Doc No:
RF0152
Navigation In Heavy Weather
Reference Material
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2
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Navigation In Heavy Weather
It is of utmost importance to watch the pattern and character of the waves. Large long waves with
rounded tops might not be as dangerous as the short high ones with collapsing crests. Trains of
waves should be watched carefully as any cross patterns might lead to wrong decisions concerning
timing of manoeuvres.
The object of any manoeuvre in heavy weather is to take on as little water on board the vessel as
possible. Large amount of water on board causes damage if its energy is not dissipated before
encountering resistance of the ship’s structure. It also alters the stability of the vessel at a critical
period.
Manoeuvring towards wind/sea
• In general, the most favorable conditions can be found when manoeuvring with bare
steerageway, with the wind and sea about 15-20 degrees on either bow.
• Masters must consider the effect on sea conditions when winds are contrary to the current or
swell patterns. Freak wave phenomena may be encountered in the Agulhas current and the Gulf
Stream.
Manoeuvring with the weather
• When manoeuvring with the weather, adjust the speed so that the ship speed is appreciably
different to that of the swell. This will reduce the rolling effect.
• The speed should be adjusted to avoid shipping heavy seas over the poop. Pooping can cause
serious damage to the accommodation and machinery space structures as their large flat
surfaces offer great resistance to waves.
Turning
• If it becomes necessary to turn the vessel around on to a reciprocal course, carry out such a
turn very carefully. First reduce the speed to the minimum where by one can still maintain
steerage.
• Ensure that the whole crew is well informed about this critical manoeuvre well in advance and
that optimum engine response is absolutely assured.
• Observe the wave pattern carefully in order to choose the correct moment to start the
manoeuvre. Usually, waves seem to follow each other in groups of three with relatively calmer
periods in between two groups. A vessel might pick up the speed during one of these calm
periods and slam into the next wave group with too much momentum. Even if the vessel
manages to escape the first wave, one or both of the next two may end up causing severe
damage. Control of the ship’s head with minimum headway, therefore, is of utmost importance.
Consider choosing the beginning of the third wave to plan the turn.
• The idea is to start the turn when the bow is just rising from a trough and climbing the wave. Use
adequate engine power with wheel hard over, so that the vessel turns parallel to the wave
before reaching it’s top.
• Once the vessel is almost parallel to the wave, use maximum power with the wheel still hard
over, to effect the final part of the turn as quickly as possible. At all costs, avoid waves breaking
over the ship while it is parallel to the wave.
