Horizontal motion of booms in rotary cranes typically generates undesirable two-dimensional load-sway; therefore, crane operators must be highly skilled to control the crane's motion. To reduce the burden on human operators, automatic control systems that can simultaneously control the boom's position while suppressing unwanted load-sway have been widely investigated. In most existing control schemes, both horizontal and vertical boom motion must be used to suppress load-sway. However, it would be less energy intensive and indeed safer if a control scheme could be developed that only utilized horizontal boom motion, i.e. without the need for any vertical motion. In this paper, we present a nonlinear controller design that enables both boom positioning and load-sway suppression using only horizontal boom motion. Numerical simulations and experimental results demonstrate the effectiveness of the proposed method.