Binnacle
The compass binnacle is a 130-cm-high teak wood pedestal with inbuilt lighting for night reading and dome-shaped top that can be
opened. The upper part of the pedestal contains a magnetic graduated compass with iron bottom to let light through and to allow
for reading, mounted on a cardan joint formed by two couples of orthogonal pivots so as to compensate the roll of the ship.
These are mounted on metal curved springs in order to absorb vibrations.
Two brass shafts are mounted on the sides of the metal dome-shaped top (brass is a non magnetic metal), and two metal spheres
are mounted on the shafts, respectively green on the left and red on the right, to compensate the magnetic field created by the iron
hull. During the calibration process, small compensation magnet are inserted in the wood pedestal in relation to the earth magnetic
field and the hull magnetic field. Please find some examples of compass binnacles in this page.
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The Binnacle
On wood ships, initially compasses were kept in a kind of triple-glazed cupboard, which soon became an engraved pedestal in precious wood, and finally they were enclosed in a brass or bronze pedestal. In 1820, Sir. H. Poham introduced a more functional and compact binnacle. It consisted of a square support bearing a frustum of a four-sided pyramid containing the compass; the instrument could be read through the glass; at night a lamp was mounted on the instrument. In 1835, Preston, an English man, patented another type of binnacle with round pedestal and brass dome-shaped top. On wood ships deviation wasn’t a real problem, so the binnacle was but a support for the compass mortar. The compensation theory perfected by Lord Kelvin provided that on iron or steel hull ships, only highly functional supports should be used. Any futile decoration disappeared from Kelvin-Bottomley binnacle which, in 1880, became a standard model.
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The decorative simplicity still retained its charm and impact. The two oil lamp holders placed at the sides of the dome-shaped top are needed to light up the rose during the night. In the binnacle wood pedestal there are holes for permanent magnets which are needed to cancel the deviations due to iron objects found on the ship. The soft-iron balls at the sides of the binnacle aim to adjust deviations caused by the position of the ship within the earth magnetic field. A vertical brass tube contains the plaques which can be adjusted in height and number to correct deviation according to the ship’s latitude. This is called Flinders tube, named as such after its inventor.
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