The Best Way to Defeat a Treasure Fleet Singlehandedly is...

This only works with a galleon or above, and using any light classes is next to impossible, unless you are an extremely good sailor or a very high level, but then it is still super hard. Take your ship and stop it in range of the treasure fleet and start using thunderbolt. When the ship gets close enough, fire firebrand or fury at it. Target the farthest ship from the main body of the fleet, and when it gets close enough, fire a volley of 4 chainshot. This will slowly deteriorate the sails and cause the fleet to move slowly. Stay IN FRONT of the ship and when it gets even closer, fire an explosive at it (optional). Repeat the process again and again and you will have defeated a treasure fleet all by yourself, and you will have bragging rights!