Join Date: Oct 2002
Location: Phuket, Thailand
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This may help...
True Course (TC): This is the course measured from your navigation plotter
when you plot your trip on your chart.
True Heading (TH): Now that you have a true course, we need to correct for winds/current which will give us a true heading.
Magnetic Heading (MH): The difference between true north and magnetic north is known as variation. Lines of variation are shown on a sectional chart as dashed magenta lines and called isogonic lines. By adding or subtracting variation from your true heading you will get your magnetic heading. Remember east is least (subtract) west is best (add)
Compass Heading (CH): Items from inside the airplane (boat?) can actually affect the performance of the compass. This is your deviation. This is normally on a small card mounted close to the compass. When you sum everything up this is your best guess on what you will read on your compass to maintain a course. This will obviously have to be updated as you make progress on your journey. You can also do this entire operation in reverse to plot your winds/current.
Part time PADI instructor, part time sailor. Full time having a blast.
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Last edited by jerryrlitton; 08-10-2010 at 11:15 PM.