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On a starboard tack it seems that my LPG bottle locker is filling with seawater. There is a drain/vent hose that connects the bottom of the locker to a hole on the stern, level with the engine exhaust.
The result is that both my bottles are completely rusted out at the base.
On a starboard tack it seems that my LPG bottle locker is filling with seawater. There is a drain/vent hose that connects the bottom of the locker to a hole on the stern, level with the engine exhaust.
The result is that both my bottles are completely rusted out at the base.
Rerouting the vent line sounds in order, but may be tricky depending on your hull design. The danger (as you've touched on) is getting propane trapped in the line when the through hull is buried and water effectively blocks the passage.
A no cost option would be to not heel the boat over so far on a starboard tack.
While not addressing the cause, since you've got to replace the tanks anyway replace them with composite tanks (best) or aluminum (better than steel.)
Gas bottles really should be elevated slightly above the floor of the locker on a low plastic/fibreglass plinth, away from the water getting in (presumably only a small amount). Stainless steel tanks are available in some places but do tend to be a little expensive..
You can probably install a flapper valve (piece of plastic on a hinge over the outside of the vent hole) that will allow stuff out but very little back in. That, plus the low plinth, should be enough to stop your tanks rusting out.
The bottom of the locker does have some raised ribbing, but I'm wondering if it's high enough. Maybe there's vertical room to raise the bottles an inch or two higher.
The fibreglass bottle sounds like a good solution. As I only do weekend sails, I'm thinking of going with just one bottle and a single regulator and saving some money. I can always add a second one later.
The bottom of the locker does have some raised ribbing, but I'm wondering if it's high enough. Maybe there's vertical room to raise the bottles an inch or two higher.
Mark, it doesn't need to be higher than an inch. Just enough to allow whatever water does leak in via the flapper valve (usually less than a half-cupful) to not reach the skin of the tank.
It does sound to me like a flapper valve on the vent is all you really need.
Propane is a bit heavier than air and needs all the help it can get to drain. The flapper valve would never open with propane and I don't believe any good surveyor would let it pass.
Propane is a bit heavier than air and needs all the help it can get to drain. The flapper valve would never open with propane and I don't believe any good surveyor would let it pass.
You might have a point there.. the only installations I've seen have either been vented out the stern or the flapper valve (a crappy piece of plastic with a rubber sealing ring but no spring) was set to hang partially open unless hit by a decent amount of water.
A new hole drilled higher than the expected water level might be the solution. Close the old one and connect the hose to the new hole. If the bottle leaks some gas might collect at the bottom but it is not very important.
I only daysail a dingy, so this may not be applicable, but I'm wondering if you couldn't use the equivalent of a scupper modification over the exterior portion of the tube?
A scupper wouldn't cause any backpressure when it's not covered by water, so it would drain like it normally does when on a port tack. And when you're on a starboard tack, the forward motion through the water creates a vacuum, which would actively suck the propane (and any water) out. The end result should be an always dry and LP-free locker.
I assume they don't make a scupper in the correct size needed for your LP drain tube, but all that's required to make a scupper work is to block the valve at (roughly) a 45* angle, going with the flow of water - it seems like it'd be pretty easy to make/modify the tube outlet.
I only daysail a dingy, so this may not be applicable, but I'm wondering if you couldn't use the equivalent of a scupper modification over the exterior portion of the tube?
A scupper wouldn't cause any backpressure when it's not covered by water, so it would drain like it normally does when on a port tack. And when you're on a starboard tack, the forward motion through the water creates a vacuum, which would actively suck the propane (and any water) out. The end result should be an always dry and LP-free locker.
I assume they don't make a scupper in the correct size needed for your LP drain tube, but all that's required to make a scupper work is to block the valve at (roughly) a 45* angle, going with the flow of water - it seems like it'd be pretty easy to make/modify the tube outlet.
I believe the flap fills the exit hole except when the weight of water opens it. Propane will not open it and it is a restriction a surveyor wouldn't approve of.
I'm not entirely sure how that specific flap works, so you may be right. But if the scupper is always open (not a close-able flap), the water moving past it actually creates a vacuum, which will suck water (and any gas) out. On my boat, if there's little or no water to be sucked out, you can actually hear the vacuum - it sounds like the saliva-sucker tool in a dentist's office.
That said, the reqs for a larger boat may not allow this sort of mechanism, unless it had some sort of stop-valve that could be shut in case of emergency?
While those ABYC definitions are considered the industry standard; they don't always work in sailboat installations; especially on boats with low freeboard. The locker vent exit should be high enough up above the waterline so water from heeling or boarding seas can't get in. That's a primary consideration. The specifics of the ABYC code for 'draining' the propane is secondary. If you have a dedicated propane 'locker' on your boat; the locker should have a sealed lid and hose ports so that if any propane gas escapes it will only exit via the vent. In this configuration there is no place for the gas to vent other than through the tube, which means that it does not matter how high it is in the locker (or at the exit) so long as the exit is to an overboard location. This configuration is similar to a gasoline tank vent or diesel tank vent. Since the locker is sealed it simulates a fuel tank and will vent in the same way.
But surveyors go by ABYC and insurers go by surveys. One boat I worked on had the locker drain a few inches above the locker bottom. The surveyor stated it had to be changed in his report and the insurer listened to the surveyor.
The composite tanks are approved in both Canada and the US. I doubt you will have a problem filling them anywhere.
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