Water tank vent

[Boomvang]

My 1984 34' O'Day does not have a vent on either of the two 25 gallon water tanks. When I turn on the water a vacuum is pulled on the tank causing the top of the tank to deflect and causing the water pump to labor. Is this normal? Was there a vent on the filler hose that's no longer there?

 

[jibes138]

There should be a vent on the topsides of the hull on each side of the boat just below the deck seam. See if the vents are there and are plugged. There is a hose going to a fitting on the top of the tank for these vents. If you don't have them then yes it is required or you will probably crack the poly of the tank.

 

[tcwaltz]

My vents had actually corroded till they were sealed. You could also have crud built up in the vent line plugging it

 

[Boomvang]

There should be a vent on the topsides of the hull on each side of the boat just below the deck seam. See if the vents are there and are plugged. There is a hose going to a fitting on the top of the tank for these vents. If you don't have them then yes it is required or you will probably crack the poly of the tank.

There are no fittings on the top of either tank except for the line necessary for filling the tank. I do have a crack in the top of the starboard tank probably as a result of no vent. The tanks are original equipment I don't understand why there is no vent unless the filler lines (which have been replaced) had something to allow air in.

 

[jibes138]

Are there vent fittings in the hull somewhere around mid ship and just below the rub rail? I'm just wondering if the hose and fitting were removed for some reason? It doesn't make sense not to have vents. What year is your 34? My 35 was built in 85 and has vents for each tank.

 

[SailingCal21]

Mine was built in 1981 and has vents where Jibes indicates. Open the starboard side hanging locker across from the head. You should see about a 1/2" ( used to be clear) hose leading from the bilge area aft to the top of the inside of the locker attached to a vent. Here in VA we have wasp that like to build mud nest in the vents which are an amazingly effective seal.

I too find it hard to believe that the system was installed w/o venting. The vent from the tank is not part of the fill tube. It has a fitting all it's own at the top of the tank somewhere.

 

[Boomvang]

Mine was built in 1981 and has vents where Jibes indicates. Open the starboard side hanging locker across from the head. You should see about a 1/2" ( used to be clear) hose leading from the bilge area aft to the top of the inside of the locker attached to a vent. Here in VA we have wasp that like to build mud nest in the vents which are an amazingly effective seal.

I too find it hard to believe that the system was installed w/o venting. The vent from the tank is not part of the fill tube. It has a fitting all it's own at the top of the tank somewhere.

I do have a vent and line (used to be clear) at that location, but it is one of two for the holding tank, not the fresh water tank.

 

[Boomvang]

Are there vent fittings in the hull somewhere around mid ship and just below the rub rail? I'm just wondering if the hose and fitting were removed for some reason? It doesn't make sense not to have vents. What year is your 34? My 35 was built in 85 and has vents for each tank.

My 34 was built in 1984 a 25 year anniversary addition. There is one vent fitting forward of the mast on each side of the hull for the holding tank only. I will attach a picture of the starboard side if I can figure out how to do it.

 

[jibes138]

You don't need two vents for your holding tank. It looks like someone modified your boat. Whatever you do don't combine vents for the holding tank and fresh water system. Their is a third vent for the holding tank, also one near the stern for the fuel tank. So go around your boat identify them all then figure out how to hook them up properly.

 

[jibes138]

Here in VA we have wasp that like to build mud nest in the vents which are an amazingly effective seal.
quote]

I get them too. I used a sink strainer in my Dorade vents attached with sticky back Velcro to help keep them out of the boat. Seems to have helped a lot. I think you can get vents with screens in them to prevent this problem if you feel like changing them out.

 

[Boomvang]

You don't need two vents for your holding tank. It looks like someone modified your boat. Whatever you do don't combine vents for the holding tank and fresh water system. Their is a third vent for the holding tank, also one near the stern for the fuel tank. So go around your boat identify them all then figure out how to hook them up properly.

I will have to drill a hole in the top of each tank to accommodate a vent of any sort. I am wondering why the vent should even be outside the hull. What would be wrong with a vacuum breaker mounted on top of each tank.

 

[RichH]

I will have to drill a hole in the top of each tank to accommodate a vent of any sort. I am wondering why the vent should even be outside the hull. What would be wrong with a vacuum breaker mounted on top of each tank.

The easiest way to establish a SANITARY vent line to a potable water tank is run a length of plastic hose to terminate at several feet above the top of the tank - placed INSIDE the boat in a 'clean' area. To keep mold, mildew and airborne bacteria from being aspirated into the tank, simply take a 'fist-sized' wad of bandage cotton covered with bandage gauze taped to the end of the hose, keep dry and change yearly.
Standard industrial hydrophobic, 0,2µM 'vent filters' are available from industrial / pharmaceutical filter suppliers and distributors at ~$80.00± each for a 'capsule' of approx. 1/2 sq. ft. surface area. All 'purity' and 'sanitary' water tanks have vent filters to prevent the aspiration of microorganisms. Bio-blocking vent filters vastly extend the interval needed to sanitize the potable water tank.