Snailboats

[Prompt: A method used to carry goods over long distances]
Along and across Olua's shell is a honeycomb of intersecting rivers, water filling in the seams of the 13 segments. These rivers are huge, fast-flowing, and dangerous. For those who can weather them, however, swift waters are incalculably useful, and profitable. They could get an object from one side of the shell to another in mere sleeps, if only someone could create a vehicle hardy enough to survive the trip.
Well, someone has. Allow me to introduce the snailboat.
The name is nothing if not apt. These boats bear strong resemblance to their gastropod namesake, both in appearance and behavior. The working body of the ship is made of heavy, hardy, flexible material, and fixed with hooks and adhesives that enable the ship to slow or even drop anchor when necessary. Atop the body is a large, spiral-shaped barrel, inside which any number of goods can be stored (these ships need no great sails because the quick and consistent flow of the rivers is much stronger than any breeze could be). Cargo is stored in the middle layers of the spiral, kept safe by their own tight packing, and unloaded easily via sealed doors on the sides. The outer layer is kept empty for reasons I'm about to explain.
Much of the time, snailboats travel upright, so that they really do look like (the world's fastest) snails cruising over the rivers. However, if things particularly turbulent, the journey is long, or a captain wishes to sacrifice steering for speed, snailboats can travel on their side. In that case, the crew will pull the body of the boat inside the shell, creating a sealed vessel. The boat then tips over and travels on the flat end. Now, it looks like a cinnamon roll on a jaunt. The bulk of its vertical drag lost, the snailboat will rocket along the river, pinballing between its shores. It's not the most comfortable way to ride, but these boats are built to be hardy. They nearly always survive the trip.
When the sailors have reached their destination, or are otherwise ready to return to snail form, they "reinflate" the working body and push it back out. Unpracticed sailors will need to hold on to something secure during tip-up, but veterans can often simply surf the craft's transition to verticality. The boat always pulls into port in snail form, where the shell is detached, rolled off, and unloaded on land. An adventure in efficiency.