Anti-syphon loop: required for insurance survey?

[Gary Fox]

I'm just about to install my refurbished Blakes sea toilet, using new skin fittings and ball valves. Previously it had long loops of pipe going up above the water line and back down again.
The cocks are left shut when the heads is not in use.
Neither inlet or outlet can leak through their pumps anyway, due to other valves in the system.

I have to get a survey for my insurance when the present policy runs out.

Will the surveyor make a compulsory note that I need to fit the long loops? In the real world, I don't need them, they merely occupy valuable space in a small compartment, and demand lots of extra pumping.
Loops above the w/l would not reduce risk of sinking.
I am not talking about anti syphon fittings with a valve and/or piddle tube. Just pointlessly extended hoses.
Any surveyors care to comment?
She's 64 yrs old, not coded. Thanks.

 

[Tranona]

Nothing to do with how old the boat is or whether it is coded, Depends on where the toilet is located in relation to the waterline. If the pan is below the heeled waterline you may need a loop between the pump and the pan. You need a loop above the waterline for the outlet. Not sure about what your "other valves" are that would make loops redundant.

if you think loops above the waterline are not required on your boat and the surveyor queries it then explain to him why you think they are redundant in your installation. If he does not query it then you have no problem.

 

[dankilb]

Genuine question - do the loops do anything without a valve?

I ask because our installation presents the same issues as Gary’s (loops taking up space inside the cabinetry). Our bowl is just above the static waterline. But without siphon breaks, surely the water can siphon through the loops anyway?

I anticipate the need to replace with valved loops. Possibly even higher (and more space!).

 

[Tranona]

See this for installation instructions for Jabsco sv-zanshin.com/r/manuals/jabscotoilet.pdf

Most modern boats have toilets above the waterline so usually only have loops for the outlet without valves, or more recently have gravity holding tanks which are vented.

 

[Gary Fox]

My pan is below the waterline. This means that the term 'syphon' is only correct if the accidental inflow , eg from an open cock, flows up above the waterline then down to the pan; the water is 'sucked' over the loop above the waterline, by the water ahead of it.
The above syphon process is often prevented by inverted-U shape inline fittings with a little valve, sometimes connected to a narrow tube. Normally installed at the top of a loop. Also seen in engine cooling water discharges.
My boat, although having the high loops in the hoses, never had the inverted-U fittings; they would have been pointlesss, because 'syphoning' would not have been occurring anyway! Gravity would suffice.

So until today, 'protection' from accidental flooding has been achieved by:
On the 38mm outlet side, a seacock and a one-way weighted clapper valve, in the discharge pump (part of the Blakes design);
On the 19mm inlet side, a seacock and a one-way valve in the inlet pump.

Loops above the waterline would not affect the risk of flooding. Therefore I contend they are pointless, and I ought not to be required to fit them.
I am wondering if an insurance surveyor would be able to sign off my installation which is safe according to the laws of physics, or if there exists an unquestionable sacred shibboleth: that pointless loops of hose are essential, for reasons unexplained.
(Like the 'renew standing rigging every 10 yrs' mantra for example. These things become embedded in culture without actually making sense on examination.)

 

[LittleSister]

I can see the dilemma in instances where it can be very challenging, verging on the impossible, to rig upward loops in a small boat (where it is most likely the toilet will be below the heeled waterline). I can't see, though, why you would not install loops and valves if the pipes are already accommodated

I think it will be down to the attitude (and observation skills!) of the surveyor whether they require them. You could ask them in advance of booking them for a survey.

No issue was raised by two separate surveyors (one of whom teaches surveying) on my current boat which has no upward loops (and rather inaccessible seacocks), nor on a previous boat some time ago (which had the toilet under the forepeak berth and loops couldn't be provided without sacrificing the berth above). Both of those toilets are below the heeled waterline, and were installed with no loops when the boats were built in the 1970s.

I suspect that many surveyors would want to insist on loops and anti-syphon valves, and take the view that it would be easy to forget to close the seacocks and the failure to do so could potentially sink the boat.

I note also that the current installation instructions for the Jabsco, with its twist-and-lock valve to stop syphoning, insist on anti-syphon valves and loops. That would seem to me to render the twist-and-lock valve redundant and pointless, so I guess its just corporate backside covering, putting the risk of its failure onto the owner/installer if it were to fail.

I agree that I can't see the point of upward loops with no anti-syphon valve*.
(*With the exception of Lavacs, where there is a small hole in the inlet pipe (which is under suction when operated, not under pressure) which breaks the syphon, and the outlet is said (though I'm not completely convinced) to not need an anti-syphon valve because the discharge pump draws in enough air from the bowl during operation to break any syphon).

 

[Gary Fox]

Thanks LittleSister. In response to your question, why wouldn't I want to install them, the answer is simple: Because they do not affect the chances of flooding.

 

[LittleSister]

Thanks LittleSister. In response to your question, why wouldn't I want to install them, the answer is simple: Because they do not affect the chances of flooding.

I have to disagree with you there (unless your toilet is above the heeled waterline).

You cannot guarantee that (a) you and/or other users will always remember to close the seacocks, or (b) the valves in the pump will not leak and allow syphoning. Therefore, if the top of your toilet is below the heeled waterline there is a risk (perhaps small) of flooding, maybe even sinking, as a result of syphoning.

Whether you (or anyone else) thinks that risk is worth taking (e.g. because of the difficulty of installing raised loops of piping) is a very different question, and I hold no firm position on that, but can't think of why one wouldn't unless it was problematic.

I have sailed one boat without anti-syphon loops, with a below waterline toilet, and for years routinely left the seacocks open all the time I was on board without problems - initially because I knew no better, later because I wasn't willing to sacrifice part of the already modest sleeping accommodation, and the appearance of the boat interior, to eliminate a risk I thought was serious but unlikely to happen.

A later boat caused me to question the wisdom of that, when the toilet flooded twice - the second time after the pump seals had been replaced in light of the first event! Fortunately, the flooding was only slight because on both occasions the boat was not underway at the time (the top of the toilet is only a fraction of an inch below stationary waterline, but well below the heeled waterline) and I had walked barefoot through the salon, immediately noticing the wet carpet. Had I had my sea boots on and underway, or had I forgotten to close the seacocks when the boat was left unattended, it could have been much more serious.

 

[LittleSister]

My pan is below the waterline. This means that the term 'syphon' is only correct if the accidental inflow , eg from an open cock, flows up above the waterline then down to the pan; the water is 'sucked' over the loop above the waterline, by the water ahead of it.
The above syphon process is often prevented by inverted-U shape inline fittings with a little valve, sometimes connected to a narrow tube. Normally installed at the top of a loop. Also seen in engine cooling water discharges.
My boat, although having the high loops in the hoses, never had the inverted-U fittings; they would have been pointlesss, because 'syphoning' would not have been occurring anyway! Gravity would suffice.

It is precisely gravity that will result in water flowing from outside the boat into the toilet that is below the external water's surface.

It will do so unless there are (a) closed seacocks; or (b) anti-syphon valves in a raised pipe bend; or (c) the valves in the pump stop it. Unfortunately the latter (pump valves) cannot be relied upon to always stop it.

Just try disconnecting the inlet and outlet pipes from the toilet pump, open the seacocks, and see what gravity does!

If gravity can keep the water (higher) outside the boat from flowing into the toilet (lower), why would you need a hull?

 

[Tranona]

I foresee an interesting discussion with the surveyor.

Suggest you read the Jabsco instructions (which apply equally to a Blakes) which explains exactly why you need a loop and antisyphon between the pump and the bowl if the bowl is below the waterline. Not that the non return valve is not doing what think it does - its purpose is to prevent the inlet water from draining back if the intake comes out of the water so the pump is always primed. It is optional independent of whether the bowl is above or below the waterline and is mainly used on flat bottomed boats where the intake is close to the waterline. It will not stop syphoning if the seacock is open. The need for a vented loop on the outlet is again to break a potential syphon when the seacock is open and the inboard end is below the waterline as otherwise you are relying just on a non positive flap valve (ie it relies on gravity and no way of positively locking it shut) that could get stuck open without you being aware.

Have a think about how you are going to convince the surveyor this does not apply in your case. BTW it is nothing like the rigging issue which is not necessarily supported by science or evidence. Marine toilet plumbing rules are based on science and supported by evidence that what the theory says happens in practice!

 

[Gary Fox]

That's all quite true on paper, but the combination of a seacock left open, at exactly the same time as a pump one-way valve 'failed', and then nobody noticing before she sank, seems far-fetched.
Using the (clearly visible at a glance) seacocks is part of everyones' routine of using the heads.
Suppose an anti-syphon valve got stuck..you would need yet another contrivance to cope with that eventuality...

(I think in my above post, judging by your comments, that I used the word 'gravity' in a way which it is possible to mis-interpret, and we both agree that gravity is our culprit.)

I think the miniscule extra risk of flooding isn't worth pumping every poop vertically up, through 2 extra metres of tubing, and back down again before it swims free. The added time and effort is not negligible, and the pipe would be far more likely to retain bits of sewage.
The same is true with the flushing water of course.
The anti syphon loops would permanently contain several litres of decomposing sea-water.
This is not an anti-LittleSister diatribe, his points are very helpful.

 

[Pye_End]

On my toilet, there is a comment about the discharge stroke having a larger capacity than the inlet by design, so that air is drawn through the discharge pipe. The inverted loop, therefore, on the discharge will end up with air at the top of the loop, stopping the risk of syphoning. Hence the loop on the discharge side is important. For the inlet, there is a bigger risk of syphoning once the air has gone, even with a loop, so an anti-syphon is recommended - but you will need a loop to put it on.

My installation does not have an anti-syphon and is below waterline, and only once has the bowl back-filled. It was a 'guest' who used it, and was not a serious problem on that occasion, but an anti-syphon device is now on my 'will do next time I have that bit of the boat in bits' list. When changing the pipes I discovered the outlet ball valve was letting by - think about this if you are relying on it 100% - it is pretty rare for the integrity of seacocks to be tested so you may not know!

As far as insurance surveyor is concerned, none of my surveys have ever commented on it, but every survey/surveyor probably sees different things with different eyes.

Personally, if you are working on it at the moment, it would be tempting to do it properly.

 

[Beneteau381]

That's all quite true on paper, but the combination of a seacock left open, at exactly the same time as a pump one-way valve 'failed', and then nobody noticing before she sank, seems far-fetched.
Using the (clearly visible at a glance) seacocks is part of everyones' routine of using the heads.
Suppose an anti-syphon valve got stuck..you would need yet another contrivance to cope with that eventuality...

(I think in my above post, judging by your comments, that I used the word 'gravity' in a way which it is possible to mis-interpret, and we both agree that gravity is our culprit.)

I think the miniscule extra risk of flooding isn't worth pumping every poop vertically up, through 2 extra metres of tubing, and back down again before it swims free. The added time and effort is not negligible, and the pipe would be far more likely to retain bits of sewage.
The same is true with the flushing water of course.
The anti syphon loops would permanently contain several litres of decomposing sea-water.
This is not an anti-LittleSister diatribe, his points are very helpful.

Gary, careful, the joker valves are not very good, the foot flap valve which the locking operating rod pushes to seal also fail regularly. I change them every year because they do fail. My heads fill to just below the rim which is the level of the water outside when they fail. They do it sneakily so you dont notice until you sit on the bowl in the middle of the night and drown the tussocks!
The serious side is that they do fail regularly, if your head rim is above the water level its not a big issue, if it isnt, in the middle of the night, you might get wet feet or worse! PS mines a Jabsco

 

[LittleSister]

That's all quite true on paper, but the combination of a seacock left open, at exactly the same time as a pump one-way valve 'failed', and then nobody noticing before she sank, seems far-fetched.

But it does happen, and owners and insurance companies are also likely to be concerned about damage short of sinking.

As I mentioned above, the only reason I noticed that my toilet was flooding by syphoning (twice) is that by chance I had on both occasions happened to walk through the saloon with bare feet (because I had been sleeping on both occasions - once overnight, the other time a daytime nap, IIRC). I wouldn't have noticed had I had boots or shoes on until it was above the cabin sole. As it was the carpet and some woodwork was wet where the water was running out of heads compartment, overtopping the shallow GRP tray in the bottom of the compartment and under a wooden bulkhead, along the cabin sole and through the carpet, and was in the process of filling the deep bilge. I still have a stain on the carpet where it was discoloured by wood stain(?) washed out of the woodwork by the water.

Using the (clearly visible at a glance) seacocks is part of everyones' routine of using the heads.

I have owned a number of boats, none of which had seacocks that were clearly visible and easily accessible! I have also often forgotten to check things, and I dare say the same applies to everyone I've had aboard.

As I said above, I am not saying you (or anyone else) should have anti-syphon valves - it is down to your judgement of risk, but there is a risk.

 

[Gary Fox]

Gary, careful, the joker valves are not very good, the foot flap valve which the locking operating rod pushes to seal also fail regularly. I change them every year because they do fail. My heads fill to just below the rim which is the level of the water outside when they fail. They do it sneakily so you dont notice until you sit on the bowl in the middle of the night and drown the tussocks!
The serious side is that they do fail regularly, if your head rim is above the water level its not a big issue, if it isnt, in the middle of the night, you might get wet feet or worse! PS mines a Jabsco

Hi Beneteau, the joker type valve is in a diaphragm pump, an 'Urchin', which I will be using instead of the supplied, Blakes inlet pump.
In fact I think there are two non-return valves in it but I will check tomorrow. It must have at least one n/r valve..
I'm using a modern plastic bilge pump instead of the old Blakes inlet pump, which is awkward and doesn't pump much per stroke.

 

[Tranona]

That's all quite true on paper, but the combination of a seacock left open, at exactly the same time as a pump one-way valve 'failed', and then nobody noticing before she sank, seems far-fetched.
Using the (clearly visible at a glance) seacocks is part of everyones' routine of using the heads.
Suppose an anti-syphon valve got stuck..you would need yet another contrivance to cope with that eventuality...

(I think in my above post, judging by your comments, that I used the word 'gravity' in a way which it is possible to mis-interpret, and we both agree that gravity is our culprit.)

I think the miniscule extra risk of flooding isn't worth pumping every poop vertically up, through 2 extra metres of tubing, and back down again before it swims free. The added time and effort is not negligible, and the pipe would be far more likely to retain bits of sewage.
The same is true with the flushing water of course.
The anti syphon loops would permanently contain several litres of decomposing sea-water.
This is not an anti-LittleSister diatribe, his points are very helpful.

While failure of the outlet anti syphon is unlikely to give an immediate problem, you completely misunderstand the one way valve in your inlet. It is there to stop water from draining OUT, not to stop water from coming in. If it were not you would not be able to pump any water in. So it is not protection against water getting in by syphon if your bowl is below the waterline and the seacock is open. A loop above the waterline with a syphon break is essential in this situation. Your outlet pipe will always contain seawater if it does not rise above the waterline. The most effective routine for keeping pipes clean and minimising the potential for smells etc is to pump seawater through - I do a minimum of 10 strikes and when the boat is left pump 2-3 litres of fresh water through from the pan and then leave the seacocks open. The only seawater in the system then is the short length from the inlet to the pump which you can't avoid but at least it is clean seawater.

It is not necessary to close seacocks when not in use - I have left mine open for years without any problem because all my toilets have been plumbed properly so that syphoning is prevented.

 

[BabaYaga]

you completely misunderstand the one way valve in your inlet. It is there to stop water from draining OUT, not to stop water from coming in. If it were not you would not be able to pump any water in. So it is not protection against water getting in by syphon if your bowl is below the waterline and the seacock is open.

Important point, this.
I also agree that vented loops in both inlet and outlet pipes is the foolproof solution, which will let you leave the sea cocks open, if that is what you want.
However, personally I am in the same position as the OP - Blake toilet and no loops. Outlet sea cock is always closed after use, as is the gate valve (turning knob) in the inlet line.
So my suggestion to the OP would be to consider installing a vented loop in the inlet pipe, since this is the more likely way for water to enter and flood the bowl (and the boat), should closing the sea cock/valve be forgotten.
Entry of water by the discharge pipe is more unlikely, since the discharge pump on the Blake IIRC has two independent features acting as one way valves, both the wheighted ball and the clack valve.

 

[Gary Fox]

That's what I was thinking BabaYaga

 

[capnsensible]

Ask a marine surveyor. ?

 

[Gary Fox]

Ask a marine surveyor. ?

Absolutely...I will be asking before hiring
the trouble is ( from my own previous encounters) they are mainly concerned with ticking boxes and covering their @rses rather than applying practical seagoing experience.
I don't know if it's their certification, or the culture which has evolved in the trade, but personally I've never been grateful to pay £100's for gems such as, 'the vessel appears to be rigged as a gaff cutter', for instance.