SAR Pattern Visualiser
Select any IAMSAR search pattern, set track spacing and drift, then animate. Coverage fills in real time as the vessel tracks through the pattern. Drift displaces the datum mid-search — the key concept the oral always tests.
What you're practising
How the five IAMSAR search patterns work visually, why track spacing controls POD, and how drift displaces the datum mid-search.
Pass criterion
Name all five patterns, explain when each is used, and state the relationship between track spacing, coverage area, and POD.
Sector Search
All legs equal to the search radius S, every turn 120° to starboard; the long legs pass back through the datum, dividing the circle into three sectors. On completion the whole pattern is re-oriented 30° to starboard and run again.
Best for: Datum known with high accuracy · small search area · one unit · person in water
Tighter S → higher probability of detection · longer search time. For VS, S is the search radius (typically 2 nm for a vessel).
Red cross = shifted datum. Observe how drift displaces the search object.
Higher drift → the datum keeps moving; correct it before you start, or use a large-area pattern (PS/CS)
Why track spacing matters
Track spacing S is the most important parameter in any search. Halving S doubles coverage density — but also doubles the time and fuel required. The Probability of Detection (POD) follows a diminishing-returns curve: the second pass over an area adds far less than the first.
Drift matters most for extended searches. After 4 hours at 1.5 knots drift, the datum has moved 6 nm. If your pattern doesn't compensate for this, you're searching an area the survivor has already left. This is why IAMSAR recommends CS or PS when drift is significant — both patterns cover larger areas relative to the time spent.
The OSC (On-Scene Commander) accounts for drift in the search plan by applying a Datum Uncertainty Radius (DUR). The DUR grows with time elapsed since last known position.
Scenario Question
Man overboard, witnessed from your own bridge thirty seconds ago. Position is known almost exactly and you are the only unit on scene. Which pattern, and what do the turns look like?
Module 18 — Study Notes
Full written notes covering IAMSAR Vol III, MRCC/OSC roles, duty to render assistance, search patterns, assisting disabled vessels and ditched aircraft, and helicopter operations.
Open Module 18 notes →