I've met up with the courser at the marina but he is in constant battle with a couple of BOS soldiers and it since neither one will die, the given task doesn't progress...the courser has an icon above him but won't talk while in battle. Thanks

You can either wait for the courser to kill of the knight, or, you can go do the mission by yourself. Courser is "protected", BOS is not. They are just REALLY tough to kill.

Where IS the mission? Is the location on my map?

Yeah, I just went into Libertalia myself while he was fighting the BoS. He caught up to me when I confronted the Raider leader.