In five days those boats could be in the water anywhere in the US.
I don’t know the odds, but the operation would be very, very easy. All they would need is a go-fast boat, and a ton of ANFO with a small kicker charge of a few blasting caps, industrial M-80s etc.
Not likely they would use these stolen boats. They would buy an old go-fast for cash, and buy used outboard motors for cash. Almost no signature. Three 250 hp motors across the back, a very typical package.
Lurk near Miami, Palm Beach or San Diego. A cruise ship on the horizon is dead easy to spot, and could not defend itself against a “Cole” type attack by a go-fast laden with explosives. The explosives would rip open the ship and cause it to sink in minutes.
Very very low hanging fruit. I see no possible defense, if the jihadists have already prepared boats and have the ANFO ingredients.