Riverboat

Any dingy can paddle around Dechue Lake or let the flow of the Tomber carry them downstream but it takes a special kind of vessel to travel upstream against the wind efficiently, especially for the larger shipping vessels that power much of Granmont's internal and external commerce.
These specially engineered riverboats use mill-like wheels to locomate themselves by paddling through the water. This is possible thanks to orichalchum flywheels, highly sophisticated kinetic energy storage devices, that are charged from the flow of the river as the boat floats downstream, unleashing that same energy to push the boat back upstream.
Because some of the flow of the river ends up in the flywheel instead of moving the boat these vehicles are relatively slow. They're even slower going upstream due to the resistence from the rivers. Additionally, even the most advanced flywheels can only store about a mile's worth of travel and overcharging can result in catastrophic failure. These limitations prevent this Riverboat design from being practically deployed elsewhere, but they're perfect for navigating within and around Granmont.