[C320-list] Sink drainage?

[Allan Field]

You have this right but one caveat.  The head sink drain will backflow into
the sink and then onto the deck when excessively healed.  This is due to
the head sink thruhull being more outboard than is the galley sink
thruhull.  When sailing, we plug the head sink drain.
Allan S. Field


On Tue, Jun 4, 2019 at 12:44 AM David Veeneman <davidv at veeneman.com> wrote:

> Thanks to all who responded—you all got me over a big hump in
> understanding the thru-hulls on my boat. For the benefit of future new boat
> owners like me, I want to recap what I have learned. If I get any of this
> wrong, please jump in and correct me.
>
> A galley sink is connected directly to a through-hull in the bottom of the
> hull that is protected by a seacock. At first glance, one might think that
> opening the seacock would cause water to rush up the drain pipe, spurt out
> the galley sink drain, and ultimately sink the boat (no pun intended). That
> doesn’t happen, at least not as long as the galley sink sits above the
> waterline. The reason is atmospheric pressure, which pushes down on water
> uniformly. When you open the seacock for the galley sink, water does flow
> into the drainpipe. But it only rises to the level of the water outside the
> boat. That’s because atmospheric pressure pushes down on the water in the
> drain with the same force as it exerts on the body of water on which the
> boat floats.
>
> So, as long as the sink drain sits above the waterline, water will not
> back up into the sink. Other thru-hulls on a boat operate on a similar
> principle. In some cases, a hose carrying water from a thru-hull will be
> routed above the waterline at some point in its run, and will be protected
> by an anti-siphon valve, to achieve the same effect.
>
> --
> David Veeneman
> Dana Point, CA
> SV Adelante, C320 #131
>
>
>
>
> > On Jun 3, 2019, at 3:24 PM, David Veeneman <davidv at veeneman.com> wrote:
> >
> > We are settling in with our new C320 (Hull #131)—it’s our first boat. I
> have located the water tank valves (under the galley sink), but I have a
> very basic question: Where does the galley sink drain? To the holding tank?
> Overboard? What settings do I need to set (valves, switches) to use the
> sink? Thanks for your help!
> >
> > —
> > David Veeneman
> > SV Adelante, 1994 C320 #131
> > Dana Point, CA
>
>