CNG Tank & Refill Question

[NewToTheRoad]

I have read through a number of posts regarding CNG and venting.  From what I see from Stu and others is that only the regulator needs to be vented.  However, when my boat was surveyed in late 2016 the surveyor stated the following (see below).  Was this incorrect?  Does this not apply because the attached capacity is not greater than 100 cubic feet?  I am assuming that the attached capacity means that of the tanks holding the CNG ????  If that assumption is correct then it would be odd that the surveyor didn't realize that.

I just want to make sure that I get it right.

Thanks,
  Bryan


Location: Under berth/seat in aft cabin (dedicated locker).
Regulator: Yes.
Pressure gauge: Yes.
Shut off valve: Manual at tank.
Ventilation: Into cabin.
ABYC A-22, MARINE COMPRESSED NATURAL GAS (CNG) SYSTEMS requires: "For CNG installations that
include an attached combined capacity of greater than 100 cubic feet (2.8 cubic meters), the cylinders,
and connected valves, regulating equipment, and safety devices shall be located on the exterior of the
boat where escaping gases can flow directly into the atmosphere outside the boat, or the cylinders and
connected devices shall be installed in a dedicated locker. Dedicated lockers shall be vapor tight to the
hull interior, and vented to the open atmosphere outside the boat, and constructed of or lined with
corrosion resistant materials, and equipped with a means to discharge incidental accumulated water.
Dedicated lockers shall be equipped with a cover that opens directly to the atmosphere, and latches
tightly, and is capable of being quickly and conveniently opened without tools, and for operating the
cylinder valves, testing the system for leakage, and viewing the pressure gauge."
Recommend CNG locker comply with ABYC A-22 requirements.

[Stu Jackson]

Bryan,

I clearly remember having a looong discussion about this, but it was most likely on another boating forum.  I checked quickly on sbo.com with a search on CNG capacity and my name.  While it didn't find that particular discussion, I did find this:

Here are the specs. on the CNG tank. 2200# psig @70 deg. when full, Capacity is 84 CF which is 100,000 BTU's. Remaining time on tank is Gauge Reading/110 Each tank holds about 20 hours on one burner.

Frank found it by finding a CNG tank supplier on the internet and pasted the specs.  You could do that, too.

My surveyor found nothing wrong with our "standard" installation in the aft cabin.

Your surveyor may have been right, but your tank is below the trigger for what he's suggesting be done.  You simply have to read it properly.      Under 100 you're just fine,he's covering his tush. 

I'll see if I can find that longer discussion, but it might take some time and I'm off on a cruise this afternoon (finally!!!).

[Stu Jackson]

Bryan, I couldn't leave you hanging. 

Here it is, read it all. 

https://forums.sailboatowners.com/index.php?threads/cng-refilling.168890/&highlight=cng%20tank%20capacity

[NewToTheRoad]

As usual you always come thru Stu.  Thanks!

Glad that you could get out on it.  Mine splashed yesterday, but then there's work to get in the way......

Bryan