Water tank vent

snorphinj · #1 (**permalink**) 06-21-2007

This may be a silly question but why should a water tank be vented out through the hull? Is there a chance of picking up salt water when healed. Can I avoid replacing a clogged vent in the hull and vent inside?

Faster · #2 (**permalink**) 06-21-2007

Properly designed, there should be little risk of salt water intrusion of your fresh water tanks from the vent.

Having said that, our last two boats had water tank vents inside the hull, high up under the hull deck joint in one case, and high up in the head compartment in our current boat. Neither set up caused us any trouble either. (and it is one less fitting piecing the hull skin)

One downside though; many people like to start to fill their tanks and walk away, shutting the water off when the fill line overflows - this is not recommeded practice in our case as the vents are slightly lower that the fill port and inside the boat.

I imagine that's the reason most are installed overboard. or in the cockpit area.

sailingdog · #3 (**permalink**) 06-21-2007

As Faster has said, the main reason for venting a fresh water tank overboard is to prevent the vent from filling the boat with water if you start filling the tank and walk away.

Boasun · #4 (**permalink**) 06-21-2007

you could have the vent coming up through the deck next to a stanchion or the house. With a loop at the top and screened to keep out the vermin. Then it is in sight as you fill your water tank. This is the way it is done on work boats. Then when we have an overflow we know that the tank is pressed up.
But what ever you do, DO NOT combine the fuel vent with the Water vent... A definite NO NO!

sailingdog · #5 (**permalink**) 06-21-2007

Quote:

Originally Posted by Boasun

you could have the vent coming up through the deck next to a stanchion or the house. With a loop at the top and screened to keep out the vermin. Then it is in sight as you fill your water tank. This is the way it is done on work boats. Then when we have an overflow we know that the tank is pressed up.
But what ever you do, DO NOT combine the fuel vent with the Water vent... A definite NO NO!

But, it would simplify the installation... really it would...

Sailormann · #6 (**permalink**) 06-22-2007

Mine runs up between the liner in the head and the hull - doesn't vent outside. Don't like this as the head is always more humid than the rest of the boat. Going to run it somewhere...maybe into the anchor locker...

TrueBlue · #7 (**permalink**) 06-22-2007

The water tank vent is necessary to release air within, as it is displaced by water from the deck fill. Conversely, as water is emptied from the tank, air displaces the water.

If a vent is not provided, resulting negative or possitive pressure could rupture either the tank, hoses, or fittings.

morganmike · #8 (**permalink**) 06-22-2007

Quote:

Originally Posted by TrueBlue

The water tank vent is necessary to release air within, as it is displaced by water from the deck fill. Conversely, as water is emptied from the tank, air displaces the water.

If a vent is not provided, resulting negative or possitive pressure could rupture either the tank, hoses, or fittings.

Wow, who would have guessed?

labatt · #9 (**permalink**) 06-22-2007

We'll have to track ours down. Is it possible that some boats don't have a vent? When we fill our tanks we get big "thunk" sounds as they fill. When you pull the hose out of the deck fitting, you usually get a big geyser shooting out of it. I'm assuming the sounds are just due to the weight of the water pushing on the tank, but I'm not sure about the geyser...

TrueBlue · #10 (**permalink**) 06-22-2007

Quote:

Is it possible that some boats don't have a vent?

Contrary to morganmike's sarcastic post, it seems the vent's function is not that obvious to some.

All tanks need to be vented labatt. Yours may just be blocked.