devtrackers.gg
They announced the feature and some details and examples in the IGN livestream a few minutes ago, we also saw some nice footage from islands and ships.
EDIT: They now have it as a dedicated video without the need for a timestamped stream https://www.youtube.com/watch?v=9gbGY0rJ80A
Base ship: https://imgur.com/yNERuY5
Extra sail: https://imgur.com/bd6H2mm
rowers: https://imgur.com/wlpQJya
archer towers: https://imgur.com/RmeXMdD
hull reinforcements (not shown)
catapult tower: https://imgur.com/bHjLMy6
Upgrades seem to come with benefits and trade-offs like less cargo space. Also given catapult towers did replace the extra sail in the video, i assume there are some limitations to how many upgrade you can do.
Hopefully a dev blog will come with better pictures later. Oh, they also talked about revealing more in April so i guess March will still be quiet.
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