What could the Coast Guard do if there was trouble in rough water, at 30 knots, in a dense fog or strong wind and rain? Which is likely when the Jihadists would choose to strike. Ask the WA State ferry system if there are enough life boats for 600+ people, you will be shocked.
Judging from the size of the gun mounted on the front of their boat I think they're there to protect from other boats attacking the ferry, like the one that got the USS Cole.