The “at-sea” environment for AAW Naval Gun System includes six-degree-of-freedom ship motion (roll, pitch, yaw, heave, surge, sway). The design of ship system which are effective at high Sea States requires consideration of ship attitude and motion. The development of Gun Fin Control (GFC) System sensitivity to the motion-induced environment aboard a ship in a seaway is a necessary design tool. A U.S. Navy Workshop Report entitled “Sea-keeping in the Ship Design Process,” July 1975, confirmed the need for definite sensitivity information on combat system responses to ship motion effects [1]. Since the Authors wrote this paper, the Navy has commenced developing new GFC Systems which consider in more detail and partially compensate for this motion-induced sensitivity. This paper addresses the ship motion effects on GFC Systems presently In the Fleet.

Coupled six-degree-of-freedom ship motion data are required to fully characterize the AAW Gun System environment. In the absence of such data, design considerations have been investigated using a six-degree-of-freedom phased sinusoidal ship motion simulation developed by Rockwell International. The sinusoidal model is only an interim procedure to be supreseded with a complete spectral model as soon as possible. The simulation uses Equations of Motion to determine velocity and position at any ship station. These data are propagated through the gun/sensor/control system simulation to determine contributions to errors in Gun Fire Control (GFC) System indications of target parameters, and to initial velocity and position of rounds. In the opinion of the Authors, uncompensated motion-induced projectile initial velocity is a major gun fire control error. The error magnitudes are dependent on gun system component locations and radar filter algorithms.

The effects of ship motion on GFC accuracy and the effect of compensating for ship motion have been examined. High !Sea state conditions cause motion at gun system stations which propagate as significant GFC System errors. A substantial reduction of the can be achieved by measuring ship motion, filtering the mesurements [2], and compensating the fire control solution.