water intake to multiple pumps?

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Originally Posted by Nicholson58 View Post
It won't matter at all if you are not using both at once. My gut feeling is don't change it. What other users are on the sea water? If you have AC and refrigerators, it would make the best sense to keep th engine isolated.

Ours is main engine alone (lower left Groco strainer). Two smaller strainers from two seperate through-hulls feed the manifold with the yellow valves. Refrigeration, two AC units, Generator, deck wash, watermaker, galley foot pump. The logic is to keep the engine alone so that problems in other places have no influence.
Now that is inspirational!

Our vessel is merely 41 feet, but we have a similar sort of engine bay below the pilothouse. You've given me some ideas involving the mostly empty aft bulkheads...
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