A new direction for ships’ magnetic compasses.

The Standard Compass

Shrouded in canvas and abandoned on the compass deck, the ‘standard’ magnetic compass is generally neglected; out of sight and out of mind.

The principal function of the ‘standard’ magnetic compass, as defined by regulation, is not a heading reference but for navigation by taking bearings. Many of the ‘standard’ compass requirements are to meet that function, particularly siting for as much an uninterrupted view of the horizon as possible. On modern vessels, the ability to take bearings from the ‘standard’ compass is not foremost in operational requirements.

The modern role for the magnetic compass is more for testing the integrity of a gyro compass and providing an emergency heading reference should the gyro fail, effectively, a ‘steering’ compass in front of the helmsman.

Regulations allow the ‘standard’ compass to take the role of a ‘steering’ compass if it can display the heading at the main steering station. The common arrangement of the ‘standard’ compass on the compass deck with a projection tube to the wheelhouse below satisfies the compass regulations.

‘Standard’ Compass on a small general purpose vessel.

Projection assembly to view the ‘standard’ compass heading from the steering station.

The use of the ‘standard’ compass as a ‘steering’ compass (by projection) has several significant weaknesses and generally fails to provide the mariner with an easy to read, stable heading reference.

The view of the compass through the projection assembly is often unclear and may diminish further with age.  Furthermore the compass card’s stability in a seaway can be affected from uncorrected vertical forces and accelerations inclining the card and bowl from the horizontal plane. Such instability may be very evident when rolling on northerly or southerly headings.

Compass Siting

Familiar with the short comings of the ‘Standard’ compass and seeking to better understand magnetism on modern ships, some research was undertaken to improve the performance of compasses on ships. The field strengths at the compass site in the binnacle and at a position near the lower mirror of the projection tube at the steering station were recorded on a number of vessels.

It soon became apparent that there is a viable option to have a magnetic compass in the wheelhouse at the main steering station. The basic magnetic information recorded for a recently built ship is shown below. (I am very grateful to Captain Ramu Ratish and 2/Off Montu Biswa for taking measurements in different geographic locations, including the magnetic equator at two in the morning.)

	Binnacle	Wheelhouse
Horizontal Directive force	79% of H	77% of H
Vertical Directive force	121% of Z	120% of Z
Horizontally induced vertical force	17% of H	3% of H

(H = horizontal component of Earth’s magnetic field,

Z = vertical component of Earth’s magnetic field.)

modern post panamax bulkcarrier.

Simultaneous three axis magnetic field strength measurements in wheelhouse and binnacle

It can be seen the uncorrected directive force (λ) at the site within the wheelhouse is not significantly less than the directive force (corrected λ₂) at the standard compass. The significant difference lies in the horizontally induce vertical field (“g” rod) which is upwards on a northerly heading and downwards on a southerly heading. 

Whilst magnetic readings taken on different ships had similar outcomes, the greatest difference observed between the directive force at the binnacle and in the wheelhouse was surprisingly on a tug , with a directive force of 86% of H at the binnacle and 68% of H in the wheelhouse. This commends further research into understanding magnetic shielding arising from wheelhouse design.

Tug Boat

Measuring magnetic field strengths on a tug boat.

As a result of the research coupled with the aim of delivering an easy to read stable compass, the following design of compass card, bowl and binnacle, along with its siting at the main steering station is submitted as a modern alternative to the ‘standard’ magnetic compass.

Proposed compass and binnacle sited in wheelhouse.

Easy to read

By placing the compass directly in front of the main steering station in the wheelhouse, the compass can be viewed directly. The design of the compass provides an easy to read and comprehend ego-centric heading reference that can also be viewed from the area adjacent the main steering station.

Compass bearings of objects beyond the wheel house windows can be taken by sighting across the sighting peg. This provides pilotage and collision assessment functions in the event of gyro failure. As for all-round bearings, a wing repeater can be used as a pelorus in the event of gyro failure.

Stable Card

Greater compass card stability than the ‘standard’ compass is achieved by

compass and binnacle design. Further, by placing the compass in the wheel house, the compass not only enjoys a more benign environment compared to extreme weather conditions outside, the compass also has a more stable vertical force by having the symmetry of a deck above and below.

For more detailed information on the compass and binnacle design, please read their details from these links at compass and binnacle.

Conclusion

The magnetic compass has long proved to be a reliable heading reference that has served the shipping industry well. The best location for a magnetic compass in a modern ship is at the main steering station in the wheelhouse where it can be viewed directly. Compass regulations should be reviewed to evolve with compass technology and mariners’ needs.

The time has come to bring the magnetic compass inside to be revived.

Further Research & Development

The current research has been limited to a small sample size and type of ship along with basic ‘proof of concept’ prototype compasses and binnacles.

The effectiveness of the proposed compass could be assessed by placing the compass in the described binnacle with a reflecting mirror so the binnacle can take the place of the projection tube into the wheel house. By this means, the current ‘standard’ compass requirements can be complied with and a direct comparison of performance made.

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