at which she can be kept on her course.
She shall if necessary take all her way
off and in any event navigate with
extreme caution until danger of collision
is over.
The importance of a lookout, one
who is looking and HEARING, for early
detection of other vessels cannot be over
stressed when experiencing restricted visibility.
Designate someone to watch and
listen for dangers that may come from
any direction. Preferably your vessel will
have lookouts fore and aft who have been
briefed during their pre-sailing briefing
to look for shadows and listen for sounds
of other vessels including low visibility
signals. All vessels are to comply with the
sound signals specified in the Rules. These
will be discussed in the section on Lights,
Shapes and Sounds. In addition to increasing
the number of lookouts and making
required sound signals, all vessels are to
reduce speed and turn-on their navigation
lights.
AUTOMATIC IDENTIFICATION
SYSTEM (AIS)—
OVERVIEW
(NOT TO BE CONFUSED WITH
AQUATIC INVASIVE SPECIES—AIS)
Picture a shipboard radar or electronic
chart display that includes a symbol for
every significant ship within radar range,
each as desired with a velocity vector
(indicating speed and heading). Each
ship “symbol” can reflect the actual size
of the ship, with position to GPS or differential
GPS accuracy. By “clicking” on a
ship symbol, you can learn the ship name,
course and speed, classification, call sign,
registration number, MMSI, and other
information. Maneuvering information,
closest point of approach (CPA), time to
closest point of approach (TCPA) and
other navigation information, more accurate
and timelier than information available
from an automatic radar plotting aid,
can also be available.
With this information, you can call any
ship over VHF radiotelephone by name,
rather than by “ship off my port bow” or
some other imprecise means. Or you can
dial up directly using GMDSS equipment.
Or you can send to the ship, or receive from
it, a short safety related email message.
The AIS is a shipboard broadcast system
that acts like a transponder, operating
in the VHF maritime band, that is capable
of handling well over 4,500 reports per
minute and updates as often as every two
seconds. It uses Self-Organizing Time Division
Multiple Access (SOTDMA) technology
to meet ship high broadcast rate and
ensure reliable ship-to-ship operation.
AUTOMATIC IDENTIFICATION
SYSTEM (AIS)—Class E
The Automatic Identification System
(AIS) is the newest tool for collision avoidance.
An AIS transceiver combines an integral
GPS with a VHF transmitter. It broadcasts
the vessel’s name, GPS course, speed,
and if enabled, data on its route and cargo
on a VHF frequency (most units are dual
frequency using VHF 87B and 88B). AIS
transceivers also pick up that data from
the vessels around then and calculate when
they’ll be at their closest point of approach
(CPA) and how close they will pass; an
alarm goes off if the vessels will pass within
a certain preset distance. Most commercial
vessels are required to use Class A transceivers,
while recreational vessels may use
the lower-power Class B transceivers. Class
B “receive only” units don’t transmit their
own position but do receive AIS signals
and allow you to determine if a risk of collision
exists. Currently, recreational vessels
over 65 feet in length are required to have
the AIS.
Several online websites track vessel
movements using AIS signals picked up
by shore-based receivers (such as www.
vesselfinder.com), that can be accessed on
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/www.vesselfinder.com