Inside vent for fresh water problem

Dec 2, 1997
8,709
- - LIttle Rock
All tanks are meant to be vented to the outside of the boat....USCG regs require it of fuel and waste tanks, but not water tanks. Any boat builder that doesn't vent a water tank to a thru-hull only does it save the cost of the thru-hull...Catalina just came up with an ingenious way to vent to the outside without one.

Venting a water tank into a bilge or anchor locker lets the air in that area--which is hardly likely to be "fresh" air--be pulled into the tank as contents are drawn out. This can have a negative impact on the taste and smell of the fresh water or even it's "purity" unless your bilge is pristine 'cuz wet dirty bilges are "primordial soups" and the same seawater critters that can generate toilet intake odor are also dying an decaying in chain lockers.

You may not drink water from your tanks, but you ingest a lot more of it than you think you do...you brush your teeth in it, shower in it, wash dishes in it....rinse out a glass with it before filling the glass with bottled water.

Just sayin'...but it's your boat and it's not illegal to vent a water tank to any location you choose whether it's a good idea or not.

--Peggie
 
Aug 1, 2011
3,972
Catalina 270 255 Wabamun. Welcome to the marina
The Catalina solution only works until the spiders get wind of a new home
 
  • Like
Likes: jssailem
Nov 16, 2012
1,037
Catalina 310, 2000, #31 31 Santa Cruz
Catalina vents all tanks--fuel, water and waste--into rail stanchions to keep sea water out 'em. It's a brilliant way to vent fuel and water tanks because the slits/holes in the stanchions are on the AFT side of it...so even if your rails are in the water, sea water runs aftward over the front of the stanchion...it doesn't get into the vent.
--Peggie
Peggie, I agree that early Catalinas vented thru a stanchion, but starting around maybe 2000 they quit doing that, at least with the C310. The waste and fuel vent to small fittings on the transom, and the water vents into the anchor locker. Of course the waste vent is too small, but it's very easy to fix that.

Oddly, the boat I race on, a Sydney 38, does vent the waste thru a stanchion. Even down under they do funny things!
 
Dec 2, 1997
8,709
- - LIttle Rock
I knew they'd finally learned to vent holding tanks to a thru-hull, but I didn't know they'd stopped venting fuel and water tanks into a stanchion too. That's good info...thanks!

--Peggie
 
Apr 5, 2009
2,774
Catalina '88 C30 tr/bs Oak Harbor, WA
I can't seem to find a thru hull with a clam shell. Do they come as one piece or is it something you screw into the hull over the thru hull?
Here is the clamshell vent I am planning to install for the holding tank. I was cleaning the deck the other day and found that the black-water tank vent stanchion had a crack in the weld that goes 90% of the circumference of the stanchion.:yikes:
 
Jul 7, 2004
8,402
Hunter 30T Cheney, KS
There's an earlier thread on holding tank vents. I followed the consensus. I removed my clamshell that plugs with insects, and installed an open mushroom fitting. The loop controls ingress.
 
Apr 5, 2009
2,774
Catalina '88 C30 tr/bs Oak Harbor, WA
I knew they'd finally learned to vent holding tanks to a thru-hull, but I didn't know they'd stopped venting fuel and water tanks into a stanchion too. That's good info...thanks!

--Peggie
Peggie, I will be installing a clamshell to replace my stanchion holding tank vent. should the holding tank vent have a loop or just run down to the tank? my plan is to mount it right below the rub rail at the red circle. If I create a loop, it would have a very tight radius and I worry about kinking the hose. I have been told by the Galley Wench that the hose must not intrude into her cabinet any more than it is now or else.:kick:
 

Attachments

Apr 5, 2009
2,774
Catalina '88 C30 tr/bs Oak Harbor, WA
There's an earlier thread on holding tank vents. I followed the consensus. I removed my clamshell that plugs with insects, and installed an open mushroom fitting. The loop controls ingress.
The clamshell I plan to install has a removable screen. My thinking is that with the screen removed it will be almost as open as a regular mushroom but with the shell angled to the stern would keep much of the water from coming in when heeled. I am also not sure how much water could come in either way because when the vent is under water, the tank is unvented and cannot take on water. Seems to be a self-solving problem.:biggrin:
 
Dec 2, 1997
8,709
- - LIttle Rock
Although it's necessary to keep sea water out of water and fuel tanks, it doesn't matter if it gets into the holding tank...you can't take on enough thru the vent to matter unless you're in conditions that keep your decks awash for a day or longer. Because holding tanks need oxygen to prevent odor, holding tank vent thru-hulls should be open bulkhead or "mushroom" thru-hulls (see photo...can be any material except nylon)...No clamshells and the vent line should be as short, straight and as horizontal as possible...no loops.

--Peggiethru-hull.jpg
 
Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
Although it's necessary to keep sea water out of water and fuel tanks, it doesn't matter if it gets into the holding tank...you can't take on enough thru the vent to matter unless you're in conditions that keep your decks awash for a day or longer. Because holding tanks need oxygen to prevent odor, holding tank vent thru-hulls should be open bulkhead or "mushroom" thru-hulls (see photo...can be any material except nylon)...No clamshells and the vent line should be as short, straight and as horizontal as possible...no loops.

--PeggieView attachment 182153
This is my B323 revamped to make use of the original thru-hull small hole and tank-top hole. The thru-hull is 1.25, big enough to stick the metal end of a garden hose into to back flush that 16 inches of hose. It is the best way I could work it in.HoldingTank.jpg
 
Last edited: