Another sample Resource: True wind vs. Apparent


Index to wind conversions.

Extracting true wind speed and direction from the apparent wind and your own boat speed is fundamental to all of marine weather. In particular, we need to detect small shifts in the average true wind direction as soon as possible for early warnings of weather changes and these are often masked in the apparent wind by our own slight changes in speed or direction. This is the page where information on this subject is gathered together.

There are articles on the subject, as well as solutions to the problem by computation using a trig calculator and by direct plotting of the vectors. There is also built in to the Weather Trainer a very convenient dedicated computation for this problem called the "true wind computer." The picture below illustrates the basic triangle of vectors that must be solved as well as the analytic trig formulas that can be used to solve it.


True wind triangle.

In the program we cover how to solve this triangle by plotting (as indicated below) and by use of a simple trig calculator, i.e. one with sines and cosines. In both cases we go step by step with specific numerical examples.


Section from the Quick Clouds window.

This is Step 4 in an animated explanation (the pencil and tools move, etc, to draw the lines). It shows show to draw the diagram to solve for true wind. It is the same procedure, by the way, that is used to solve current flow problems. Every reader will know precisely how to figure true wind from apparent after watching this explanation. It goes slowly, step by step and can be repeated at will until it is mastered.