Propane locker

[higgs]

I posted this topic before, but now I have had a new thought. My boat was converted from CNG so the locker was not originally vented. Venting the locker for propane meant that the only possible solution put the vent under water whaebn on stbd tack. Otherwise it is fine. I don't like this arrangement. considering the situation, I began to compare this situation to the bilge of a boat with a gas engine. Ventilation is acheived by two vents. One at the bottom of the bilge and one to let air in at a higher point. Typically the inlet faces forward and the vent faces aft. Now, in my situation, at rest I have a proper vent. It is only on starboard tack that I do not. In theory, why would not the same type of system work for me on starboard tack?

 

[Peter]

Do you run t.he stove on the stbd tack?

Propane is heavier than air, so the requirement for "cross ventilation" isn't necessary. Propane will naturally drain overboard whenever the drain fitting is above the water. I don't see the problem unless your vent (under water on the stbd tack) is critical because you run the stove while you're on that tack, and the vent is then cut off from draining by the waterline, for a long period of time. I'd think, if you're like most of us and run the stove for the most part while anchored/tied, when the vent is above the waterline, no problem. Only an issue if you're the stbd tack for several days without any tack or change in attitude that would allow the vent to drain overboard on the other tack, or while on even keel.Maybe if you are hard on the stbd tack for a long period while you're using the stove, you can tack after you're done cooking for a minute or two, allowing the vent ot drain the propance, then come back to stbd tack.

 

[Ross]

I built

a propane locker on Bietzpadlin. The cover is a loose fit and the vent/drain (propane is heavier that air) is a 1 1/2 inch brass pipe with a bronze screen at the outboard end as a flame arrester. It is under water on a hard port tack but that doesn't last all day. The locker is air tight to the rest of the boat so that the only way to vent is through the hatch or through the drain. The is NO ignition source in the locker. I didn't install a solenoid in the system. Just a manual valve in the cabin and the ability to shut off the tanks at their own valves.

 

[higgs]

Nice responses!!!

I have made similar posts on another site and the responses have not been anywhere near as thoughtful and informed. ross and Peter: thank you for thoughtful and informative responses. My problem is solved.

 

[patrick]

Drain is needed for a leak situation

which has little or nothing to do with cooking. It is a plumbing or mechanical problem. A leak may occur during sailing from something caused or exascerbated by the motion of the boat. I really don't think a flame arrester is of much use in this case.

 

[Ross]

The reason for a flame

arrestor is to prevent a fire from entering the locker from the outside. The tanks MUST be anchored securely within the locker and the tubing from the locker fastened to the structure of the boat at close intervals. The reason for the loose lid on the locker is to allow ventilation and if there is a fire to allow the lid to blow off without bursting the rest of the locker. It will do no good to make a neat locker that is air tight to the boat an then drill holes in it for the tubing unless you run the tube through a gas tight bushing.

 

[patrick]

If my boat was heeled hard over,

and the water was on fire, *o and I was baking cookies, ;D I doubt that a "flame arrester" would help me much. *! It sounds to me like a good time to grab the cookies, :{ pull my lip over my nose, *sry inflate my helium rescue balloon *pop and make an escape. *yks*! Upon reaching land, I would immediately buy a lottery ticket! *5

 

[Ross]

Gasoline floats

and burns on water.:-( You can use your appliances without fear if you do not have a propane leak. But if you do have a propane leak in the locker, and there is an ignition source nearby, without a flame arrestor you could have a fire in your locker. That will not be amusing to anyone. While the preceeding post was probably done with tongue firmly in cheek. under estimating the dangers of a propane leak can be deadly.

 

[R Bounds]

leak prevention is the best defense

Working in petrochemical I understand leaks do happen, but at the low pressure used in a propane system they can be avoided with a little planning. Whenever connecting from an appliance or the tank from hard piping use a length of braided S.S. flex hose. At bulkheads or anchoring points put rubber spacers in to eliminate abrasive wear. If budget allows use stainless tubing and a good compression fitting like Swagelok for end connections.Turn off and depressure when not in use. Inspect the system periodicaly and you should never have to worry about leaks ruining your boating time. I know this response was'nt exactly an answer to the question, just wanted to remind everyone prevention best; but never give up on planning for the worst. Happy sailing and flame on if you feel you need to. OBTW, #@!% no I'm not a safety man.- LOL R. Bounds

 

[higgs]

I have reached a decision

I truly appreciate all the responses. Unless I hear something to convince me otherwise, this is what I will do: No cooking on stbd tack since the locker will not be vented then.Tank will always be shut of except when I am cooking, which I would do anyways. I realize that the tank itself could leak while I am on Stbd tack and that would put me at risk, but I am willing to operate on the assumption that the tank, closed , is not going to leak. If it does, since I am not going to be igniting anything until the vent is functioning, I am comfortable with this solution. Again, thanks for the input.

 

[Moody Buccaneer]

Use a raw water intake ...

Change the vent fitting on the hull to a engine raw water intake through hull. Face the intake aft. When its above the water line it will vent just fine, when its submerged it will vacuum the vent line(like a dinghy bailer). There will a little added drag and it might make strange sucking sounds, but any propane will leave the locker.Depending on the local pressure at the existing vent, it might be doing this now. Put a piece of clear hose on the hull vent fitting (make sure the hose is long enough so the open end is above the waterline) and sail the boat. If no water enters the hose when on starboard, try pouring some in and see if it gets sucked out. You might not have a problem at all.Of course any through hull that is below the waterline should have two gear type clamps, I would think that the vent would qualify on starboard tack.No worries.

 

[Ross]

install a guage

on the pressure side of the regulator. Turn the tank on and pressurize the system and shut the tank off. Observe the pressure gauge for five minutes. If it holds the pressure there is no leak and you can open the valve and do what ever you please.

 

[patrick]

The reason for a drain and vent is

to allow propane to escape if it leaks out of your tank or plumbing. That is not a predictable event. If it cannot drain in certain conditions, it becomes a statistical issue for you to decide.A pressure test (while a good idea) will not affect the drain either. It won't make any difference if you are cooking or not. The venturi effect of a moving liquid will not remove a gas to any appreciable extent. Ross, if there is enough gasoline on the water around your boat to catch fire, you have a bigger problem than your drain will prevent - spark arrester or not.What has happened to critical thinking? I have tried to illustrate this with a little humor but I am beginning to wonder...

 

[Moody Buccaneer]

Don't tell my bailer

Please don't tell my bailer, "The venturi effect of a moving liquid will not remove a gas to any appreciable extent." Air and water are both fluids with different densities. If they weren't your boat would not sail.The bailer on a dinghy creates enough suction to leave a bubble trail of air behind it after the cockpit is dry. On my LaserII when the bailer is open with the boat at rest, the cockpit floor is about an inch below the waterline and water comes into the cockpit from the bailer. As soon as the boat moves at more than 2 knots or so, the bailer sucks the water out and starts sucking air. At 5 knots it sounds like a vacuum cleaner and there is a visible trail of air bubbles from the bailer in the wake.Force = Area * CD * 1 * V^2 for water.(for air the density number is .0012, water is 1)1 in^2 Area = 0.000579 ft^2CD = 1.17 for square plate5 knots = 8.44 fps0.048 = 0.000579*1.17*1*8.44^2Each square inch of area below the water creates .048 psi pressure. Behind the plate it is negative pressure.When there is pressure difference, flow is created."What has happened to critical thinking?"Good question

 

[Ross]

Patrick

You know that if there is no leak then venting the locker is moot. 90% of my cooking is done while I am at anchor so a drain from the locker must be passive. The code also calls for the drain to be above water at all times and for the outlet to be at least three feet away from the engine exhaust outlet. A pressure test is the quickest and most reliable way to detect a leak in the system.

 

[patrick]

Moody, Ross

Neither of these meets the requirements as I understand them for venting a propane locker. I personally don't care enough to discuss it any further. My suggestion to Higgs is to think it through and ask a CG inspector or a surveyer if you really want to know for sure.

 

[Gord May]

Pressure relief?

Your dinghy cockpit is open to the atmosphere, whereas a properly constructed propane locker is not (except at the drain).How does the pressure equalize within the compartment, when the drain venturi effect creates suction?