If he survived and escaped back to King's City, he would definitely never be promoted, so his only chance of gaining Timothy's approval was to defeat the rebel king's ship. Even though this ship might have been produced by demons, the crew on it was still human and defeatable!
He believed that he was a good judge of opportunity—this blockade was his chance to prove himself and be crowned as a real nobleman, since most of the noblemen were not willing to leave the comfort of their homes to fight on ships for months.