13.2.9.1 For a vessel of less than 500GT this
alarm may consist of the ship's whistle or siren providing it can
be heard in all parts of the vessel.
13.2.9.2 For a vessel of 500GT and above the requirement
of 13.2.9.1 is to be supplemented by an electrically operated bell
or Klaxon system, which is to be powered from the vessel's main supply
and also the emergency source of power (see section 8).
13.2.9.3 For a vessel of 85m in length and above,
in addition to the requirements of 13.2.9.2, a public address system
or other suitable means of communication should be provided.