The “Lay Line” is the straight line tracing the course following which a boat can fetch an upwind mark (the shortest track to reach the target).
The location of lay-lines is affected not only by wind direction shifts, but by changes in wind velocity as well. Watching for wind shifts means to take advantage of, and try to evaluate which side of the course is favorable, understanding the upwind impact. When we are exploring, we lay line to ensure our continuous guideline back to the surface, but also to allow us to survey and map the new passage. When we lay line, we do not necessarily lay the line for the easiest navigation. Each run of line is made to try to go as long as possible in a straight line.