The class B transmitter, as you know, is a “light” version of the class A transmitter. The differences are:Class B: lower rate of telegrams (e.g. every 30s for a speed of 14kn, whereas for the class A transmitter it is every 10s). Does not transmit the IMO number or the call sign. Does not transmit ETA ordestination. Does not transmit the status of navigation. It is necessary to receive or transmit binary messages. Does not transmit if the the ship is turning. Does not transmit the draft.