Here is the full list of all 20 Nelly Cootalot: The Fowl Fleet achievements.
Trounce Moses Melly first time around
Join the Merchant Navy
Make sure everyone's a winner
Meet the denizens of the Toff Races
Escape the MS Undeliverable
Make the lookout see a harmless tug boat
Wrap your ears around all of Spry's groove
Catalogue all the stolen goods
When two seashells come together
Keep your eyes peeled in Chinatown
Become an aromatic master manipulator
Don't forget to return what you borrow
Track down Widebeard's Fowl Fleet
Shoot down all the varmints on your first attempt
Interview the head Ptarmigan's supporter
Take an interest in Gloomholm's deceased citizens
Fulfil an ancient prophecy
Find out what Sebastian thinks about 20 characters
Recruit an unexpected crewmember
Unlock all achievements in Nelly Cootalot: The Fowl Fleet