Calculating the upwind layline: it’s all about trigonometry

Anyone who has done some regattas will surely have heard the fateful phrase “do I get the buoy or not if I tack now?” The typical situation of calculating the layline, that imaginary line that in one tack, without performing any further tacking or gybing, takes us to the buoy. But what are laylines really, and how can one make a precise enough calculation to “get” them without too many mistakes? It somehow takes trigonometry, or better to have the geometry of the race course in your head based on the wind swings and to be quick in some angle calculations even without the help of navigation software.

What are lay lines

These are two imaginary lines, along which we reach the windward or aft buoy with a single edge without performing any other maneuvers. If we take them in the right way, deciding with the right timing on the last tack or gybe, to reach the windward mark we will be upwind tight and for the stern mark at deep leeward (more or less depending on wind strength). Wanting to give more precise angles to the wind, a good upwind lay is when we reach the buoy in one tack keeping about 45 degrees to the wind, in the stern we will instead be around 145-150 but in this case the number may vary depending on whether we sail with a gennaker or a spinnaker, two sails that impose different angles. Variations in the optimal angle also depend on the type of boat: the more the boat is pulled and racing, the more it will be able to make narrower optimal angles upwind.

Being able to take a layline without mistakes depends first of all on the distance from which we “pull” it; the longer the tack we want to reach the buoy, the more complicated it will be to center the layline at the right angle and without going the extra distance. Better, therefore, to “ladder,” that is, to execute a positioning by a series of approach turns to the right or left layline we choose, possibly choosing the right or left side of the race course according to the average wind swings. If the wind has an average swing to the right, it will be better to go“laddering” on the right center of the course, and vice versa: in fact, by staying on the part of the course toward which the wind rotates, and trying not to stay on the shorts for long, we will reach the buoy by traveling less distance than by choosing the opposite part of the course.

Sometimes, in the case of major wind shifts, it will also happen that you will be able to reach the layline in a single tack, but in low-swinging wind conditions this will often not be the best choice.

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How to navigate good and poor to reach the upwind layline

Starting upwind, let’s take an example with a buoy positioned for 300 degrees. If in the pre-start we notice that the wind tends to swing from 300 to 310-315 degrees, it will mean that the average swing is to the right and it will be appropriate to start in committee boat and go sailing on the center-right of the course. How, however, to decide when to place the turns?

If by the time we get out of the start, with the starboard tack, the wind will have returned to 295-300 degrees, that is a good phase to immediately place a tack and sail to the right side of the course to then go for possible wind rotations. In fact, at that time the wind direction is fairly neutral with respect to the placement of the buoys but we know, because we have noticed it in the pre-start stages, that the tendency of the swings is to the right and it is toward that area that we will take tack to port, taking advantage of a neutral phase of the wind or a very slight left.

When we begin to feel the first wind shift, we will notice that the direction will shift more or less quickly to 305-310 degrees or beyond. At that time, if we sail port tack, we will be on the so-called scarce, that is, our boat will follow the wind swing to stay properly to windward and we will no longer have an optimal approach angle toward the buoy, which as mentioned is positioned for 300. With a wind direction from 310 our course will be approximately for 355 degrees if we sail tacking to port, conversely tacking to starboard we will have a course for about 265 degrees, thus better than the buoy which is positioned for 300. Numbers that we cite as an example, to be taken with a pinch because they also vary significantly depending on wind strength and type of boat, but they are useful for understanding the reasoning and dynamics of choices.

How long to stay on the scarce before tacking? This depends on at least two factors, the positioning of the other boats and thus whether or not it is possible to make a turn and sail to the next edge in clear air and without cover, and the extent of the scarcity itself. The greater the right wind shift, the more it will be necessary to hasten the tack so as not to throw meters into a bad approach course. Once made, sailing starboard tack, any swing to the right wind will at this point become a good one, that is, we will be on a better course of approach to the buoy than on port tack.

If the wind continues to remain around 310 degrees we will not tack and continue on our starboard tack approach. we will probably be in the second part of our upwind approach to the buoy by now, but we have not reached the layline and will still be downwind of it. When to turn back to tack to reach the right layline? Once again it will be the wind direction that will suggest the moment. If the wind returns to the left on 295-300 we will tack fairly quickly if possible, sailing left tack to the right lay.

At that point there are two possible situations: the lay will arrive first if the wind shifts back to the right, on the 305-310, vice versa if it remains neutral it will be a little further away. Wanting to imagine the “glimpse,” we can say that if we visually draw an imaginary line from the buoy to our position, and it falls more or less in the middle of the boat (thus at about 90 degrees to our course) we will likely be in or near the layline and it is time to tack.

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Be careful not to do this too late, ending up beyond the layline; every extra meter traveled beyond this will be extra road we have covered without going in the right direction, i.e., the one that gets us to the buoy most quickly, with an avoidable waste of precious seconds. In choosing between tacking before or after the layline, we tend to always choose anticipation, so that we try to go less distance. Particularly so in our example we know that the average wind swings are to the right, if we are in a neutral phase (300 degrees heading), we might slightly anticipate the last tack from port tack to starboard tack imagining that a small wind shift to the right might help us catch the buoy without then tacking further. In any case, it is better to risk an extra tack than to throw away meters, unless the wind conditions are very light or the current pushes us downwind: in the latter two cases it is better to “abound” by delaying the layline tack a little, to avoid then having to maneuver again in unfavorable conditions.

Let us close with one last important consideration: we have not mentioned wind intensity in this discussion, but only its rotation. In fact, the choices described above may vary according to the wind intensity, and sometimes, especially on days with little air or on days when the wind has significantly different intensity in different areas of the field, rather than the “phases” of the wind it will be necessary to follow the “pressures,” thus going after the areas with the most wind, and then reaching the layline.

Mauro Giuffrè