The Modren Pirates

There has been a lot in the news the last couple of years about the modern pirates. The seize a ship and then hold it for ransom. At time they get millions of dollars. A ship was boarded a couple of days ago. The crew regained control of the ship, but the captain went with the pirates as a hostage to save the crew. To prevent this the ships should carry some big guns and have instrumentation that would detect an approaching boat. The just sink it without any questions. It would be rare that anyone that far away from the coast in a small boat would be seeking help. If they needed help, they could signal that they need help and then they could approach the ship with guns trained on them.