Assuming that the boat has an outboard engine and "starboard aft corner under the settee" means in a locker under the cockpit seat; the structure is to hold a the outboard engine's portable gas tank. Should that be the case: 1) the portable tank needs to be secured in place (not by bungee cords). 2) the compartment needs adequate passive ventilation as portable tanks vent at the tank. 3) the compartment should not; contain any electrical equipment - switches-batteries etc.; open into any interior space or any space containing electrical switches / equipment. 4) feed line (tank to engine) should be protected from chafe-strain-wear.
The following is a section of ABYC standard H-25 PORTABLE MARINE GASOLINE FUEL SYSTEMS
Frank (marine surveyor NY)
25.4 DEFINITIONS
For the purposes of this standard, the following definitions apply.
25.4.1 Equipment Under Test (EUT) – All associated equipment providing methods of compliance with this
standard.
25.4.2 Gasoline - Includes all gasoline based fuels. The Federal Hazardous Substance Act classifies gasoline as
"extremely flammable" having a flash point at, or below, -7°C (20°F).
25.4.3 Open to the atmosphere - a space or compartment that has at least 15 square inches of net open area
directly exposed to the atmosphere for each cubic foot (0.34 m² per m³) of net compartment volume.
25.4.4 Portable Marine Fuel Systems - Tanks, fuel lines, primer bulbs and related accessories that are not intended
for permanent installations, but are used as an assembly conveying fuel to a marine engine. (Hereby known as
portable fuel systems)
25.4.5 Portable Marine Fuel Tank (hereby known as portable fuel tanks) – A fuel tank that meets each of the
following criteria:
25.4.5.1 It has design features indicative of use in portable applications, such as a carrying handle and fuel line
fitting that can be readily attached to and detached from a marine engine.
25.4.5.2 It has a nominal fuel capacity of 12 gallons (45.4 L) or less.
25.4.5.3 It is designed to supply fuel to an engine while the engine is operating.
25.4.6 Pressure Relief Method – An integrated or external manually activated device designed to temporarily
relieve pressure prior to fuel filling or connection to the engine.
25.5 GENERAL REQUIREMENTS
25.5.1 Portable tanks with capacities from seven to 12 gallons (26.5 L to 45.4 L) shall be located and arranged so
that no overflowing fuel can enter the boat when it is in its static floating position.
EXCEPTION: Open outboard boats without accommodation spaces and other enclosed spaces and with a
continuous floor that is liquid-tight to the hull interior and bilge compartments containing electrical
components or batteries.
25.5.2 Portable fuel tanks shall have provisions to permit handling, securing aboard and removal for refilling.
25.5.3 Portable fuel tanks, pressurized by means other than vapor pressure of the fuel, shall not be used.
25.5.4 Portable gasoline fuel tanks shall be colored red.
25.5.5 All portable tanks associated fittings, lines and primer bulbs shall meet the applicable emission requirements
of 40 CFR part 1060.
