- The course and speed over ground are the true course and speed, which the vessel makes across the surface of the earth. These data are measured by GPS (a satellite-supported global positioning system); wind and current do not affect them.
- The speed through water means the vessel’s speed through the surrounding water. One has to add the vessel’s wind drift to leeward and the set by wind current and tidal streams in order to get the true course and speed. Max speed through water refers to the highest speed measured over the latest period of time.
- UTC stands for Universal Time Coordinated (formerly Greenwich Mean Time). This is also the standard (winter) time for the West European time zone.
- Average and maximum wind speed refer to the latest period measured.
- Wind direction refers to true north. The wind’s deviation from this direction is also given.
Wind force scale
Observation of the sea state
Ripples without crests
Small wavelets. Crests of glassy appearance
Large wavelets. Crests begin to break, scattered whitecaps
Small waves becoming larger,frequent white crests
Moderate waves, many white crests, spray
Large waves, white foam crests
Seas heap up, white foam, breaking waves blown in streaks
Moderately high waves, breaking crests, foam streaks
High waves, crests tumble, spray affects visibility
Very high waves with long breaking crests, reduced visibility
Exceptionally high waves
Huge waves. Air filled with foam and spray. Sea completely white with drifting spray. Visibility greatly reduced
Source: DMI and Met Office