The magnetic compass plays a very vital role in maritime navigation. As per SOLAS Chapter 5, Regulation 19 “all ships irrespective of size shall have a properly adjusted standard magnetic compass or other means, independent of any power supply to determine the ship’s heading and display the reading at the main steering position”. Owing to the exposure of the magnetic compass to the weather and harsh conditions, it becomes necessary to safeguard the compass. The navigation instrument that helps serve this purpose is the binnacle. Alongside this aid, binnacles also safeguard the compasses from toppling over due to the constant rolling and pitching of the vessel.
What is the binnacle?
The binnacle is a cylindrical container made of non-ferrous material that houses the different components of the magnetic compass and that as a whole. Earlier, wood was used for the construction of the binnacle. The compass bowl is housed in the top part of the binnacle whereas the middle part is accessible through a door housing the corrector magnets extending to the projector towards the forward.
History of the Marine Binnacle
Binnacles have been in utilization since the 1700s. Over the years though, several developments to the technology of binnacles have been carried out to suit the developments in the vessels’ building technology. The instrument consists of a round stand upon which a plinth is mounted. Separate divisions constructed, store the compass and other navigational equipment on the plinth of the binnacle.
A ship binnacle is positioned right before the helmsman’s line of vision. The compass and all other navigation equipment are safeguarded within the binnacle, making it easy for the steersman to observe and steer the vessel accordingly. For this purpose, binnacles have always been constructed to come up to the waist of steersmen handling the vessel.
Magnetic compass correctors in a binnacle
- Flinders Bar
- Quadrantal Spheres
- Heeling Magnet
- Athwartship Magnets
- Fore and Aft Magnets
In the centre part of the lower half of the binnacle are contained many holes which contain inside them corrector magnets to negate disturbing effects of magnetism caused by the hull of the ship. The specifications of the corrector magnets are decided by an authorised ‘compass adjuster’ whose services are usually called upon in port. The access door to these corrector magnets must be kept locked at all times unless when needed to be opened for adjustment.
The Flinders Bar is a soft iron corrector vertically placed in the for’d or aft part of the binnacle depending on the extension of the superstructure area abaft of or forward of the binnacle. The length of the bar may be changed during adjustment of the compass.
The Quadrantal Correctors are two soft iron spheres fitted in brackets on either side of the binnacle. Again, the distance between the quadrantal correctors can be altered during adjustent of the compass.
The helmet is fitted on top of the binnacle and is non-ferrous. This is in place to protect the compass bowl from the weather and harsh conditions.
Care and maintenance
- Access doors to be kept locked at all times
- If made of wood, the binnacle should be varnished and not painted
- The quadrantal corrector must be painted from time to time to prevent rust from settling
- The brass parts are to be polished regularly
- All materials with magnetic properties must be kept away from the compass
- Helmet to be kept in position at all times
- All adjustment to be carried out by an authorised compass adjuster
- Remove any bubbles that may be present in the compass bowl within the binnacle
Removal of bubbles
Following steps should be taken to remove bubbles:
- Tilt the bowl till the filler hole comes up and can be seen
- Unscrew the screw
- Top up with ethyl alcohol. If ethyl alcohol is not available, use distilled water
- Screw the screw back
- Return the bowl to position
The magnetic compass is housed on the monkey island and the compass course needs to be viewed from the bridge. The compass projector is in place to enable the same via subsequent reflections. It is in place to enable the helmsman to in the wheelhouse to view the coincident compass card reading and lubber line to steer the ship correctly.
While binnacles refer to navigation instrument, the term ‘binnacle lists’ refers to those seafarers who have been relieved from duty on a particular day on account of medical unfitness.
Ref: Bridge Equipment, Charts and Publications by Capt. H. Subramaniam