The Douglas Sea State Scale

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Sea state is the condition of the sea surface at a particular place and time by reference to wind waves and swell.

Wind waves are formed by the wind within a particular generating area, the height of which will depend on the length of time the wind has been blowing from a direction, the fetch (distance over which the waves have travelled), currents and strength of wind.

Swell is the wave motion caused by distant winds, and has flat crests. It can be caused by a meteorological event such as a storm. As swell moves away from its generating area, it will die down but retain its wave length and speed.

Swell

Swell can be measured as follows:

The Douglas Sea and Swell Scales

The Douglas Sea and Swell Scales originally did not include wave height or period. They have no official status, but can be used to describe sea state.

Length
Short
Average
Long

Height
Low
Moderate
Heavy

Metres
0 - 100
100 - 200
Over 200

Metres
0 - 2
2 - 4
Over 4

State of the Sea
Calm (glassy)
Calm (rippled)
Smooth
Slight
Moderate
Rough
Very rough
High
Very high
Phenomenal

Average Height (m)
-
0 - 0.10
0.10 - 0.50
0.50 - 1.25
1.25 - 2.50
2.50 - 4.00
4.00 - 6.00
6.00 - 9.00
9.00 - 14.00
Over 14

Swell
0
1
2
3
4
5
6
7
8
9

State of the Sea
No swell
Very low (short or low wave)
Low (long and low wave)
Light (short and moderate wave)
Moderate (average and moderate wave)
Moderate rough (long and moderate wave)
Rough (short and heavy wave)
High (average and heavy wave)
Very high (long and heavy wave)
Confused (wave length and height indefinable)