46 C.F.R. § 28.335 – Fuel systems.

(a) Applicability. Except for the components of an outboard engine or portable bilge pump, each vessel must meet the requirements of this section.
(b) Portable fuel systems. Portable fuel systems including portable tanks and related fuel lines and accessories are prohibited except where used for outboard engines or portable bilge pumps. The design, construction, and stowage of portable tanks and related fuel lines and accessories must meet the requirements of ABYC H-25.
(c) Fuel restrictions. Except for outboard engines, the use of fuel other than bunker C or diesel is prohibited. An installation using bunker C must comply with the requirements of subchapter F of this chapter.
(d) Vent pipes for integral fuel tanks. Each integral fuel tank must meet the requirements of this paragraph.
1. (1) Each fuel tank must be fitted with a vent pipe connected to the highest point of the tank terminating in a 180 degree (3.14 radians) bend on a weather deck and fitted with a flame screen.
2. (2) Except where provision is made to fill a tank under pressure, the net cross-sectional area of the vent pipe for a fuel tank must not be less than 0.484 square inches (312.3 square millimeters).
3. (3) Where provision is made to fill a tank under pressure, the net cross-sectional area of the vent pipe must not be less than that of the fill pipe.
(e) Fuel piping. Except as permitted in paragraph (e)(1) and (e)(2) of this section, each fuel line must be seamless and must be of steel, annealed copper, nickel-copper, or copper-nickel. Each fuel line must have a wall thickness of not less than that of 0.035 inch (0.9 millimeters) except that:
1. (1) Aluminum piping is acceptable on an aluminum hull vessel provided it is installed outside the machinery space and is at least Schedule 80 in thickness; and
2. (2) Nonmetallic flexible hose is acceptable but must—
  1. (i) Not be used in lengths of more than 30 inches (0.82 meters);
  2. (ii) Be visible, easily accessible, and must not penetrate a watertight bulkhead;
  3. (iii) Be fabricated with an inner tube and a cover of synthetic rubber or other suitable material reinforced with wire braid.
  4. (iv) Be fitted with suitable, corrosion resistant, compression fittings; and
  5. (v) Be installed with two clamps at each end of the hose, if designed for use with clamps. Clamps must not rely on spring tension and must be installed beyond the bead or flare or over the serrations of the mating spud, pipe, or hose fitting.
(f) A fuel line subject to internal head pressure from fuel in the tank must be fitted with a positive shutoff valve located at the tank which is operable from a safe location outside the space in which the valve is located.
(g) A vessel less than 79 feet (24 meters) in length may comply with one of the following standards in lieu of the requirements of paragraphs (e) and (f) of this section.
1. (1) ABYC H-33.
2. (2) Chapter 5 of NFPA 302.
3. (3) 33 CFR chapter I, subchapter S (Boating Safety).