Position of skin fittings on hull .. does it matter?

[Albert Ross]

I'm re-plumbing the galley sink drain on my Jeanneau 36i. I want to have the sink drain going out through the hull directly under the sink .. that is on the flat bottom of the boat ... rather than the side of the hull, just below the water level, as it is now.

Is there a good reason why skin fitting are usually sited on the sides of the boat, rather than on the bottom of the hull? Obviously the engine cooling intake comes from the bottom surface, but is it also alright to exit the drains in the same sort of area, or must they go on the sides?

Thanks for your learned comments

 

[sailorman]

mine is fitted as you want yours, under the sink

 

[pvb]

Doesn't matter where skin fittings are, as long as they're easily accessible.

 

[salar]

If it is going to the bottom of the hull you will want a seacock not just a skin fitting, but I expect that is what you meant. Intakes and outlets for toilets are well below waterline (on the bottom of the hull on mine) so why not sink drains. Just make sure you don't site the skin fitting in front of echo sounder/fishfinder transducers as the turbulence in the water flow will upset them.

 

[prv]

My cockpit drain is more or less on the centreline, between the keel and the saildrive. Can't see any reason not to site the galley sink drain where you propose.

My suspicion would be that seacocks tend to be in the sides because it's easier to reach in the factory!

Pete

 

[Albert Ross]

My cockpit drain is more or less on the centreline, between the keel and the saildrive. Can't see any reason not to site the galley sink drain where you propose.

My suspicion would be that seacocks tend to be in the sides because it's easier to reach in the factory!

Pete

That makes sense !

 

[AntarcticPilot]

Surely the reason is so that the pipe empties every time it is used? My sink drains both exit on or just above the water line; there's never any dirty water trapped in the pipe. Routing it below the water line would mean that there would be stale dirty water trapped in the pipe unless I used fresh-water to flush it through every time.

 

[sailorman]

when we turn off the seacock upon leaving the vessel we use disinfectant down the sink

 

[prv]

Surely the reason is so that the pipe empties every time it is used? My sink drains both exit on or just above the water line; there's never any dirty water trapped in the pipe. Routing it below the water line would mean that there would be stale dirty water trapped in the pipe unless I used fresh-water to flush it through every time.

That makes a lot of sense, but it's not a trick that most boats seem to use.

Pete

 

[michael_w]

Just don't fit head seacocks like my old X-Yacht. They were so close together that the poo would "recycle".

 

[pvb]

Just don't fit head seacocks like my old X-Yacht. They were so close together that the poo would "recycle".

Too much information!

 

[prv]

Just don't fit head seacocks like my old X-Yacht. They were so close together that the poo would "recycle".

I once read an old article about installing holding tanks, presumably written when they first started being used. It discussed the various types - rigid, flexible, gravity, pumped, etc - and also a kind we thankfully don't see any more: recirculating. Then as now, we want to minimise the amount of seawater we use to flush because it takes up space in the tank. The principle of the recirculating tank was that most of the contents is water, or at least liquid, so you use it as the source of flush water instead of the sea! You would prime the tank with a half-load of clean seawater as the final part of the emptying drill, and from then on the contents would go round and round between tank and bowl being topped up with your contributions. Once the fluid squirting out of the flush jets got too disgusting, it was time to empty.

Towards the end of the cycle, the smell released by vigorous flushing must have been awesome!

Pete

 

[Resolution]

Surely the reason is so that the pipe empties every time it is used? My sink drains both exit on or just above the water line; there's never any dirty water trapped in the pipe. Routing it below the water line would mean that there would be stale dirty water trapped in the pipe unless I used fresh-water to flush it through every time.

You would think so, but in practice a sea cock below the waterline does not seem to trap smelly water. Mine goes straight down and is roughly amidships and has never given off nasty wiffs.
Back to the OPs question, my guess is that the seacock will be positioned to give the drain pipe the shortest near vertical run to the hull. As galley positioning varies for other reasons, I reckon the siting of the sea cock is a consequence.

 

[ghostlymoron]

I would put a sink drain above the water level for 2 reasons
1. If the hose comes off or splits, it's not going to sink your boat.
2. In a lively sea you could get seawater 'pumping' up the drain and into the sink. This doesn't happen on engine intake or WC connections but will on an open drain.

 

[PuffTheMagicDragon]

I'm with Antarticpilot on this one. The problem with smelly drains is not the dirty liquid that is trapped. It is the bits of food particles, like pasta and, especially, rice that remain floating on the inside of the pipe and which rapidly putrefy.

 

[sailorman]

I'm with Antarticpilot on this one. The problem with smelly drains is not the dirty liquid that is trapped. It is the bits of food particles, like pasta and, especially, rice that remain floating on the inside of the pipe and which rapidly putrefy.

we dont all live in the Meddy govner :encouragement:

 

[PuffTheMagicDragon]

we dont all live in the Meddy govner :encouragement:

I'm truly very sorry sorry for you, my friend! :encouragement:

BTW. One third of the fleet for this year's Rolex Middle Sea Race have retired due to bad weather. We have had one dismasting and two broken rudders amongst other mishaps. Mascalzone Latino managed to save their mast after suffering a broken spreader but were out of the race. Italian Coast Guard at Palermo was sending out DSC warnings every half-hour, advising yachts to seek shelter because they were no longer in a position to answer all calls for assistance. Life is not always like the tourist brochures!

 

[KenMcCulloch]

I would put a sink drain above the water level for 2 reasons
1. If the hose comes off or splits, it's not going to sink your boat.
2. In a lively sea you could get seawater 'pumping' up the drain and into the sink. This doesn't happen on engine intake or WC connections but will on an open drain.

I don't think seawater coming up into the sink has much to do with the position of the seacock, it's where the sink is in relation to the waterline that's critical. We get back flow into the galley sink when heeled on port tack, moving the seacock up t side of the boat wouldn't make any difference.

 

[aquaplane]

The galley sink drain on my Copland Harrier is just above the waterline and doesn't have a seacock, it does drain OK.

The Centaur galley sink drain is well below the water level and we are paraniod about putting washing up water down it. Fat floats and goes solid when it cools forming a disc at the waterline blocking the sink. It's a bugger to clear.

 

[GrahamM376]

I would put a sink drain above the water level for 2 reasons
1. If the hose comes off or splits, it's not going to sink your boat.
2. In a lively sea you could get seawater 'pumping' up the drain and into the sink. This doesn't happen on engine intake or WC connections but will on an open drain.

We only have heads and engine intake below water, all the rest are above waterline. Only problem is if it's lively and we're heeled on port tack, water squirts up the forward heads wash basin drain so have to close that seacock. Aft cabin wash basin and the galley not a problem.

Having a galley drain in the bottom of the hull as the OP proposes shouldn't be a problem as when underway water flow will create low pressure in the pipe, sucking grey water out. Personally though I'm against holes below the waterline if it can be avoided.