https://www.polygon.com/2018/7/31/17628958/sea-of-thieves-is-under-siege-in-new-expansion-cursed-sails

Since Sea of Thieves launched in March, the developers have been adding to the core pirate experience with weekly events and larger expansion packs. The first expansion, The Hungering Deep, focused on adding to the natural threats of the ocean with the terrifying Megaladon. The second expansion pack, Cursed Sails, arrives today, and is free and available for all players.

Much like The Hungering Deep, Cursed Sails offers a limited-time campaign with tools and mechanics that will forever change the existing world of Sea of Thieves. Skeleton ships are on the rise, along with cursed ammunition that not only tears through hulls but dish out serious gameplay effects like dropping an anchor or intoxicating the crew. The brigantine is a new, three-crew ship, and ships can now join together in Alliances to formalize peace treaties and share loot.