Surf high and low
The equipment used for windsurfing has developed greatly in the last ten years. This applies not least to equipment for track sailing, or so-called Formula windsurfing. In this form of competition, you sail a cross-wind course (also called an I-course after its appearance). This means being able to sail high into the wind on the tack and as low as possible on the leeward side.
Sailing flat luff (completely with the wind) is slower than lying on a fast sail, where you can maintain planing at all times. Sailing flat luff (completely with the wind) is slower than lying on a fast sail, where you can maintain planing at all times. In these contexts, the point is to get to the mark as quickly as possible and we then talk about "Velocity Made Good" abbreviated to VMG in everyday speech. It is important to go high into the wind on the tack but not so high that you lose speed, so there is an optimal angle where the speed up to the mark, i.e. VMG, is the highest. This angle depends on equipment, wind strength and sail trim, etc., and it is something that you have to try to feel on the water when you are out sailing. On the leeward side down towards the leeward mark, the same applies, it is important to find an optimal angle that takes you down to the mark as quickly as possible (i.e. maximum VMG again). Now that this form of competition has been around for about ten years, the equipment has been optimized to be able to go both high and low into the wind, even in very light winds. It only takes about 4m/s to maintain planing with the largest sails (12.5 m 2 ) and in winds around 6m/s a slightly smaller sail of around 11m 2 is enough. To trim your equipment for optimal speed and altitude gain, you can use a GPS. You attach this to your upper arm so that you have a good signal and then you sail around a course while the GPS stores positions once per second. After sailing, you can easily transfer the measurement data to a laptop and there you can see how you have sailed. As an example of this, we have sailed a small course from Örsholmen and out around Märrholmen and back. The GPS data from this is shown in Figure 1 superimposed on a satellite map.
Figure 1. GPS data for a sail from Örsholmen and out around Märrholmen (clockwise) three times in total. The wind here was about 6-7m/s (southeasterly direction) and was sailed with a Formula board and 11m 2 sail.
It is quite easy to see that the height gain, and also the angle of the veils, is good, but the question is how good? To check this, you can plot the speed in a polar diagram (solid line in Figure 2). In such a diagram, the speed is marked as a distance from the origin and the angular position corresponds to the angle to the wind (i.e. the wind comes from 0 degrees in the diagram). You can easily see that you are at speeds of around 16 knots and up to just under 25 knots. During this sailing, the wind was about 6-7m/s and the equipment used was a Starboard 162 surfboard and a Severne Code Red 11.0 sail.
How fast have you traveled against the wind, or up towards a mark in windward? This can be calculated by taking the component of the speed projected onto the prevailing wind direction. This then gives our VMG and it can then be shown in the same polar diagram as the speed in figure 2, here with a dashed line. You can then see that the highest speed up towards the mark is around 10 knots and is achieved at an angle of around 50° from the eye of the wind. The relative wind direction is only around 25° as we maintain a relatively high speed relative to the wind force (6 m/s is approximately 11 knots). When we sail with the wind, in this case we get a maximum VMG of around 140-150°, and then reach a maximum of 16-18 knots in pure speed towards the mark. It is also noteworthy that the highest speed is easily around 22-23 knots and thus you are sailing approximately twice as fast as the wind (22 knots is approximately 12m/s).
In addition to competing on cross-country courses, Formula equipment is excellent for getting around the archipelago in light winds. A trip from Örsholmen and out around Märrholmen takes just over 20 minutes, and by then you have covered a distance of about 10km.
Figure 2. An angular representation of the speed (solid line) and VMG (dashed line) for the sail shown in Figure 1.
/Krister Svensson