This pirate issue could be settled quite easily.
Put a few navy guys on one in ten of the ships passing through the problem area with small missiles.
Blow the attacking boats out of the water and just keep steaming, leaving the survivors to the sharks.
Piracy will stop quickly.
I was thinking the same thing.
Take a small freighter and put some deck guns on her and hide them. Crew it with SEALS. Let the pirates come out and engage, then let the SEALS have at 'em. Leave one survivior to go home and tell the story. Repaint the ship, wait a week or two and do it again. Pretty soon the pirates stop thinking like a group and start thinking like individuals.