4.1.1 It is important that speed should be appropriate
for the sea conditions. In a following or stern-quartering seas, it
is comparatively easy to determine whether the craft is moving faster
or slower than the dominant waves in daylight. At night-time, however,
such assessments are not so easy.
4.1.2 Craft speed, it is assumed, will be known
with some accuracy. If not, then, when moving at or near the dominant
wave speed (and possibly trapped or in danger of surfing), pitch and
heave motions will be considerably reduced, but surge motions will
be significantly increased.
4.1.3 A rough idea of the speed of the dominant
waves in a given sea state can be obtained from table 1, according
to the type of waters in which the craft is operating.
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Table 1 – Tabulated typical wave speeds (knots)
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Significant wave height (m)
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1
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2
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3
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4
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5
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6
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Coastal waves (knots)
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15 – 18
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17 – 23
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19 – 27
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20 – 30
|
21 – 33
|
23 – 35
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Ocean waves (knots)
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19 – 29
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21 – 31
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25 – 35
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29 – 39
|
32 – 42
|
36 – 46
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