Flap gate is a shield that pivots on two pivot bearings about a horizontal axis, is located near the threshold of the head section of the dock. In general, the gate is loaded lateral load, which does not coincide with the resultant of the direction of the principal axes of inertia and does not pass through the center of curvature (or stiffness centers), coinciding with the centers of torsion. Therefore closures are almost always on the oblique bending and torsion constrained. In this regard, the task of calculating the shutter, after bringing the load to the axis stiffness, is divided into two: the shutter calculation for oblique bending and calculation of constrained torsion moments that arise when the ghost said. If the bolt is long enough as compared to the cross-sectional dimensions, the calculation is performed on the oblique bending on the well-known formulas of strength of materials; at a small gate to the flight height of the section is necessary to consider the impact of changes. The paper proposes an approach to solving the problem is not associated with any arbitrary simplifying assumptions, except the assumption of non-deformable shutter profile as a thin-walled bar.