Abstract
Course stability and yaw response of tow and towed ships are investigated by eigen value analysis based on linearized motion equations for the ships. Then, towing cable is assumed to be a truss element. We found that there exist two slewing motion modes with long and short period. The slewing motion with long period is no relation with size of tow ship and is determined by hydrodynamic characteristics of the towed ship only and parameters of towing cable such as cable length and the towing position. In short period mode, on the contrary, the natural period and the amplitude reduction time by half become long with increasing the size of tow ship. It is useful for safe towing to enlarge the size of tow ship more than towed ship. On the other hands, course unstable zone slightly increases while the tow ship becomes smaller than towed ship. Cable length and the towing position at the towed ship almost determine the course stability. The towing position at the tow ship does not influence the course stability if the position is in aft part of the tow ship. For reducing the course instability remarkably, it is useful to take the towing position at the towed ship large. The desirable value is that 2/L2 is almost 0.8 where 2 is the towing position at the towed ship and L2 the ship length of towed ship. However, the yaw response against the steering action becomes worse.
