We have a guide on how to be successful in whaling in Assassin’s Creed 4: Black Flag. All players have access to harpooning and whaling if they seek it out, and this guide is for the sake of players who want to move forward in the game by exploring this option.
Before you continue reading, I want to make it clear this guide is by no means related to taking a stand on whaling, and it neither condones nor condemns Ubisoft’s decision to add it in the game. This will simply be a guide to playing the game. This is also not a guide on the basics of whaling, which the game will teach you anyway. Again, this is a guide on increasing your chances of successfully getting a whale.
Before you start, you will want to upgrade the boat armor at least three times over and your harpoon at least two times over. After you have found and snagged a whale, you should aim just above where you expect the whale to go. You will just have to anticipate this using your best judgement. If the whale attacks you with its tail, hit the tail when it is up in the air. You will be OK even if you just hit the base of the tail.
When the whale goes underwater, it will either move a short distance away so it can ram you, or it will come up to try and body slam you. The tell for a possible body slam is the bubbles that appear on the water right before it tries it.
If it goes for ramming, you should have enough time to harpoon it. If you see bubbles, you should wait for the bubbles to boil up and harpoon when you see it hitting its zenith. You should also go for rapid fire at this juncture to beat it as quickly as possible and minimize the damage it does to your ship.
Source: Reddit