SOLAS - Safety Of Life At Sea

In the GMDSS , the procedure to communicate a situation is to first transmit a DSC alert (to indicate to the Receiver to set a manual watch on the appropriate voice frequency ).This is Followed by a voice call (on the appropriate voice frequency ) and thereafter the actual message (containing relevant info about the situation / assistance required).

If the message is to be sent by Radiotelex , this will be indicated in the DSC Alert.

ALERT   --------------> CALL  ------------------> MESSAGE

The Communication Transmitted to convey the Situation / Request for assistance will generally be classified as   DISTRESS  /  URGENCY   /  SAFETY  /  DISTRESS RELAY  / ROUTINE

(1) DISTRESS ;-

The transmission of a distress alert indicates that a mobile unit or person is in distress and requires immediate assistance.
The frequency used for alerting will depend on the GMDSS Sea Area of the alerting Vessel and the stations to which are to be alerted.
Distress alerts can be sent using the following frequencies ;

Terrestrial -

• VHF  DSC  CH  70  
•  MF DSC 2187.5 KHZ   
•  HF DSC 4207.5 KHZ  &  6312 KHZ & 8414.5 KHZ & 12577 KHZ & 16804.5 KHZ

Satellite -

• INMARSAT -C
• COSPAS SARSAT EPIRB

In a distress situation , if enough time is not available, an undesignated alert is sent by just pressing button on the DSC equipment which contains the below minimum information ;

• Distress Vessels Identification (MMSI No )
• Distress Vessels Position( Obtained from GPS )
• Time of this Position Update

In a distress situation , if time is available, a Designated  alert is programmed and then transmitted., which contains the following information;

• Distress vessels Indetification (MMSI No )
• Distress Vessel Position (GPS)
• Time of this Position
• Nature of Distress ( Collision/ Fire / Flooding / Abandon / List / Sinking / MOB / Piracy etc )
• Class of emission ( Voice or Radiotelex )

Note :- Distress signal consists of the word MAYDAY

format of distress call would be ; (lets assume name of Vessel ASHISH )

MAYDAY  (3 times )

this is 

ASHISH (3 times)

PDIH , 412783452 (call sign & MMSI no of vessel ASHISH )

after this voice call , distress msg transmitted would be like this 

MAYDAY

ASHISH

18 ; 00; North 053 ; 00 EAST

Fire onboard

Request Immediate assistance

Wind Noth East 20 Knots

OVER

Receiving Stations would ack like this 

MAYDAY & MMSI No of Distress Station  (3 times )

this is

Name & Callsign of own Vessel (3 times )

Received Mayday

Over