Sink Drains and Seacocks/Thru Hulls

[Ward H]

Hi All,
I just installed a Raritan toilet that uses pressurized fresh water.
So now I have two seacocks that are only used for sink drains, galley and head.

Obviously the bottoms of the sinks are above the water line so I'm wondering about the feasibility of running the drain lines to new thru hulls located about 6" above the water line.
I would then plug the two obsolete seacocks, leaving them in place.

Benefits would be: Sinks would drain faster, no more opening/closing seacocks just to do a quick hand wash (I never leave the boat with open seacocks) and I would only have the engine cooling intake seacock to open/close and maintain. (I've already plugged the holding tank discharge seacock when I removed the leaking macerator)

Thoughts/suggestions?

 

[capta]

You need to consider if the new seacock location will allow the water to drain out when you are heeled over and whether water will enter the sinks from the new seacocks when you are sailing. Normally only motor boats can have sink drains above the waterline.

 

[Peggie Hall HeadMistress]

If you opt to install above-waterline sink drain thru-hulls, you might want to just plug the current ones...or maybe just put y-valves in the drain lines. 'Cuz unused below-waterline thru-hulls can come in handy for adding washdown pumps or central HVAC. And at the rate over-zealous politicians and marinas are making new laws and rules we don't need, you never know when the ability to drain a sink out of sight below waterline might also come in handy.

--Peggie

 

[JamesG161]

whether water will enter the sinks from the new seacocks when you are sailing.

I went below during a sail in 4 foot seas. I saw water on the deck near the galley sink.
What the heck?
Then as we sailed over a wave...
Geyser!
There was a big spurt up in the Galley sink, like a porpoise.
We now put our sink stopper in place.
Jim...

 

[Don S/V ILLusion]

Hi All,
I just installed a Raritan toilet that uses pressurized fresh water.
So now I have two seacocks that are only used for sink drains, galley and head.

Obviously the bottoms of the sinks are above the water line so I'm wondering about the feasibility of running the drain lines to new thru hulls located about 6" above the water line.
I would then plug the two obsolete seacocks, leaving them in place.

Benefits would be: Sinks would drain faster, no more opening/closing seacocks just to do a quick hand wash (I never leave the boat with open seacocks) and I would only have the engine cooling intake seacock to open/close and maintain. (I've already plugged the holding tank discharge seacock when I removed the leaking macerator)

Thoughts/suggestions?

Ever have the rail in the water when heeled?

 

[capta]

I went below during a sail in 4 foot seas. I saw water on the deck near the galley sink.
What the heck?
Then as we sailed over a wave...
Geyser!
There was a big spurt up in the Galley sink, like a porpoise.
We now put our sink stopper in place.
Jim...

The original design went to a sump, but have we installed a thru-hull for use at anchor to keep all the gunk out of the sump. We have a Y valve to choose, but most often just close the seacock for short sails under a hundred miles.

 

[Ward H]

All good points to consider. Sounds like I should move the idea to the bottom of my project list. If I ever get to it Peggie's idea of using the Y valve sounds like the way to go.

Thanks for the replies.

 

[Jackdaw]

A sink drain above the waterline will eventually create a NASTY drip line from the thru-hull to the waterline, made up of all the soap and stuff you watch of your hands and dishes.

 

[Ward H]

Another good point.

 

[JamesG161]

the waterline will eventually create a NASTY drip line

True enough.
Our solution is to use hot water with bilge cleaner to flush our bilges and the Galley sink line. We do this about once a month.

Tip: You can get a "inside the cabin' reference point of your boat's static water line... Use a "Dip Stick" in your Galley Drain. "Dipping" let me reference to our counter top as being 24" above the boats water line.
Jim...

 

[Ward H]

@JamesG161 It sounds like your galley drain is above the water line?

 

[JamesG161]

The bottom of the sink is about 16" above the static water line and a straight drop to a through hull, that is offset from centerline about 18". Also a bit forward of midships.
I never worry about heeling or sailing in moderate seas. I close accessory seacocks if I am expecting heavy seas.
Jim...

 

[Charlie Jones s/v Tehani]

lol- or you can do what I did and remove ALL the thru hulls, and glass them over My sink lifts out and gets dumped overboard. The head is an MSD, plumbed JUST for pump out, which when I'm on the boat alone (usually) runs about every 12- 14 days

 

[MitchM]

we once saw a boat nearly sink on lake erie. the owner had proudly newly plumbed his galley sink to a thru hull WITHOUT any seacock, forgetting that said thru hull was underwater on a heel . so a siphon was created. he only discovered water siphoning in when he went below as he had no bilge alarm. our boat, by contrast, has a seacock on each sink thru hull and a label on the sink cabinet door stating "CLOSE SEACOCKS WHEN SAILING.' (and 2 bilge alarms, one for each bilge...)

 

[Jackdaw]

we once saw a boat nearly sink on lake erie. the owner had proudly newly plumbed his galley sink to a thru hull WITHOUT any seacock, forgetting that said thru hull was underwater on a heel . so a siphon was created. he only discovered water siphoning in when he went below as he had no bilge alarm. our boat, by contrast, has a seacock on each sink thru hull and a label on the sink cabinet door stating "CLOSE SEACOCKS WHEN SAILING.' (and 2 bilge alarms, one for each bilge...)

I’m curious how this created a siphon. A siphon requires more downhill hose than uphill. You find this often in head plumbing, but I’m never seen it in sink drains which generally run straight down and out.

 

[Scott T-Bird]

Our galley sink drains underwater right next to the raw water intake. Our vanity sink drains just above the water line on the port side. I find that the galley sink drains faster than the vanity. I think it is because the sideways run of the vanity drain slows the flow down substantially. I've never had any problem with water in the galley sink draining and I've never had any water in the sink while motoring or sailing in any kind of condition. I always have the galley drain seacock open when in the boat and underway and never have even given it a thought. There is no possibility for siphon because it is a straight vertical rise into the sink. I have siphoned the toilet bowl when I forget to close the joker valve. That's because the intake hose is not looped (a job for another time). The bowl fills almost to the rim and only sloshes out when heeling. Luckily the head & vanity area is confined with fiberglass, so it is an easy clean-up!
I think you will find a slower draining galley sink if you re-route to the topsides. If it drains fine where it is, why change?

 

[Scott T-Bird]

I’m curious how this created a siphon. Normally a siphon requires more downhill hose than uphill. You find this often in head plumbing, but I’m never seen it in sink drains which generally run straight down and out.

It would have to be a very unusual condition on a boat that has a sink that is below the water line only when the boat is heeling. I can't picture it on a normal sailboat, where sinks drain by gravity. For sure, the drain should have a seacock even if it drains above normal waterline, but I don't buy the story that lack of a seacock allowed a siphon … a disconnected, open seacock, sure, but not a siphon into a sink just because the boat is heeling.
For sure, it is feasible for a sink to be below the rail and if the boat is heeled to submerge the rail with the sink on the same side, water could come in. This wouldn't really be a siphon … it is water just seeking it's level. A siphon is a closed system with a hose that rises above the water line. The sink drain would simply be submerged.

 

[thinwater]

You need to consider if the new seacock location will allow the water to drain out when you are heeled over and whether water will enter the sinks from the new seacocks when you are sailing. Normally only motor boats can have sink drains above the waterline.

And multihulls.

 

[Jackdaw]

It would have to be a very unusual condition on a boat that has a sink that is below the water line only when the boat is heeling. I can't picture it on a normal sailboat, where sinks drain by gravity. For sure, the drain should have a seacock even if it drains above normal waterline, but I don't buy the story that lack of a seacock allowed a siphon … a disconnected, open seacock, sure, but not a siphon into a sink just because the boat is heeling.

Indeed, that was my point. It's one of the reasons sinks are better mounted near the centerline. But in any case a situation that allow flooding thru a sink drain is not a siphon, its a hole in the boat.

 

[Scott T-Bird]

Indeed, that was my point. It's one of the reasons sinks are better mounted near the centerline. But in any case a situation that allow flooding thru a sink drain is not a siphon, its a hole in the boat.

Agreed … I had to give that some thought. A siphon involves a hose that rises above the water line and then opens again somewhere below the waterline. It's how I used to drain my above ground pool.