Here we present detailed experimental results concerning flow-induced vibrations of long-span, shell-type gates in which the upstream gate face consists of vertical and inclined skin plates (also referred to as weir plates). Such shell-type gates possess two degrees-of-freedom, one each in the streamwise (horizontal) and vertical directions, due to bending flexibility in those two directions.The streamwise and vertical vibrations can become closely coupled with each other through the hydrodynamic forces acting on the weir plates, resulting in severe self excited vibrations. A two-dimensional laboratory model of a long-span, shell-type gate was operated with underflow only (i.e., no overflow) at small gate openings with several different inclined weir plate geometries, ranging from a 17.5°to a 65°inclination angle (relative to the horizontal) for the inclined weir plate. By measuring the gate's vertical and horizontal displacements, it was possible to determine the vibration frequency, the excitation ratio (negative damping ratio) and the trajectories of gate motion. These results show that inclination angle of the inclined weir plate angle plays a significant role in determining the gate's susceptibility to this type of dynamic instability. Long-span, shell-type gates with an inclined weir plate angle of about 60°relative to the horizontal were found to be the most unstable.