LS10.21 PROBABLE ERRORS OF POSITION

Section: LS10 SAR Operations

Date: 20th September 2016

Page: 4 of 4 the water in the direction its hull is designed to move. Almost the same conditions exist when the boat is pointed directly into the wind and is being pushed backwards through the water longitudinally. When the boat’s heading is perpendicular to the local wind, however, the greatest amount of underwater drag will exist since the boat must now be pushed sideways through the water. Between these extremes the amount of underwater drag will varies depending on the heading of the boat.

Divergence

When a search object first begins to drift, the wind will push the object in a downwind direction. As the search object continues to drift, the wind will cause the search object to deflect (or diverge) to either the left or to the right of the downwind direction. The amount of divergence is dependent upon the shape of the “sail” area of the search object. Divergence is caused by the lack of symmetry of the drift object.

Modification of the Probability Area

Modification of a calculated probability area may be suggested from an assessment of intelligence information received in the SurfCom, limitations imposed by search unit availability or for other reasons.

It should always be understood that SAR calculations are intended to be a guide to search planning, and may be modified to suit any particular situation as suggested by the accumulated SAR experience within the SurfCom.

Any member of the SurfCom team who considers that a modification would be to advantage shall make the IC aware of the suggestion. When offering such suggestions, every attempt should be made to present viable alternatives, together with a summary of the advantages, and disadvantages of each. The authority to make any such modification rests solely with the IC.

Modification suggested by Intelligence information

During the course of a SAR action, reports and information may be received from a variety of sources claiming that the missing craft had been seen or heard. Detailed analysis of these reports, and comparison with known data, may lead the IC to delineate a modified, or totally different, search area.

Modification resulting from a shortage of Vessels

When it is not possible to search the whole of the probability area due to a shortage of vessels, a number of factors may be changed to facilitate modification of the area. For example: track spacing, vessel speed and size of the probability area. After consideration of these factors, the IC will make a decision which section of a probability area should be searched first.