Vickers range clock

The Vickers Range Clock was a clockwork device for calculating the range to an enemy ship used by the Royal Navy from around 1906.

In 1903 a device siimlar to that which became the Vickers clock was described by its inventor, Percy Scott. In April 1904 the device was patented by Vickers, who were working with Scott, and samples were available for trials in 1905. In 1906 the Royal Navy ordered 246 of the devices to be installed on their ships. More than one might be installed, to allow for tracking multiple targets. [Brooks p.43]

The device consisted of a circular dial with a single central rotating pointer, like a clock. The dial was engraved with the range to an enemy ship. The clockwork motor drove the pointer at a rate determined by a control on the right hand side of the device. This had a handle and its own dial, on which the rate of change of range could be selected. This was calculated by other means, particularly using another mechanical calculating device, the Dumaresq. A second rotating handle was fitted to the left of the clock. This was connected by gears to the dial plate, which rather than being fixed as on a clock, could be rotated. One turn of the handle would rotate the scale 100 yards relative to the pointer. Thus the clock could be set to the initial range to a ship, or corrections could be made to update the reading without disturbing the mechanism. [Brookes p.25-27]

The range on the dial was the range as passed to gunners for firing, and as such included any corrections necessitated by time of flight, wind, etc., rather than being a true instantaneous record of distance to the enemy. By 1913 a second red pointer had been added to the original black one, attached to it by a friction grip, which could be adjusted relative to the original hand, so that one indicated true range and the other the corrected range for targetting. [ Brooks p. 53]

Once some shots had been fired, spotters would report the fall of shell (which could be observed because of the large waterspouts where the shells hit the sea) and the range would be corrected up or down depending whether the shells were short or over the enemy. Initial estimates of range were obtained using optical rangefinders.

The dial was fiited with three separate scales reading 2,000-6,000 yards, 6,000-10,000 and 10,000-14,000 yards in 100 yard steps, with marked subdivisions every 25 yards. The handle for adjusting the dial was added from 1908; previously the initial position of the dial plate had to be set by rotating it directly. Initial models had the rate setting dial calibrated in both knots and 'seconds per 50 yards'. This was altered in 1909 to yards per minute, which standardised measurement was used on other equipment designed to work with the clock. [Brooks p.53-54]

Mechanism

Variable speed was obtained using a rotating metal disc driving a rubber wheel resting against it. The position of the wheel could be moved in and out along a radius of the disc, so that the wheel turned at different speeds (faster the further out). Operating errors would occur from adjusting the wheel, as side slip meant drive would be lost while it was adjusted. However, the main source of inaccuracy was due to the rnage rate having to be corrected manually when other instruments determined it had changed. Errors from updating delays were likely to be greater than those due to the mechanism. In 1909 alterations were made to the clockwork drive to improve reliabilitiy of the governed speed and increase the power of the drive. [Brooks p.54-55]

References

*cite book |title=Dreadnought Gunnery at the Battle of Jutland: The Question of Fire Control |last=Brooks |first=John |year=2005 |publisher=Frank Cass Publishers |location=London |isbn=0-714-65702-6