From Your US Coast Guard:

“The U.S. Coast Guard is pleased to announce the availability of type-approved Automatic Identification System (AIS) Class B devices. These lower cost AIS devices are interoperable with AIS Class A devices and make use of expanded AIS messaging capabilities. Unfortunately, not all existing Class A devices are able to take full advantage of these new messaging capabilities. All existing AIS stations will be able to receive and process these new messages from a Class B device.
However, they may not be able to display all Class B information on their Minimum Keyboard Display (MKD) or other onboard navigation systems. In most cases, a software update or patch will be required to do so. Therefore, the U.S. Coast Guard cautions new AIS Class B users to not assume that they are being ‘seen’ by all other AIS users or that all their information is available to all AIS users. Further, the U.S. Coast Guard strongly recommends that all users of out-dated AIS software update their systems as soon as practicable.”
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