Sec. 80.921  Proof of capacity.

    (a) When directed by a representative of the Commission the vessel 
must prove by demonstration as prescribed in paragraphs (b), (c), (d) 
and (e) of this section, that the requirements of Sec. 80.919 are met.
    (b) Proof of the ability of a storage battery used as a main or 
reserve power supply to operate over the 3-hour period established by a 
discharge test over the prescribed period of time, when supplying power 
at the voltage required for an electrical loss as prescribed by 
paragraph (d) of this section.
    (c) When the required power supply consists of an engine-driven 
generator, proof of the adequacy of the engine fuel supply to operate 
the unit over the 3-hour period of time may be established by using as a 
basis the fuel consumption during a 1 hour period when supplying power, 
at the voltage required for operating an electrical load as prescribed 
by paragraph (d) of this section.
    (d) In determining the required electrical load the following 
formula must be used:
    (1) One-half of the current of the required transmitter at its rated 
output power; plus
    (2) Current of the required receiver; plus
    (3) Current of electric light, if required by Sec. 80.925; plus
    (4) The sum of the current of all other loads the reserve power 
supply may provide in time of emergency.
    (e) At the conclusion of the test specified in paragraphs (b) and 
(c) of this section, no part of the main or reserve power supply must 
have an excessive temperature rise, nor must the specific gravity or 
voltage of any storage battery be below the 90 percent discharge point.