Page 77 - Collision Avoidance Rules Guide

The rudder will begin to lose its effect as soon as the engines are
stopped and it will become increasingly difficult to steer the vessel as
astern power is developed. With a right-handed single screw ship the
effect of the propeller when going astern on the engines is usually to
slew the stem round to port so that by the time the vessel has been
brought to rest in a crash stop she may have come off her course by
90” or more. If a strong wind is blowing this may have a greater effect
on a vessel in light conditions than the transverse thrust of the pro-
peller. Shallow water effect may also influence the vessel’s heading
during a crash stop.
The above comments apply mainly to the stopping of a vessel with
a right-handed single screw conventional propeller. In Rule 8(e) it is
stated that, if necessary, a vessel shall ‘take all way off by stopping
or reversing her means of propulsion’. The wording takes account of
the fact that controllable pitch propellers are being fitted to an
increasing number of ships. It will normally be possible to stop a
vessel more rapidly with reduced head reach if a controllable pitch
propeller is fitted. The most effective method of taking off the way
when using a propeller of this type may be to gradually change the
pitch as the speed is reduced so as to give maximum reverse thrust
but there is some difference of opinion on this point.
Helm action taken in the initial stage of a crash top, when still
moving at high speed, will result in a considerable increase of resist-
ance and reduce the stopping distance. A method which may be used
in some circumstances is to put the helm hard over one way then hard
over to the other side with the engines on dead slow ahead, then to put
the engines full astern. This should reduce the period of applying astern
power so that the vessel is less likely to be slewed in the final stage.

Sailing vessels
Rule 8(e) also applies to sailing vessels. Sailing vessels must, if nec-
essary, slacken speed in order to avoid collision or allow more time
to assess the situation. This can be achieved by luffing up into the
wind or reducing sail. Moving the rudder hard over to one side then
hard over to the other may also help to bring the speed down.

cfl Not to impede
Rule 8(f) was first adopted by IMO in 1987 to cover the Guidance for
the uniform application of the words ‘not to impede’ which appear in
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