After improved twice, the choice "I would like to land my ships here next to this settlement." for the first time. The player cannot know that ships is landable till improve twice, and can't have a strategy for whether or not to build the first and only settlement near the sea (or rivers leading to the sea).
(https://img.atwiki.jp/awoiafwb/attach/1/245/ship_near_settlement1a.jpg)
- Game version (and steam or downloaded):
AWoIaF v9.4, Warband v1.174 downloaded