The effects of leeway is one of the reason why your water track (heading) may not be the same as your ground track or COG. The difference between the heading of the boat and the reciprocal of the wake, measured in degrees, is what we call leeway (Fig 7.5).
The leeway experienced depends on many things including, the type of vessel, your boat speed, the sail plan, strength of wind and waves. We can measure leeway and once you are familiar with a boat can estimate quite easily.
We can determine the value for leeway using the ships steering compass and the hand-bearing compass (Fig 7.5).
If the vessel is heading at 000°/360° and the bearing of the wake as sighted with the hand-bearing compass is 195°. If we add or subtract 180° from the bearing of the wake will give its reciprocal bearing. The reciprocal bearing is 015° and can immediately see that the vessel is experiencing the sideways effect of leeway of 15° (reciprocal of wake 015°M – heading 000°M = 015°M leeway)