Wind – pretty essential to what we do, huh? In this section we will consider some subtleties you may not have thought of. Master them and you could make some nice gains.
Apparent versus true
Everyone understands about apparent wind, even if subconsciously. Stick your hand out of a moving car window on a windless day and you will feel a big breeze – that’s apparent wind – generated by the vehicle’s movement through the air, rather than the air’s own movement. We deal with this effect all the time when sailing but tend not to think about it – but we should.
Upwind, it is changes in wind-speed that have the most impact – although the effect can take on a disguise. Imagine you are sailing close-hauled in a moderate breeze when all of a sudden the wind completely disappears. Your boat will still maintain some momentum – but as you are now moving through still air, you are effectively head-to-wind. The boat will act in precisely the same way as if you had hit a 45-degree header. In a more real-world scenario, where the wind lulls from, say, eight mph to five mph (direction remaining constant) a similar but less extreme effect takes place. It feels as though you have been headed – tell-tales lift and sails even back. Do not be fooled into tacking. If you do,you will experience the dreadful feeling that has made us all groan so many times in the past – that of turning the boat seemingly forever before the sails will fill on the other side.
Technically this is known as a velocity-sheer But from now on, forewarned is forearmed. When it feels like a header but it is also a lull, just wait a second and do not make a knee-jerk reaction. Adjust to get the boat upright again of course, but a big bear away will just lose you distance to windward and speed from the braking effect of the rudder to no benefit. If it really is only a wind-speed issue, things will normalise in a moment. So hang on in there and let it settle so you can make an informed decision what to do next.
Of course sometimes you can see these coming and be ready to react.
Conversely, as a gust hits, you can get the opposite effect, particularly in heavy or under-canvassed boats. The apparent wind effect is reduced by an increase in windspeed, giving the appearance of a lift until a new equilibrium is reached, at which point the short-lived ‘lift’ will end, resulting in what appears to be a small header. Again it may well not be, so let things settle and do not be misled into tacking.
Sailing into the wind also speeds up the frequency with which you encounter windshifts. Running downwind is the opposite – sailing away from the breeze reduces the frequency with which you encounter windshifts. So if there are typically four shifts on your beat, you might only get one or two on a run so it is even more important to get them right.
While close-hauled sailing also by definition creates apparent windspeed, running does the opposite. When you add to that the danger of air not flowing cleanly around the sails (instead pushing one side and creating turbulent stalled air on the other) it is no real surprise that dead-running can be horribly slow. Therefore in virtually every class it pays to create a bit of angle to ensure there is some decent airflow across the rig. How much depends on the boat and wind strength – to find the sweet spot, watch your class hotshots and do not be afraid to try heading up more than you have in the past.
With unstayed masts as on a Laser, it is often faster to sail a run by the lee, with the airflow reversed, so it rolls from leech to luff, with the tell-tales pointing at the mast. Weird but true. Just do not let the boom out beyond perpendicular.
The whole business of running before the wind has become an irrelevance in many modern classes. Asymmetric spinnakers and hydrofoils create a virtuous circle – heading up increases power and so speed, increasing apparent wind, which creates more power and so on. Get this right and you can find yourself going faster and lower than other boats that rounded, hoisted and pointed passively towards the mark. As a result it is often possible to gain more downwind in these classes than upwind.
Wind variations up the rig
In Frank Bethwaite’s ‘magnum opus’ textbook High Performance Sailing he reports some experiments on variations in wind speed at different heights up the rig. To summarise, friction between air and water slows the wind at surface level but this effect dissipates a few feet up. Those of us sailing inland and in estuaries also experience wind-shadows from trees and hills that exacerbate the situation. However, even in open water in light breezes the effect is most pronounced – you could have 2mph at water level and 6mph at the top of the rig. Which brings us back to apparent wind. If this is driving the boat at say 1 mph, at deck level the sails may need to be set as if close-hauled even on a reach – whereas at the top of the rig, the apparent wind effect is far less so the sails may need to be sheeted at a far broader angle. This leads to the conclusion that in light airs it could be hugely faster to sail with a quite exaggerated amount of twist – so negligible vang and jib leads right back. The feedback is all there in the tell-tales – but sometimes we need a scientific explanation to rationalise the evidence of our eyes. So here you go; twist can be really cool.
Downdrafts
The wind does not always blow horizontally (thankfully, or some of us would not get any!). Often gusts blow downwards, sometimes at quite a steep angle, again particularly inland and on estuaries. As this moving air hits the water it spreads out in perhaps a semi-circle from the impact point. To demonstrate this effect hold your hand out flat and horizontal, fingers together, then move it downwards whilst splaying your fingers out.
Sailing upwind, this can have a devastating impact. As you reach one gust cell, first you get headed – perhaps 20 or 30 degrees. Then almost straightaway you get lifted and lifted and lifted and lifted, well above the direction you were going before the header. This feels fantastic at the time but the next gust cell is approaching rapidly and now you are pointing well above the mean wind direction, perhaps by 35-40 degrees. The first part of that next gust cell will now present itself as a huge header of more than 45 degrees. This spells big trouble – as you are likely sitting out hard in a gust and the sails are about to fill on the opposite side. Uh-oh. Splash.
And that is why I used to keep capsizing to windward.
All this scientific insight is good to know, but what can you DO about it? First, be aware it is coming – forewarned is forearmed. Second, rather than head up and bear-off so dramatically in each cell, sail a more average course, ease the sails in the lift, stay upright and go for speed instead. Third, be ready to move fast, even if this means not sitting out to the ultimate (but keep the boat upright of course). Fourth, particularly in the likes of a Laser with its low freeboard, sometimes you can let the water take your body-weight, aided by the buoyancy in your lifejacket, and relieve the windward heeling force that way. Don’t forget, though, that grabbing the far toe strap or gunwale is actually pulling the boat over on top of you!
