How should you make a routine call to a vessel with the call sign DFB870 using your call sign ABC 263?

When making a routine call to a vessel, it's essential to use the correct working frequency, which is typically designated for maritime communications. Channel 16 is the international distress, safety, and calling channel. It is primarily used for initial contact and establishing communication with another vessel before potentially switching to a working frequency for operational communication.

In this situation, when you want to call DFB870 using your call sign ABC 263, starting the communication on Channel 16 ensures that the call is made effectively, as this is the channel where vessels monitor for distress calls and communications. Once the vessel answers, you can then switch to another channel for further conversation, which is standard practice in maritime communication to keep Channel 16 clear for emergencies.

The other channels listed might not be designated for initial calling or could be less monitored, making them less effective for establishing contact with DFB870. Thus, Channel 16 is the appropriate choice for making a routine call in this scenario.