Assassin's Creed Black Flag Resynced Guide | How to Get Harpoon Strength Ultimate Plan

Here’s a guide on how to get the Harpoon Strength Ultimate Plan in Assassin's Creed Black Flag Resynced.

Game Guide by Ragib Rawnak on Jul 22, 2026

Get the maximum harpoon damage with the Harpoon Strength Ultimate Plan and take down the toughest ocean predators in Assassin's Creed Black Flag Resynced with significantly less hits.

To craft this final whaling upgrade, you need to grab a hidden treasure map and dig up the chest. Here is the exact path to get it done.

Treasure Map on Mariguana Island

Before going to the chest, you need to pick up the treasure map that triggers the dig spot. Sail over to Mariguana Island at coordinates (848, 515), and drop anchor on your ship.

Head to the south west part of the island and look for the small crevice in the rocks. You have to look for a hidden cave entrance hidden behind the hanging vines and white flowers.

Then, you have to sneak down and squeeze through the small entrance to find a body lying on the ground. Loot the body to get the treasure map in Assassin’s Creed Black Flag Resynced.

Dig Up the Blueprint in Andreas Island

The map indicates a buried chest at (544, 693) at Andreas Island. Use fast-travel or sail to the island and go to the southern shore.

Start at the rowboat on the beach and look out toward the small, isolated islet nearby that features three distinct palm trees.

Swim or wade over to this tiny patch of sand. Interact with the ground right in the middle of the trees to dig up the hidden chest. Inside, you will find the Harpoon Strength Ultimate Plan alongside a batch of Reales in Assassin's Creed Black Flag Resynced.

Once you have the blueprint, open your ship upgrade menu while aboard the Jackdaw or visit any local Harbourmaster. Navigating to your whaling upgrades allows you to craft the maximum strength boost using your collected materials and currency.

FAQ

Q. Do I need to buy this treasure map from a store?

A. No, you cannot buy it from a General Store. You must manually loot the body hidden inside the vine-covered cave on Mariguana Island at (848, 515).

Q. Can I dig up the chest on Andreas Island without the map?

A. No. Buried Chests in Assassin's Creed Black Flag Resynced will not render or show a dig prompt until you have picked up the map first.

Q. What wildlife is this upgrade best used for?

A. Maxing out your harpoon damage helps tremendously when hunting high-tier marine targets like the Killer Whale, Great White Shark, and Humpback Whale.

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