You will need a pinnace for this achievement. They are rare but can be obtained early on in the trader campaign or as the starting ship in Free Play. Once you obtain a pinnace, make sure it is fully supplied with sailors and cannon shots.
You will need to locate a convoy with at least 60 guns and engage it in a manual battle. As soon as the battle starts, pull away and place some distance between your ship and the AI’s. You will be able to fire on the enemy without them firing on you as long as they don’t get too close. You can take some hits but don’t get too close, as you will go down quickly. Once the enemy is defeated the achievement will unlock.
Alternate Method: Ensure you have a pinnace fully loaded with sailors, and a 2nd convoy consisting of much more powerful ships. Keep your main convoy and pinnace close together and find an enemy military convoy that has 60 guns (merchant convoys will surrender.) Once you locate one, initiate the battle with your strong convoy.
The goal is to wear down the enemy ships to about 10-15 health each. As the enemy ships wear down, swap your strategy to defensive behaviour (blue shield) and let the enemy sink your ships. As soon as you lose the battle, move your pinnace to attack. You need to follow the strategy mentioned above, but will find it much easier to sink them.