Coast station is asking you to become the osc (u are alone).distress message rcvd 12 hrs before. patttern you will choose and the

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FOLLOW

The first stage in every SAR incident is the establishment of a geographical reference or DATUM for commencing the search and depends upon:
Reported position
Time of incident
Any bearings or sightings
Time interval between the incident and arrival of SAR facilities
Size, type and condition of the search object
Estimated surface movements of the distressed craft or survival craft, depending on drift

Liferaft Leeway is calculated from IAMSAR Vol III table.


Time interval is the interval between the incident time or last computed datum and the commencement of search time. This emphasises the requirement of working out the ETA precisely.

In order to search effectively, units have to cover the search area following designated tracks. The distance between adjacent tracks is called track spacing. The IAMSAR manual provides tables for recommended track spacing based upon meteorological visibility. Track spacing is dependent upon:
Size of the search object
Type of the search object
Meteorological visibility
Sea state/condition
Time of the day (day/night/twilight)
Position of the sun
Effectiveness of the observers (height, etc)
Number of assisting craft


Recommended track spacing for merchant vessels are give in a table in IAMSAR Vol III, entering with Search Object & Meteorological visibility.
Weather correction factor is then found out from the next table.

If Wind from 0 to 15 kt or seas 0 to 1 m then the  Weather correction factor is 1.0 for Person in water and Liferaft.

Track spacing (S) = Recommended track spacing x Weather correction factor

If search units are in the immediate vicinity and arrive on scene very rapidly and commence the search, use radius of 10NM, draw circle and box with tangents.


CALCULATED SEARCH AREA (A)
Where time is available for computation, the area is:
A = Track space (S) x Search speed (V) x Time (T)

A ship with a speed of 14 knots and planning to search for 2 hours for the 25 person liferaft, can search an area = 4.7 x 14 x 2 = 131.6 NM2


Where more than one unit is available, their individual areas can be added to obtain the total area that can be searched:
At = A1 add  A2 add etc



SEARCH PATTERNS

1. Expanding square
Can only be used by a single ship and is often appropriate for vessels  to use when searching for persons in the water or other search objects with little or no leeway. It is most effective when the location of the search object is known within relatively close limits. The commence search point (CSP) is always the datum position.


2. Sector Search  
It is used to search a circular area centred at the datum and can only be used by only one craft at a time at a certain location.It is most effective when the position of the search object is accurately known and the search area is small. It is most appropriate after man overboard incident immediate action for searching the person.
CSP is where the search unit enters the area. Sectors are marked from datum as 1st, 2nd, 3rd, and the course alterations are 120deg. After initial search, the pattern is oriented 30deg in the direction of turn.


3. Parallel Sweep
It is employed where a large area has to be searched and survivor location is uncertain.
The area may be assigned to individual search units on-scene at the same time, after it is divided into smaller sub-areas.
CSP for each ship is S/2 inwards from edge of the area. All turns and outer most legs are planned at not more than S/2 inwards of the edges.


If there is uncertainty about the position of the distressed unit and significant time has lapsed since the incident, wind effect on the search object may be different.
There may be a number of other factors that introduce errors in the calculations. Search planners allow for these factors and work out maximum allowable error radius for each of the three datum points. These radii are used to draw error circles from the three datum points. The search area is then obtained by enclosing the error circles in the smallest possible rectangle. In actual fact there may be a numerous datum points on the arc between the down wind and two extreme datum points.