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Old 20-03-2017, 13:38   #1
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Salt Water contamination

Seems we have a problem with salt water intrusion into the Fresh water and Fuel tanks when running in heavy seas.

48 hours running in 4-5m swell with the decks heavily awash. Fresh water tanks are vented through the topsides and fuel vents actually run up through deck into stanchions. Not sure how high those hose ends are above the deck but just pulled 6 litres of water out of the port tank. 1/2 litre in the starboard tank but this was the weather side. Gunnel rails are at least 8" above the deck so water can get that high over the base of the stanchions.

As all these vents have to exit either outboard or above deck how do you prevent water intrusion into the tanks if they can be submerged in sea water at some point in time?

Water is not getting into the deck fittings as the O rings are all in good shape.
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Old 20-03-2017, 14:38   #2
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Re: Salt Water contamination

The water vents can be moved to vent into the galley sink.
The fuel vent into the stanchion, if there is room, you can add a hardtube U turn so they at least face down.
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Old 20-03-2017, 14:51   #3
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Re: Salt Water contamination

Is your vent hose looped above the exit fitting? Your orings are not only there but good/not pinched and seated properly? I liked to put a bit of lanolin on them.
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Old 20-03-2017, 16:18   #4
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Re: Salt Water contamination

Two answers and 2 decent suggestions. Must be why I hang around here.

I will checking for looping ahead of the discharge port for the water tanks. Venting to the galley sink is another good option. 3 water tanks though so might be interesting. Wondering if you could combine them together.

Fuel tank vents might be a bigger project as life lines are welded SS tube to stanchions where the vents come up through. Next haul out I guess.
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Old 20-03-2017, 16:25   #5
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Re: Salt Water contamination

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Originally Posted by undercutter View Post
Seems we have a problem with salt water intrusion into the Fresh water and Fuel tanks when running in heavy seas.

48 hours running in 4-5m swell with the decks heavily awash. Fresh water tanks are vented through the topsides and fuel vents actually run up through deck into stanchions. Not sure how high those hose ends are above the deck but just pulled 6 litres of water out of the port tank. 1/2 litre in the starboard tank but this was the weather side. Gunnel rails are at least 8" above the deck so water can get that high over the base of the stanchions.

As all these vents have to exit either outboard or above deck how do you prevent water intrusion into the tanks if they can be submerged in sea water at some point in time?

Water is not getting into the deck fittings as the O rings are all in good shape.
The answer seems straightforward. The fuel vent opening should be well above the possible heeled sea water level and face downwards. There many ways of achieving this.

Water vents can be internal.
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Old 20-03-2017, 17:18   #6
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Re: Salt Water contamination

What if one were to put leather flaps over their openings, to act as a check valve? Is there any reason that that wouldn't be viable? You'd need to lubricate or oil/grease the leather from time to time. But I'd think it would mitigate the amount of water entering.
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Old 20-03-2017, 17:31   #7
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Re: Salt Water contamination

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Two answers and 2 decent suggestions. Must be why I hang around here.

I will checking for looping ahead of the discharge port for the water tanks. Venting to the galley sink is another good option. 3 water tanks though so might be interesting. Wondering if you could combine them together.

Fuel tank vents might be a bigger project as life lines are welded SS tube to stanchions where the vents come up through. Next haul out I guess.
You can combine the 3 water tanks into a single vent. My two tanks go into one sink vent. You can use a short chromed spout to look good.
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Old 20-03-2017, 17:42   #8
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Re: Salt Water contamination

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......

Fuel tank vents might be a bigger project as life lines are welded SS tube to stanchions where the vents come up through. Next haul out I guess.
Am I right in thinking the fuel vents are hose pushed up into the stanchion and the stanchion is vented to the outside via a small hole at the bottom end of the stanchion.

If so, maybe the hose has either slipped down or was never pushed up high enough to begin with. Either way is easy to fix.
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Old 20-03-2017, 17:54   #9
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Re: Salt Water contamination

Looking at the photo of your boat I'm guessing the engine is somewhere under the centre cockpit and the tanks are nearby or just aft of there with the vents going into stanchions somewhere on the quarter.

While it might be a long run, could not the fuel vents be combined into one hose (at the centreline) and taken right aft internally and then out though the topsides near the davit supports and then routed up the davit support and a small u turn at the top of the davit support.

???
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Old 20-03-2017, 20:00   #10
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Re: Salt Water contamination

Check the o rings on your tank fill caps in the side decks. I would bet that is how most of your water is getting in.
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Old 21-03-2017, 08:33   #11
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Re: Salt Water contamination

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Originally Posted by UNCIVILIZED View Post
What if one were to put leather flaps over their openings, to act as a check valve? Is there any reason that that wouldn't be viable? You'd need to lubricate or oil/grease the leather from time to time. But I'd think it would mitigate the amount of water entering.
I don't see how they will seal over the mushroom-ish shaped exit fittings...?


OP: Your water tank exit fitting could go into the cockpit footwell side wall.
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Old 21-03-2017, 09:05   #12
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Re: Salt Water contamination

Another problem (slightly unrelated) with stanchion vents is that they are always far too small to meet any installation code. When filling at high rate, the air has no where to go, other than out the fill, and the result is froth and kick-back when the tank fills. The vent should be large enough to manage the maximum filling flow rate, and thus typically needs to be at least 1/2 the size of the fill hose, and not too long.

I don't understand their use. Even if you don't want holes where you can see them (which is girly if it defies function--a boat is a tool, not a fashion statement), there are problems and better answers:
  • Fresh water can be into the sink.
  • Fuel has to be larger.
  • Holding tank is stupid on the face of it (it will clog).
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Old 21-03-2017, 09:27   #13
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Re: Salt Water contamination

check your deck fittings for intact O rings..water from deck does get into tanks--andnot just the water ones. fuel gets some foogly looking bilge-ish looking contaminants via the deck fitting fail. change O rings and hose dopwn decks with empty tanks and see oif that could be your issue. certainly helped my fuel situation when i repaired that fail.
ohmy so simple and yet so overlooked

as for vent hosing-- loop the hoses high enough to be deck level before feeding DOWN to your vent holes for solution to that issue. i have known no issues from venting, only from the O ring fail at deck level. all my out flow hoses have risers except my bilge pumps.
deck wash happens
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Old 21-03-2017, 09:40   #14
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Re: Salt Water contamination

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Check the o rings on your tank fill caps in the side decks. I would bet that is how most of your water is getting in.
Ditto. You need to replace those neoprene o-rings regularly, or they will definitely leak. I'd do this before fiddling around with your tank vents.
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Old 21-03-2017, 09:43   #15
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Re: Salt Water contamination

Vent the water tanks internal. To a sink perhaps.

Our diesel tanks vent to the cockpit. They have an inline check valve, below deck, oriented horizontal to stop fuel exiting the vent. They vent air for vacuum and pressure.

Also check your fillers and fill hoses. That slipperly little H2O molecule will find its way into any minute gap.
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