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Introduction
The
AIS
WatchMate
is a device which provides information to assist in avoiding collisions at
sea. It works by receiving and transmitting data as part of the Universal Shipborne
Automated Identification Systems (AIS). The AIS system uses two dedicated VHF channels
designated for this purpose and with the installation of the
AIS
WatchMate
to receive signals
from other AIS-equipped vessels you can view this information. In addition, your vessel data
is transmitted to other AIS-equipped vessels within range.
The AIS system provides several types of messages from other vessels and base stations.
Each type of message is sent at a different interval based on the navigation status of the
vessel. Vessels moving or turning faster send out navigation information more frequently
than vessels at anchor. Data received from other vessels is split between two types:
navigation information and voyage information. Vessel navigation and position information is
generated by an on-board GPS or similar navigation device and is sent frequently. Voyage
information contains the ship's name, its destination, size, type, cargo, etc. This data is
typically only sent once every few minutes.
The
AIS
WatchMate
provides a means to view how recently information has been received
from each vessel and this data is designed to help you determine how accurate and
dependable the information may be at any given time.
The
AIS
WatchMate
refers to each vessel other than your own as a
target
. Associated with
each target are the most recently received position, navigation, and voyage information. Also
associated with each target are computed data to help determine the risk of a collision.
The targets are contained within a
target list
. The
AIS
WatchMate
allows you to view the
target list and also examine each target in detail. By default, the target list is ordered by
priority
. You can disable priority ordering if you wish. However, by viewing targets in a
prioritized fashion you can focus your interest on the targets most likely to pose a collision
risk first. Similarly, whenever a target triggers an alarm you don't have to scroll to find it. The
target is displayed immediately with an indication of the cause of the alarm.
The
AIS
WatchMate
utilizes data from its built-in GPS receiver to assist you in determining the
risk of a collision with each target. Multiple targets are automatically and continuously
tracked simultaneously. Alarms are associated with each individual target and when an
alarm is muted for one target it does not affect any other targets which might also trigger
alarms.
The computed data for each target includes the following items. Note that in order to
compute this data your vessel's current position, course, and speed are required. The
AIS
WatchMate
receives this information continuously from its built-in GPS.
If the built-
in GPS does not have a valid “fix” then this information will not be
computed and displayed. In addition, your own information will not be transmitted to
other vessels.
Range
The
AIS
WatchMate
computes the range (distance in nautical miles)
to each target and displays it along with the target information.
Bearing
The bearing to each target is also displayed. The bearing may be
shown as magnetic to facilitate quick visual identification using a
compass or binoculars. However, if you wish you can change a
setting to display bearings in degrees true or relative to your vessel's
current heading.
