On Porpoise (Bronze) - Get three dolphins to follow the boat
During Chapter 12, shortly after getting the Marco Polo Returns! trophy (it's in the same area), there will be three dolphins that you can get to follow you in your boat. One will be close to the island with the wrecked, while the second will be in between that previously mentioned island and a set of three rocks on the one side of the big island (view video above for a location). You'll know it's the right spots when Sam makes a remark about the dolphins.
The annoying part about this trophy is that sometimes the dolphin doesn't follow you, plus Sam and Nathan will have some banter about their adventures that will prevent Sam from commenting on the dolphins (such as in the video). Your best bet is to keep trying if you don't succeed on your first attempt.
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