Drifting

Unfortunately, the boat does not move as indicated by the compass. It's drifting.
It is drifting for at least two reasons:

The wind is generating some leeway
There is some current

Those two factors will make the Course Over the Ground (COG) look different from the Heading (HDG). They have to be computed separately, and have a direct impact on the Course Over the Ground (COG), and the Speed Over the Ground (SOG).

Those two values are to be understood in a slightly different way. The leeway is an angle that is to be added or substracted from the heading (HDG), as opposed to the current, which is to be represented as a vector having a speed and a direction, to combine with the vector represented by the boat speed (BSP) and direction (HDG) modified with the leeway (Course Over the Surface) to find the Course Over the Ground.

Any comment ?