Fuel hose looks like any other black hose until it fails. A weeping joint in a diesel engine room is a mess and a fire risk; in a gasoline engine space it's an explosion waiting for the starter motor. The hose's printed marking is the first thing a surveyor reads, and the hose's feel is the second.
The hose types
US Coast Guard fuel hose comes in four types under SAE J1527. As the Ask Andrew column in BoatTEST puts it, construction is based on fire resistance and permeability. Type A has passed a two and a half minute burn test; Type B has less fire resistance. Type 1 lets less vapour through the wall than Type 2.
For gasoline inboards, the supply line to the engine must be Type A1, with B1 allowed where an anti-siphon valve is fitted. Vent and fill lines must be A1 or A2, and ABYC H-24 asks for Type A2 on fill hoses inside engine compartments. Diesel systems under ABYC H-33 can use any of the four types for fill and vent hoses.
Approved hose carries its USCG type, maker and date of manufacture on the outside, repeated at intervals of 12 inches or less. Without it, hose in a gasoline system isn't legal.
How a surveyor checks it
Follow each fuel line from the tank to the engine, including fill and vent hoses. Read the marking. Flex the hose: cracks on the cover at bends, hardness, swelling and softness all mean replacement. Smell for fuel and look for weeping at every joint and clamp. Clamps should be stainless all through, and Boat Blurb notes some Type A hose isn't designed to be clamped at all, so check the maker's instructions.
Age matters with the fuel in use. A Seattle surveyor writing on fuel hoses warns that newer alcohol-based fuels make older approved hoses deteriorate and leak. The date on the hose tells you how long it's been in that fight.