Considering an electronic compass, I wondered, does a person still have to deal with compass deviations? I know with my regular compass I do, but I cant seem to get a straight answer about an electronic one???????????? Before I invest! thanks
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Yes, there is deviation
Dennis, Yes, you will still encounter deviation with and electronic compass. This can be minimized by the latitude you have in the mounting location of the fluxgate sensor, however. When I calibrate my Autohelm (Raymarine) ST50 system, it usually shows no more than a maximum of 2 degrees of deviation. Fair winds, Tim
Dennis, Yes, you will still encounter deviation with and electronic compass. This can be minimized by the latitude you have in the mounting location of the fluxgate sensor, however. When I calibrate my Autohelm (Raymarine) ST50 system, it usually shows no more than a maximum of 2 degrees of deviation. Fair winds, Tim
Fluxgate Compass Deviation
Dennis It would seem that the definition of deviation would be the answer. Deviation is caused by "on board" items that affect the compass. The flexibility of moving the fluxgate head of your compass will enable you to help to offset the deviation limited to a traditional compass location, but, of course, will not eliminate it, because there is always some metal, like your engine, that will cause it. Stu PS I hesitate to suggest a Google search on deviation, amazing what one could get! Try compass deviation.
Dennis It would seem that the definition of deviation would be the answer. Deviation is caused by "on board" items that affect the compass. The flexibility of moving the fluxgate head of your compass will enable you to help to offset the deviation limited to a traditional compass location, but, of course, will not eliminate it, because there is always some metal, like your engine, that will cause it. Stu PS I hesitate to suggest a Google search on deviation, amazing what one could get! Try compass deviation.
Auto' Compass Correction
ELECTRONIC FLUX-GATE COMPASSES: As Tim & Stu have indicated, deviation is still a factor with Electronic Flux-Gate compasses. A Flux-Gate compass is just as sensitive to magnetic disturbances as a Magnetic Compass, but has two redeeming benefits: 1) The Sensor can be mounted away from (relatively) the worst disturbances. 2) The transducer/sensor can be Automatically Compensated at the Instrument. Fluxgate compasses work quite differently than conventional compasses - internally, they have two (or more) sensors and compare the fore-and-aft component of the earth's magnetic field to the athwartships component to determine magnetic direction rather than actually swinging a magnetized needle. Generally (Please REFER TO YOUR MANUAL for product-specific instructions): Mount the Flux-Gate sensor as near to the boat’s Vertical Centre of Gravity as possible, though other factors (below) might become more critical. The sensor MUST BE mounted Plumb, and perfectly aligned in the Fore and Aft orientation. The Sensor should not be mounted in the extreme ends (bow or stern) of the boat. The Sensor must be mounted as far from sources of magnetic disturbance as possible; but not less than 3 feet from any source of magnetic interference (10 Feet from Antennas, 7 Ft from Engine, 7 Ft from Radar Magnetron, and > 3 Ft from Motors, Speakers, Magnetic Compass, & etc). The strength of a magnetic field is inversely proportional to the square of the distance from the source - so increasing the distance (of the sensor from the disturbance) by a factor of 1.414 (from say 3 Ft to 4.25 Ft) will reduce the disturbance to one-half. On steel boats, the Sensor is usually mounted about 6 - 10 Feet above deck. Most (all?) Flux-Gate Compasses have a simple procedure for performing an Automatic Compensation Adjustment - and some can be interfaced with your GPS to provide Automatic Deviation Correction. Usually, the Auto’ Adjustment requires that you execute several slow 360 degree circles (perhaps diameter of 5-10 times boat length). These compensating circles should be performed on a calm day (level), and as far from made-made magnetic anomalies (Bridges, Steel Ships, etc) as possible. Note of Caution: The Automatic Compensation only corrects for the magnetic disturbances present at that time. Many disturbances are transitory and/or variable in nature (a Pump cycles on-off, Lights on-off, etc). It might be usefull to prepare a Deviation Card (Many Flux-Gate Instruments will provide Deviation info' at the Instrument) under several differing operating scenarios (Lights On, Light off, etc). The Automatic Compensation must be re-done after any significant changes to the vessell's condition (new equipment, after a re-launch, etc). Please REFER TO YOUR MANUAL for product-specific instructions. Hope this helps, Regards, Gord
ELECTRONIC FLUX-GATE COMPASSES: As Tim & Stu have indicated, deviation is still a factor with Electronic Flux-Gate compasses. A Flux-Gate compass is just as sensitive to magnetic disturbances as a Magnetic Compass, but has two redeeming benefits: 1) The Sensor can be mounted away from (relatively) the worst disturbances. 2) The transducer/sensor can be Automatically Compensated at the Instrument. Fluxgate compasses work quite differently than conventional compasses - internally, they have two (or more) sensors and compare the fore-and-aft component of the earth's magnetic field to the athwartships component to determine magnetic direction rather than actually swinging a magnetized needle. Generally (Please REFER TO YOUR MANUAL for product-specific instructions): Mount the Flux-Gate sensor as near to the boat’s Vertical Centre of Gravity as possible, though other factors (below) might become more critical. The sensor MUST BE mounted Plumb, and perfectly aligned in the Fore and Aft orientation. The Sensor should not be mounted in the extreme ends (bow or stern) of the boat. The Sensor must be mounted as far from sources of magnetic disturbance as possible; but not less than 3 feet from any source of magnetic interference (10 Feet from Antennas, 7 Ft from Engine, 7 Ft from Radar Magnetron, and > 3 Ft from Motors, Speakers, Magnetic Compass, & etc). The strength of a magnetic field is inversely proportional to the square of the distance from the source - so increasing the distance (of the sensor from the disturbance) by a factor of 1.414 (from say 3 Ft to 4.25 Ft) will reduce the disturbance to one-half. On steel boats, the Sensor is usually mounted about 6 - 10 Feet above deck. Most (all?) Flux-Gate Compasses have a simple procedure for performing an Automatic Compensation Adjustment - and some can be interfaced with your GPS to provide Automatic Deviation Correction. Usually, the Auto’ Adjustment requires that you execute several slow 360 degree circles (perhaps diameter of 5-10 times boat length). These compensating circles should be performed on a calm day (level), and as far from made-made magnetic anomalies (Bridges, Steel Ships, etc) as possible. Note of Caution: The Automatic Compensation only corrects for the magnetic disturbances present at that time. Many disturbances are transitory and/or variable in nature (a Pump cycles on-off, Lights on-off, etc). It might be usefull to prepare a Deviation Card (Many Flux-Gate Instruments will provide Deviation info' at the Instrument) under several differing operating scenarios (Lights On, Light off, etc). The Automatic Compensation must be re-done after any significant changes to the vessell's condition (new equipment, after a re-launch, etc). Please REFER TO YOUR MANUAL for product-specific instructions. Hope this helps, Regards, Gord
Tim - 2 Deg. Deviation
TIM: I (mostly) do not PERSONALLY find 2 degrees of compass error to be a problem - I cannot steer to that level of accuracy.
- BUT others may find it to be VERY significant (under their differing circumstances). Compass Error: For every degree of course error you can expect to miss your target by 1/60 (0.01666) of your distance traveled. At 5 Knots, you will travel 5 miles in an hour, and develop a cross-track error of 507 Feet: (1/60 x 5) x 6080 = 506.66 Ft. Cross-Track Error Hence a 2 degree Compass error, will put you 1013 feet off course over a 5 mile run. This may or may not be significant over the short haul; but lets extrapolate the same 2 degree error over a 50 mile run. (1/60 x 50) x 6080 = 5,666.65 Foot Cross-Track Error - Nearly a mile off course! Utilizing basic triangle trigonometry: CTE = Sine θ x DT where: CTE = Cross-Track Error in Miles Sine θ = Sine of the Course Angle (degrees) Error DT = Distance Traveled in miles Regards, Gord
TIM: I (mostly) do not PERSONALLY find 2 degrees of compass error to be a problem - I cannot steer to that level of accuracy.
- BUT others may find it to be VERY significant (under their differing circumstances). Compass Error: For every degree of course error you can expect to miss your target by 1/60 (0.01666) of your distance traveled. At 5 Knots, you will travel 5 miles in an hour, and develop a cross-track error of 507 Feet: (1/60 x 5) x 6080 = 506.66 Ft. Cross-Track Error Hence a 2 degree Compass error, will put you 1013 feet off course over a 5 mile run. This may or may not be significant over the short haul; but lets extrapolate the same 2 degree error over a 50 mile run. (1/60 x 50) x 6080 = 5,666.65 Foot Cross-Track Error - Nearly a mile off course! Utilizing basic triangle trigonometry: CTE = Sine θ x DT where: CTE = Cross-Track Error in Miles Sine θ = Sine of the Course Angle (degrees) Error DT = Distance Traveled in miles Regards, Gord- Status