John,
Of course, I gave these matters serious thought before doing this installation on my own boat. You addressed some of the factors I considered 18 years ago when doing this installation.
John R. wrote: The CNG regulator needs to be vented overboard, preferably as far aft as possible.
On Rhiannon the regulator is vented overboard via the old holding tank vent hose that exits through the transom.
John R. wrote: You don't want any gas vapors of any type collecting inside any boat hull whether the gas is lighter than air or not. CNG being lighter than air still needs a way to escape the confines of a hull and cabin via ventilation of one method or another.
Whatever gas vapors get into the cabin (usually not the kind one can put into a tank) dissipate quickly through the two dorades on the cabin top and the cowl vents in the engine compartment. Also, Cape Dories are noted for their almost total lack of airtightness. The fits around the companionway sliding hatch and hatch boards, to wit. I cannot find a place where gas can pool in sufficient concentration to be combustible. Broyle's (or is it Boyles?) Law is operative here.
John R. wrote: A prudent installer will also incorporate a sniffer and alarm unit as a leak fail safe shutdown and audio visual warning indicator. An electric shut off solenoid will be employed in that type of system.
The human nose can detect an order of magnitude fewer ppb than any electronic sniffer -- this is a practical matter on a boat where ultimate simplicity (and safety) is the byword. If I were doing this for a customer there would be no question that solenoids, sniffer, warnings, etc. would be incorporated and ASBA specs followed to the letter. This is not a customer's boat, though.
John R. wrote: However, the use of a shut off solenoid on CNG needs to be placed after the outlet port of the regulator due to the high pressures involved.
On every CNG installation I've seen the regulator is hard-plumbed to the tank connection, making it impossible to put the shutoff in the high-pressure line. Good point, though.
Thanks for the concern, John. There are practical limits to "rules and regulations" I think. Many of the regulatory specs, like so many of our laws, are written to protect a certain group of people from themselves. To me, sailing, and sailboats, is one of the few remaining things where we can appreciate the benefits of our own resposibilities and due diligence to boat and crew. It's an almost Darwinian thing - and to that group who needs the protection of an excess of laws and regulations because they can't take care of themselves, then there might often be a catastrophic price to pay without the excess regulation.
That said, before I ever sell Rhiannon (unlikely as my daughter wants her when I'm too old to sail), I'll put a sniffer, alarms, and cutoff valve on her. Meanwhile, I'll use mother nature's sniffer and adherence to a practical safety regimen to keep life (and the boat) as simple as possible.
Remember: an elephant is a mouse designed to MIL Specs.
As a matter of interest, when I ran Sailcraft Service we averaged a boat or so per year where the interior required major reconstructive work from fire damage due to alcohol-fueled stoves. A handful of alcohol fires resulted in total losses. In that same 12-year time frame there were probably two local boats that were destroyed by LPG explosions. There was never an accident involving accidental CNG combustion that I was aware of.
Andy
John R. wrote: Mario wrote: Andy Denmark wrote: Warren,
The very first thing I replaced when Rhiannon was commissioned in 1984 was the Kenyon stove. I gave the thing away to one of the waterway gypsies and considered it good riddance -- alcohol in any form is lousy for cooking, IMHO. (Alcohol is for drinking but that marine stuff makes your fingernails hurt! Coleman fuel is not much better and makes terrible Dark & Stormies!)
Replaced the Kenyon with a Force Ten CNG flush mounted unit. The CNG tank is under the port settee berth (heavy things get put low and close to the centerline in Rhiannon). A 1/4" trim ring was necessary to get the Force Ten stove to mount properly but that will not be necessary when I put Corian on the countertops (see another post).
The main reasons I went with CNG: my daughter and friends could use the boat without fear (mine - they have no fear as teenagers) of blowing the boat up with LPG, cheap: (Public Service Gas fills the tank for $15 and it lasts all season, much better heat than alcohol (though admittedly not as good as LPG), and ease of containing a lighter-than-air gas in a normal storage compartment.
This stove has seen a lot of use. It works perfectly and is a snap to clean completely. Heeled over under sail I use a Forespar Mini-Galley mounted over the sink. Under power in reasonably flat water, the Force Ten works great. It has fiddles and tolerates some heeling and we actually use it like that sometimes. The Mini Galley is gimballed so heeling is not a problem.
Here's a great cookbook for sailors and a bit of a different philosophy for meal planning: "The Two Burner Gourmet: The Cookbook for the Cruising Yachtsman" by Terry Searfoss. Don't know if this is available anymore but it's worth the price.
One of the greatest pleasures of cruising is preparing really nice meals. The hassle (and odor) free stove helps make this possible.
For what it's worth,
Andy Denmark
CD-27 #270 "Rhiannon"
Oriental, NC (90 degrees, 10-12 SW wind and no clouds today)
trekker@coastalnet.com