Crace's Change of Bearing Instrument
Crace's Change of Bearing Instrument was a Torpedo Control instrument conceived by a Lt. Crace of H.M.A.S. Australia to determine the bearing rate of a target so that the deflection can be computed to set a Torpedo Director.
It used a special telescope atop a gyro compass receiver. The telescope had crosswires and a prism in it that permitted the operator to simultaneously observe the target beneath a 5 degree arc of the gyro compass card below. The operator worked a training gear to keep the crosshairs on target and call out the bearing to a second man. This second number was equipped with a circular slide rule and also received ranges by voicepipe.
The sliderule had two discs:
- the inner one had OwnSpeed * sin(Bearing)
- the outer one (pi * Range) / (100 * TimeIntervalBetweenBearings)
By late 1914, it was determined that sufficient practice gave good results, but the amount of calculation required seemed worrisome.
- Annual Report of the Torpedo School, 1914, Plate 18.
- Annual Report of the Torpedo School, 1914, p. 32.
- Annual Report of the Torpedo School, 1914, pp. 32-33. I am inferring that "S" given in the source document represents "Own Speed".
- Annual Report of the Torpedo School, 1914, p. 33.
- H.M.S. Vernon. Annual Report of the Torpedo School, 1914. Copy 5 at The National Archives. ADM 189/34.
- H.M.S. Vernon. (Jan 1916) Annual Report of the Torpedo School, 1915. C.B. 1166. Copy 1025 at The National Archives. ADM 189/35.
- Admiralty, Gunnery Branch (1917). Handbook of Torpedo Control, 1916. C.B. 302. Copy No. 141 at The National Archives. ADM 186/381.