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.