Hiergamenon + Technology

The hiergamenon shows the technologies. It's great. I want to know how to make ships. So I go there, browse, and find Seafaring.

Unfortunately, this piece of info is worthless. I have no idea what tree I must research to get it. Is it military? Or trade related so I should seel it in diplomacy? Or where?

Technologies MUST show their tree and prerequisites if any in the Hiergamenon. As it is, the tech hiergamenon is not very helpful.