The problem is formulated as a boundary-value problem for a strip in the complex potential plane and converted to a boundary-value problem for a half-plane by conformal mapping. The solution is obtained using a Cauchy type integral for the density of which a nonlinear integral equation is derived. Its solution is found with the Galerkin method and the Newton–Raphson technique. The calculated results are compared with the experimental data and the calculations by other researchers. The lower limit of the speed of a solitary wave is found.