Combining Thru-Hulls

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Senior Member
Dec 2, 2007
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36' 1961 Sather ex-Gill Netter
Have any of you had any success combining thru-hulls for the likes of a head sink and a bilge pump? I want to reduce the number of holes/thru-hulls I have to install and am considering the plan of combining as stated with the sink feeding down into the "T" and then the bilge pump line having a slight down-hill run to the "T" so that the water would drain "down hill" from both sources. The pump is a small 1500 gal/hr unit and the "T" would be right before the thru-hull valve so there should be no back pressure.
Any thoughts of wisdom out there?
Thanks Guys
Sidney, BC
John, We have done this often but you need to be careful and factor in the flow for either intake or discharge. The flow should not be restricted as a result of additional connections. Chuck
We went from 9 through hulls under the water for 3 through hulls and from 8 though hulls above the water line to 6 though hulls.* The 3 below the water line are 1 for the main engine, 1 for the gen set and 1 for a manifold/sea chest.* The 6 above the water are for the bilge pumps combines with the sink, shower and washer drains.* When the boat is sitting at the dock all the through hulls below the water line are closed.
Great guys and thanks, I now know it was not such a crazy idea after all.

Mike - thanks for catching my mistake in terms, I was intending to use a "W" but was thinking "T" when I typed the posting - great to be old and feeble

Phil - we will be much like you in that originally there were 5 below water thru-hulls and 6 above however most of them had to do with Penta's past as a fishing boat. We will now have two below water, one each for head intake and holding tank discharge and two above water for the bilge pumps combined with the head sink and galley sink.

I am planing on all thru-hulls to be fully accessible so that they can readily be shut off when the boat is not in operation.

Again, thanks guys

Have you considered a Raw water manifold.
Allows you to plumb multiple raw water consumers to a single inlet. Google it you just tread it onto your seacock.. Better than a flimsy thru-hull I would go with a seacock and the manifold.

SKIPPERDUDE - I have no need to install a manifold as the only raw water used is for the one head. The engine is keel cooled, thank gawd, so she is a real simple ship.
Thanks for the suggestion anyway,
I was refering to any thru hull. It is my opinion all thruhulls below waterline should be a seacock the manifold is a hard brass attachment that has multiple ports. Instead of a simple tailpiece there should be a valve at the thru-hull to be able to close. Simple thru hulls below the waterline can be broken off. A true seacock is much heaver. Made of either merleon or brass If you are going to have a hole in your boat*below waterline. Wouldn't it be wise to have a safe one ?

Perhaps a discussion for another thread.**

skipperdude - oh, now I understand, I think, what you are driving at. In my case ALL the thru - hulls are bronze with shut off valves right at the hull. If needed I would rather plumb the raw water through the boat rather than have multiple thru - hulls but I don't have the need. In our boat there are only two below water line thru - hulls in addition to the massive keel cooler fittings. Further to your post re straight v/c tapered threads, what I have done is measured the length of thru - hull needed, cut the stem down to as short as possible and then run a tapered pipe thread die down the stem far enough to allow a pipe fitting to thread on properly. What I now have is a standard fitting for the attachment nut but a proper tapered thread for the following pipe thread attachments. Seems like it is going to work out just fine and in both cases the valves etc are protected by structure or a "box" so that they cannot be hit and broken.
All I need now is to get the boat back in the water and get using her !!
this is something I plan on doing next time BA is hauled
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