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Discussion Starter #1
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?
 

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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.
 

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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.
 

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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!
 

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Boasun said:
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... :eek::eek::eek::eek:
 

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Discussion Starter #6
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...
 

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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.
 

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TrueBlue said:
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?
 

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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...
 

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labatt said:
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...
The geyser you experience could be from feeding water at a rate that exceeds the vent's ability to handle it.

Upsize your vent lines/fittings and that should help. (or fill your tank more slowly)
 

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TrueBlue said:
All tanks need to be vented labatt. Yours may just be blocked.
That's actually what I was figuring... the geyser just seemed strange and made me question whether it was vented. Being blocked makes more sense.
 

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Mine vent into the bilges. Bloody annoying. I am going to group my fuel, water and exhaust vents and send them vertically, inside a big brass pole I'll get from a strip club (plenty of Nevr-Dull on it first, shine or not!) to multiple goosenecks atop the pilothouse. If I overfill something, the pitter-patter of little raindrops will let me know.

Vents at the hull/deck join are idiotic. I can't tell you how many stories I've read about fuel or water contamination once the rail is buried and the salt water goes (inevitably) downhill.
 

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Labatt-

Sounds like you've got either a blocked vent—insects and such do this a lot—or no vent at all.
 

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Thinking about this problem... Maybe if you routed your vent into the cockpit. That way while filling the water tank you can nap in the cockpit and when your feet get wet you know the tank is full. Also when you are sailing with beam ends in the water you won't worry about your tanks being contaminated.
 

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Boasun said:
Thinking about this problem... Maybe if you routed your vent into the cockpit. That way while filling the water tank you can nap in the cockpit and when your feet get wet you know the tank is full. Also when you are sailing with beam ends in the water you won't worry about your tanks being contaminated.
Amusing, but the idea of having all vents leading up and out well above the waterline is a good practice. When diagnosing an exhaust problem, I cable-tied a hose from the siphon break right out of the engine compartment and into the cockpit in order to achieve the recommended "16 inches above the waterline" requirement. The cheerful little ejaculations of H20 during engine operations were proof that I had both good flow and no water siphoning back into the manifold, as had been the case.

Now, running those vents to where I can see them is SOP.
 

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The tank has to have a vent or the resulting vacuum would be such that no liquid could be extracted. Vacuum is stronger than pressure.
 

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Discussion Starter #18 (Edited)
a big brass pole I'll get from a strip club (plenty of Nevr-Dull on it first, shine or not!)
Or you could leave it dirty and have a unique air freshener "Memories of Amber" (and Tiffany, and Kristal, etc., etc.....) ;)
 

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I'm not arguing that there are some clueless people out there, I'm arguing that your post did nothing to answer the OP's question. The OP asked about best location for a tank vent, discussion ensued around that topic. You come in, master of the obvious, and post an off-topic know-it-all response about WHY we need a tank vent, which nobody was debating. The fact that someone came in afterward and asked if their tank might not have a vent does nothing to vindicate you.
 

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Found one of my vents - it's inside one of my interior cabinets (where I store all my emergency equipment such as flares). The geyser must be due to filling the tank too rapidly for the vent to keep up.
 
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