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Discussion Starter #21
I'm interested to hear of your findings. I'm in the purchase process of a boat with CNG tanks and I'm not all that familiar with CNG. I do have a CNG fill station (for cars and trucks) near me so I'm exploring the adapter route.
One issue may be having a currently certified tank is a requirement of the filling stations. I think certifications were typically marked on the tank some how. It wasn’t an issue when tanks were just exchanged. I’ll probably look for a source for a new tank.
 

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I found a local welding gas operation that said they could do the recertification of my CNG tank. It would be shipped from my location in CT to MA for the hydro test, with pickup twice a week. They haven’t got back on an adapter for filling the tank, but I did get a confirmation from Airgas in Providence that their location at the former Corp Brothers site would fill my tank without my providing an adapter.

This is not as convenient as an exchange, but the hydro test is good for several years (5 years, I think). The Providence Airgas location is probably about 50 minutes away, which is not that convenient, either, but I have gotten more than one season from a tank and I carry 2 tanks. I added a second tank many years ago, because CNG exchanges were not always convenient, either, when they were available. With 2 tanks, I never ran out in more than 20 years.
 

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Sounds great. We don’t exchange propane bottles, but get them refilled. Most sailboats have to do the same as we don’t use/ fit standard BBQ home grill bottle sizes/ shapes.
 

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I'm in the Annapolis area and I decided to give the CNG refill adapter from Circleville CNG (on eBay) a try based on the reviews. It's great, I can fill a tank for about $2. The regulator has a valve that lets you throttle and fill from a 3600 psi (for fleet busses and such) system down to the 2200 psi our tanks are rated for.

DC area fill: Washington Gas, operated by Trillium, 7685 Penn Belt Dr, Forestville, MD 20747

Adapter:

How to video:
 

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Xintex and Trident both make a combination propane alarm and solenoid system. Control mounted at the stove, push a button and the gas gets turned on at the tank. If the system detects a leak, the alarm sounds and gas shuts off automatically. Has two sensors, mount one in the bilge high enough so it won't get wet, the other under the stove or near the tank locker. Propane is heavier than air so it can collect in the bilge, and it's more explosive than gasoline.
 

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Control mounted at the stove, push a button and the gas gets turned on at the tank.
I’ve seen these often mounted near the stove, for the convenience of turning the gas on/off for normal use. I propose that this cutoff switch should not be adjacent to the potential fire, where one might need to exit quickly and still want to shut off the gas. My cutoff is directly across the cabin, from the galley. I always extinguish the stove, with that switch, to confirm it works. Then I close the stove knob in the galley.
 

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A 5-pound propane tank which takes up an 8" X 12" space, holds 107,955 BTUs.

Regular (not the longer-larger volume tanks) CNG tanks yield a "20-hour burn"; which they rate using a 4,000 BTU burner running for 20 hours(perfect world - in reality, I bet all fills vary of any gas).

An apples to apples comparison shows the LPG 5pounder will yield nearly a 27-hour burn.

Two LPG 5 pounders should yield 54-hour burns which means nearly equivalent to 3 CNG tanks. These days, with two onboard for more than a month, we'll use 2 CNG tanks for the season.

10 pounds of LPG will be more than ample. Why go to a bigger tank?

Further, the volume for the two LPG tanks, if you have to build a locker, will need a vented locker about 10" X 17" X 13". Compared to my two side by side CNG tanks in a rack that is about 12" X 20" X 24".

The little tanks will be easier to haul weighing about 10+ pounds full compared to CNG tanks weighing,... 40 pounds?
I use those 1 gallon (5 lb) propane tanks. It's what fits in my two small aft vented lockers. When I bought the boat 11 years ago, I was concerned about the small size and lack of a spare if I ran out when cruising. Considered an adapter for the 1 lb cylinders, but decided on a second 1 gallon tank as a spare. I find a single tank will easily get me through a season with maybe 20 to 25 nights spent onboard overnight. Costs $10 to refill a tank.
 

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I found a local welding gas operation that said they could do the recertification of my CNG tank. It would be shipped from my location in CT to MA for the hydro test, with pickup twice a week. They haven’t got back on an adapter for filling the tank, but I did get a confirmation from Airgas in Providence that their location at the former Corp Brothers site would fill my tank without my providing an adapter.

This is not as convenient as an exchange, but the hydro test is good for several years (5 years, I think). The Providence Airgas location is probably about 50 minutes away, which is not that convenient, either, but I have gotten more than one season from a tank and I carry 2 tanks. I added a second tank many years ago, because CNG exchanges were not always convenient, either, when they were available. With 2 tanks, I never ran out in more than 20 years.
I have 1 or 2 CNG tanks that need to get tested and certified. Can you share the contact info for the place it MA you found? If certifying my existing tanks doesn't work out I'm looking to pickup either newer used tanks or new tanks. I also purchased the CNG refill adapter from Circleville CNG (on eBay) that Reefpoints mentioned in previous post.
 

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Discussion Starter #30
Fallard thanks for the lead on MaineOxy.

Looks like MaineOxy has many locations in New England. Just called their Rockland ME location. Was told I could drop off a tank at their Rockland location and they would take it to their Auburn ME location for refill and recertification if necessary. Might take a week or so to truck down and back. About $84 + tax for a refill.
 
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