True & Apparent Wind Calculator
Maritime CalculatorsConvert ship anemometer readings into geographic true weather or evaluate deck relative windage stress
Click number to type or spin mouse wheel. Enter ship log speed through water (Vs).
Ship's true compass heading over ground (000° = North, 090° = East).
Apparent speed measured by bridge masthead anemometer.
Angle relative to ship's centerline bow head (0° = Dead Ahead, 180° = Dead Astern).
Beam wind; causes leeward ship drift during slow maneuvers.
Absolute geographic compass bearing (not relative to ship). Wind blowing directly from SE (136°) relative to True North 000°.
Why commercial ships require constant mathematical translation between Apparent and True wind:
- Masthead Anemometer Readings: Shipboard masthead instruments solely measure relative (apparent) wind velocity and direction across the moving vessel. Logging raw anemometer data directly into shipdeck meteorological reports creates severe synoptic errors!
- ECDIS & VDR Integration:Modern bridge navigation systems continuously solve this nautical vector triangle by subtracting the vessel's Doppler log speed and gyro heading to derive True Wind over water for official SOLAS weather routing.
How ship speed transforms moderate ocean breezes into severe structural deck hazards:
- Velocity Compounding: When a post-Panamax container ship streams forward at 24 knots directly into a moderate 16-knot oceanic wind (Force 4), the forward tier container stacks experience an effective apparent gale wind of 40 knots (Beaufort Force 8)!
- Lashing Tension Checks: Deck officers must anticipate apparent wind amplification before leaving sheltered coastlines to ensure twist-locks and lashing rods exceed structural break thresholds under dynamic windage drag.