The National Marine Manufacturers Association (NMMA) Handbook for Boat Certification, uses the exact same language as the ABYC.

Both the Coast Guard regulations and the ABYC standards specify maximum acceptable tolerances between fuel-line hoses and any nipples to which they are attached; require a bead, flare, or serration on the nipple (but do not allow installation of hose over a pipe thread); and require a hose clamp that does not "depend solely on the spring tension of the clamp for compressive force" (33 CFR 183.560d). Double clamps are required on fuel-fill pipes, each with a minimum band width of 1/2" ABYC requires the clamp to be "beyond the flare or bead, or fully on serration where provided, and at least 1/4" (6mm) from the end of the hose" (H24-24.11.6).
Fill pipes are required to have a minimum 1 1/2" ID; vent pipes a minimum 9/16". ID ABYC states that they must be self-draining (that is; not normally full of fuel), but this is not included in the Coast Guard regulations.

LPG, CNG, and Drinking-Water HOSES
For drinking water ABYC and NMMA standards state that the entire system should be plumbed with hose or tubing manufactured from Food and Drug Administration (FDA)-approved materials, with the hoses or tubing so labeled. The FDA, in turn, requires PVC hoses to be manufactured from virgin, rather than recycled, PVC and textile reinforcement. Compliant hoses are stamped "FDA approved." Although such hoses are commonly clear plastic, this has never made much sense to me, since the light that gets into the drinking water promotes the growth of algae. It is far better to use opaque FDA-grade hose or pipe, and in fact must household-style PVC water pipe is ideal. If this is combined with opaque water tanks, so that no light gets into the system, water will stay clean and drinkable almost indefinitely. (Note that PVC pipe from the hardware store is rated for cold water; CPVC pipe is required For hot-water systems.)

LPG (propane) or CNG (compressed natural gas) hoses, which either constitute the supply line or make the flexible connection from a copper supply line to a gimbaled galley stove, are clearly a critical safety item. For LPG systems, ABYC Al, Marine Liquefied Petroleum Gas/LPG/ Systems, requires that the hose should be marked as complying with "UL 21 LP Gas Hose"; while A22, Marine Compressed Natural Gas /CNG/ Systems, states that CNG hose should be marked as complying with "NFPA (National Fire Protection Association) 52." In both cases, the standards call for end fittings to be permanently attached. Swaging is one acceptable method of attachment; a hose clamp is not.

The two standards also specify that every appliance should be served by a continuous fuel line (that is, one with no joints or connections) from the gas cylinder regulator to the appliance or, in the case of gimbaled stoves, to a length of flexible hose connecting to the appliance. This means that if a boat has more than one gas appliance, it is unacceptable to run a common supply line, and then tee off this line to the devices. Any connections or tees must be made inside the gas-bottle locker which, if designed according to the standards, will be sealed to the accommodation spaces and vented overboard. This will keep any gas leaks from the connections or tees out of the boat.

Choosing a Supplier
It must be clear by now that the business of building a quality hose for a specific  purpose is more complicated than first meets the eye. On the face of it, most hoses are round and black or white, with a hole in the middle--but that's where the similarity ends. Even with two hoses that look identical, there may be all sorts of differences in the chemicals that have gone into compounding the hose, the type of fabric reinforcement, the skill with which the hose has been laid up (much hose is still hand-built), and the quality of the adhesion between different layers in the hose.

Hose manufacturing is a worldwide cottage industry, with factories scattered all the way from the Far East to Turkey, Italy, and the United States. Almost none of the handful of wholesales or retailers of marine hoses in this country actually make their own hoses. Unfortunately, some pretty awful hose finds its way into the marketplace from time to time, making the boat builder or consumer very much dependent on the wholesaler or retailer. Consequently, it's best to buy from a recognized dealer, and to make sure that the hose is manufactured to recognized standards (UL, SAE, CG, and ISO--the European standards setting body).

Maintenance
Even with high quality, properly installed hoses, there is always the potential for an unforeseeable failure. Many boat owners leave crucial sea-cocks open from one season to another, and never look at their hoses and hose clamps. After a year or two, the valves become frozen in place and the hose clamps are covered in rust The boat is an accident waiting to happen.

Or, consider a completely different problem: A rat once made its way aboard some friends' boat, and it chewed through the flexible connection to their propane galley stove. Luckily, being safety conscious cruisers, they always close the tank valve after using the stove-otherwise, the rat might have killed them. Once they realized what was going on, they had the foresight to close their sea-cocks--which was fortunate, because before they finally cornered it and bludgeoned it to death, it took a bite out of half the hoses on the boat!
Encourage your customers to inspect the hoses on their boats on a regular basis. Any kind of below-the-waterline hose failure has the potential to sink the boat.         

  About the Author: Nigel Calder is a contributing editor of Professional Boat Builder. Also, Nigel wrote the definitive book for general boat repair.

If you like this type of  in-depth article, and want to go to the source of some of the best technical information about boats, their design, and construction, get yourself a subscription to Professional BoatBuilder. It's worth every penny. ( No, I don't get a kickback)

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