Ian Waugh - A Mariner\'s Guide to Marine Communications

Chapter 1

G MDSS Overview

ALL PASSENGER VESSELS AND CARGO VESSELS over 300 tons, engaged on

international voyages, have to carry a range of radio/satellite

communications equipment specifically to meet the 'functional

requirements' of the GMDSS. The actual equipment fitted depends on

the vessel's 'Sea Area of Operation' This chapter lists the functions that

a GMDSS vessel should be able to carry out; introduces GMDSS

equipment that may be used for each function (with alternatives where

appropriate); explains 'GMDSS Sea Areas of Operation' and describes

the land-based GMDSS communications infrastructure.

Priority of communications

In the GMDSS, maritime radio/satellite communications fall into

four 'priority' groups:

Distress, Urgency, Safety and Other.

Mariners have to decide, for each circumstance, which category a

particular incident/requirement falls into before making contact with

shore or other vessels. The official definitions are shown below. (An

expanded explanation, to aid understanding, is provided at Appendix I)

Definitions

DISTRESS (Mayday)

'a mobile unit, or a person, is in grave and imminent danger and

requires immediate assistance'

URGENCY (Pan Pan)

is where you have 'an urgent message to send concerning the safety

of a mobile unit, or a person'

In Distress and Urgency situations, you are asking for assistance. For

Distress, that usually means 'rescue'. For Urgency, you are specifjing a particular

type of assistance which should solve your problem. (See the expanded explanatiOns

in Appendix I to help distinguish between Distress and Urgency situations)
SAFETY
is where you have 'an important navigational or meteorolOgical
warning' to send - including 'bridge-to-bridge' communications, between
ships, concerning the safety of navigation.
In a Saftty situation - unlike Distress and Urgency - you are not asking
for assistance.

2 THE NAUTICAL INSTITUTE