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Old 15-12-2015, 14:31   #1
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shared seacock for engine and head?

hey guys!

im about to install manual head in my cape dory 28 but first I need to install two new throughulls

Im considering to use the seacock for engine cooling also for head intake as this way I would need to install only one new seacock instead of two

possibly I would also use the same seacock for outlet in the sink in galley ... with foot pump attached to it ... so I would use one seacock for 3 purposes:
- engine cooling
- head intake
- sink outlet

1) would you suggest such a setup or is there some hidden issue with this setup?

2) my second question is about the waste seacock - I have bras seacock with diameter 1 1/4'' ... is it big enough? I hope so as I dont want to buy a new one, its so expensive
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Old 15-12-2015, 14:49   #2
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Re: shared seacock for engine and head?

You should never piggy back on your engine water intake! Nor is it a good idea to run discharge through and intake. If you giggy back your intake you stand the chance of causing the engine intake to get air bound.
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Old 18-12-2015, 23:06   #3
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Re: shared seacock for engine and head?

If some guest lets food waste go down the sink drain it's not unlike your salt water coolant pump sucking up sea grass or kelp. It could eat up an impeller or plug the heat exchanger.
1 1/4" valve should work. The material going thru should reform to fit. It could make pumping a little harder. If it was electric with a macerator pump, no problem.
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Old 19-12-2015, 09:00   #4
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Re: shared seacock for engine and head?

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Originally Posted by mike d. View Post
You should never piggy back on your engine water intake! Nor is it a good idea to run discharge through and intake. If you giggy back your intake you stand the chance of causing the engine intake to get air bound.
I agree completely with Mike, especially when it comes to ANY thru-hull sharing both discharge and intake. Not only do you not want to risk pulling any galley waste into your engine, you don't want to pull it into the toilet either...not only can that create a blockage in the intake line, pump and/or the channel in the rim of bowl--any of which can be a real PITA to clean out--it will STINK as it rots and decays even if it doesn't block the intake.

It's less risky to use the same thru-hull for the toilet and engine water intake, but still not a good idea 'cuz it's not uncommon for the toilet to suck in animal or vegetable sea life that can block or seriously reduce the flow of water to the toilet AND the engine. A strainer would keep anything out of the toilet and the engine, but also block the flow of water to both.

I'm hoping that what you called a "brass" seacock is really bronze, 'cuz brass isn't durable enough to be used for seacocks.
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Old 19-12-2015, 09:03   #5
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shared seacock for engine and head?

In 1987 Island Packet built my boat with both heads drawing from the engine seacock.
Tieing in the sink outlet would be bad for a couple of reasons, even if you made sure nothing went down the drain, it's likely that the engine would suck air through the sink inlet as it could draw air easier than water.



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Old 23-12-2015, 07:11   #6
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Re: shared seacock for engine and head?

Okey so i keep engine cooling system completely separated

But what about sharing one seacock for head and sink intakes?
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Old 23-12-2015, 09:15   #7
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Re: shared seacock for engine and head?

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Okey so i keep engine cooling system completely separated But what about sharing one seacock for head and sink intakes?
I'm guessing you mean head intake and sink DRAIN. Teeing the head intake into the HEAD sink drain is a great way to eliminate a thru-hull and provide a safe means of flushing all the sea water out of the whole system before the boat will sit. But NOT a good idea to connect head intake to a galley sink drain because galley waste--grease, food bits--is much different from head sink waste and can be a real PITA to clean out if it gets into the head pump or plumbing. Plus, if the galley and head are on opposite sides of the keel--which they often are because of weight distribution--plumbing the head intake to the galley sink drain can be a nightmare.

You may just have to accept the idea that it can be necessary to have more than one hole in a boat!
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Old 23-12-2015, 21:17   #8
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Re: shared seacock for engine and head?

No i mean head intake and sink intake, id like to have raw water tap in galley
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Old 24-12-2015, 07:40   #9
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Re: shared seacock for engine and head?

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No i mean head intake and sink intake, id like to have raw water tap in galley
Oh...that's different. In that case it should work as long as the sink and the toilet are on the same side of the keel. I'd also strongly consider that you install a strainer on that line as close to the seacock as possible to keep animal and vegetable sea life out of both your toilet and sink water plumbing. It's best, but not necessary, to put it above the waterline so it can easily be removed for cleaning.
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Old 24-12-2015, 08:17   #10
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Re: shared seacock for engine and head?

the one disadvantage of combined seacocks is that you can't isolate either system if need be.
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Old 24-12-2015, 15:22   #11
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Re: shared seacock for engine and head?

Our head and engine have shared the same seacock for over 25 years and the system works well.
There are a few small negatives:
1. With the engine running fast, the raw water pump suction makes the head pump a little heavy to use.
2. If the valves in your head pump are worn, there is a chance of air sucking into your engine cooling line. I have an inline cock on our head inlet pump which I close on long runs.
3. You will probably have a long run of pipe from the seacock to the head. If it has been unused for a couple of weeks or more , the first bowl or two of flush water smells putrid.
None of the above outweighs the bonus of having one less thru hull.

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Old 25-12-2015, 05:29   #12
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Re: shared seacock for engine and head?

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Oh...that's different. In that case it should work as long as the sink and the toilet are on the same side of the keel.
Why that? Dont see the point ...
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Old 25-12-2015, 07:13   #13
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Re: shared seacock for engine and head?

I have a common seacock for my head and galley saltwater pump. No strainer on it. Never a problem. Rarely I'll find a fish swimming in the toilet. More fun than a problem. The thru hull is located on the opposite side of the boat from both the galley and head. I live a aboard full time.

I also share my engine intake with a deck wash down pump. Never had any problems with that either. Have no idea how air would get into the system. The least amount of holes in your hull the better.
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