CNG to Propane Conversion [Master Thread]

[Prairie Schooner]

I used one of these: https://www.westmarine.com/ancor-se...3-8inch-npt-gauges-18-16-14-12-10-175492.html in the "18-10AWG, 3/8" NPT" variety

View attachment 49563

Hi Bryan,
Did you put the T and extra valve in there to feed a grill? It's still controlled by the solenoid, so you just turn the switch on when you want to use the grill?
I got the old CNG hose out today. Thankfully, it wasn't as difficult as some of the rest of you have reported.
Thanks, Jeff

 

[vanilladuck]

Hi Bryan,
Did you put the T and extra valve in there to feed a grill? It's still controlled by the solenoid, so you just turn the switch on when you want to use the grill?
I got the old CNG hose out today. Thankfully, it wasn't as difficult as some of the rest of you have reported.
Thanks, Jeff

Hi Jeff! Aye, the T was my dad's suggestion to be able to feed a stern pulpit round Magma grill. We've used it a few times. And yes the solenoid has to be opened for it to work. I figured that would be safer. With an 11lb propane tank there is enough room to leave the hose coiled on top when the lazarette is closed.

I'm happy the hose came out easy. Replacing that hose was one of the more difficult projects I've had

 

[Prairie Schooner]

Those of you who have done this conversion, how do you power the system? Do you run it through a switch on the DC panel? There's no Stove switch on our panel.

This is what we'll have for a control. If properly fused (1 amp), why would it need to go through an additional switch? That seems like unecessary complexity. Can I just run power directly from the battery?
@peaman - Steven, I've found some of the wires you referenced, but need to dive further for the rest. The E35-3 wiring diagram shows a solenoid option, but as I said, ours has no panel switch for that.

Thanks,
Jeff

 

[peaman]

You might not need anything more than a fuse. It just depends on how the Trident panel works. I would guess that the panel is completely off by the OFF switch, and completely functional, with the solenoid open by the ON switch. As a point of comparison with my own controller, when the "stove" switch is on, the panel is powered, and the leak detector is enabled, but the solenoid stays closed until I press a switch on the control panel. There isn't much difference operationally between the two.

There are three "ALARM" LEDs on the Trident panel. Do you know which each is? I assume at least one will light when a leak is detected (along with the horn), but I don't know what the other two would be for. On my own controller, when it is powered on, the controller goes through an integrity check which causes each of several LEDs to light in sequence before it is ready for use. Maybe the Trident functions similarly.

For the wires on my boat, there was a pair (grey with white stripe, and black as I recall) from the DC panel to the stove, which were connected and in use with the original CNG tank, and there was another unused pair (same colors) running from the area between the CNG tank and the stove back to the area of the propane locker.

 

[vanilladuck]

You definitely want to protect the wire run from the battery to solenoid control panel, either with a fuse or a breaker. I would not wire this directly to the battery as it would then become a 24-hr unprotected load, which is a dangerous fire hazard, electrically speaking.

I'm not familiar with that control panel. Rumour didn't have a solenoid valve setup for the CNG, so when I converted to LPG I bought https://defender.com/en_us/fireboy-xintex-propane-fume-detector-with-1-sensor-and-solenoid. Wiring (gray + and black - ) were already run from the galley bulkhead to the propane locker and from the galley to the DC panel. I repurposed an unused DC breaker. Why? I wanted to be able to be 110% sure when I turned the breaker off at the DC panel there was no way the solenoid would be energized -- which would result in an open valve. Propane, heavier than air, pooling, bilge, dangerous stuff, yada yada

 

[Prairie Schooner]

@peaman
Thanks Steven. This unit has the option to hook up a total of three sniffers. The lights would tell you which zone, if hooked up, is getting gas. Maybe more useful on a 90' yacht.

@vanilladuck
Thanks Bryan. Would it make sense to run it off the other side of the battery switch? That would give me the double safety without having to take up a switch/breaker on the panel. That might be stupid for some reason. I'm a total newb on electrical stuff. Worse, perhaps, because I know a little bit.

J

 

[vanilladuck]

@peaman
Thanks Steven. This unit has the option to hook up a total of three sniffers. The lights would tell you which zone, if hooked up, is getting gas. Maybe more useful on a 90' yacht.

You could put an additional sniffer in the LPG locker to detect if the plumbing was leaking and not escaping through the locker propane drain. Might be overkill, but might be good information ¯⁠\⁠_⁠(⁠ツ⁠)⁠_⁠/⁠¯

@vanilladuck
Thanks Bryan. Would it make sense to run it off the other side of the battery switch? That would give me the double safety without having to take up a switch/breaker on the panel. That might be stupid for some reason. I'm a total newb on electrical stuff. Worse, perhaps, because I know a little bit.

J

You could take the positive lead off the battery 1-off-2 switch, but I would still put a fuse as close to that connection as reasonable. The protection provided is in case more current (amps) are drawn than the wire can handle. The fuse would blow before the wire caught fire. www.boathowto.com has some ampacity charts and tools for determining the fuse size.

DC electrical can be daunting, but there are some concepts which, once learned, can always be applied with regularity. Happy to help more if you're interested

 

[peaman]

Would it make sense to run it off the other side of the battery switch? That would give me the double safety without having to take up a switch/breaker on the panel

Agree that having it depowered with everything else is smart. Rather than connecting to the switched side of the selector switch itself, maybe better to connect to a +12V supply on the back side of the DC panel. Each breaker in each row of breakers is connected to a common 12V bus which should be easy to connect to, and it will be switched off when the selector switch goes to off, and it kind of makes sense when you revisit that wiring. It would be good to label the wire where ever you choose to connect it.

 

[Prairie Schooner]

A sniffer in the locker is a good idea. I'll run wires for it while I'm at it. I can add it later.

Contemplating potential weather damage to that sniffer brings up another question. Technically, I think the locker is supposed to be airtight. Have any of you sealed the locker up? How?
LPG is heavier than air so I should be okay. But it would sure be awkward to settle on the poop deck with an apres-sail cigar and discover the tank leaking and the drain plugged.

 

[Pete the Cat]

A sniffer in the locker is a good idea. I'll run wires for it while I'm at it. I can add it later.

Contemplating potential weather damage to that sniffer brings up another question. Technically, I think the locker is supposed to be airtight. Have any of you sealed the locker up? How?
LPG is heavier than air so I should be okay. But it would sure be awkward to settle on the poop deck with an apres-sail cigar and discover the tank leaking and the drain plugged.

I think you may have some false alarms with a sniffer in the propane locker and the lockers on neither of my boats are meant to be water tight--they depend on some flow of air downward and out of the boat to drain the locker of fumes. If you turn the physical valve on the tank off (something I think is a good practice) when it is not in use, I believe there is a small amount of gas emitted as the valve transits from open to closed--and might trigger the alarm. Also, the idea that all these systems are propane tight and emit nothing does not seem true. The ABYC testing for allows for the pressure gauge at the tank to drop (where is the gas going?) over several minutes--I forget what the standard is--some leakage is acceptable is my point. On top of that, the Trident sensors do not appear to me to be water tight. FWIW.

 

[vanilladuck]

Perhaps the phrase we're looking for is "vapor-tight" (vs air-tight). Practical Sailor has a short reference document that highlights all the important parts of a safe LPG installation: https://www.practical-sailor.com/wp-content/uploads/2020/02/0310-ABYC-OFFERS.pdf



I didn't realize the locker lid should have a gasketed seal, but that makes sense. I also wasn't aware that "leaks" in the propane locker are typical/expected.

I tested my locker by filling it with water and ensuring the water a) all drained out, b) non of it went into the bowels of the boat. I've also added this to my regular maintenance schedule: disconnected the tank, remove it, check for corrosion, test the drain with water, etc

I also tested the LPG sniffer with a butane lighter (a technique suggested in the install directions). One presses the button of a butane lighter without activating the flint while holding the lighter direction above the sniffer. The control panel should alarm and close the solenoid. I recall it taking about 45-60 seconds for the test to work, even with the lighter practically touching the top of the sniffer.

 

[Prairie Schooner]

Vapor Tight. Which is the more rigorous constraint, vapor or air tight? I wonder if 'sealed' is for lockers which are totally inside the boat. Most I have seen are boxes buried deep back in a lazarette. It seems the typical Ericson locker is a somewhat different case, being open to the cockpit only (if they include glands to seal hose and wires), kind of outside the boat. When we got our boat the propane lockers would fill with water because the drains were plugged. Since cleaned out. Routine checking is a great idea. If I leave the hole open, I'd want to make a sleeve to go over the tank to protect it from rain. I'm still not sure. It's a puzzlement.
Did you seal yours up Bryan?

 

[peaman]

Regarding open, versus sealed but drainable lockers, I think the regulations are based on the understanding that, like water, propane vapor is a fluid heavier than air. Given that, if there is a propane vapor leak, you do not want it to flow into the boat. The original Ericson propane lockers had drains. But apparently, someone figured that a blocked drain could cause an "overflow" into the cockpit, which could potentially get into the cabin. That's not likely, given the overboard cockpit drains, and the high bridge deck in most of our boats, but the regulations are intended for general application. So boats with a cockpit locker need to have a gasketed lid, whether or not they have a substantial bridge deck.

Also, note in Bryan's sketch above, the requirement for the overboard drain to be "24" minimum from hull opening to interior or engine exhaust". I could put a ruler on it, but I bet my propane locker drain outlet is less than 12 inches from my engine exhaust outlet, and it would be pretty ugly to try to fix that. We do what we can.

 

[vanilladuck]

I think @peaman's notes are pretty spot on. The key is just to ensure that any leaking propane in the LPG locker only has one place to go: directly out of the boat

Did you seal yours up Bryan?

There were a couple screw holes in my propane locker from other things that had been mounted there. I used MarineRx to seal them. I used 4200 on the fasteners for any new holes made for mounting the retaining strap. Also used 4200 and vapor tight fittings for LPG hose and wiring.

I didn't bother with adding a gasket to the lazarette lid, but that seems easy enough to add.

I have it on my list to add a locking latch to all three of my cockpit lazarette lids before going offshore.

 

[Prairie Schooner]

The challenge of getting wires from the DC panel on the port side over to the galley on the starboard has had me flummoxed. If I can accomplish that, I think I can figure out the rest of the stove wiring. I’ve identified two unused wires that make that trip.*

One is gray with white stripe, about 16 ga. It ended in a coil hanging from the stbd lazarette forward ‘ceiling’. The panel end of that was in the bundle for the breakers but not connected to anything.

The other wire is purple, about 12 ga. I’m pretty sure it is left over from when I removed the old VHF radio that was mounted just above the engine instrument panel. (In its stead we had a remote mic installed at the pedestal.) The panel end of that purple wire was connected to a common bus (?) on the aft wall of the panel cavity with a bunch of black wires.

This is the wiring ‘diagram’ from Trident.


So I need two wires from the panel area, a positive and a negative, correct? Is it okay to use asymmetrical wire gauges (16 & 12) or do they need to be the same?

The cable bundles are burdened with so many zip ties that I doubt I could use one of those wires to pull a different wire.

There’s another gray/wht that goes from a coil aft by the propane locker forward to where the power gray coil was hanging. There are no stove wires in the galley that I can see.

It’s possible there’s another unused lazarette wire in the panel bundle which I didn’t find yet.

* I managed to check continuity with my multi-meter (and jumpers) for the first time without help. I felt proud like I’d earned an EE degree from MIT.

 

[Loren Beach]

So I need two wires from the panel area, a positive and a negative, correct? Is it okay to use asymmetrical wire gauges (16 & 12) or do they need to be the same?

I believe that there just needs to be minimum gauge for the predicted max current the circuit will carry. If 16 is sufficient for one side then any gauge that is equal or larger will do for the other.

 

[Pete the Cat]

I have a different boat, but my 32-200 had a set of wires from the panel ("Stove") that went through a conduit in the TAFG to the stove area (cabinet above). I am not sure about the routing of the wires to the locker but I think these also were routed through the TAFG in a bundle that went down the starboard side of the engine and under the TAFG to the stove area. I would not rely on the original wire for any color coding. Ericson seemed to have big rolls of gray 14 for everything. You do need a ground, but --as you probably know-- you can provide ground buses according to ABYC to shorten some runs. Seems like ground buses, other than the ones in the panel, were not really in the Ericson designs as they came from the factory, but this is a way to simplify things. Not sure I am answering your direct questions.

 

[peaman]

I wrote this reply last night, but seems there was a problem with upload, so here it is…

Gray with white stripe and black is the correct color code for the LP solenoid and stove wiring according to the wiring diagram on page 5-1A in the owner's manual for the 35-3. The wire gauges are mostly illegible on that diagram. If you have a circuit with one wire of 12ga, and the other of 16ga, that circuit should not carry more current that the smaller 16ga wire is rated for. But my source says that a 16ga wire can safely carry 5A over a distance (total of positive and negative wires) of 50 feet with no more than 10% voltage drop. The LP panel with solenoid on my boat draws just less than 1A, so your 16ga wire should be okay. Check the Trident rated current requirement to be sure. The coils of wire you describe in the lazarette and near the propane locker match what I found in my boat.

"The panel end of that purple wire was connected to a common bus (?) on the aft wall of the panel cavity with a bunch of black wires."

Sounds like that common bus was for ground wires. I started with a rat's nest of wiring including a great number of black wires at my DC panel. I ended up installing a couple of ground strips (or buses?) where I connected all of the grounds which greatly cleaned up the space. The aforementioned wiring diagram calls for a purple wire for the pressure water pump, with a black ground.

It appears to me that you should identify a suitable location, probably on the back of your DC panel, to connect a fuse to a 12V source, perhaps the same point that feeds all of the breakers. To that fuse, connect your grey/white wire which should then extend to the area of your Trident control. You can install a new toggle switch, or push button so that the Trident may be switched on and off. The black wire corresponding to that grey/white should connect to a ground, perhaps to a common ground bus. The other Grey/white + black pair should connect the solenoid in the propane locker with the Trident panel.

On a somewhat related electrical matter, I think that your new-to-you stove is a Force 10? If it is like mine, the stove does not require an outside electrical supply, but the igniter does rely on a small battery located in the most difficult to reach location on the bottom of the stove. Save this piece of info for when the other work is in place.

 

[Prairie Schooner]

@Pete the Cat - Ray, the sole is still out so I checked today and nada on wires through the bilge/TAFG.
This photo shows the old common bar (bus?) in our boat to which the 12 ga purple wire was attached. There are at least 4 purple wires, and they're a very dark purple. There are also black lines attached to this bar. Maybe they had lots of dark purple 12 ga in 1986 and used that as black. Mabye by 1989 they got a deal on a palette of gray 14.


I'm convinced the wiring diagram is like the Pirates Code:

It's a useful starting point, but . . .

@peaman - Steven, there is one true purple colored wire and it is connected to the water pressure breaker. Thanks for the wire load data. The instructions call for a 1a fuse so I don't think the whole system draws much. With my new found multi-meter confidence I'll check the voltage at the solenoid when installed.
The electronics folks put a fuse panel in when they installed the the radio, AIS, and chartplotter.

There are two empty slots, but I don't know how many they will need for the radar. I can always install another or put an inline fuse in. I wish they'd installed a bigger one.
If the Trident control has an on/off button, it seems redundant to have an additional switch. By pulling power out of the panel area I will already disable the LPG controls when the battery switch is off. Is there a compelling reason for adding an additional switch?
Yes, our stove is a three burner Force 10. Thanks for the heads up on the stove battery.

@Loren Beach - I checked with an EE friend today and he confirmed there shouldn't be a safety problem using one wire bigger than the other as long as the smallest one still is adequate for the circuit's needs. He said it may not be strictly kosher for ABYC standards. As Steven said, "We do what we can." I'll be sure and label them. I can't find any guidance on what color the gas wiring should be so I'm using brown and will label them at both ends.

I think I have a clear path forward with wiring now. Thanks guys.

 

[Prairie Schooner]

I think @peaman's notes are pretty spot on. The key is just to ensure that any leaking propane in the LPG locker only has one place to go: directly out of the boat

There were a couple screw holes in my propane locker from other things that had been mounted there. I used MarineRx to seal them. I used 4200 on the fasteners for any new holes made for mounting the retaining strap. Also used 4200 and vapor tight fittings for LPG hose and wiring.

I didn't bother with adding a gasket to the lazarette lid, but that seems easy enough to add.

I have it on my list to add a locking latch to all three of my cockpit lazarette lids before going offshore.

Bryan,
Does your locker lid have a hole in it like this?

Even though a leak and overflow is unlikely, there is an opening portlight at the foot of the quarter berth which opens to the cockpit deck. I'm thinking about plugging those lid holes with something like this:

It should keep some of the rain out too. With turning off the valve and routine drain checks, I'll be able to smoke the occasional stogie with a little more peace of mind.
J