The paper briefly reviews the background to the development of a mathematical model for the estimation of the loads in the lashing systems of box-type road trailers on board roll-on/roll-off (RoRo) ships. The theoretical basis employs a defined case of ship motion representative of the behaviour of such vessels in severe conditions. The mathematical model allows a range of lashing configurations and characteristics to be explored, together with the effect of parameters such as suspension stiffness, tyre stiffness, height of the centre of mass of the load and tyre and trestle friction with respect to the deck. The effects on the magnitude of the loads induced in the lashings by altering the motion of the ship and the position of the trailer on the ship are also investigated.