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Discussion Starter #1
I'm looking at re-plumbing a 27ft fiberglass yacht with what I think is a very strange plumbing arrangement. Currently there are 2 through hull fittings below the water line (ignoring the head).

#1. Combined Engine inlet, sink outlet and two secondary cockpit drains.
#2. Dedicated primary cockpit drain.

I don't like the idea of Engine inlet and sink outlet sharing the same through hull so I am tempted to combine all cockpit drains and the sink and give the engine a dedicated inlet. Combining cockpit drains obviously has it's down side (less possible flow) but without adding new holes, so far, I think that's the best solution.

I'd be very keen to hear other people opinions on the matter.
 

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For the life of me, I can't remember the name of it just now (Cruisehimers?) but how about a box that has one through hull fitting to the sea and multiple outlets inside the boat. One on one side for all pickups, one on the other side for all outflow?

Just an idea.

Greg
 

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Bob you are right , Engine should have it's own thru hull sea **** . Sink with it's own drain ? You can fix that later . Sooner rather than later , as galley needs to have it's own thru hull drain so that it is easy to clean . The way I clean mine is I tie a little piece of cloth on a stiff rubber tube use soap and water . The galley mouse calls me the chimney sweep.
 

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technically I don't see a problem with the combined arrangement. The engine is providing a suction and the more sources providing water to it can't hurt. The engine suction could also help the drainage. Does greywater foul the engine heat exchanger? The engine should have a sea water strainer that would take care of that. The problem with a combined thru hull is where you're combining several pump suctions. in that case the cross section area of the thru hull needs to be greater than the sum of the areas of the individual suctions. Even then there could be a problem if one pump's capacity is a lot greater than annotator's. As for cockpit drains I think you're ok there unless you go where waves sweep into the cockpit and you need a lot of draining capacity or if the drain is up on one side so it might not drain on one tack. If the boat has a class website that would be a good question to ask. If it were me I'd avoid adding a thru-hull unless there was a problem.
 

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Discussion Starter #7 (Edited)
Thanks for all the great responses! Walt I was under the impression that combining inlets and outlets was not really done, but had no real info to support this however.
If the plumbing is left as it is currently set up it does have the advantage that the cockpit drains are able to utilise both through hulls if necessary.

Also just to be clear, I'm not considering adding any new through hull fittings, just looking for the best combination for:

1 x engine inlet
1 x sink outlet
1 x primary cockpit drain
2 x secondary drain

using 2 through hull fittings. Cheers!
 

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Yikes I got moderated . Mod. no pun intended . I should have said seacock . Not sea **** . Or I could have said , one of those thing ah ma bobs with the lever on it that shuts off the water. But seriously every drain / inlet needs it's own thing ah ma bob with a lever on it .
 

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It is fine to combine multiple inlets into one thru hull, but it must be sized to provide enough water when all systems are operating. In this case you have one inlet and multiple discharges, so at a minimum you can intake at least what your engine requires. So it's fine.

The problem is that drains, sinks, showers, ect... May discharge things that shouldn't really be pulled thru the coolant system of the engine. Most of the time it isn't likely a problem, but i have no idea what soap from the sink could do to a heat exchanger.

Technically I think this passes muster, but I would put it down as bad practice. Not because I know it will lead to an issue, but because I don't know it won't.
 

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Just a thought but if the sink is too far outboard there could be a possibility of the cockpit draining through the sink if heeled to that side too far - and you with no way to shut it off when it is needed most to drain the cockpit. Cockpit drains should be only that.

As far as the combined sink drain/engine intake - that risks either a clogged heat exchanger or if salt water cooled clogged engine passages. A strainer may not stop grease etc from the sink getting to these.

I would install seacocks for each. A properly installed seacock is stronger than the hull it is attached to.

Standpipes are seen on steel and aluminum boats, rarely if ever on fiberglass boats and best installed during construction.
 
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