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Fresh Water Tank Vent Location?

jviss

.
Feb 5, 2004
4,615
Tartan 3800 Westport, MA
The fresh water stopped, even though the gauge read nearly full; so I thought my gauge was not working. When I began diagnosing it, I loosened an access plate on the port tank, and heard a whooshing of air, and gurgling of water. Water came back. I have a clogged vent.

Where is the vent? I cannot locate it. Any ideas?

The manual has just a generic schematic, not T3800 specific. But it indicates that there's a loop.

There are two tanks, one port side under the settee, the other under the v-berth. The deck fills are next to each other, port side, near the main bulkhead location.

 
Dec 2, 1997
8,073
- - LIttle Rock
Most boat builders use the same vent thru-hull for all tanks--fuel, water and waste. Your nose should be able to tell you which is fuel and which is waste...what's left should be the water tank vent thru-hull.
 
Oct 22, 2014
15,751
CAL 35 Cruiser moored EVERETT WA
The diagram tells the story.
"NOTE: Location of tank fittings will vary among boats."​
I fear this boat will foster your inner Sherlock Holmes to develop trying to solve such issues.

Two possibilities come to mind. Are there any fittings that could be vent openings on the outside of boat. Might look like this.
IMG_0598.JPG
Some are vented inside of a stanchion. I traced mine from the water tank through the boat. Found the loop and opening.
 
Feb 14, 2014
5,587
Hunter 430 Waveland, MS
Mine are done with Hunter's innovative approach. The vent is a Stainless vertical grab bar inside the cabin and pokes its vent head under the Cockpit line cover plate on the deck.:clap:
Jim...
 

jviss

.
Feb 5, 2004
4,615
Tartan 3800 Westport, MA
Ah! Found a huge kink in the vent line for that tank; the vent lines are a scrambled mess in the bottom of the port hanging locker. One line goes up, and I know not where. One goes under the sole, likewise, to parts unknown.

Debug in process....
 
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jviss

.
Feb 5, 2004
4,615
Tartan 3800 Westport, MA
OK, solved it. There's a loop with a "T" at the top, to which are connected the forward and port water tank vents, and a line running to the bilge. The loop is behind the cedar lining of the port hanging locker. It had fallen down, kinking the port vent hose, completely blocking it.

I re-did the hoses, and pulled the "T" up with a string, which is fixed there to hold it, and also lower it if ever need be.
 
Jan 4, 2006
3,797
Hunter 310 West Vancouver, B.C.
What's with the vented loop ?

Can't figure that one out no matter which way I rotate the drawing. It passes air, not water but it only passes water as an overflow.
 
Dec 2, 1997
8,073
- - LIttle Rock
There's no need for a vented loop in any vent line, only an arch in water and fuel tank vent lines to protect them from sea water contamination. NO tank--water, fuel or waste--should be allowed to overflow into the bilge.
 

jviss

.
Feb 5, 2004
4,615
Tartan 3800 Westport, MA
NO tank--water, fuel or waste--should be allowed to overflow into the bilge.
I take your point on waste and fuel, of course. Fresh water - not so much. I can easily route this vent line to the shower sump, where the shower and fridge drain. This has its own pump, to pump overboard.

But, fresh water vent into the bilge is how this was builtfound! I don't know if it was built this way, or modified by a previous owner. But my guess is that it was built this way.
 
Last edited:

jviss

.
Feb 5, 2004
4,615
Tartan 3800 Westport, MA
What's with the vented loop ?

Can't figure that one out no matter which way I rotate the drawing. It passes air, not water but it only passes water as an overflow.
It's not a vented loop, just a loop.
 
Dec 2, 1997
8,073
- - LIttle Rock
Fresh water - not so much. I can easily route this vent line to the shower sump, where the shower and fridge drain. This has its own pump, to pump overboard.
You'd be smart to do that...or anything as long as it doesn't drain into the bilge (and neither should showers or icebox/fridge drains) unless you want to spend far too much time cleaning the bilge...'cuz wet bilges--especially in hot weather--quickly turn into primordial soups that can make a whole boat smell like a swamp or even a sewer.
 
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Feb 14, 2014
5,587
Hunter 430 Waveland, MS
The "T" is high up, behind the cedar lining
Clever way to make sure overfilling of your tanks go to the Bilge and not the cabin.

The air drawn into the tanks when using water, will be essentially cabin air, if your Bilge is clean.
Jim...
 

jviss

.
Feb 5, 2004
4,615
Tartan 3800 Westport, MA
Clever way to make sure overfilling of your tanks go to the Bilge and not the cabin.

The air drawn into the tanks when using water, will be essentially cabin air, if your Bilge is clean.
Jim...
Yea, well that's what kind of bothers me. I don't want to suck bilge air into my water tanks.

I'm going to investigate and review all of the tank vents in the boat.
 

jviss

.
Feb 5, 2004
4,615
Tartan 3800 Westport, MA
O.K., dear readers who are following this; rather than start a new thread, I thought I would continue this one. I'm still struggling with the fresh water management. I have two tanks, one to port, under the settee, that's aluminum, 38 gallons; the other, plastic, under the v-berth, 42 gallons. The v-berth one is seemingly higher in elevation that the port tank. They are vented per this thread. The supply lines run through the bilge to a manifold under the galley sink, above the cabin sole. There are ball valves on the supply lines before the manifold; the manifold feeds a small strainer with a clear bowl, and the line from that runs back below the sole, and up to a pump mounted high in the port cockpit locker, which feeds an accumulator. The output is split to "cold" and a 10 gallon water heater.

I have never had a boat with valved tanks. While debugging my vents, I just opened both ball valves; one had been closed. I don't know which tank was closed, since there's a contradiction in the pipe and valve labeling, in that a supply line is labeled "port tank," while a ball valve labeled "port" is fed from the other supply line.

With both open, I started sucking air into the pump, and it couldn't build pressure. I fiddled a while and found a combination of OFF/ON that seems to work, and the tank level gauge now indicates 1/2.

I'm thinking:
  • when winterizing the yard disconnected the supply lines, and when recommissioning reconnected reversed;
  • when one tank empties, the pump will suck air from that, through the manifold, unless I shut it off.
Does this make any sense at all?
 

Rick D

.
Jun 14, 2008
6,997
Hunter Legend 40.5 Shoreline Marina Long Beach CA
when one tank empties, the pump will suck air from that, through the manifold, unless I shut it off.
Does this make any sense at all?
That is exactly what my system does if I leave two valves open, assuming the full one does not drain into the empty one.
 

jviss

.
Feb 5, 2004
4,615
Tartan 3800 Westport, MA
I think there are a lot of reasons to use a y valve. Forespar also makes on in the North Americam markets.

It visually allows you to see which tank is on line
I didn't "get" this until now. I assumed when I first looked that it was a waste Y-valve. But I see you can use then for a variety of purposes. Thanks.

I think the issue is manifold (pun intended). First, the level gauge apparently only measures one tank. Then, I think when one tank runs dry, presumably the bow tank, the pump sucks air.

The only real solution without adding a second tank gauge is to live with a water level gauge with a weird, non-straight-line curve for remaining water versus gauge indication.

The gauge is on the port tank. I think the bow tank is mostly above the level of the port tank. This means that if both tank valves are open, the bow tank will keep the port tank full actually, over-full, to the point where the vent line will fill up to the water level in the bow tank. The gauge will read full until the bow tank is empty, and the level starts to come down in the port tank.

To interested readers, thank you. This is a puzzle to me, perhaps you can solve it.

I'm attaching a diagram, partial, of the water system as I know it. Note that there's a mistake in it, as installed, in that the pipe from the port tank is not connected to the manifold port marked "PORT." I think this may have occurred when the yard winterized and then recommissioned the system, and carelessly connected the port line to the wrong manifold port. I assume it's marked because it's important! My suspicion is that when the bow tank empties, it allows the pump to suck air from the bow tank, because the communication between the tanks is only at the manifold, and the flow between can't keep up with the pump's suction. I think if I rectify the connection mistake, it will work since the tank with water will be closer to the pump. Does that make sense? What I've done for now is to close the bow tank ball valve.