Difference between revisions of "Tangent Bar"

Revision as of 16:14, 21 June 2011

A Tangent Bar is a small metal accessory that could be added to a simple torpedo director designed to be placed near the firing tube to permit the director to be situated at a distance from the firing tube. This was often necessary on capital ships with submerged broadside tubes, or desirable on ships where the aiming and control of torpedo fire was deemed better kept near the command centre.

Nature

A tangent bar looked like a small metal ruler of 3-5 inches and would be fitted to the rear post of the director. The rear sighting arch of the director would be removed from its former position on the rear post and placed on a slider that rode along the tangent bar. The proper use of the device, then, was to orient the tangent bar to point to the firing tube and position the slider to the present range to the target against a irregularly graduated scale. The purpose was to factor out the offset between tube and sight to cause the sighting line to converge on the torpedo's track.

Intrinsic in this function is that the markings on the tangent bar are related to a given fixed distance from director to firing tube. As such, each ship's director positions would require their own tangent bars. The range set upon the tangent bar need not be extremely precise, but the convergence will be imperfect if the range is not correct.

Use in Gyro Angle Firing

In 1912, Vernon studied the geometry of how the radius of turning of a torpedo seeking to take up a given Gyro Angle impacted the use of tangent bars. The solution hit upon was to affix a disc at the base of the tangent bar and to not point the bar directly at the mouth of the tube. Its markings were arrived at through considerable graphical analysis and exemplify the further complexity the tangent bars were imposing.^[1]

Impressions on Use

The tangent bar was generally seen as a distasteful accoutrement which was often the source of director user error. In 1911, the Royal Navy was opting to retrofit armored sighting positions at the gunwale immediately over the broadside tubes of some battlecruisers. While this change may have in part been inspired by a wish to free up space within the conning tower, it also would eliminate the need for a tangent bar.

See Also

• Torpedo Director
• Video depicting a torpedo director being used with a tangent bar

Footnotes

Bibliography