Expanding square search
An expanding square starts at datum and turns 90° after each leg, with the leg length increasing every two legs. It is used when the last known position is fairly good and the search object is likely close to datum. Track spacing S depends on visibility, target size and sea state. IAMSAR is the controlling reference.
How this calculator works
First two legs are length S, then 2S, 2S, 3S, 3S and so on. Course starts at the initial course and adds 90° each leg. If speed is entered, time for each leg is shown. OSC and SMC decide the real pattern. This page is a training aid only.
Who should use it
Useful for officers practising IAMSAR patterns. In a real SAR case follow the OSC and the IAMSAR Manual.