Furuno FA-150 Operator's Manual page 9

Not all ships carry AIS
The Officer of the Watch (OOW) should always be aware that other ships, and in particular
leisure craft, fishing boats and warships, and some coastal shore stations (including
Vessel Traffic Service centers) might not be fitted with AIS.
The OOW should also be aware that AIS fitted on other ships as a mandatory carriage
requirement might be switched off by the master if its use might compromise the security
of the vessel. Thus, users are therefore cautioned to always bear in mind that information
provided by AIS may not be giving a complete or correct "picture" of shipping traffic in their
vicinity.
Use of AIS in collision avoidance
As an anti-collision aid the AIS has the following advantages over radar:
• Information provided in near real-time
• Capable of instant presentation of target course alterations
• Not subject to target swap
• Not subject to target loss in clutter
• Not subject to target loss due to fast maneuvers
• Able to detect ships within VHF/FM coverage, including in some circumstances, around
bends and behind islands.
When using the AIS for anti-collision purposes it is important to remember that the AIS is
an additional source of navigation information. It does not replace other navigational
systems. The AIS may not be giving a complete or correct "picture" of shipping traffic in its
vicinity.
The use of the AIS does not negate the responsibility of the OOW to comply with all
collision regulation requirements, especially the maintaining of a proper look-out. The
prudent navigator uses all aids available to navigate the ship.
Erroneous information
Erroneous information implies a risk to other ships as well as your own. Poorly configured
or improperly calibrated sensors might lead to incorrect information being transmitted. It is
the user's responsibility to ensure that all information entered into the system is correct
and up to date.
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