Navigation data

Definitions

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.

Beaufort	m/s	Knots	km/h	Terms	Observation of the sea state
0	0.0-0.2	<1	<1	Calm	Flat
1	0.3-1.5	1-3	1-5	Light air	Ripples without crests
2	1.6-3.3	4-6	6-11	Light breeze	Small wavelets. Crests of glassy appearance
3	3.4-5.4	7-10	12-19	Gentle breeze	Large wavelets. Crests begin to break, scattered whitecaps
4	5.5-7.9	11-16	20-28	Moderate breeze	Small waves becoming larger,frequent white crests
5	8.0-10.7	17-21	29-38	Fresh breeze	Moderate waves, many white crests, spray
6	10.8-13.8	22-27	39-49	Strong breeze	Large waves, white foam crests
7	13.9-17.1	28-33	50-61	Near gale	Seas heap up, white foam, breaking waves blown in streaks
8	17.2-20.7	34-40	62-74	Gale	Moderately high waves, breaking crests, foam streaks
9	20.8-24.4	41-47	75-88	Severe gale	High waves, crests tumble, spray affects visibility
10	24.5-28.4	48-55	89-102	Storm	Very high waves with long breaking crests, reduced visibility
11	28.5-32.6	56-63	103-117	Violent storm	Exceptionally high waves
12	>32.6	>63	>117	Hurricane	Huge waves. Air filled with foam and spray. Sea completely white with drifting spray. Visibility greatly reduced

Source: DMI and Met Office