Anti syphon on shower discharge
I currently have fitted what I think is a anti syphon valve on the discharge pipe to seacock for the shower / sump tank . Is this required as no mention on drawings?

John B 411-010

Hi John,
I am pretty sure that an anti-siphon device is not necessary in the sump discharge line because its seacock in our boats is quite high, well above the waterline. If the line or the pump does not have good check valves there might be a small water back flow after the pump stops but it is of no importance. If a goseneck with its vertex up is fitted before the seacock (a good idea) the anti-sphon valve would not avoid such back-flow but only reduce it of a negligible amount.

Daniel, 411/004

Dear John and Daniel
An anti-siphon vent is not needed if the hull outlet is always above the water. But if the sump tank is ever pumped out with the yacht heeled so the outlet is underwater the vent is necessary to prevent siphoning back, and the recommendation is to have one fitted to avoid surprises.
Kind regards
Lars

Dear John and Lars,
of course I cannot but agree with what Lars writes but I would like to recommend that if one foresees the usage of the sump pump in cases of such high heeling, the goose neck should extend quite high.
I myself would rather rely on the check valves of the pump in first approximation and on closing the seacock as the safest solution.
Please notice that in the 411 the inlet/outlet vent seacock of the holding tank is close and at the same height. Is fitting an anti-siphon valve also to that line advisable?

Daniele, 411/004

Dear Daniel
Yes, a careful crew can do without an anti-siphon vent, particularly if manual pumping is used. Closing the seacock is also a good way. Afraid there are not such crews on all yachts.
If the holding tank outlet is above the waterline this is not an original installation. The rule at the yard is to put it below water, for obvious reasons, and then an anti-siphon vent is recommended.
Kind regards
Lars

Dear Lars,
sorry there was a misunderstanding: what I mentioned is the vent seacock of the holding tank that is close to the discharge seacock of the toilet sump. Both are rather small (1/2" or so), above the water level and very close. The large discharge line (1 1/2") of the holding tank goes to the same seacock of the toilet, obviously under water level.

Daniel, 411/004

Dear Daniel
Thank you for the clarification.
Would suggest that the holding tank vent line is usually terminated near the deck edge, therefore siphoning back is very unlikely, and a seacock is not required.
It can be commented that a holding tank is completely closed off from the interior, and even if it should be filled by backflow the water stays in the tank. This assumes that the water can not flow back through the toilet.
A shower sump tank is open to the interior, and if siphoning back occurs this will sink the boat if not stopped in time.
Sailors are living a somewhat risky life, as the lower part of the interior is under the water surface, and the water is continuously trying to make its way into the boat.
Siphoning is insidious, as one does not expect water to run uphill.
Kind regards
Lars

Thank you Lars, now everything is quite clear.
Just to summarize:
1) in the 411 the seacocks of the shower sump and of the holding tank vent are both originally placed above the water line by the shipyard, somewhere behind the cabinets of the toilet,
2) the sump line should have a gooseneck and an anti-siphon valve,
3) the holding tank vent line should have a gooseneck but an anti-siphon valve is not necessary,
4) both goosenecks should extend as high as possible - this is an addendum of mine!
Thank you again,

Daniel, 411/004

Dear Lars,
My 44 has all the seacocks under the water line with goose necks .
Can you confirm me if that was the original Nautor's choice and what are the reasons?

Thanks.

Alberto

Pippus 44-011

Dear Alberto
Having all seacocks below the waterline means that pumping out for example the shower sump tank in harbour will not disturb the neighbours.
I would expect your cockpit drains to be above water?
Would appreciate to hear from other 44 owners if their draining arrangements are similar.
Kind regards
Lars

John and Lars,
to-day I had time to go to the boat and finally check.. I am afraid to admit that my memory is not as good as it used to be.
On the 411 originally there are 3 thru-hulls behind the cabinet of the toilet. Two small (1/2", or so) very high, just below the deck and without seacocks; one larger (presumably 1") about 20 cm above the water level.
One of the small is the vent of the holding tank, I do not know what is the second for (there is a hose that goes down but I did not have all that time to search). It is the vent of something, maybe the shower sump itself? The third, the large one, is the discharge of the shower sump line and presumably has got a seacock (it is too recessed and the cabinet needed to be emptied...); the line of the latter has a visible goose neck going high presently without anti-siphon valve.
Now everything is more clear to me and I plan to follow Lars suggestion which is, as always, very wise.
Daniel, 411/004

Thanks Lars,
But having all the seacocks below the waterline the probabilities that water get into the boat are higher than having them above the water line.
Why Nautor decided in that way?

Alberto

Pippus 44/011

Daniel / Lars.

I eventually fitted a syphon after un seizing the seacock. It is in a very confined space so difficult to service and so gets neglected.  The pipe work was the original black pipe and was very stiff despite using a hot air gun. I also found on line what looks like a blanked off breather. I have thrown this out.

Given the height of the seacock just above the water line it makes a lot of sense to fit the syphon. So money and time well spent.