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Sea and Swell


SEA [in open sea]
Description Height (metres) Effect
Calm (glassy) 0 No waves breaking on beach
Calm (rippled) 0 - 0.1 No waves breaking on beach
Smooth 0.1 - 0.5 Slight waves breaking on beach
Slight 0.5 - 1.25 Waves rock buoys and small craft
Moderate 1.25 - 2.5 Sea becoming furrowed
Rough 2.5 - 4 Sea deeply furrowed 
Very rough 4-6 Sea much disturbed with rollers having steep fronts
High 6-9 Sea much disturbed with rollers having steep fronts (damage to foreshore)
Very high 9-14 Towering seas
Phenomenal over 14 Precipitous seas (experienced only in cyclones)


SWELL
Description Wave Length Period Wave Height
Low swell of short or average length 0 - 200 m Less than 11 sec  0-2 m 
Long, low swell over 200 m Greater than 11 sec 0-2 m
Short swell of moderate height 0-100 m Less than 8 sec 2-4 m
Average swell of moderate height 100-200 m Greater than 8 sec, less than 11 sec 2-4 m
Long swell of moderate height over 200 m Greater than 11 sec 2-4 m
Short heavy swell 0-100 m Less than 8 sec over 4 m
Average length heavy swell 100-200 m Greater than 8 sec, less than 11 sec over 4 m
Long heavy swell over 200 m Greater than 11 sec over 4 m




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