CNG (Compressed Natural Gas) System Example

[GuerrillaCamper]

Image of Marine safety valve in propane locker.
Solid copper line (right side) goes to stove.
Black hose goes to regulated tank.

[Hoodsail]

SrHaas: I have CNG too and works great....havent tried to refill tank yet tho, but love that methane is lighter than air so no potential for accumulation in the bilge (secondary to a leak) and no need for dedicated compartment for my tank that is secured in the top of my starboard cockpit lazarette...Pics attached arent that great, but may help you...my tank is about 37 inches in length. thnks

[tstano]

I’ve been using this for 10 years and have found more stations available on the east coast that are at the higher pressure. Talk with a gas company near you. If I had to upgrade, I’d do it. For now we’re using Tom at Virginia Gas. He has been very helpful.

[srhaas]

Thank you everyone for the responses! I think I am in a good place. Really appreciate the help

[oleman]

CNG is basically handled like propane and butane but the pressures are considerably greater. I have seen numerous transit authority vehicles at commercial auctions BUT being a non-diesel or gasoline powered is a downer of bids. They sell so cheaply that I have considered a used vehicle but can't make it work for everyday use. The commercial consensus is that outside of the transit district there is the junkyard, I expect all electric transit vehicles will go the same way.

[Moxie 38]

Brewgyver's post above is the most important comment you will read in this thread. CNG tanks are filled at 3-3.5 K psi. CNG stoves receive gas at between 8 and 12 millibars which is less than 1 psi. This CNG pressure regulator MUST be either a single two stage type regulator to reduce the 3000 - 3500 psi fill pressure to a workable 8-10 millibars or two separate regulators in succession with the high pressure vented regulator first in line followed by a low pressure regulator immediately down stream.

Appropriate pressure gauges - one at the tank head and a second, low pressure gauge downstream of the first regulator are required.

You should be sure that your stove has the appropriate orifices (not burners) for CNG use. The CNG gas line MUST be co-extruded pressure rated and of appropriate ID - typically 3/8" such as Parker, and fitted at both ends with code approved threaded fittings - not barbed!

Other than that, if you are not familiar with CNG systems and normally accepted gas plumbing practices, I would strongly recommend having this system installed and calibrated professionally. You will be happy and a whole lot safer if you do.

[patrick brooks]

I have a cng stove, I found changing refill station closing, bottle swaps being discontinued,... so I began using CL and people converting there systems to propane, and bought tanks, and regulators one stove for parts. I found I will be able to get tanks recertified at local dive shop. I have been considering purchasing filling adapter from ebay, allowing self refill at vehicle station. jury out on the 100$ for adapter. people selling cng stock all said they looked into convertion to propane and could convert stove top but not oven, so opt to sell or give away I accumulated several full bottles which will delay my decision. fair winds

[Island Time O25]

Been using CNG for the past 10 years. The system was original on 1980 Mariner 36. No problem finding exchange refills locally. Not cheap compared to swapping LP tanks but IMO my life is somewhat more valuable than the savings of using LP onboard.

Our boat came with 2 tanks, 27# and 36#. Plus I bought 2 additional 36#s at a marine charity yard sale for a few dollars. I got them for when I finally get to cruise. Just bring the old empties to a large CNG distributor and that's that.

Since then I learned that pretty much every midsize city and larger has a CNG depot of some sorts as many urban fleets are now CNG. Some re-fill for few dollars, provided the tanks are withing certification due dates. Other just exchange, regardless of expiration dates.

With my seasonal weekends aboard use a full 36# lasts between 1 and 1.5 seasons. I figured that my 4 tanks should be good for about a year liveaboard with judicial use of stove top pressure cookers, electric coffee pot heaters, etc. Certainly enough time to find a re-fill or exchange place.

One caveat to CNG beginners. Make sure that the place you're getting your exchanges fills the tank to at least 2,500-2,800psi. Some tanks are filled to as low as 2,000-2,200 or even 1,500-1,800. At one place I had to go through 3 or 4 tanks to get to around 2,500. Good thing it was not the yard owner or manager but some "boatyard guy" who wasn't looking to cheap out on me. At 1,500 you're getting about 1/2 tankful.

[srhaas]

Hi! Does your regulator have a venting hose or is it capped?

[kmacdonald]

Most boat CNG tanks are 2200 psi tanks. They are still available. Newer 3600 psi tanks are the way to go if installing a new system. More energy dense. It will require a different regulator than the 2200 psi systems used. An adapter can be made to fill the tanks yourself. It will cost about $150.00 in parts. A 37 inch high tank costs a $1.50 to fill.

[kmacdonald]

Originally Posted by srhaas

Hi! Does your regulator have a venting hose or is it capped?

It should never be capped.

[srhaas]

So should I have a vented hose? I got the regulator used and it had a 3-4 inch hose attached to the vent, but the hose was cut. Thinking I should get a hose to extend into the cockpit, but not sure.

[kmacdonald]

FYI: It takes five 2200 psi, 37" tall, 100cf size dive tanks to equal the energy in a 20 lb propane tank. Its stored as a gas and not a liquid like propane so is not nearly as energy dense. Thats why it's not still widely in use.

[kmacdonald]

Originally Posted by srhaas

So should I have a vented hose? I got the regulator used and it had a 3-4 inch hose attached to the vent, but the hose was cut. Thinking I should get a hose to extend into the cockpit, but not sure.

Yes. That's what you need to do.

[Bill Seal]

Hoodsail,

Restraining a 35# tank of 3000psi explosive gas, using only hose clamps, doesn't seem too safe an installation.