- The sensitivity of heave response predictions for long riserless drill strings hanging from a floating vessel are examined. A general analytical procedure is presented which is suitable for a variety of deepwater pipe systems. The dynamic response behavior is characterized in terms of the dynamic magnification, phase angle and total stress. The examples presented here focus on drill string systems, which vary in length from 9000 ft (2743 m) to 27,000 ft (8230 m) and can include a large package to be lowered to the seafloor. A procedure for evaluating the undamped natural periods and the corresponding mode shapes is presented. The sensitivity of the natural period estimates to hydrodynamic added mass approximations is examined. Numerical results for both design wave and random sea simulations are used to illustrate the sensitivity of the dynamic response in near resonant conditions and the possibility of exciting higher modes for very long riserless drill string systems. Finally, the sensitivity of the displacement predictions to reasonable variations in skin friciton and viscous drag coefficients are presented and discussed. 1988.