All two-way communication equipment carried on board a ship
to which this chapter applies which is capable of automatically including
the ship's position in the distress alert shall be automatically provided
with this information from an internal or external navigation receiver,
if either is installed. If such a receiver is not installed, the ship's
position and the time at which the position was determined shall be
manually updated at intervals not exceeding 4 h, while the ship is
underway, so that it is always ready for transmission by the equipment.