Originally Posted by davidpm
So there must not be any current where you are?
There is David, quite a bit in fact, but ones bearing lines and closing-opening angles are taken from the yacht relative to the (hopefully) fixed mark hence they incorporate the yacht's relative movement. If you are your own tactician, you have to take bearings fairly often, particularly when crossing a current stream as the speed of the stream will vary relative to depth but these are nuances you will learn as your race in your own venue. For example, if you are racing on a River current tends to slacken near the banks because of shoaling while, at the same time, the wind tends to veer or back as wind always tries to cross a water/land boundary at right angles, just as waves always wash up on a beach at right angles. Hence when the mark is up-stream, an apparently longer course near shore may prove much faster than a shorter route through the stream with adverse current and less favorable wind. Likewise, if racing on a lake, reaching around the banks may prove much faster then beating a straight line across the breadth of the Lake.