I think all they had for defense were water hoses. No kidding.
If the pirates had managed to board, they would have been able to steal a king's fortune in cash and jewelry from the very rich passengers.
The ship was very lucky.
The goal was to kidnap and behead the 150 Americans on-board. These "pirates" were Al Qaeada, and the goal wasn't to steal jewelry.
Or, have a lot of hostages for ransom or videotaped slaughter.
And had a damned fine captain. You gotta have confidence in a guy named Sven Eric...