How maritime search works

Every search answers three questions: where could they be (probability of containment, POC), how well can we see them (probability of detection, POD), and how good is the plan(probability of success, POS = POC × POD).

Datum

The most probable position of the target, corrected for drift since the incident.[S1][S6]

Drift

Total water current plus leeway (wind push on the object). A person drifts less than a raft.[S1][S6]

Sweep width (W)

How wide a strip a searcher effectively clears. Depends on target, sea state, visibility, sensor, height.[S1][S6]

Coverage (C = W/S)

Sweep width divided by track spacing. C = 1 gives roughly 63% POD with conservative assumptions.[S1][S6]

Standard patterns (IAMSAR)

1 NM (1.9 km)

Move the cursor over the chart

Expanding square (SS)[S1][S5][S6]

When to use it

Datum is known quite accurately and the area is small. One vessel spirals outward in growing square legs.

Technical

Legs S, S, 2S, 2S, 3S... Turns are 90°. Needs accurate navigation; best for a single unit.

Why offshore structures break these patterns

A square or sector search assumes you can steer any heading. Inside a wind farm, turbines every ~1 km block straight legs, rotor blades limit where helicopters can fly and hover, and towers create radar shadows. That is why the Pattern Explorer aligns legs with the turbine rows instead.[S2][S3][S4]

Irregular and asymmetric wind farms

Checking your access…

Searching close to structures

Checking your access…

Sources and assumptions

Checking your access…

Concept study for education and planning discussion. Not an official SAR procedure — always follow your rescue coordination centre, IAMSAR and national guidance.