Join Date: Nov 2009
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I have CNG on my boat and added a second tank after running out on a cruise and finding the cruising guide was out of date on where I could get an exchange. Despite the inconvenience, I would not switch to propane, which is heavier than air and can settle in your bilge if you have a leak inside the boat. I may eat my words if ever I go on an extended cruise where I can't get CNG!
I picked up my second tank at a used gear chandlery in Newport, RI about a dozen years ago and it came with a cradle for mounting. This place had 2 tank sizes. the more popular size is the same size as an 80 cu ft scuba tank. the other tank size wouldn't fit in my locker and would have been a problem with the exchange locally. I'd make sure of the size before you picked up another tank.
BTW, the advantage of an exchange is that the CNG supplier handles the tank certification, so your exchange fee includes more than the gas. I would be leary of converting a scuba tank unless you know what you are doing. If you have your tank refilled (which I did in '96 at Fort Pierce) you can bet your tank will be checked by a legitimate supplier or they won't fill it. If you need good advice on CNG, I'd check with Corp Brothers in Providence, RI. I had them provide me with a new regulator several years ago. They aren't cheap, but they know what they are doing.