water Tank breather - flawed design!!!

[carrswood]

cracking sail yesterday until I go below to find the Leward water tank emtying out of the breather pipe and into our overhead lockers, over the bunks etc !

previous owner obviously didn't use his water tanks!!! Basically I have 2 x 90 litre nylon tanks under the port & stbd saloon berths. These are not filled thru a deck filler but a simple 2" hole ontop of each tank (then capped). At back of each tank runs a 10mm breather pipe. This raises vertically to the highest point in the overhead lockers (midships) where it loops at the highest point (deck height) but in the locker.

All is fine until sailing on the wind and heeling. Then the tank drains into our lockers!

Is there a simple soloution?

• do I need a breather if i'm filling thru a large hole in the top of the tank?

 

[pvb]

If they're flexible tanks, you don't need a breather.

 

[VicS]

But if they are not flexible or flexible but not designed to collapse as they empty you need the breather to allow air to enter as you use the water!

If you need the breather to allow air to enter you could modify and fit an antisyphon valve that will open to allow air to enter but otherwise be shut and so stop water being ejected.

Or just a check valve that opens under very small pressure differential

 

[sarabande]

lower the tanks into the bilges, or raise the breather. It sounds as if the 'slosh' factor is forcing water up the pipe, so you could try bending the breather over to constrict the pipe and prevent air being forced out quickly.

Umm, the breathers aren't crossed over to the opposite side, or joined are they ?

If you stuff a whistle in to the end of the pipe, you will be alarmed when it happens again :0

 

[pvb]

But if they are not flexible or flexible but not designed to collapse as they empty you need the breather to allow air to enter as you use the water!

You're right, but "nylon tanks" suggests flexible to me, and I've not yet come across any flexible tanks which don't collapse as they empty.

 

[Martin_J]

On the Moody I am on, the breather hoses run up from each tank to the rear of the lockers just like yours do... unlike yours though, they then head all the way along behind the lockers and then appear at outlets in the middle of the transom (under the same covers that cover the engine air intakes). I have never noticed water come out of them though - but at least it would drain overboard.

Perhaps extend the hoses to somewhere where the water would not matter so much.

 

[lw395]

If the two tanks are linked, then the breather will leeak when the windward tank is higher than the leeward breather. If they are not linked, less of a problem.

In general, a breather helps when filling, and you need to let air in when using water. The deck filler must be water and airtight.
My last boat had the breather in the shower.
If possible the breather should go straight up from the tank so there is no manky water trapped in the piping.
If the filler hose is big bore, you could fit non return valves in the breathers to only let air in. Motor cycle petrol tanks have suitable inline valves sometimes...
HTH

 

[VicS]

You're right, but "nylon tanks" suggests flexible to me, and I've not yet come across any flexible tanks which don't collapse as they empty.

It's along time since I seriously looked at flexible tanks. My original one was disaster but the one I replaced it with has been in service for the largest part of 30 years.

My understanding was that a pillow shaped tank was designed to completely collapse as it emptied and therefore did not require a vent. In fact the outlet could conveniently be positioned on the top so it could sit happily on a flat base. A vent could then prevent you drawing water off because the pump would be tending to suck air.

The trouble with pillow tanks is that they don't make very good use of the space available. So make a three dimensional tank with sides as well as the top and bottom. This can then fully occupy the space available.
The snag is that as they collapse which, they will obviously do if there is no vent, they tend to crease and they always tend to crease at the same places. Eventually the points at which they crease tend to become holes ... so they leak ... something which campers discovered happened if you tried to use the bladders out of wine boxes for water ... been there, got the tee shirt!
So you treat a shaped flexible tank much like a rigid tank and fit a vent. Ok they still tend to collapse a bit but are not sucked flat as they would be without a vent so do not crease as badly.
IIRC some larger shaped flexible tanks where supplied with a means of supporting the top edges to maintain some sort of shape as they emptied.

My original one was a shaped one without a vent I think I got about two, maybe three years service from it. The new one is a pillow tank, has no vent of course, holds nowhere near as much water as the old one did but as I said has lasted for best part of thirty years and will probably see me out.

Maybe they are made of more flexible materials now.

I'd guess "nylon tanks" means made of a plastic coated nylon fabric similar perhaps to that used for inflatable boats.

 

[carrswood]

Hi Guys
Thanks for all the responses.
To satify your curiosity the tanks are solid plastic tanks.
This gush effect must be considerable when I sponged out 15 litres of water. I'm not sure restricting the pipe is the answer. I don't think extending the loop will help as because I can't get the loop any higher the water will still siphon round at present deck level - which is just where the natural sea level is on a good/normal 16-18kt heel with full sail up

Sounds as if the valve is the answer - but where from?
Any more solutions glady received

Thanks again

 

[VicS]

Sounds as if the valve is the answer - but where from?

When suggesting it I was at first thinking of adapting an anti-syphon valve intended for a toilet installation or perhaps one intended for an engine cooling water system.

Alternatively perhaps there is something HERE that would do the trick.

Your local plumbers' merchant may even have something.

 

[sarabande]

I'm sure you could rig up a passive slosh control system without any valves.

Add a length of pipe to the end of the existing breather one, and cross it over to the other side of the boat; When the boat heels, the tank that is 'downhill' has a breather which is uphill.

I think 10mm dia pipe for a breather is too much, especially as you have an open cap on the tank when filling.

 

[maxi77]

One thought may be to move the ends of the breathers closer to the centre line so they have much more chance of being well above the tank. My water tanks vent into the cockpit, a pain when watering as you have to move cusions etc but never show any wayer even when well healed,

 

[pvb]

Any more solutions glady received

Why not just connect the breather pipes to a through-hull tank vent? See here for the sort of thing to look for (it's a through-deck one actually, but there are similar through-hull models).

 

[Danny Jo]

. . . which is just where the natural sea level is on a good/normal 16-18kt heel with full sail up

Try reefing at 14-16kt - you may find you go just as quickly, and have more comfort and control.

 

[Danny Jo]

Hi Guys
Thanks for all the responses.
To satify your curiosity the tanks are solid plastic tanks.
This gush effect must be considerable when I sponged out 15 litres of water. I'm not sure restricting the pipe is the answer. I don't think extending the loop will help as because I can't get the loop any higher the water will still siphon round at present deck level - which is just where the natural sea level is on a good/normal 16-18kt heel with full sail up

Sounds as if the valve is the answer - but where from?
Any more solutions glady received

Thanks again

I'll try and add to my previous, rather unhelpful, response.

Firstly, the sea level itself is irrelevant (as the tanks are not connected to the sea), but the "head" of water at each angle of heel needs to be considered.

Secondly, a question: are the tanks linked? If they are, instal a switching valve arrangement so that your domestic supply is linked to one or other tank, and water from the windward tank cannot flow into the leeward tank.

Danny Jo has a similar problem owing to a dodgy but inaccessible join between the filler pipe and the starboard tank. On one occasion, during a single port tack lasting 26 hours, an otherwise insignificant leak became something of a flood, because the port and starboard tanks were connected, and the higher port tank created a 2-3 foot head at the dodgy joint. The problem was cured by isolating the tanks from each other whenever sailing.

 

[colvic987]

As i see it, a non return will only let the air or water thru one way, the tank wound need to let the air out when filling and in when emptying. so a non return valve might not help, unless the filler hole was large enough to let the air out, you could also create a splashback situation and slow filling if non return valve was fitted in the system breather.

if non return valve required whale do various types suitable for water systems, i know it depends on how your system is fitted and what is used for a breather, plastic i assume, you could do the following:

fit and non return valve and fill slowly expecting splashback, (allowing air to escape from filler hole).

fit a valve to the breather system, you can close when sailing which will prevent lose of water and open when using the water. (remembering to open or close when needed)


extending the existing breather system or replanning to vent overboard, or to somewhere it wont make a mess ( small funnel and pipe vented to bilges..), easy pump out with bilge pump and no wet magazines to read or soggy ipod.

 

[VicS]

this wont work properly, as i see it, a non return will only let the air or water thru one way, the tank wound need to let the air out when filling and in when emptying. so a non return valve might not help, unless the filler hole was large enough to let the air out, you could also create a splashback situation and slow filling if non return valve was fitted in the system breather.

The OP says that the fillers are 2" diameter caps on the tops of the tanks.
I reckon air will be able to escape from those Ok while filling!

 

[colvic987]

The OP says that the fillers are 2" diameter caps on the tops of the tanks.
I reckon air will be able to escape from those Ok while filling!

i didn't notice that till i had posted, thats why i ended up deleting the quote post, your definately quick on your toes today vic.

i think that it might not make to much difference to the poster if he fits non return valves and has a bit of splashback and he's happy to have that instead of leaking lockers.

it will depend on how the flexible tanks sit in the locker and if they are prone to trapping bubbles when filling, which is when a breather comes in handy.

lots of solutions to a simple problem, dependant on how it all works on his boat...

 

[Tranona]

Yes, your system is badly designed. The breather has to go above the heeled waterline - otherwise, guess what - when the boat is heeled and the tanks full, water will come out!

Figure out a way of getting the breather higher up and use a proper fitting to take it outside rather than in an internal locker. Also makes sense to have an external filler. Taking a hose below, lifting bunks etc must be a PITA and again any overflow ends up in the boat rather than outside.