Beaufort Wind Scale Calculator
Maritime CalculatorsCalculate sea state wave height ranges, surface conditions, and tactical vessel advisories from wind speed
Measurement System & Wave Units
Observed Open-Sea Wind Speed
knots
Click directly on the number to type, or hover and spin mouse wheel to step wind speed.
Simulate WMO Beaufort Force Level
Force 6— Strong Breeze
0 Calm4 Breeze8 Gale12 Hurricane
Sea State Analysis & Commercial Ship Advisory
Expected Wave Height & Surface
9 - 13 ft
Beaufort Force 6 (Strong Breeze)
Large waves begin to form; white foam crests are extensive everywhere; significant driving sea spray.
Commercial Vessel & Deck Operations
Normal Transit Parameters
Pilot ladder boarding approaches maximum safe sea swell threshold (2.5m+); windward tug assistance mandatory for port maneuvering.
Wind Speed Threshold:22 – 27 knots
Complete WMO Beaufort Sea Scale Reference (0 – 12)
| Force | Classification | Wind (kts) | Wave (ft) | Commercial Ship Operations Advisory |
|---|---|---|---|---|
| 0 | Calm | 0 – 0.9 kts | 0.0 ft | Optimum sea passage condition; negligible hydrodynamic propeller slip and zero atmospheric windage drag. |
| 1 | Light Air | 1 – 3 kts | 0.25 ft | Ideal conditions for open sea transit, harbor piloting, and unhindered terminal crane berthing. |
| 2 | Light Breeze | 4 – 6 kts | 0.5 - 1 ft | Standard commercial sea passage; zero measurable impact on vessel shaft horsepower or fuel oil consumption (FOC). |
| 3 | Gentle Breeze | 7 – 10 kts | 2 - 3 ft | Routine deep-sea navigation and port approach; pilot boats and tugs operate safely alongside without hull pounding. |
| 4 | Moderate Breeze | 11 – 16 kts | 3.5 - 5 ft | Noticeable cross-wind drift (windage) on high-profile vessels (container ships, car carriers, ballasted bulkers) during slow-speed berthing. |
| 5 | Fresh Breeze | 17 – 21 kts | 6 - 8 ft | Onset of minor added hydrodynamic wave resistance and propeller slip; check container lashing tension on upper deck tiers. |
| 6 | Strong Breeze | 22 – 27 kts | 9 - 13 ft | Pilot ladder boarding approaches maximum safe sea swell threshold (2.5m+); windward tug assistance mandatory for port maneuvering. |
| 7 | Near Gale | 28 – 33 kts | 13 - 18 ft | Significant sea margin speed reduction due to head seas; pilot boarding suspended at unsheltered offshore stations; monitor anchor drag in roads. |
| 8 | Fresh Gale | 34 – 40 kts | 18 - 25 ft | High danger of parametric rolling in container vessels in quartering seas; alter course/speed to prevent heavy bow slamming and propeller emergence. |
| 9 | Strong Gale | 41 – 47 kts | 23 - 32 ft | Green seas shipped over exposed weather decks; severe dynamic lashing stresses on container stacks; bulkers must guard against cargo shifting/liquefaction. |
| 10 | Storm / Whole Gale | 48 – 55 kts | 29 - 41 ft | Heavy hull girder structural stress; steam at minimum maneuvering RPM to maintain steerage and avoid broaching in heavy following seas. |
| 11 | Violent Storm | 56 – 63 kts | 37 - 52 ft | Extreme navigational survival hazard; heavy risk of bottom pounding, hawser parting, and deck equipment damage; remain in deep sea room. |
| 12 | Hurricane Force | 64 – 150 kts | 46+ ft | Catastrophic cyclone sea conditions; strict avoidance via strategic meteorological routing (SOLAS weather routing) days in advance is mandatory. |
Commercial Tonnage Windage & Port Berthing
While high sea swells impact open-sea passages, strong atmospheric wind speeds directly govern port entry safety for commercial shipping.
- Container Vessel & LNG Carrier Windage: Large modern container ships (15,000+ TEU) and light ballasted bulkers present immense high-profile windage areas. At Force 5 to 6+, wind drift forces can exceed bow thruster capacity during low-speed harbor turns.
- Pilot Ladder Restrictions: Under IMO SOLAS requirements, offshore pilot boat transfers become severely restricted or hazardous in swell heights exceeding 2.5 meters (Beaufort Force 6+), requiring vessel lee creation or helicopter transfers.
Added Resistance & Parametric Rolling
Why sea states demand tactical engine RPM and course alterations on large bulk vessels:
- Hydrodynamic Propeller Slip & Added Resistance: In head seas of Force 6 to 7, wave impact against large blunted bulk carrier bows increases hydrodynamic resistance. Maintaining set engine RPM causes thermal overload and extreme fuel oil consumption (FOC); masters must apply weather routing sea margins.
- Parametric Rolling in Following Seas:In heavy quartering seas (Force 8+), when wave encounter frequency matches a container vessel's natural roll period, dynamic parametric rolling can develop within cycles, subjecting container tier lashings to breaking strain!
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