Perhaps strategic placement of radar/movement activated GPS systems to early identify the scurge pirates once they are more than a few miles offshore, coupled with onboard armed security, remote controlled drones capable of fire power, convoy style/wagon train shipping methods, might help.
Obviously, the area is too vast to spot each and every little piss-ant boat these sea terrorists can launch. But it might be possible to track and identify their movements from space once the boat moves further offshore. Once sighted, marked, and identified an armed drone could be dispached to do recon. If it is determined to be an enemy threat, it can be eliminated before it reaches the ship. It takes quite a while to get 200-300 miles offshore in a small craft. The pirate "mother crafts" that harbor these attack boats should be easy enough to identify. Perhaps mandate that all boats in the area, more than 50 miles offshore emit an internatinal friend or foe frequency. Those pirate boats not emitting this frequency are legal targets for demise.
If the pirates get past this outer perimeter of defence, onboard radar can spot them a few miles out, giving the convoy's armed helicopters time to get in the air and engage. If, in a worst case scenerio, the pirates actually get within firing distance of the ship, the onboard security from the collective convoy can set-up for a real nice turkey-shoot.