There are 3 upgrades available at the moment:
Jib is a triangular sail fixed to the tackle between the bowsprit and the foremost mast. It increases the ship's speed, yet one jib will only last for 240 days of travel.
Extra Bales allow you to carry 750 extra kilos of cargo by maintaining the balance of the vessel. They become unfit for use after 200 days of travel.
Bard entertains sailors with his ballads, which allows you to travel 1 day longer. The bard's contract expires after 200 days of travel.
❗️ Attention! All these upgrades are temporary, which means you CAN'T remove them from your ship and put them to storage. If you do so, you'll loose the upgrade.