There are 5 total Group Missions. For each you will need to buy a ticket to The Open Sea from any dockmaster. They are lore. You will need a new one for each quest. It seems as though there are several versions of several Missions. Do not worry your head over this. If you hit the 3 Mission givers, three docks, and all 5 ships, you will complete these.
The Buried Sea> Exploration> The Open Sea Traveler>
This updates the following 5 tasks in your achievements window:
1. Merchant and Pirate Ships
2. Merchant and Undead Ships
3. Pirates and Undead Ships
4. Undead Ships
5. Merchant Ships
#1 The Open Sea (Merchant vs Merchant)
From Captain Zeke- Camp by dock
Hired Hands on the Open Sea
#2 The Open Sea (Merchant vs Pirate)
From Whent Goldspire- Camp by dock
Open Sea: Protect My Ship
#3 The Open Sea (Merchant vs Pirate)
From Shental Darkmind - near -225, -100 (middle of the zone)
Open Sea: Pirating Ways
#4 The Open Sea (Pirate vs Undead)
From Captain Jafar who is in the SW lobe and wanders
Kill the LIVING. Leave the dead alone. Be careful with targeting.
#5 The Open Sea (Merchant vs Undead)
From Captain Jafar who is in the SW lobe and wanders
Open Sea: Stop Kenox!
There will be Necromantic Soul Barrier drop- looks like purple dolly. Everyone in mission needs one.
You need to kill until you get a Coral Key which gets you into the Kenox’s room. Then you can gank him in his room.