The owner of a 36-foot lobster yacht called with a problem: He couldn’t use his propane galley stove. His propane sensor had been tripping the alarm repeatedly, and he had removed the fuse. With the fuse in, the system would not work because of the alarm, and with the fuse out, the system also would not work.
Was the problem an actual propane leak or a failed component? From a troubleshooting perspective, we could talk through component failure and find a work-around, but first we had to make sure the boat was safe.
Fundamentally, if a boat has a cabin, the crew is going to want hot food—not to mention the necessary coffee or tea. Boats with generators can utilize AC appliances, and there is a compelling point to be made about those appliances’ convenience and safety. A contrasting point can be made about generator noise first thing in the morning in a quiet anchorage, although this problem can be mitigated with inverters and large battery banks.
Through time, boats have carried wood or coal for heat, and there were the dark ages of pressurized kerosene or alcohol. Some boats are still carrying nonpressurized alcohol stoves, which are safe and inexpensive, and which work well if you are patient with how long they take to heat. Liquefied petroleum gas (known as LPG or propane) has risen to the top over these other fuels as the most popular because of its quick heat, power density in a small package, and availability.
There are two critical things to know about LPG: It is incredibly explosive, and it is heavier than air. In the American Boat and Yacht Council’s Standards, the section on LPG is listed first, as A-1, because of how important it is to follow the guidelines.
LPG is actually 1.55 times heavier than air, which means that if a bottle is stowed improperly and leaks, it could fill the bilge and cabin with gas. This is dangerous as an explosion hazard, and a major leak will displace breathable air, creating a suffocation hazard.
Stowage of LPG requires compressing the gas to 177 pounds per square inch, which transforms it into a liquid where it is 270 times denser than as a gas. As LPG transforms from a liquid back to a gas, it becomes very cold and can seriously damage the skin (LPG can be used as a refrigerant because of this property).
Propane in its natural state has no smell. Because it is so explosive, manufacturers are required to add a product called ethyl mercaptan, which gives it the distinctive rotten-egg smell to highlight the danger.
If you suspect an LPG leak aboard a boat, turn off the propane with the manual valve on the tank. Do not turn on any electrical or electronic gear, breakers or switches. Kill power to all electrical and electronic devices by turning off the main battery switches and shore power. Next, open everything up: hatches, portholes, bilge access panels and so forth. If the boat is at the dock, get off and allow it to air out. The boat may require active ventilation, which must be ignition-proof (meaning the device is certified not to make a spark when it runs). Alert any boat neighbors and the fire department.
Most modern boat manufacturers are aware of the liabilities and do a good job of following the rules, but this wasn’t always the case. The requirements for installing a proper LPG locker are steep, and retrofitting lockers can be a challenge.
LPG lockers must be vapor-tight to the hull interior, be located above the waterline, be corrosion-resistant, open only from the top with a gasketed cover that latches tightly, and be capable of being quickly and conveniently opened without tools. That means the LPG locker can’t be buried deep in a locker where other gear can be piled on top of it. It must be easy to access the lid, bottles and valves, and the bottles must be secured against movement.
The pressure gauge has to be installed such that you can see it. Nothing else can be stowed in the locker other than the LPG bottles, valves, regulator and solenoid. Portable 14.1-ounce and 16-ounce LPG bottles must be stowed the same way.
Commercially available LPG lockers can be purchased and installed, provided that the location meets the criteria above. Many trawlers were built with LPG bottles stowed under the flybridge seats without being in a sealed locker. These installations would not pass ABYC muster because any leaking gas could flow into open lower cabin windows, and the wiring and equipment under the flybridge console may not be ignition-proof.
The standards require at least a half-inch vent at the bottom of the LPG locker that leads outside the boat above the waterline. The vent has to be at least 20 inches from any hull opening into the boat’s interior. If a hose is used, it should flow downward without any kinks or dips that could trap water and prevent spilled gas from flowing out. A crush-proof hose, such as wire-reinforced exhaust hose or sanitation hose, meets this need.
There are three LPG bottle material choices. Steel bottles are the cheapest, but can quickly rust if they are not closely monitored and maintained. Most gas companies will not fill a bottle with any significant rust on it. Aluminum bottles are much more corrosion-resistant and lighter weight. Fiberglass bottles are slightly lighter than aluminum and are more corrosion-resistant, but they are physically larger and may not fit in the same locker as aluminum or steel bottles. (Because compressed LPG is a liquid, horizontal and vertical bottles’ internal pickups are different, and the bottles are not interchangeable. Steel and aluminum come in horizontal versions.)
How much LPG to carry on the boat will depend on the boat’s usage, and on any other LPG-powered devices aboard, such as grills or heaters. Typical setups might have two 10- or 20-pound bottles. The bottle descriptions can be confusing; a 10-pound-capacity metal vertical bottle contains 2.4 gallons of LPG, while a 20-pounder carries just less than 5 gallons. For fiberglass bottles, an 11-pound bottle carries 2.5 gallons, and a 17-pounder carries 4.2 gallons. There is also some variation between brands.
It is possible to install bottles on the exterior of the boat if there is no practical way to install a dedicated locker, as long as the valving and hoses can be protected against the weather and mechanical damage, and the bottles can be made secure. The location should be 20 inches away from any opening into the inside of the boat.
Stowing bottles outside should be a last resort because even the best installation will have a higher risk of mechanical or UV damage to the gear compared with a dedicated locker system. A propane locker can be installed on deck, although the aesthetics may not be pleasing.
Most systems have one or two LPG bottles. Two-bottle systems need a valve to determine which bottle is active, unless only one bottle can be connected at a time. Both types of systems will need a connecting hose and fitting (called a pigtail) for each bottle, plumbed to a gauge, a regulator and then solenoid.
The pressure gauge should show up to 300 psi to deal with heat expansion within the bottle. The gauge is installed not to indicate the level of the bottle, but to aid in leak detection. Weighing the bottle is the most accurate way to determine volume, unless a translucent fiberglass tank is installed, in which case the liquid gas level can be seen through the bottle. Steel tanks can utilize magnetic temperature strips.
Since LPG is stowed under high pressure, it has to be regulated to a lower pressure (10.5 inches of water column, or 0.37 psi) for it to be used safely aboard. The regulator takes the high-pressure gas and lowers it to the usable pressure.
The fitting that connects to the bottle is called a POL fitting. They were originally made by Prest-O-Lite, and the name has stuck for all subsequent versions. Modern versions have a knurled plastic nut to facilitate hand-tightening. A POL fitting requires no sealant or tape to make a good connection. If the fitting does not make a good connection, either the bottle connection or the POL will need to be replaced immediately.
The solenoid is a DC electric valve that can be controlled by a switch or control panel inside the boat—typically near the stove, but not over a burner. (This control panel is the one mentioned earlier, in our customer’s request for help: The fuse had been removed to stop the alarm.) The idea of keeping the location away from a burner is that if there were a fire, you shouldn’t have to reach over it to turn the solenoid off.
The solenoid is a 12- or 24-volt DC, electrically-actuated valve. When power is applied, the valve opens, and when power is cut, the valve closes. You can hear the valve clicking when it is operated. These valves can get stuck over time, and they periodically need replacement.
Each device served by the LPG will need a separate gas supply. This means that if there is more than one device inside or outside the boat, there needs to be a T or manifold with valves for each device after the solenoid. The manifold should be mounted inside the LP locker. Each supply will need a separate airtight bulkhead fitting for where it leaves the locker.
The hose or tubing that leaves the locker needs to be rated to carry LPG. Copper tubing can be used, but we prefer hose because it is much easier to install and repair, or to modify the end fittings during the life of the boat. Trident Marine and Fireboy-Xintex offer premade lengths of hoses with fittings already installed. Parker carries a line of black fabric-covered hose with white stripes, called series 7243. This hose uses sleeved brass flare fittings that are installed on the hose with special mandrels. Hose clamps and hose barbs may not be used.
The diameter of the hose depends on the length of the run and the Btu requirements of the device. For instance, a four-burner Force 10 galley stove with an oven and broiler and every burner lit will use 29,000 Btu. With 3/8-inch hose, the run from the regulator to the stove can be as long as 100 feet. Tables to determine larger hose size can be found online if a device or length of run exceeding this is required.
ABYC does not allow any connections inside the boat other than at the device. If the boat was fitted with copper tubing, it is OK to switch to a flexible hose to connect the tubing to a gimbaled hose. This should be done in the compartment with the device, and not hidden. At all other points, the hose needs to be secured against movement or vibration.
If the hose passes through bulkheads, then it needs to be protected against abrasion or damage. LPG systems use a combination of brass fittings with different thread types. Pipe fittings require gas tape or sealant, but flare and compression fittings do not.
A gas detection and control system should be included with any installation. The two main companies producing these devices are Trident Marine and Fireboy-Xintex. Most systems will trip the solenoid and sound an alarm if they sense a leak. That’s what happened to the boat owner who called us for help.
These systems should be wired directly to the battery (with labeled circuit protection) so that they constantly sniff for gas. They have a low amperage draw, but fuses should be removed (and labeled) if the boat is going to be out of commission for more than a month without battery charging.
Electrical connections to the solenoid should be made with heat-shrink protection, and the wiring should have a service loop before passing through a vapor-proof connection out of the LPG locker.
Gas detectors can be fooled by certain cleaners, solvents and off-gassing batteries. Even though LPG is heavier than air and will sink to the bilge, it is generally unwise to place a sensor in the bilge because of the risk of frequent false-positive alarms. A better location is below each device’s LPG connection, which should catch the leak before it reaches the bilge.
Dinner is Served
Our hungry boat owner had a dilemma: The propane alarm prevented the system from functioning, but he couldn’t smell gas anywhere. To cook, he had to determine that the system was safe, and he needed a way to circumvent the alarm and shutdown solenoid.
The ABYC recommends testing any installation with not less than 5 psi of compressed air. Most people, including this boat owner, do not have access to compressed air and need a way to test—cautiously—with the gas itself. If any work is done on the plumbing, or if a bottle is switched, then the system must be checked for leaks.
First, close all appliance valves. Open the cylinder valve to pressurize the system, and then close the valve. (If you do this in the wrong order, vapor pressure from the tank will maintain the gauge reading.)
Next, note the gauge reading. Be aware of any smell of LPG.
Spray connections with soapy water (do not use cleaners with ammonia, which can crack brass fittings).
If the gauge doesn’t move for three minutes and there are no soap bubbles, actuate the solenoid. This will likely require opening the cylinder valve to repressurize the system, and then closing the valve.
Note the gauge and check each fitting connection. If the gauge has moved down at all, there is a leak, and it must be corrected before using the system.
When all leaks have been corrected and verified, light a burner and turn off the solenoid to make sure the valve completely closes. The burner should go out once it burns the LPG in the hose. Open the valve again and light the burner. Use an unlit butane lighter to release some butane near the LPG sensor. The solenoid should shut off and stop the burner. The gas flow from a lighter may be slow enough to require as much as a minute to trigger the sensor.
Note that if the sun shines into an open LPG locker while you are performing these tests, it can warm tanks and lines, causing an increase in system pressure that can mask leaks. Never use a flame to check for leaks, and turn off the valve at the bottle when not using the LPG.
The system on the boat we were troubleshooting passed the leak test, but that didn’t stop the alarm from going off. It turns out that the boat owner had been using bilge cleaner to clean the bilges, and the fumes were setting off the LPG sensor.
While that problem would eventually clear up, dinner was not going to wait. To provide a temporary solution, the owner, with coaching from a technician, accessed the LPG control panel wiring and used a jumper wire to trigger the LPG solenoid so that dinner could be made.
Once the bilge cleaner was flushed from the bilge, the sensor was moved from the bilge to below the oven. The panel was returned to normal so the sensor could continue its job of sniffing for leaks.