Seamanship
Search patterns (IAMSAR)
Courses, lengths and times for the IAMSAR expanding square and sector search, ready for the bridge.
Often into the wind or current
Fill in the fields to see the result.
How it works
Expanding square (SS): starts at the datum, legs of S, S, 2S, 2S, 3S, 3S… nautical miles, each turn 90° to starboard. Used when the search object is close to a well-known datum. S is the track spacing (IAMSAR Volume III tables, by search object, visibility and weather).
Sector search (VS): three triangles from the datum, every leg the radius R, every turn 120° to starboard; nine legs bring you back to the datum. For a second search, turn the pattern 30°. Best for a small area around an accurate datum, such as a person in the water.
The on-scene coordinator decides the pattern, spacing and first course; follow IAMSAR and the instructions of the rescue coordination centre.
For training and cross-checking. Not a substitute for approved navigation equipment, nautical publications and the ship’s own procedures. Calculations run in your browser and nothing you type is stored; a PDF you download is made on our server and not kept.
More tools
All tools- Port to port distances
- Compass error
- Great circle and rhumb line
- Speed, distance, time and ETA
- Current triangle
- Compass error by the sun
- Sunrise, sunset and twilight
- Dead reckoning position
- Distance off
- Sextant altitude and noon latitude
- Required speed for an ETA
- CPA and TCPA
- True wind
- Horizon and light range
- MLC hours of rest
- Ship’s clocks and time zones
- IMO and MMSI number check
- Dock water allowance and loading
- Height of tide
- Mean draught and trim
- GM from rolling period
- Squat and under-keel clearance
- Anchoring
- Fuel consumption and endurance
- Speed and consumption
- Propeller slip
- Indicated power
- Bunker quantity
- Fuel heating temperature
- Cylinder oil feed rate
- Electrical power
- Pay and contract dates
- Unit and position converter
- Signal flags and phonetic alphabet
- COLREGs lights and shapes
- Beaufort and sea state scales
- Marine VHF channels