Beneteau 400 overfilled water tanks

[YOLO110]

Mmmmm!

I was filling up my aft integral water tank">fresh water tank, quite big at 250L, so I decided to leave the hose running into the water filler cap inlet. Previous experience has shown me that when the tank is full, the water simply overflows out of the water inlet..

... well, not this time! After about 20 mins with still no sign of the above, I turned the hose off and went below... to find ALL the floor cavities and bilges full of water!

I have NO idea how this has happened! I thought all these tanks have an overfill pipe/vent that simply acts as an overflow when the tank is brimmed. Never mind back flowing out of the filler cap inlet!

I do know the aft tank was previously partly full as I have been running water from it over several days so I am guessing it is not an integral tank leak?

I know I may need to repeat the filling exercise to view things with all the tank plywood covers off... but any suggestions to avoid this from others with similar experiences would be very welcome please!

Cheers, Peter

[MarkJ]

You put the hose too far down the filler hole and/ or put too much water pressure on the hose.

This can split the the plastic water tank and as they are made of PTFE they are very difficult to fix ( but there is a new two part glue for PTFE).

I rig the hose so its over the rail and dont put the nozzle in the hole.

Hope is ok and just a hose pop off

[GordMay]

Most plastic water tanks are made from High Density PolyEthylene (HDPE).

PTFE is Polytetrafluoroethylene, commonly branded as "Teflon".

[ReMetau]

Unless the OP had completely blocked the filler hole and the vent was clogged, I really doubt filling the tank would have split the tank.

There was probably already a problem with the tank or the fittings. Best thing to do would be to try to fill again while watching it to see where the leak is from.

Also,why didn't your bilge pump kick on?

[Capt.Alex]

maybe the vent hose came off the barb on the inside of the hull fitting?

[YOLO110]

Originally Posted by ReMetau

Also,why didn't your bilge pump kick on?

... Blige pump... yes the previous owners never fitted an auto one!!!! On the jobs to do list!

Thanks for the reply... the hose pressure is low so I would be astonished if that happened... the tank has to be robust enough to cope with being half full in a full gale with waves at sea!

I will repeat the exercise whilst watching...

[rockDAWG]

Originally Posted by petersuren

... Blige pump... yes the previous owners never fitted an auto one!!!! On the jobs to do list!

Hahaha.... fix the auto start for the bilge pump before any things else. Don't want to see another submarine, do we. :P

[YOLO110]

No subs here! I am amazed it has not got an auto one, esp considering the boat has sailed 1/2 round the world!!!

[sandy stone]

On some boats the water tank vents are mounted inside the hull (maybe to keep bugs out?) If the top of the tank vent is lower than the deck fill then you could see the problem you describe.

[crashkahuna]

I had that happen and it was the gasket on the cap over the inspection port. Does the tank hold water now?

[noelex 77]

A small pressure over the large surface area of a tank exerts enormous force.

Hose pressure even it is reduced considerably by some of the water escaping from the vent is enough to blow tanks. You need an air gap between the hose and the tank. Many people push the hose into the tank and get away with it, but it's not a good idea.

If its any consolation we used to fill gliders with water balast. The tanks were in the wings and I have seen two considerably damaged doing just what you did. In one the carbon fibre was completely split. Ouch

It is not clear from your post the source of the leak. Sometimes the pressure will just blow off off a pipe rather than split the tank. The first job is to find where the water is coming from.

[boatman61]

I'll second the inspection hatch.. both my Bene's had that problem when overfilled.. till they reached a level again.. crawled all over the water system replacing Jubilee's before I twigged on my 321..

[MarkSF]

The water tanks on my boat have a vented loop which drains into the bilge. A hose runs from the lowest water tank, up to deck level, and back down. The purpose of this is twofold : to allow air into the tanks when you use water, and to allow air out of the tanks when filling.

On my boat it will vent excess water when filling, into the bilge space.

Suggest looking carefully for such a vented loop.

[bstreep]

Just so everyone understands. There's a big difference between volume and pressure. Just because you had the hose turned on "slow" doesn't mean anything. If the water pressure supplying your pier is 60psi, it doesn't matter how much you slow the flow, the water pressure will still be 60psi. And nothing on our boat's water systems is designed for typical household pressures.

[Vasco]

Originally Posted by MarkSF

The water tanks on my boat have a vented loop which drains into the bilge. A hose runs from the lowest water tank, up to deck level, and back down. The purpose of this is twofold : to allow air into the tanks when you use water, and to allow air out of the tanks when filling.

On my boat it will vent excess water when filling, into the bilge space.

Suggest looking carefully for such a vented loop.

Interesting Mark, my 393 has vent hoses, not loops. The forward tank vent is in the topsides just below the toe rail,port side with a clamshell over it. The aft tank vents on the cockpit coaming aft, starboard side. just forward of the fuel tank vent. Both have little clamshells over them. I fill my water tanks until it pees out of the vents. With the fuel tank I'm a bit more careful.