Water tank empty too soon

[moiuk 4]

Hi all,

 

Strange issue I thought I would get your brains to help with some ideas of what is going on.

 

New boat (to me, actually 6 years old), with supposed 1,000 l water tank, but it ran out of water (air coming through the taps), so we refilled using a flow meter to measure the tank size.  The tank filled (water overflowing) at 355 litres. Flushed through the air and all back to normal.

 

Now 355litres is far too small for the supposed tank, a widebeam, and I have the boat builders spec saying its 1,000 litres.

 

Any ideas as to what could be happening? 

 

Thanks for your ideas..

Edited August 1, 2020 by moiuk

[system 4-50 1159]

Take-off too high?

[moiuk 4]

3 minutes ago, system 4-50 said:

Take-off too high?

can you explain what you mean ?

[David Mack 2126]

14 minutes ago, moiuk said:

 

Now 355litres is far too small for the supposed tank

 

Can you measure the outside dimensions of the tank to estimate its volume?

[Alan de Enfield 8327]

12 minutes ago, moiuk said:

Thanks for your ideas..

If you can get to measure your tank you can get a very good idea of its capacity.

 

Multiply the height x length x width (in metres) and if it comes somewhere close to 1 cubic metre then it is 1000 litres.

 

Example tank is 2 metres long x 1 metre wide x 0.5 metres high that is 1 cubic metre (so 1000 litres)

 

If it is (for example)  1 metre long x 0.5 metres high x 0.5metres wide it is 0.25 cubic metres (250 litres)

[PhilR 66]

12 minutes ago, moiuk said:

Hi all,

 

Strange issue I thought I would get your brains to help with some ideas of what is going on.

 

New boat, with supposed 1,000 l water tank, but it ran out of water (air coming through the taps), so we refilled using a flow meter to measure the tank size.  The tank filled (water overflowing) at 355 litres. Flushed through the air and all back to normal.

 

Now 355litres is far too small for the supposed tank, a widebeam, and I have the boat builders spec saying its 1,000 litres.

 

Any ideas as to what could be happening? 

 

Thanks for your ideas..

There is a massive difference between 1000 litres and 355 litres. You must know the answer? Go back to the builder and ask them  why they didn't build it to spec.

[moiuk 4]

8 minutes ago, Alan de Enfield said:

If you can get to measure your tank you can get a very good idea of its capacity.

 

Multiply the height x length x width (in metres) and if it comes somewhere close to 1 cubic metre then it is 1000 litres.

 

Example tank is 2 metres long x 1 metre wide x 0.5 metres high that is 1 cubic metre (so 1000 litres)

 

If it is (for example)  1 metre long x 0.5 metres high x 0.5metres wide it is 0.25 cubic metres (250 litres)

Just measured it, and can confirm that it is 2 meters x 1 meter x 0.5 meters.. so confirmed that it is a 1,000 litre tank.

[Alan de Enfield 8327]

1 minute ago, moiuk said:

Just measured it, and can confirm that it is 2 meters x 1 meter x 0.5 meters.. so confirmed that it is a 1,000 litre tank.

In which case, the tank was not empty when you thought it was, if you were not getting water, then you have another some other problem.

[dmr 1493]

So the air in the water was not due to an empty tank, likely an air leak somewhere on the suction side of the plumbing, or if its a brand new boat then maybe just a bit of trapped air finding its way out.

 

................Dave

[Tracy D'arth 979]

Long shot, there is a vent on the tank to let air in as it empties?

[Cheese 73]

Unless the builder has done something daft, like put the outlet at 0.33m above the base...

[TheBiscuits 4401]

1 minute ago, Tracy D'arth said:

Long shot, there is a vent on the tank to let air in as it empties?

Good call, and around a third of a tank would be enough vacuum pressure to stop flow.

 

If it happens again in 300 litres time, simply unscrewing the filler cap will test this.

[moiuk 4]

2 minutes ago, Tracy D'arth said:

Long shot, there is a vent on the tank to let air in as it empties?

there is what looks to be a vent installed, but doesn't look to be original.

 

 

[Alan de Enfield 8327]

5 minutes ago, moiuk said:

there is what looks to be a vent installed, but doesn't look to be original.

 

 

That looks like the vent on the fuel (diesel) tank and have a anti-flame flash gauze in the little holes.

 

Are you sure you have not put water into the diesel tank ?

 

 

 

If that picture shows the typical condition of a 'new boat' I'd be taking it back to the manufacturer and expecting my money returned.

[Tracy D'arth 979]

That's a terrible thought. Are you sure?

[moiuk 4]

7 minutes ago, Alan de Enfield said:

That looks like the vent on the fuel (diesel) tank and have a anti-flame flash gauze in the little holes.

 

Are you sure you have not put water into the diesel tank ?

 

 

 

If that picture shows the typical condition of a 'new boat' I'd be taking it back to the manufacturer and expecting my money returned.

Its a new boat for me, but actually 6 years old.

 

I'm sure its not the wrong tank, the diesel tank is at the back of the boat and this is at the front. 

[Alan de Enfield 8327]

2 minutes ago, Tracy D'arth said:

That's a terrible thought. Are you sure?

It is identical to the anti-flash vent on my NB diesel tank and it looks nothing like any vent I've had on a water tank, but 'who knows' who the manufacturer is or what they have used.

Just a suggestion that the OP checks his tanks.

[dmr 1493]

Flame arrester is good, at least the water won't explode 😀. Maybe somebody installed a water tank vent and that was a convenient way to reduce rain and splash ingress? (hopefully)

 

..............Dave

[Detling 225]

9 minutes ago, Alan de Enfield said:

If that picture shows the typical condition of a 'new boat' I'd be taking it back to the manufacturer and expecting my money returned.

Seconded looks several years of grime there, plus the sealant round that vent is dreadful. Have you paid him?

 

[Alan de Enfield 8327]

Just now, moiuk said:

Its a new boat for me, but actually 6 years old.

 

I'm sure its not the wrong tank, the diesel tank is at the back of the boat and this is at the front. 

 

 

That sounds like you are OK then :

 

[system 4-50 1159]

The tank will only give out water until the level in the tank reaches the level of the outlet (the take-off point). If this is too high, or had an elbow dipping down into the tank that has accidently turned up, you will get less water out than you expect.

[Arthur Marshall 3261]

My tank has an almost invisible hole in the filler cap which acts as the vent. Might be worth having a look at how the water gets out. If it's a replacement tank, there might be a fixed pipe halfway up with a bend in it to get to the bottom of the tank and the pipe has split somewhere so you're only drawing from the top half. I'd empty it and have a ferret around with a torch!

ETA crossed with post above

Edited August 1, 2020 by Arthur Marshall

[zenataomm 1437]

Probably nothing to do with your problem ... but

 

Years ago I was called out to a similar problem.

The water tank wasn't integral and had been formed from thin gauge steel sheet.

Cutting to the chase, due to poor ventilation and a healthy pump a partial vacuum was formed which in turn partially collapsed the tank.

 

We had to cut the top off in order to hammer the collapsed side out, we also put in a bracing strap to strengthen it, and of course increase the ventilation.

[system 4-50 1159]

Try unscrewing the vent and dipping the tank when you think it is empty?

[moiuk 4]

3 minutes ago, system 4-50 said:

The tank will only give out water until the level in the tank reaches the level of the outlet (the take-off point). If this is too high, or had an elbow dipping down into the tank that has accidently turned up, you will get less water out than you expect.

Smart thinking,  here is the takeoff point, looks to be low enough. No idea how to check if an elbow has rotated on the inside, but all looks stand enough so assume its just a regular outlet with no elbow?

 

5 minutes ago, Arthur Marshall said:

My tank has an almost invisible hole in the filler cap which acts as the vent. Might be worth having a look at how the water gets out. If it's a replacement tank, there might be a fixed pipe halfway up with a bend in it to get to the bottom of the tank and the pipe has split somewhere so you're only drawing from the top half. I'd empty it and have a ferret around with a torch!

ETA crossed with post above

Seems to be original tank as installed when built. I'll take a look inside as best I can, maybe I can find a miniature camera or something  if needed.