The harpoon plans are required to construct a Harpoon to catch the Thalassus. They are given by Jones the fisherman after talking to him. You will need to take the plans to Linza in Hemenster, just north-east of the fishing guild. She will make you a giant harpoon, which she feels is more appropriate than the harpoon described in the plans.
The Harpoon plans, being read
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