Since it is virtually impossible to comply with ABYC safety standard 1.7.3 with a manual shut off valve at the cylinder inside the locker, most boats have electric solenoid valves at each appliance.
A-1.7 CYLINDERS, VALVES, AND SAFETY DEVICES 1.7.1 Cylinders used in LPG systems shall meet applicable DOT regulations or ASME requirements.
1.7.2 Each appliance shall be served by a separate low pressure, (i.e., 14 in water column [3.5 kPa]), regulated supply line that shall originate inside the cylinder locker or protective enclosure.
1.7.3 A readily accessible manual or electrically operated (e.g., solenoid) shutoff valve shall be installed in the low or high-pressure line at the fuel supply (see A-1.7.6.1 for valve location requirements).
1.7.3.1 The valve(s) or its control shall be operable in the vicinity of the appliance(s) in the event of a fire at any appliance(s). If the cylinder shutoff valve is readily accessible from the vicinity of the appliance, the shutoff valve on the supply line is not required.
1.7.3.1.1 The valve or its control shall be operable without reaching over the top of any open flame appliance (e.g., cooking appliance burners).
1.7.4 In addition to the valve required at the cylinder, a multiple cylinder system shall be provided with a shutoff valve, or automatic check valve, at the cylinder manifold so that each cylinder can be isolated from pressure feedback from other cylinders.
Note: there is no USCG approved hose. The USCG has no specifications on the hose. ABYC requires as follows:
A-1.9 FUEL LINES
1.9.1 As installed, the fuel supply line system and its components shall be compatible with LPG, and shall withstand the stresses and exposure of the marine environment.
1.9.2 LPG fuel supply line shall comply with the construction, performance, manufacturing, and production test, and marking requirements of UL 21, LP Gas Hose or
1.9.2.1 be corrosion resistant metallic tubing such as annealed copper tubing, standard type, Grade K or L, conforming to ASTM B88-75a, Specifications for Seamless Copper Water Tube , with a wall thickness of not less than 0.032 in (0.813 mm).