Note 5 — Chapter X · THE BALLISTIC DEFLECTION

The ballistic deflection is dependent upon the rate at which the northerly component of the ship’s speed is being changed. The difference in the north steaming errors is dependent upon the initial and final values of the speed towards the north, and would not appear to be affected by the length of time occupied in changing the speed. It would seem, therefore, that the ballistic deflection can only be dead-beat in the chosen latitude if the speed towards the north is reduced or increased at one particular rate. Thus if the ship is steaming due north at 20 knots and changes its speed to 10 knots in (a) 10 minutes or (b) 5 minutes, the initial and final values of the north steaming error will be the same in both cases, since the initial and final speeds are the same, but the ballistic deflection will be greater in the second case than in the first, since the rate at which the speed is changed is greater. If, then, the ballistic deflection is dead-beat in the first case it cannot be so in the second. The statement that the ballistic deflection in the chosen latitude is dead-beat thus appears, it may be suggested, to require qualification. On the other hand, the British Admiralty in connection with the use of gyro-compasses on destroyers and similar fast-manœuvring vessels wherein the ballistic deflection is a factor of very great importance has carried out lengthy experiments on the matter, and, although the results have not been divulged, it is understood that the ballistic deflection was found to be dead-beat independently of the rate at which the speed was changed.