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Old 04-01-2021, 08:05 PM   #1
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Seacock Question

I have a 2001 Mainship 390. Can anyone tell me what the seacock in the well at the bottom of the steps supplies? It's right beside the sump pump that carries the shower and bath sink water overboard.
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Old 04-01-2021, 10:28 PM   #2
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Seacock in 390

That seacock allows seawater to come into the electric head.
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Old 04-01-2021, 10:36 PM   #3
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Originally Posted by skipper724 View Post
That seacock allows seawater to come into the electric head.
Thank you!

I assumed the seacock under the engine on the starboard side went to the head.
ON my boat the starboard side has three seacocks, one for the muffler, one for the AC pump, and one I assumed went to the head. It has white hose attached to it.
Any idea what it supplies?

Thanks
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Old 04-01-2021, 10:39 PM   #4
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Have not seen a muffler that has a seacock supplying water to it. Maybe some sort of drain if it goes to the muffler.
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Old 04-02-2021, 06:04 AM   #5
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May be an exhaust water separator for Genset to eliminate splash.


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Old 04-04-2021, 08:53 AM   #6
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Went to the boat yesterday and for some reason, that I don't understand, I have two seacocks that supply water to the head. One is slightly to the starboard side of the engine but almost under it and the other is under the cover at the bottom of the steps. the tee there and then it appears they go to the head. I am thinking the PO added it. It isn't bonded like all of the others. He also added a shut off at the head I don't understand. I am also interested to know why the boat has a supply line to the muffler.
Why would I have two supplies hoses/seacocks to the head?
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Old 04-04-2021, 08:59 AM   #7
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If you care, as far as I can see.... none of them are true seacocks and slightly more dangerous than not having them true seacocks.

The one in the second picture is, as far as I can tell,, almost assuredly not, the upper one is harder to see completely. Neither is the one in the bottom pic.

If the bottom pic is the muffler, it may be an overflow drain line so the exhaust water doesn't back up into the engine. Assuming the muffler outlet is above the waterline.

Where exactly does the lower line connect to the head?
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Old 04-04-2021, 09:02 AM   #8
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I think the upper one is original. I agree with you, the second one does not seem original. When I pull it I'll address that.
Thank you
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Old 04-04-2021, 10:22 AM   #9
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Original or not, seacocks are usually preferred over tnru-hulls with ball valves screwed on.

If the first and last picture have that set up, may want to think about replacing them at so m e point
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Old 04-04-2021, 11:31 AM   #10
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Quote:
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Original or not, seacocks are usually preferred over tnru-hulls with ball valves screwed on.

If the first and last picture have that set up, may want to think about replacing them at so m e point
You are 100% correct. Many production boat builders used a straight threaded through hull with a straight nut to secure it.

That in and of itself was no problem until they connected a NPT ball valvt to the thing.

My boat has two of these and both will be replaced with regular pick your brand sea cocks next haulout.
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Old 04-04-2021, 11:38 AM   #11
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Yes, the NPT and NPS threads do not work well together. Only a few threads will engage and the installation is suspect. Also through hulls are supposed to withstand 500 pounds sideways load for 30 seconds. It is likely that the install in the photos would not do that. I have no idea why there are 2 “seacocks” feeding the head. Sometimes you just can’t figure out the POs intentions. Just fix it and walk away shaking your head.
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Old 04-04-2021, 11:43 AM   #12
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Yes, the NPT and NPS threads do not work well together. Only a few threads will engage and the installation is suspect. Also through hulls are supposed to withstand 500 pounds sideways load for 30 seconds. It is likely that the install in the photos would not do that. I have no idea why there are 2 “seacocks” feeding the head. Sometimes you just can’t figure out the POs intentions. Just fix it and walk away shaking your head.
Agreed, you also wonder why so many boat builders used the technique. Probably because a 1" ball valve is a lot cheaper than a 1" seacock, and costs add of.

OEM installation time would have been about the same.

Frankly I have not seen a production boat that used actual seacocks for anything other than the propulsion engines.
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Old 04-04-2021, 01:25 PM   #13
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Probably the same reason people still use wire nuts.

90+ percent of them probably work for decades without mishap.....maybe failure but nothing serious.

Not saying it's the best way, but so many of TF posts are overly dramatic.

Sure, be safe do it the right way. I redid all my thru hulls when I bought my boat whether they needed it or not... but I also have enough experience that loosing your boat to a through hull failure ranks up there with being hit by lightning.
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Old 04-05-2021, 02:27 AM   #14
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Psneeld, there is no shortage of scaremongers to be found on boating forums. My favorite "must-haves-just-in-case" are fuel polishing systems and dual Racor filter heads.
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Probably the same reason people still use wire nuts.

90+ percent of them probably work for decades without mishap.....maybe failure but nothing serious.

Not saying it's the best way, but so many of TF posts are overly dramatic.

Sure, be safe do it the right way. I redid all my thru hulls when I bought my boat whether they needed it or not... but I also have enough experience that loosing your boat to a through hull failure ranks up there with being hit by lightning.
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Old 04-05-2021, 06:52 PM   #15
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The head
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Old 04-09-2021, 01:05 PM   #16
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On our 1997 390, that seacock next to the shower sump is for the seawater wash down hose outlet.
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Old 04-09-2021, 01:21 PM   #17
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Originally Posted by Duane Z View Post
On our 1997 390, that seacock next to the shower sump is for the seawater wash down hose outlet.
1997 was technically a 350. My 1999 350 has the head seacock right in the bilge space at the bottom of the stairs where the sump box is located. Technically, I think that is accessed inside of the door to the master.

In the OP's pictures, I also had the same quarter-turn plastic shut off behind the head (mine was red). The additional one looks like the OP's weird way of replacing hose and connecting (not sure why they didn't run a entire run.

The OP might has used that as a way to winterize the head.

What is the black tank?
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Old 04-09-2021, 01:37 PM   #18
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Yep, meant to say 350, not 390. Our Vacuflush head uses fresh water, so it doesn’t have a seacock.
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Old 04-09-2021, 01:53 PM   #19
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Yep, meant to say 350, not 390. Our Vacuflush head uses fresh water, so it doesn’t have a seacock.
OP is using a Jabsco Electric Flush head. That is what was installed on my 350 and where the raw water was being drawn for.
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Old 04-10-2021, 07:42 AM   #20
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I think I may know what happened. I know the precious owner liked to beach the boat on a sand bar because he had some glass a sand shoe onto the hull at the bow. I am guessing this caused a problem pulling fresh water from the original seacock so he added a second one in the engine room.
Always more to learn,
Thank you all.
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