Quick guide to instrument calibration - 11 Pages

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Quick guide to instrument calibration

Catalog excerpts

INSTRUMENT CALIBRATION

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INSTRUMENT CALIBRATION Accurate calibration of your chosen instrument system is essential for ensuring that you are getting meaningful information that you can then use to measure the performance of the yacht. The following sections describe how to do this on a typical B&G system and where appropriate the headings detail the relevant B&G menu structure. RemoteVision Inputting of these values can be via the standard FFD or using the new RemoteVision, a wireless link to your Hydra and Hercules instrument system. Hydra 2000 FFD Depth DEPTH > DEPTH + CALBRATE > DATUM For obvious safety reasons...

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Heading In order to eliminate compass deviation errors caused by magnetic fields in the yacht, heading calibration is carried out using B&G's Autoswing. An offset is then entered to account for the alignment of the compass as installed on the yacht. 1. Autoswing NAVIGATE > COMP CAL + CALBRATE > START Prior to commencing the swing ensure that no magnetic or large metallic objects are placed near to the compass. Choose a calm open stretch of water and then begin the calibration process as outlined in the User Manual ensuring you steer a steady circle not exceeding 2-3 degrees per second with...

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1. Auto-Calibration SPEED > BOAT SPD + CALBRATE > AUTO CAL The B&G three run method eliminates any changes in current during the calibration procedure since the runs are carried out in alternate directions. When carrying out each run maintain a constant compass course to ensure that the distance covered is the same as that measured on the chart. If possible choose a measured distance with clearly visible transits marking each end. It is prudent to manually calibrate boatspeed using the trip log function on another FFD whilst running the AUTO CAL feature. By recording the log at the...

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Therefore by reducing the SINGLE HZ value for the above calibration by 1% will address the under-reading of the log. 3.42 - 1% = 3.39 If you are using the latest B&G Hercules system with a heel sensor you can also adjust the speed from tack to tack and apply more correction at higher speeds in the case of the paddle-wheel. See the Owner's Manual for more information on this. Once boatspeed has been verified as accurate, it should be monitored against other functions, and only adjusted if the wrong speed cannot be attributed to different sail trim, helms-man, rig settings, wind shear, crew...

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Using identical trim and crew weight distribution (not necessarily a full racing crew) complete half a dozen tacks with the helm concentrating purely on boatspeed. A consistent speed (not necessarily from the targets table) on each tack should be achieved without changing trim, and without using any reference to APP W/A. The navigator or tactician should monitor the APP W/A from tack to tack, and average each tack. Any difference between Port and Starboard tack can be corrected in the MHU offset. If Starboard APP W/A is greater than Port then subtract half the difference from the MHU...

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BASIC CALIBRATION DATA The table below can be used to store important calibration and damping data as required, including the boatspeed and AWA values discussed above. Date: DATE: CAL VAL DAMPING Depth Datum Heading Offset Boatspeed Correction APP or MEAS W/A MHU Offset Heel Offset Leeway Coefficient N/A Mast Angle Offset N/A Rudder Angle Offset N/A Sea Temp Correction N/A Trim Offset Load cell Calibration Volts N/A Use the space below to note any other important calibration data. www.bandg.com 6

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True Wind Calibration Tips 1. True Wind Angle Calibration WIND > TRUE W/A + CALBRATE > CORRECTION A TRUE W/A calibration matrix is utilised for corrections upwind, reaching, and downwind across the TRUE W/S ranges. Two methods of calibrating TRUE W/A are available, either monitoring TRUE DIR from tack to tack or gybe to gybe, or using the compass to verify the angles the yacht is tacking or gybing through. 1. If an error is seen in TRUE DIR, then the following rule applies: • If TRUE DIR is lifting you tack to tack then TRUE W/A is reading too wide, half the error must be subtracted from...

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2. If according to the compass you are tacking through an angle different than the sum of the TRUE W/A's on each tack (Port TRUE W/A + Starboard TRUE W/A) then the following rule applies • If the tack angle < the sum of the TRUE W/A's, the TRUE W/A is reading too wide, half the error must be subtracted from the correction table. • If the tack angle > the sum of the TRUE W/A's, the TRUE W/A is reading too narrow, add half the error to the TRUE W/A table. A Worked Example: Your TRUE DIR is telling you that you are being lifted by 10 degrees from tack to tack (or the sum of your TRUE W/A is 10...

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Typically, when graphed, a TRUE W/A table for upwind might have a curve like the following: If it has only been possible to achieve reliable values for the TRUE W/S 5, 10 and 20 range and the rest of the table left blank then the table would look as follows: It is clear to see that the 15, 25, and 30 kt values can be accurately guessed at as opposed to being left with zero values. You should repeat the process for reaching and running as well as beating. 9 www.bandg.com

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2. True Wind Speed Calibration WIND > TRUE W/S + CALBRATE > CORRECTION TRUE W/S errors are seen from sailing upwind to downwind. This is most noticeable on Mast Head boats, however all yachts are affected to some degree. This is due to the acceleration of the airflow over the top of the mast and around the sails when sailing downwind. The introduction of the Vertical Mast Head unit has gone some way to solving this, however calibration may still be necessary. As a rule of thumb, it is safe to put a correction of -10% into the table before first sailing and this is the value entered by B&G...

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