Assassin’s Creed IV Black Flag Resynced has 12 Ultimate Upgrade Plan Locations. The Ultimate Plans are needed for the final upgrades of your ship, the Jackdaw. Fully upgrading the ship unlocks the Ship This trophy & achievement.
6 of them come from Underwater Shipwrecks, which are only accessible after story Sequence 06 – Mission 01: Diving for Medicines. The ones from shipwrecks also give the best upgrades. The remaining 6 are from collecting specific Treasure Maps and digging up their treasures.
Afterward you can use the Ultimate Upgrade Plans at the Harbourmaster in the “Upgrade Ship” menu. The upgrades cost money and materials. A good way to farm money passively is through Kenway’s Fleet (unlocks in Sequence 4) by sending 5 Schooners and 5 Brigs on missions. The schooners generate money and the Brigs generate materials. You must also have upgraded the harbourmaster shop at Great Inagua. This is the total cost to fully upgrade the ship and harbourmaster: 309,800 Reales, 4755 Metal, 2750 Wood, 550 Cloth.
Nothing is missable, you can still do everything after the story.
Quick Overview:
- Hull Armor Ultimate Plan – from underwater chest in San Ignacio Shipwreck (348, 744)
- Mortars Ultimate Plan – from underwater chest in Antocha Shipwreck (600, 636)
- Ram Ultimate Plan – from underwater chest in La Concepción Shipwreck (184, 425)
- Swivel Guns Ultimate Plan – from underwater chest in Devil’s Eye Caverns Shipwreck (456, 332)
- Broadside Cannons Number Ultimate Plan – from underwater chest in The Blue Hole Shipwreck (440, 145)
- Round Shot Strength Ultimate Plan – from underwater chest in Kabah Ruins Shipwreck (738, 120)
- Heavy Shot Strength Ultimate Plan – solve Treasure Map from Ambergris Key (Misteriosa) (28, 160 > 271, 178)
- Fire Barrel Strength Ultimate Plan – solve Treasure Map from Santanillas (San Juan) (191, 218 > 455, 462)
- Heavy Shot Storage Ultimate Plan – solve Treasure Map from Cayman Sound (Petite Caverne) (298, 311 > 863, 235)
- Mortar Storage Ultimate Plan – solve Treasure Map from Tortuga (Matanzas) (851, 352 > (312, 617)
- Harpoon Strength Ultimate Plan – solve Treasure Map from Mariguana Island (Andreas Island) (847, 514 > 544, 693)
- Fire Barrel Storage Ultimate Plan – solve Treasure Map from Petite Caverne (Tulum) (862, 237 > 40, 372)
Ultimate Upgrade Plans from Underwater Shipwrecks
The Underwater Shipwrecks become accessible after story Sequence 06 – Mission 01: Diving for Medicines.
#1 – Hull Armor Ultimate Plan
From underwater chest in San Ignacio Shipwreck (348, 744).
#2 – Mortars Ultimate Plan
From underwater chest in Antocha Shipwreck (600, 636).
#3 – Ram Ultimate Plan
From underwater chest in La Concepción Shipwreck (184, 425).
#4 – Swivel Guns Ultimate Plan
From underwater chest in Devil’s Eye Caverns Shipwreck (456, 332).
#5 – Broadside Cannons Number Ultimate Plan
From underwater chest in The Blue Hole Shipwreck (440, 145).
#6 – Round Shot Strength Ultimate Plan
From underwater chest in Kabah Ruins Shipwreck (738, 120).
Ultimate Upgrade Plans from Treasure Maps (Buried Chests)
#7 – Heavy Shot Strength Ultimate Plan
Solve Treasure Map from Ambergris Key (Misteriosa).
Location: Ambergris Key (28, 160) – swim into the cave through the underwater tunnel, then enter the big room with a locked chest and many enemies. Climb the pillars around the middle of the room to find it on the upper floor.
Solution: Misteriosa (271, 178) – Fast travel to the viewpoint but turn around instead of jumping down, you’ll see a water fountain behind the mayan temple (on the top level). The buried treasure is to the left of the fountain in the grass, behind tall white flowers.
#8 – Fire Barrel Strength Ultimate Plan
Solve Treasure Map from Santanillas (San Juan).
Location: Santanillas (191, 218) – on a little hill, climb up via the tree branches around it
Solution: San Juan (455, 462) – swim into the cave through the underwater tunnel, as soon as you exit the water there will be a cave section with a single enemy. The treasure is there on the right, just before climbing up the wooden scaffold.
#9 – Heavy Shot Storage Ultimate Plan
Solve Treasure Map from Cayman Sound (Petite Caverne).
Location: Cayman Sound (298, 311) – from a skeleton at the beach
Solution: Petite Caverne (863, 235) – go to where the Hutia hunting spot (rat icon) is in the southern edge of the cave. It’s behind the rocks with a waterfall.
#10 – Mortar Storage Ultimate Plan
Solve Treasure Map from Tortuga (Matanzas).
Location: Tortuga (851, 352) – at the eastern shoreline of Tortuga, from a skeleton at the beach.
Solution: Matanzas (312, 617) – in the south-east corner of Matanzas, to the left of the Mayan Stelae behind the waterfall.
#11 – Harpoon Strength Ultimate Plan
Solve Treasure Map from Mariguana Island (Andreas Island).
Location: Mariguana Island (847, 514) – Approach the treasure map icon from the north to find a small cave, in the middle of the cave you can crouch through a small tunnel covered by green leaves. It’s a bit hidden because the leaves camouflage the entrance, just 8 meters from the treasure map.
Solution: Andreas Island (544, 693) – on a small island in the south of Andreas Island
#12 – Fire Barrel Storage Ultimate Plan
Solve Treasure Map from Petite Caverne (Tulum).
Location: Petite Caverne (862, 237) – from a skeleton inside Petite Caverne
Solution: Tulum (40, 372) – at the southernmost tip of Tulum, at the beach behind a shipwreck
Reward: Fire Barrel Storage Ultimate Plan, 3000 Reales
That’s all of the Ultimate Plans in AC IV Black Flag (2026 Remake). For all other collectible types refer to the Assassin’s Creed IV: Black Flag Resynced Collectible Guide.
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