CHIRP annual digest 2016 6th

CHIRP Annual Digest 2016
OOWs on vessels required to give way should bear in mind
that encounters may become more complex. Planning well
ahead of the anticipated areas of interception should be
considered together with the likely behaviour of vessels to
be encountered well before an avoidance manoeuvre is
initiated.
Masters and OOWs should be aware of the approximate
manoeuvring domain, not only of their own vessel, but for
other vessels in an encounter. Such dimensions can only
be an estimate but navigating officers should be urged
tlearn the different variations. Opportunities to do this
could be during their training when they could serve on a
variety of vessel types or whilst at college, by comparison
with other officers from different service experience.
When overtaking the relative overtaking speed between
each vessel directly relates to the time and distance it will
take for the overtaking vessel to move from safe position
astern to a safe position ahead. When passing within a TSS
lane or any confined waters the timing between starting
and completing the overtaking manoeuvre MUST be a
carefully considered so that it falls entirely within a straight
and clear section of water and be unencumbered by
restricted sections or intermediate alterations of course.
Within a TSS a typical section would be between the buoys
marking the next leg of the navigational passage. A
constriction of searoom whilst overtaking must be avoided.
This especially so as to avoid overtaking and simultaneously
altering course on a navigational leg at the same. Such
overtaking and altering course around buoys creates a
“sandwich” effect where the vessels have to calculate the
time their commencing of turn for navigational purposes
and also be restricted by close proximity to another vessel
and the risk of collision. Only overtake when you can be
past and clear before the next navigational alteration of
course on a straight leg. If the relatively low overtaking
speed does not permit this to be achieved then the safe
option is to slow down a little, match the speed of the
vessel previously being overtaken and to remain on their
quarter all the way up the routing. The little time lost is
not worth the considerably increased risk of prolonged
overtaking and foreseeable constriction of searoom when
it will be need most to maintain a safe CPA.
Whilst it is recognised that extreme movements on large
engines can be damaging and therefore are likely to be
discouraged, the Colregs do still include slowing and
stopping as alternatives to course alterations. In areas of
high congestion engines should be in a state of readiness
that can respond to slowing and stopping movements.
Overtaking vessels should offset their course, preferably
to pass on the starboard side of vessels they are overtaking
(leaving the overtaken vessel to port) and should avoid
following directly astern.
VHF and Colregs
Many reports are received at CHIRP that refer to VHF
conversations between vessels during manoeuvres to avoid
collision. The collision regulations are written to enable
actions to be decided based upon the behaviour of vessels
approaching one another and the ascertainment of a
collision risk. There is very little provision for communication
between vessels during these manoeu vres. It is restricted
to sound signals, which most mariners of large powered
vessels would recognise are of little use in open waters,
especially with noise interference from large fans or funnels
close to the bridge. Light signals however, are permissible
in similar form to the sound signals i.e:
■ one short or morse “E”- I am turning to starboard;
■ two short or morse “I” – I am turning to port; and
■ three short or morse “S” – My engines are going
astern.
VHF is not mentioned and neither is AIS. The important
points to remember are:
■ Identification of vessels may be difficult to match
between the VHF and visual and/or radar targets and
mistaken identity is possible;
■ AIS provides some measure of identification and also
heading and destination information that can be
helpful in advance planning but it involves time that
can be better spent conducting manoeuvres; and
■ VHF exchanges, if conducted properly, use up con -
siderable valuable time that close to a manoeuvre
would be better invested in the action of manoeu -
vring itself.
It is a fact that accident investigators often use the
expression “VHF Assisted Collision” in similar fashion to
“Radar Assisted Collision”. Both expressions, whilst con -
veying a meaning that is understood by professional
mariners, are inaccurate as it is the action of the operator
not the equipment itself that causes the error.
Maintaining appropriate Closest Point of Approach
(CPA)s
A minimum 2 miles CPA is best practice for all vessel sizes
in open water. Where this is to be achieved in a fine
crossing ahead scenario the minimum safe Bow Crossing
Range (BCR) would be in fact TWICE that… If one vessel
indicates discomfort as to what distance constitutes
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