The Harpoon Strength Ultimate Plan is required to unlock the maximum harpoon damage upgrade in Assassin’s Creed Black Flag Resynced. Once unlocked, you can increase your harpoon’s damage, making naval hunting much easier. This guide explains where to find the treasure map, locate the buried blueprint, and unlock the max strength harpoon upgrade.
Find the Treasure Map
Travel to Maraguana Island and make your way to the location marked on the map. Once you reach the location, you will find a Skeleton. Interact with it to obtain a Treasure Map, which reveals the location of the Harpoon Strength Ultimate Plan.
Travel to Andreas Island
After collecting the treasure map, head to Andreas Island, where the blueprint is buried. Follow the map to the small islet, located in the southern part of the area.
Once there, look for a dig site prompt on the ground and interact with it to dig up the treasure chest. Inside, you’ll find the Harpoon Strength Ultimate Plan.
Upgrade Your Harpoon
With the blueprint in your inventory, travel to the Harbor Master building on Great Inagua. Select the harpoon upgrades and purchase the Harpoon Strength upgrade. The upgrade costs 4,000 Gold and increases your harpoon damage from 20 to 30, giving you the maximum possible harpoon strength.
After purchasing the upgrade, you’ll unlock the strongest harpoon available in the game, allowing you to hunt legendary sea creatures and other large marine animals much more efficiently.