CNG Refilling

[Rick D]

I Appreciate The Information & Time Taken

I see the CNG requirement is now basically the same as LPG except for the cut off.

OK, standards change. I get that. I'll just make an observation. We have no representation in the formation of those standards. By we, I mean the boaters. We have no representation at the underwriter's desk either.

The surveyor documents exceptions to ABYC standards (regardless of when they were effective). To not do so would be to open themselves to liability. To use individual judgement instead of ABYC rules would further invite liability. By using ABYC standards, the surveyor can duck behind another wall with respect to liability.

The insurer's underwriter will be subject to review if there is a serious loss on the vessel. That underwriter likely has only a cursory knowledge of boat construction, standards, etc. Therefore, the underwriter relies on the surveyor's report and will not issue a policy until issues are "rectified". If you are the underwriter, who's opinion will you accept: a whining boat owner faced with an expense or a knowledgeable professional listing exceptions based upon published industry standards?

So, at the end of the day, the surveyor gets work and a liability shield, the underwriter gets a clean file review, the marine mechanics get work, parts manufactures get to sell stuff and the boat owner gets to cough up thousands of dollars and have the boat hacked up to no better end.

Rant over. I sincerely appreciate the information and the manner in which it was offered. It isn't personal. I just also happen to be extremely annoyed at US Sailing's equipment "recommendations" at the moment which is resulting in some parallel tracking to this. It spilled over into this subject. :cussing:

 

[Stu Jackson]

CNG Cylinder Volume

Thanks, fa102. Do you happen to know what the standard CNG tank capacity is?

Let's try this: let's say the standard cylinder is 2 feet in diameter and four feet long. That's about the size of the standard cylinders I have onboard, actually slightly larger for this exercise.

From my Engineer's Companion (July 1979), the VOLUME of a cylinder =

[PI * radius>squared divided by 2] times the height (length)

3.14 * (1) squared divided by 2 times 4 = 6.28 cubic feet.

My conclusion is that the volume of the standard cylinders is WAY LESS than the 100 cubic feet which seems to preclude the need for a dedicated, sealed, vented locker.

Please, again, help me out here. If this is true, and even if I'm off by a factor of THREE, the standard tanks we use do not "qualify" for this deficiency notice and the reference to this standard appears to be meaningless unless specific to a particular installation that has other issues.

Reference to the standard during a survey which could imply insurability issues seems over-the-top to me.

Comments?

Thanks again.

Fortunately the actuarial odds usually are in our favor (until there not).Discussions with insurance underwriters (regarding recent surveys) indicated that they do not
"grandfather" systems like CNG or LPG. There is no pleasure in delivering negative survey findings.

Dedicated locker is required when tank capacity is >100cu ft. There are separate standards for devices using cylinders <16oz.
22.7.4.7 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
22.7.4.7.1 the cylinders and connected devices shall be installed in a dedicated locker.
22.7.4.7.1.1 Dedicated lockers shall be vapor tight to the hull interior, and
22.7.4.7.1.1.1 vented to the open atmosphere outside the boat, and
22.7.4.7.1.1.2 constructed of or lined with corrosion resistant materials, and
22.7.4.7.1.1.3 equipped with a means to discharge incidental accumulated water.
22.7.4.7.1.2 Dedicated lockers shall be equipped with a cover that
22.7.4.7.1.2.1 opens directly to the atmosphere, and
22.7.4.7.1.2.2 latches tightly, and
22.7.4.7.1.2.3 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.

I provide my survey clients with the text of the ABYC standard relevant to the survey discovered deficiency.

FYI ABYC membership starts now at $255.00 per year.

 

[Johann]

Pretty sure the CF capacity for CNG is the volume measured at standard pressure and temperature, not its compressed volume.

 

[Stu Jackson]

CNG volume

Pretty sure the CF capacity for CNG is the volume measured at standard pressure and temperature, not its compressed volume.

Excuse me, but that makes absolutely no sense, and is not discussed in the ABYC reference so kindly hared by fA102.

Do you have anything to support this?

 

[Johann]

Excuse me, but that makes absolutely no sense, and is not discussed in the ABYC reference so kindly hared by fA102.

Do you have anything to support this?

You measured tank volume. Usually measured as gallons of water the tank would hold. Gas volume capacity is the volume of the gas the tank can hold at its rated pressure, if that mass of gas was at standard temp and pressure (15C/14.7psi).

I will try to find a reference for you...

 

[fa102]

Thanks, fa102. Do you happen to know what the standard CNG tank capacity is?

Let's try this: let's say the standard cylinder is 2 feet in diameter and four feet long. That's about the size of the standard cylinders I have onboard, actually slightly larger for this exercise.

From my Engineer's Companion (July 1979), the VOLUME of a cylinder =

[PI * radius>squared divided by 2] times the height (length)

3.14 * (1) squared divided by 2 times 4 = 6.28 cubic feet.

My conclusion is that the volume of the standard cylinders is WAY LESS than the 100 cubic feet which seems to preclude the need for a dedicated, sealed, vented locker.

Please, again, help me out here. If this is true, and even if I'm off by a factor of THREE, the standard tanks we use do not "qualify" for this deficiency notice and the reference to this standard appears to be meaningless unless specific to a particular installation that has other issues.

Reference to the standard during a survey which could imply insurability issues seems over-the-top to me.

Comments?

Thanks again.

Tank size is one criteria regarding installation compliance. I hate to be didactic but note that the standard provides:
22.6.1 All electrical sources of ignition located in a compartment containing CNG appliances, cylinders, fittings,valves, or regulators shall be ignition protected, and
22.6.1.1 have all potential electrical sources of ignition located in the compartment ignition protected and so marked (for example “SAE J1171 Marine”, “UL 1500 Ignition Protected”, or “Ignition Protected”), when located within 40 inches (one meter) of, or located above the level of any CNG appliance, storage cylinder, fittings, valves or theregulator. If the potential leakage source is high pressure (the storage cylinder or associated fittings) the potential
ignition source shall not be within 40 inches (one meter) in any direction, and
22.6.1.2 have no open flame devices, or devices or equipment capable of emitting sparks, and
22.6.1.3 have no exhaust pipes or heat producing devices capable of producing a temperature in excess of 300˚F (149˚C).

A factor often overlooked is that: Diesel engine powered vessels are not required to have
Ignition Protected electrical devices: Therefor any DC or AC electric device in the vicinity of the CNG tank / device presents a hazard if they are not (as are diesel engine starters, alternators, solenoids etc) ignition protected.

Another potential problem (overlooked) is rusted portable small size butane / LPG canisters laying - rolling around in a bilge / engine space / locker. Don't want to be difficult but why rely on the law of averages to stay safe.

 

[Steverhnm]

as I noted in an earlier post, a properly filled CNG tank of the original era that Hunter installed them was a 72 Cubic Foot SCUBA tank (at 2250 PSIG) with a specialized Gas valve on it. That is 72 CF of Compressed Gas. It does have a tag making it specific for CNG.

What concerns me most on this is the question if the tanks people have are getting Hydrostatic tested on a regular basis (your local SCUBA shop can do that for you) and that people do not overfill their tanks. Unless explicitly stamped on the bottle, those tanks are only good for 2250 PSIG. If you do not regulate the pressure of your fill, you are asking for deadly trouble. Also, I do not think the stock regulator is rated for anything > 3000 PSIG, therefore even if you had a 3000 PSIG tank, your regulator will be under-rated, as it should be 133% > the max system pressure. That is mostly due to temperature changes which greatly affect gas volume.

Actually, I think my Hunter installation would pass with one modification. I might increase the size of the vent (yes, mine has a vent!!) and some gap insulation on the little covers (maybe "vapor snug". But otherwise, I am very happy with it and would not go to LPG if I can help it. Great thread....

 

[Steverhnm]

Pretty sure the CF capacity for CNG is the volume measured at standard pressure and temperature, not its compressed volume.

Can't imagine they would not see it as volume of compressed gas, as that is what it will be when it fills your cabin.

 

[Johann]

Can't imagine they would not see it as volume of compressed gas, as that is what it will be when it fills your cabin.

I think we are saying the same thing. But it is uncompressed when it fills your cabin.

I am assuming that since SCUBA tanks are rated by CF volume of uncompressed air, that CNG tanks would be the same. Can't find support other than CNG tank specs that show CF volume as tank volume x tank pressure.

 

[Stu Jackson]

Thanks, again. didactic ? Not at all. Again, I'm simply trying to make sense of "deficiencies" which could be related to my installation, which is quite common on boats of its vintage and size.

The engine is in its own compartment, the tank is in the aft cabin in its own compartment under one of the settees with nothing else in it.

...but why rely on the law of averages to stay safe...

Couldn't agree more. Just trying to find places where I do not comply, and, except for the regulator vent I mentioned earlier, I can't find one, as hard as I try.

Tank size is one criteria regarding installation compliance. I hate to be didactic but note that the standard provides:
22.6.1 All electrical sources of ignition located in a compartment containing CNG appliances, cylinders, fittings,valves, or regulators shall be ignition protected, and
22.6.1.1 have all potential electrical sources of ignition located in the compartment ignition protected and so marked (for example “SAE J1171 Marine”, “UL 1500 Ignition Protected”, or “Ignition Protected”), when located within 40 inches (one meter) of, or located above the level of any CNG appliance, storage cylinder, fittings, valves or theregulator. If the potential leakage source is high pressure (the storage cylinder or associated fittings) the potential
ignition source shall not be within 40 inches (one meter) in any direction, and
22.6.1.2 have no open flame devices, or devices or equipment capable of emitting sparks, and
22.6.1.3 have no exhaust pipes or heat producing devices capable of producing a temperature in excess of 300˚F (149˚C).

A factor often overlooked is that: Diesel engine powered vessels are not required to have
Ignition Protected electrical devices: Therefor any DC or AC electric device in the vicinity of the CNG tank / device presents a hazard if they are not (as are diesel engine starters, alternators, solenoids etc) ignition protected.

Another potential problem (overlooked) is rusted portable small size butane / LPG canisters laying - rolling around in a bilge / engine space / locker. Don't want to be difficult but why rely on the law of averages to stay safe.

 

[fa102]

To be safe look to see that: 1) tank compartment is vented to the outside. 2) the tank compartment space does not communicate / have an opening (of any size) int a space with an engine / non ignition protected device or flame device. 3) lines to the appliance are neatly routed - secure - protected from chafe and all the rest of the criteria in A-22 along with your evident good sense.

The real problem with these "survey found deficient system installations" is that: the ABYC standards are not available with out a $255 membership; marine equipment manufacturers and retailers sell components often lacking the details of the relevant Federal Requirements (CFRs) or ABYC "STANDARDS AND TECHNICAL INFORMATION REPORTS FOR SMALL CRAFT" (which admittedly can be obtuse & obscure); which results in those survey discovered non compliant installations (by a boat owners or marine technician).

 

[Stu Jackson]

CNG Muster

OK, that's clear and I can do that.

I understand paragraph 2, also.

Again, thanks for staying with me on this one.

Much appreciated.

To be safe look to see that: 1) tank compartment is vented to the outside. 2) the tank compartment space does not communicate / have an opening (of any size) int a space with an engine / non ignition protected device or flame device. 3) lines to the appliance are neatly routed - secure - protected from chafe and all the rest of the criteria in A-22 along with your evident good sense.

The real problem with these "survey found deficient system installations" is that: the ABYC standards are not available with out a $255 membership; marine equipment manufacturers and retailers sell components often lacking the details of the relevant Federal Requirements (CFRs) or ABYC "STANDARDS AND TECHNICAL INFORMATION REPORTS FOR SMALL CRAFT" (which admittedly can be obtuse & obscure); which results in those survey discovered non compliant installations (by a boat owners or marine technician).

 

[Benny17441]

If the new regulations require a CNG tank to be kept in an airtight locker vented to the outside I would like for someone to explain to me how does the leaked gas evacuates from the locker. CNG does not flow, like water, like LPG does so I do not understand how a locker full of a high concentration of CNG gas will flow out of a single vent through hull to the outside. Seems to me you would need air flow to evacuate the gas. Perhaps a vent at the top of the locker will allow some of the lighter than air gas to escape but seems to me that in any case there will remain a high concentration of the gas in an enclosed container that could be set up by static electricity. I think it makes more sense to keep it in an open space even inside the cabin where the gas may dissipate in a lrger volume of air keeping the concentration at a safe level. Of course keep away from an open flame or a source of sparks.

 

[Steverhnm]

I think we are saying the same thing. But it is uncompressed when it fills your cabin.

I am assuming that since SCUBA tanks are rated by CF volume of uncompressed air, that CNG tanks would be the same. Can't find support other than CNG tank specs that show CF volume as tank volume x tank pressure.

Sorry Johann, SCUBA tanks are rated for the volume of compressed air they hold. A small steel SCUBA tank is 72 CF of gas at 2250 PSIG, Aluminum tank 80 CF at 3000PSIG. You can get them with thicker walls, all kinds of higher pressure ratings, but they are all rated for the volume of compressed air/gas they hold, not their internal volume at atmosphere. Maybe I was not clear. Obviously, when it is expelled from the tank it is uncompressed.

 

[Johann]

Sorry Johann, SCUBA tanks are rated for the volume of compressed air they hold. A small steel SCUBA tank is 72 CF of gas at 2250 PSIG, Aluminum tank 80 CF at 3000PSIG. You can get them with thicker walls, all kinds of higher pressure ratings, but they are all rated for the volume of compressed air/gas they hold, not their internal volume at atmosphere. Maybe I was not clear. Obviously, when it is expelled from the tank it is uncompressed.

No problem, that's what I was trying to say as well. I was just postulating that CNG would be measured the same way, not by internal volume...

 

[Stu Jackson]

OK, good info. However, the amount in "standard" tanks remains less than the 100 cubic foot amount in the ABYC excerpt from fas102. Thanks.

 

[Steverhnm]

I meant to ask everyone, I am interested in getting a second/replacement CNG tank. Especially the one with the gas fitting. Maybe somebody that has changed to LPG?

Please PM me if you have a used tank you want to get rid of or know where I can get one. They key part here is the valve on the top. At one time I had a link for the company that actually made these, but can't find it anymore.

 

[Rick D]

Minney's?

I meant to ask everyone, I am interested in getting a second/replacement CNG tank.

I got mine at Minney's Yacht Surplus; they had several. I assume you are talking about getting one in the states as opposed to SC? I wonder if the yard in SC might have some left over from a Gringo conversion?
http://minneysyachtsurplus.com/

 

[rfrye1]

All this discussion. I have a question. Is there an advantage to CNG over LPG? I know LPG is heavier than air and carries that huge risk. Anything else?
Thanks. Bob.

 

[ben solomon]

I meant to ask everyone, I am interested in getting a second/replacement CNG tank. Especially the one with the gas fitting. Maybe somebody that has changed to LPG? Please PM me if you have a used tank you want to get rid of or know where I can get one. They key part here is the valve on the top. At one time I had a link for the company that actually made these, but can't find it anymore.

Haven Harbour marina in Rock Hall, Maryland sells full CNG tanks, valve and all for $65.00. That's where I get mine.

ben