Bladder water tank piddling from vent?

[Wing Mark]

AIUI, my 'new to me' boat has a bladder type water tank , hidden under a settee.
I've used some water, but there still seems to be dampness around the vent outlet.
Is this normal?
The vent is say 2 ft above the tank.
There are only 2 'manual by hand' water pumps drawing from the tank.

I assume the vent is supposed to let air out as the tank is filled, but should not need to let air in?
I've not investigated as I only noticed today when packing up and it was getting dark.

What's normal with these things? Is the motion of the boat enough to pump a trickle of water 2ft?
Doesn't seem right.


As it happens the vent outlet is in the anchor well, kind of close to the shore power inlet.
Gotta love previous owners.

I've unplugged the mains and I'm keen to empty the tank and change the water, but this seems odd to me.

 

[neil_s]

I don't have vents on mine. As you draw off water, the bladders collapse down flat. When empty, you inflate them again, with water!

 

[VicS]

I have a triangular pillow type tank. Designed to go flat as it empties. It does not have a vent.

My recollection is that pillow tanks are not vented and go dead flat when emptied but shaped tanks, ie those with top, bottom, end and side panels are vented and not intended to go flat but rather retain their shape, more or less.

Is your vent actually spitting water out or is the wetness due to having overflowed when filling.


The rigid tank on the boat i used to crew always spat water out when being filled. We had to stick the vent pipe out of the heads porthole while filling the tank or it soaked the bog roll! Soaking wet bog paper is bad news.

Having a water tank vent close to a shorepower inlet sounds a bad idea.