Very narrow mono-hull boats such as canoes and kayaks have little initial stability, but twin-hull W-kayaks are considerably more stable due to the fact that their buoyancy is distributed at a greater distance from their center line and therefore acts more effectively to reduce tilting. For purposes of stability, it is advantageous to keep the centre of gravity as low as possible in small boats, so occupants are generally seated. Flatwater rowing shells, which have length-to- beam ratios of up to 30:1, are inherently unstable.