To get aboard the Smuggler's ship you need to board the ferries that travel from the docks in Thermock Hold. They automatically circle every couple of minutes, just jump aboard and you'll be in the Skyship in no time! If you're having trouble finding them, look up towards the Skyship and you'll be able to spot them, just follow them down until you see where they dock.

Picture of platform, look for it to the West of main part of the city.

The ship you're looking for is right in front of the box of rum. (Unless there's more than one box of rum. Possible, but I didn't see any.) Pick up the quest, chill out for a minute sitting on the dock of the bay, then the ship should come around. Take it up to the smuggler's ship, get your rum, head back to Thermock. You can jump over the side and swim, which was fun for me but maybe I'm crazy. It took me a while to ask zone chat, and then I felt dumb. Good luck!