A yacht\u2019s instrument system can only be as good as the care with which it was set-up; \u2018garbage in, garbage out\u2019 is as true of a boat\u2019s computer as any other, writes Mark ChisnellChoose flat water and a quiet time of day for instrument calibration as you need to maintain consistent speeds and rate of turn under engine. Photo: Paul WyethThese tweaks will help make any integrated instrument system accurate and effective, whether the goal is to win races, or cruise efficiently, comfortably and safely.
\nThe real key to setting up any instrument is careful calibration. I hate to say it, but this is one of the times when it\u2019s worth reading the manual. It\u2019s particularly important to approach sailing instrument calibration in a systematic order.
\nA lot of the data is interdependent, with much of the most useful information derived from the measurement of only five values: boat speed; compass heading; heel angle; apparent wind speed; and apparent wind angle.
\nIt\u2019s vital to calibrate these sensors first, and only when they are done accurately move onto whatever calibrations are provided for other functions like true wind speed and direction.
\nCompass set up and calibration
\nElectronic compasses will have the exact details of the best calibration routine described in their manuals, but it usually involves turning the boat in a circle or two. This allows the compass to calculate its own deviation curve and compensate for the local magnetic environment.
\nFor example, to set up a Simrad Precision-9 compass requires the yacht to complete a 390\u00b0 turn with a steady turn rate of 2\u00b0-3\u00b0 per second. Once the turns are completed the compass applies the new deviation adjustment and sends a message that it\u2019s finished.
\nThere are a few things to watch out for in this process. It\u2019s a lot easier and more accurate in flat, open water with no wind and no current because the turns need to be steady and even \u2013 so it won\u2019t work if the yacht has to adjust course to avoid hitting something during the calibration.
\nArticle continues below\u2026<\/p>\n
\t\t\t\t\t\tHow new-age sailing autopilot systems are putting computers at the helm<\/p>\n
\t\t\t\t\t\t\tA couple of decades ago I\u2019d have recommended anyone planning an ocean crossing without a big crew to fit wind\u2026<\/p>\n
\t\t\t\t\t\tCan augmented reality really give us a vision of the future of sailing?<\/p>\n
\t\t\t\t\t\t\tGoogle\u2019s mission statement is \u2018to organise the world\u2019s information.\u2019 This almost impossibly ambitious declaration of intent underpins the technology giant\u2019s\u2026<\/p>\n
Check beforehand that there is no magnetic material anywhere near the compass sensor, with everything stowed in its normal sailing position. Beware of mobile phones in pockets of people sitting on deck, often right above the compass fitted below.
\nOnce compass calibration is done, check the physical alignment of the instrument relative to the centreline of the boat by sailing down a known transit line. I also always check the boat compass against any hand bearing compasses on board \u2013 it\u2019s useful to know if they disagree, because then a deviation card can be created for the difference.
\nBoat speed
\nBoat speed calibration should be one of the first jobs completed on any new boat, or at the beginning of a new season \u2013 particularly on a race boat. The helmsman and trimmers will get used to the setting, and it will be disruptive if the sensor has to subsequently be calibrated after a lot of sailing time.
\nAgain, each individual system has its own calibration routines. The B&G H5000 has three variations. The first allows the navigator to compare directly with the GPS speed over the ground. This is only useful when there is absolutely no current.
\nSecondly, boat speed calibration can be manually adjusted as a percentage of a previous value. Or, for old school obsessives like myself, there\u2019s a routine for correction against a measured mile.
\nWhatever system is used, some general rules can be followed to get a more accurate result. Set up when the water is flat; the logs measure the water flowing past it and are not too choosy whether the flow is created by the boat moving forward or up and down. If the boat is pitching it will record more distance than has actually been travelled.
\nDo the runs at fixed engine revs to keep the speed consistent. If using a measured mile, make sure the speed is the same at the beginning and end of every run \u2013 otherwise the acceleration will affect the results \u2013 so don\u2019t slow the boat during the turn between runs.
\nAlways steer as straight a line as possible between the chosen distance marks. If it is a proper measured mile then the chart will provide the bearings.
\nAny wavering from a straight line means the log will measure extra distance that will not be accounted for in the calibration calculation.
\nAnd finally, if the measured mile is in a tidal area then three runs are required to eliminate the tidal error and get an accurate calibration.
\nApparent wind angle
\nThe only real calibration possible for the apparent wind angle is symmetry on both tacks. The critical thing is to set this up on a day when there is very little or no wind sheer \u2013 usually a day with a well-mixed, gradient (not thermal or sea breeze) wind.
\nApparent wind speed
\nIt\u2019s impossible to do much with this one, unless you\u2019ve got access to a wind tunnel! If you have concerns ask the dealer or manufacturer, as they should be able to check the sensor.
\nHeel angle
\nOn a calm day set the boat up with slack warps in the dock and put all the gear in its normal sailing position \u2013 including boom and spinnaker pole on the centre line. Whoever stays on board should also stand on the centreline while they read the heel meter.
\nUnder these conditions the heel angle should read zero; if it does not then adjust it till it does, either with a software calibration or by physically moving the unit.
\nFirst published in the July 2019 edition of Yachting World.
\nThe post Sailing instrument calibration: How to set up your yacht for accurate readings appeared first on Yachting World.<\/p>\n","protected":false},"excerpt":{"rendered":"
A yacht\u2019s instrument system can only be as good as the care with which it was set-up; \u2018garbage in, garbage out\u2019 is as true of a boat\u2019s computer as any other, writes Mark ChisnellChoose flat water and a quiet time … <\/p>\n