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Old 19-10-2014, 11:39   #1
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CNG in a Sealed, Vented Locker

In the August, 2014 BoatUS magazine, a writer asked about CNG on a boat he was looking to buy, and was wondering if he needed a sealed locker.

The response was technically accurate, but highly misleading and very unnerving for any of us that use CNG (and probably soured the deal for the reader).

The response stated that CNG must be in a sealed locker if the capacity is over 100CF, and the insurance company may well enforce that requirement. An accurate statement, for sure.

The problem is that 99.99% of CNG tanks out there, the standard white SCUBA size tanks that are available for exchange, are about 73CF.

Bottom line, contrary to what the BoatUS article implies, or CNG lockers are compliant without being sealed and vented.

I hate misleading and inflammatory "news" stories....
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Old 19-10-2014, 11:58   #2
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Re: CNG in a sealed, vented locker

You might write the editor informing him/ her of the disservice the author has done and suggest that, in a future edition, they post a clarification if they really want to serve of value to their subscribers.

The problem is ubiquitous as we often read here in this forum when people write opinion as fact or perpetuate bad info by repeating it simply because some jerk wrote a book or claimed some non-existent expertise.
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Old 19-10-2014, 15:25   #3
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Re: CNG in a sealed, vented locker

Just curious: how can a locker be both vented and sealed?

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Old 19-10-2014, 16:23   #4
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Quote:
Originally Posted by Jim Cate View Post
Just curious: how can a locker be both vented and sealed?

Jim
CNG being heavy, Will settle in the bilge if not vented via hose to the outside. The hatch may be watertight yet not airtight. Best interpretation is, a bowl to catch leaking CNG and plumbing to vent that CNG from the bottom of that bowl to overboard.
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Old 19-10-2014, 16:38   #5
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Re: CNG in a sealed, vented locker

I thought CNG (methane) was lighter than air and would dissipate in air, unlike LPG (propane ) which is heavier than air and will sink to the low point waiting for a spark.
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Old 19-10-2014, 17:42   #6
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Re: CNG in a sealed, vented locker

CNG is lighter than air. That is why it is promoted as safer than propane. At normal temperatures it has to be stored at high pressures in heavy tanks.

Large quantities of propane can be stored in light tanks because it turns into a liquid at low pressures and normal temperatures.
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Old 19-10-2014, 17:51   #7
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Re: CNG in a sealed, vented locker

Quote:
Originally Posted by lonesoldier0408 View Post
CNG being heavy, Will settle in the bilge if not vented via hose to the outside. The hatch may be watertight yet not airtight. Best interpretation is, a bowl to catch leaking CNG and plumbing to vent that CNG from the bottom of that bowl to overboard.
You are confusing CNG with LPG. CNG, when out of the cylinder, is lighter than air and will dissipate if it leaks. The only danger is to have a spark or other source of ignition right next to it at the time of a massive leak. And unlike LPG it does not accumulate in the bilge. Therefore CNG is much safer than LPG most of the time. And this is the main reason I'm not converting for now from CNG as it is plentiful, although not cheap, where I am based.
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Old 19-10-2014, 17:55   #8
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Re: CNG in a sealed, vented locker

HopCar is right. Man, there are sooooooooo many CNG vs Propane discussions, it is remarkable.

There was a thread just yesterday on another boating forum where someone suggested he was considering switching from propane to CNG even though he already had a legal propane system. Weirdos strike again. I guess it's OK, though, it's boating, right?

The ONLY thing one should do is to vent the CNG regulator overboard. There is a connection to do so right on the regulators. Most folks don't.
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Old 19-10-2014, 20:05   #9
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Re: CNG in a sealed, vented locker

Quote:
Originally Posted by sailingharry View Post
----
The response stated that CNG must be in a sealed locker if the capacity is over 100CF, and the insurance company may well enforce that requirement. An accurate statement, for sure.

The problem is that 99.99% of CNG tanks out there, the standard white SCUBA size tanks that are available for exchange, are about 73CF.

Bottom line, contrary to what the BoatUS article implies, or CNG lockers are compliant without being sealed and vented.
I wonder if the "capacity" refers to the total of CNG aboard, rather than one tank. Most cruisers I know carry two tanks of their fuel of choice to prevent running out in remote locations.
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Old 19-10-2014, 20:18   #10
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Re: CNG in a sealed, vented locker

Quote:
Originally Posted by FSMike View Post
I wonder if the "capacity" refers to the total of CNG aboard, rather than one tank. Most cruisers I know carry two tanks of their fuel of choice to prevent running out in remote locations.
ABYC A22.7.4.7 says "attached combined capacity of greater than 100 cubic feet" ... "shall be located on the exterior of the boat where escaping gases can flow directly into the atmosphere outside the boat, or

22.7.4.7.1 "the cylinders and connected devices hsall be installed in a dedicated locker"

If you have less than 100 CF in cylinders "attached" to the system, you are ok with

A22.7.4.6: "For CNG installations that include cylinders with an attached combined capacity of 100 cubic feet or less, cylinders, cylinder valves, regulating equipment, and safety devices shall be:

22.7.4.6.1 readily accessible, secured for sea conditions, and protected from the weather and against mechanical damage" and there are a couple of other more stringent options listed, as well.

The above is from the July 2014/2015 edition of the ABYC Standards.
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Old 19-10-2014, 20:21   #11
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Re: CNG in a sealed, vented locker

From the source (at least in the US):

Quote:
22.12.1 CNG systems with connected capacity greater than 100 cubic feet shall provide for storage lockers (see A-22.13S2).
Quote:
22.13.5 If the CNG installation includes attached cylinders of greater than 2.8 cubic meters (100 cubic feet) combined capacity, the cylinders shall be:

22.13.5.1 located on the exterior of the boat where escaping gases can directly escape into the open air, or

22.13.5.2 installed in a locker which shall be:
a. vapor tight to the hull interior,
b. vented to the open atmosphere outside the boat,
c. constructed of or lined with corrosion resistant materials,
d. equipped with a means to discharge incidental accumulated water,
e. equipped with a cover which
i. opens directly to the atmosphere,
ii. latches tightly,
111. 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.
Both of those seem to indicate that it is only the capacity of "connected" or "attached" cylinders that is counted, although there is no definition of either term in the document. And or course, to my mind conflicts with:

Quote:
22.13.3 Storage provisions for unconnected reserve cylinders, filled or empty, shall be the same as the provisions for the cylinder in use.
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Old 19-10-2014, 20:30   #12
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Re: CNG in a sealed, vented locker

[QUOTE=Dsanduril;1658271]From the source (at least in the US):

You are quoting an old version of the standard. A-22 doesn't even go up to 13 anymore. Be careful getting the standards from the Internet. They are updated frequently. A-22 was last updated in 2012.
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Old 19-10-2014, 21:34   #13
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Re: CNG in a sealed, vented locker

Quote:
Originally Posted by Cuttyhunk View Post
You are quoting an old version of the standard. A-22 doesn't even go up to 13 anymore. Be careful getting the standards from the Internet. They are updated frequently. A-22 was last updated in 2012.
Not according to the ABYC themselves:

Standards Index - American Boat and Yacht Council

Scroll down and you'll see that they say 2012 is still the "current version". 2014/15 has not made it through legislation yet.

Minor point, as either way the text in question is pretty much identical, just a matter of numbering.
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Old 19-10-2014, 23:35   #14
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Re: CNG in a sealed, vented locker

Thanks to all those correcting my confusion on CNG and LPG.
Again, it must be sealed off from the interior of the vessel and vented overboard to dissipate. CNG above ignition sources and LPG below ignition sources. :thumbup:
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Old 01-11-2014, 15:29   #15
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Re: CNG in a sealed, vented locker

I got away from the internet a bit, and missed all the responses. Just read them, and have two comments.

With regard to Jim Cate's comment about "both vented and sealed," I'll admit my guilt. I should have said "sealed from the interior of the hull, and vented to the outside atmosphere." I hope that anyone who is struggling with fuel storage issues immediately understood the intent of my note. Regardless, I thank you for clearing this up for anyone not familiar with tank storage issues.

With regard to S/v Illusion's comment that I contact the author, I actually did. Her response was disappointing, as she made some sort of comment about "word limited column sizes" and seemed indifferent to the fact that her article was "accurate" but very misleading -- and in particular, left the person who asked the question with the wrong understanding.

Interesting, in the most recent BoatUS mag, she stated that a longer waterline boat, that increases hull speed from 7 to 8 (or so, I forget) allows a day sail to increase from 25 to 35 miles. Wow, a 15% increase in speed allows a 40% increase in distance? The standards for "Technical Editor" don't include "technical expertise."

Harry
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