On a small hill to the northeast of the Brandywine Bridge is First Mate Argirion. Talk to him, take the quest he offers and prepare for a long-ass walk/swim up the Brandywine/Baranduin.
Stop reading here if you don't want a guide through the whole thing.
You'll come across various crates and kegs and possibly lockers on the way. Collect them. You'll need them to complete the quest.
People under level 35 will want to be careful as they get further up-river. Either stay in the water and swim or stay right on the edge of the water, avoiding the high level critters and bandits at various points.
If you're over level 35, feel free to murder them all to help the lowbies.
Eventually you'll see a damaged boat beached on the western bank of the river with the Captain of the boat on the far side. Have a chat!
At that point you can either swim back down the river (booooring) or use your map/teleport to go somewhere closer to the Brandywine Bridge.
Assuming you've collected enough of the crates and kegs you can turn in the quest... which opens up the Quartermaster vendor beside the First Mate.
Collect enough ale/cram again and you can buy the following cosmetic items:
Eyepatch!
Hat!
Eyepatch WITH hat.
Each is a single item. I got all 3.
While collecting ale and cram you may also find Waterlogged Lockers - these contain some random loot and potentially an eyepatch or hat, though these have stats on them. The two I found required level 25 so I can't wear them to show pictures yet.
Enjoy your piratical themed stuff!
