MARB050 — Adjust a magnetic compass

Elements & performance criteria

Performance evidence

• adjusting a magnetic compass onboard a variety of International Convention for the Safety of Life as Sea (SOLAS) compliant commercial vessels on at least six (6) separate occasions and must include:
• three (3) swings onboard SOLAS compliant commercial vessels between 500 Gross Tonnage (GT) and 3,000 GT, and
• three (3) swings onboard SOLAS compliant commercial vessels greater than 3,000 GT
• Or:
• three (3) swings onboard a SOLAS compliant commercial vessels between 500 GT and 3,000 GT, and
• three (3) swings onboard a SOLAS compliant commercial vessels greater than 500 GT trading between hemispheres.
• adjusting deviations from coefficients taking into consideration limitations and practicalities and accuracy of results when adjusting a magnetic compass
• analysing the ships compass deviation book and records to determine causes of irregular deviations and determining measures for their removal
• ascertaining the magnetic bearing of a distant object and/or magnetic heading to determine compass deviation
• assessing the safe distances of electronic equipment in the vicinity of the compass
• checking accuracy of instruments used during the adjustment compasses, including pelorus, azimuth mirror/circle and alignment of gyro repeaters (as required)
• constructing a table and curve of deviations to determine coefficients
• swinging a ship using a fixed distant object, calculate the magnetic bearing to use for the observations and state how the correctors should be placed to correct the deviations and minimise the coefficients
• taking a celestial and terrestrial bearing using an azimuth mirror
• using a pelorus to determine a magnetic bearing and magnetic heading
• using methods of swinging a ship to obtain a table of deviations
• using the analysis method of adjustment and the tentative method of adjustment to adjust a magnetic compass
• using the appropriate equipment, methods, theories and calculations for finding and compensating compass deviations
• using vertical force instrument (VFI) correctly and accurately.

Knowledge evidence

• analysis method of adjustment and the tentative method of adjustment
• calculate maximum and minimum deviation due to permanent B and C and the heading on which these occur, including:
• the effect on these values when the ship locates to another position on the earth’s surface and horizontal component of the earths magnetic field (H) and dip change
• calculations and solving problems, including:
• how to solve problems involving an independent variable, including:
• equations with direct, partial and inverse dependency
• how to solve simultaneous equations with two unknowns
• graphs and rectangular coordinates, including:
• graphs which are developed using rectangular coordinates
• information which can be extracted from a graph which uses rectangular coordinates
• interpretation of graphs with rectangular coordinates
• plane triangles, with or without right angles, including:
• cosine formula
• sine formula
• trigonometry
• spherical triangles, including:
• definition of spherical triangles
• the use of spherical triangles to solve azimuth
• use of algebraic formulae, including:
• how to use equations to assist in determining a solution
• vector quantities, including:
• vector additions completed graphically and mathematically
• calculations and heeling error constant, including:
• calculations to derive the value of coefficient J
• calculations to estimate deviation when variables H, Z and i (angle of heel) are changed along with a change in heel from port or starboard and vice versa
• calculations to find deviation on any heading with the vessel heeled
• condition for no deviation due to heeling error
• calculations and mathematical theories, including:
• Fourier’s Theorem and derivation of equation of condition
• mathematical theory of the deviation at the compass (vessel upright)
• Poisson’s equations and calculations
• slewing soft iron correctors to correct coefficient D and E together
• slewing soft iron correctors to correct coefficient induced B and induced C together
• calculations involving approximate and exact coefficients, including:
• how to derive the exact coefficients
• threshold for deciding when to use exact instead of approximate in the equation of condition, and vice versa
• calculations involving quadrantal correctors, including:
• calculations to describe the effects of the soft iron correctors
• how coefficient D is minimised by the increase and decrease of soft iron rods a and e
• positioning of quadrantal correctors to correct for coefficients +D and -D
• calculations involving the approximate coefficients by the method of least squares, including:
• approximate method of analysis to show that A, D and E have the same value as if derived by least squares
• use of two formula derived from the least squares method to calculate the correct coefficients B and C and thereby, also derive sextantal coefficients F and G, if existing
• causes of sextantal and octantal deviations including coefficients F, G, H and K
• construction of curve of deviations and its practical use in coefficient analysis
• directive force and calculations to find:
• mean directive force on board, its effect on deflection and relationship with Lambda (λ)
• methods to determine directive force, including modern instruments and magnetometers
• effect of heel on forces and rods
• forces P, Q and R
• general magnetism, magneto statistics and magnetometry, including:
• calculations involving:
• comparison of magnetic fields of magnets
• first and second laws of magnetism
• force exerted by a bar magnet on a point pole, including:
• at right angles to the bar magnet
• in line with bar magnet
• when the point pole is any other direction
• force exerted by a short and long bar magnet
• how to calculate the direction of freely suspended needle onboard a ship given values for P, Q, R and soft iron rods
• how to calculate the position of the neutral point between two bar magnets
• how to calculate when the length of the magnet is not small when compared to the distance
• how to calculate the magnetic length of a magnet
• magnetic moment and moment of inertia of a magnet bar
• magnetic potential and work done in moving a bar magnet
• sine and tangent rule and maximum deflection when disturbing force is at right angles to the deflected compass needle
• tangent rule and combining it with the expression for the force exerted by a bar magnet, including:
• end-on and broadside-on
• heeling error, including:
• correct use of the vertical force instrument (VFI)
• effect of the g rod on error
• effect on deviation of uncompensated c and e rods
• identifying heeling error
• measuring vertical force at the compass position
• ship’s multiplier (λ₂)
• using vertical magnets to compensate heeling error
• how to test soft iron correctors for permanent magnetism and if permanent magnetism is found, how it is removed
• limitations of the accuracy of results from carrying out a compass adjustment, including:
• apparent coefficient A
• Gaussin error
• gyro repeater not in the F&A line of the vessel
• inherent errors when using gyro headings for a compass adjustment
• instruments
• magnetic bearing in error
• method used to determine the deviation and coefficients, including:
• effect on coefficients B and C, when coefficients F and G have sensible values
• misalignment of lubberline and/or pelorus heading marker
• observational errors, including:
• constant errors
• gross errors
• random errors
• observation of celestial body if altitude is high vs amplitude observation
• recording errors
• uncorrected or poorly compensated HE (heeling error) producing oscillations on N/S (north and/or south) headings which can deliver large errors when attempting to compare with the master gyro/repeater:
• causes and identification of pitching errors on E/W headings
• vessel movement
• weather conditions and environment, including:
• pitching
• rolling
• methods used for:
• detecting mechanical errors in a liquid magnetic compass
• taking a bearing, using and testing a pelorus and azimuth mirror
• process for reviewing ship’s compass deviation book and ship’s records to identify causes of irregular deviations and recording outcomes of compass adjustment
• rods a, b, c, d, e, f, g, h and k and their connection with coefficients A, D and E
• ships magnetism, including:
• calculation of:
• coefficients A - E derived from deviations on the eight principle compass headings and the deviation expected on a given compass heading
• split B and C calculations with a compensated and uncompensated compass
• how to determine:
• the compass should be adjusted or re-adjusted given the position of the correctors and the coefficients derived from a set of deviations
• the most probable values of B and C should higher order coefficients F and G exist
• swinging a ship using a fixed distant object, calculate the magnetic bearing to use for the observations and state how the correctors should be placed to correct the deviations and minimise the coefficients
• standard for compass adjusting ISO 25862:2019 Ships and marine technology — Marine magnetic compasses, binnacles and azimuth reading devices
• terrestrial magnetism and calculations, including:
• change of latitude and its effect on the coefficients A – E, including:
• relationship between induced magnetism and dip
• relationship between permanent magnetism and H
• separation of permanent and induced magnetism P and cZ – split B
• separation of permanent and induced magnetism Q and fZ – split C
• directive force and calculations to find:
• mean directive force on board and its effects on deflection and relationship with Lambda (λ)
• methods to determine directive force, including modern instruments and magnetometers
• the earth as a dipole and relationships are made between magnetic latitude, H, Z and T, including:
• how to calculate the approximate values of H, Z and dip at a geographic position
• tools and equipment used to inspect and adjust a compass, including:
• alignment of gyro repeater in the F and A line of the ship if it is used in the adjustment
• azimuth circle and mirror
• correctors
• pelorus
• VFI
• ‘wiping’ and degaussing a ship’s hull
• work health and safety (WHS)/occupational health and safety (OHS) work procedures including:
• embarking and disembarking from a ship safely
• manufacturers specifications
• Marine Order and SOLAS, including requirements of a safely rigged pilot ladder
• personal protective equipment (PPE) requirements.

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