Maritime search patterns, one to four SRUs
Watch how each standard IAMSAR search pattern is run by a single search and rescue unit (SRU), then by two, three and four rescue boats working together. Pick a pattern, choose how many SRUs, and press Play.
Datum
The most probable position of the search object, corrected for drift.
Track spacing (S)
Distance between neighbouring search legs. Smaller S means better coverage but more time.
Commence search point (CSP)
Where each SRU starts its pattern — shown as a dot at the start of each track.
Sub-areas
With several SRUs the OSC or SMC splits the area so every unit has its own, without gaps or overlaps.
Choose a pattern
Parallel track (PS) — 1 SRU
When to use it
The search object's position is uncertain and the area is large, with the object equally likely anywhere in it.
How it is performed
Straight legs run parallel to the long side of the area, each one track spacing (S) from the last, joined by short turns. It gives even coverage of a rectangle.
With 1 SRU
One SRU covers the whole area alone. It is simple, but slow for a big area.
Safety with several units
The on-scene coordinator gives every SRU its own area or offset, start point, track spacing and radio checks. Units report reaching their start point, each leg, and anything sighted.
Based on the search patterns in the IAMSAR Manual, Volume II (coordination) and Volume III (mobile facilities). Charts are simplified teaching drawings, not to scale for real planning. Expanding square and sector search are shown with at most two units, as IAMSAR allows. For offshore structures see the Offshore SAR Learn page. To see the real rescue boats that run these patterns, browse the SARfleet rescue boat database.