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Track optimization

Introduction

Actually this chapter isn't about the optimal route but the shortest route. This chapter will help you to find the shortest route from the start to the finishing line.  This is the most important part of our racing strategy.  This mainly concerns wind shifts, and the aim of this chapter is to show how best to use them in order to gain an advantage over the competition.

First a couple of definitions:  'Oscillating shift' means that the wind turns to the left or right of the main wind direction.

'Consistent shift' means that the wind turns continously either to the left or to the right during a longer period.

The challenge with finding the optimal route is to correctly evaluate all available data.  In an ideal case a concrete statement like this one can be made: 'The wind is turning between 350 o and 10o. The main wind direction is 0o, the phase is 3 minutes so, under the current conditions we will need 15 minutes for the initial upwind leg'.

If you are a top yachtsman, you will possibly get this information from your coach and you trust him.  But mostly you have to depend on yourself alone to gather and interpret data.  In the chapter 'Prestart' you will find some suggestions which should help you to collect and interpret data.
Hint:  In shorter races an oscillating wind becomes a constant wind shift. If the phase of the oscilating wind is longer than the time you need to reach the next mark, you are not allowed to make use of the rules for oscillating winds.  You must sail as if you were dealing with a consistent wind shift, because before the wind begins to turn back you will already be at the next mark.

Hint:  Don't forget, the shortest route is only one strategic factor, though its the most important one, but don't forget to watch all the other factors (wind strength, currents, wave strength, etc.).

Our tactics depend on the type of wind that we have identified.  Depending on the type of wind, differing methods should be pursued;  we will discuss these further in the following headings:

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Oscillating Winds

On the windward leg

Everyone understands that by oscillating winds the best tack is that one with the best VMG to the average wind direction. That means if the wind is to the left of the average we should sail with wind from port, if the wind is to the right of the average we should sail on starboard. We also say we shall always sail in a 'lift'.
In contrast to the 'Header' when the wind comes more from the front and hits us on the head so to speak. 

In order to sail by the shortest route when winds are oscillating, you should always sail on a lift.  Consequently, it follows that you shouldn't sail into a Header.   So far, so good.  We know now that we should always sail on a lift, but if we get a smack on the nose (i.e. if we sail into a header), when is the right time to tack?

In order to decide the right time to tack, you have to know the mean wind direction.  If you don't know that, you can only sail by instinct/feeling and that seldom works well.  If you don't know the mean wind direction and  have to bear away, then you will probably tack, although actually you were really still sailing on a lift.

After the tack, you will be sailing below your mean course and that's exactly what we wanted to avoid.  On the other hand, if we wait too long we might be travelling at the highest point after the tack, but then we have to bear away again because, of course, the wind then begins to turn the other way.

Who hasn't experienced that? Wind is shifting into one direction. We are bearing away, bearing away. The devil in our head tells us ' Hold back on the tack, because it will go further up on the other beat'.  Finally you tack.  After tacking, things speed up well but - what bad luck - we have to bear away again.  Bad luck?  No!  That was just the result of not tacking at the right time. Precisely at the point of the tack, the wind had begun to turn in the other direction.  I can't emphasise enough: In order to be able to sail by the the shortest route we must know the mean wind direction.  Then everything suddenly becomes simple and we don't need any psychic powers to find the shortest route.  Its actually quite simple: Always sail on a lift.  As soon as you have to fall away from the mean compass course, its time to tack – not before and not after.  Every meter earlier or later will cost you valuable distance.  In case you don't believe me, look at the following examples.

 

In this example, the wind ocillates uniformly around the centre line.  Green always tacks when the wind direction crosses the average wind direction.  Yellow always tacks if he gets a header. Red is simply always underway against the wind shifts and always tacks if the wind starts to be in his favour. At the beginning of the animation, all three boats find themselves at the same distance from the windward mark. We can see that green always turns if the wind blows beyond the average wind direction.  As a result it is always sailing in a lift and reaches the windward mark with a good distance between it and the yellow boat.  The gap from red is hardly surprising because, as expected, it has a much longer path to travel.

Tack, tack, tack

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Another tip for sailing in oscillating winds:

Try to sail fast as much as possible.  A little less height and higher speed will bring you faster to the next wind gust and thereby to the next lift after the tack.  This way your VMG will improve in the direction of the mean wind.  Why? No idea, but I do it and many authors write about it.  I really must analyse that precisely soon.

Because you normally determine headers and lifts using the compass headings, you should be aware what influence a dropping or increasing wind can have on your compass heading.  We all know that we always sail with the apparent wind.  That is the wind that we can measure directly on the boat, without maths calculations.  This apparent wind is composed of true wind and boat speed.

 

:The following animation shows you the influence of a dropping wind on the direction and strength of the apparent wind.

 

In Phase A, the boat sails with constant speed and height.  At the beginning of Phase B the wind decreases significantly.   Because our boat is still travelling at the 'old' speed, the direction of the apparent wind changes to the left, the sail drops, and we have to bear away.  The true wind direction has not changed however.  Our boat gradually loses its speed through the water. In Phase C our boat has reached the target speed for the now lighter wind.  As a result, the influence of the airstream on the apparent wind direction becomes lower and we can move to windward again. 

If we wrongly interpret this effect as a header, and tack because we have to travel below our main course for a short while, we will find, to our amazement, that we are travelling below our main course.  'Shit, the wind changed again just as we tacked'.  How often have we already heard that on board, or said it ourselves?  In reality, we have just interpreted the data wrongly and arrived at the wrong conclusion.  Things go exactly the opposite way if we are travelling in a squall; in this case, the boat speed isn't yet adequate to the wind and the apparent wind changes its direction, so that we can travel higher for a short time.  After the accelerating phase the apparent wind again comes from the original direction, and we fall back to the original course.  

A further effect appears if we don't decide whether we are in a header or a lift with the help of the true wind direction indicator, but to compass headings, whatever the case may then be, if we don't have well calibrated instruments available on board, so always on dinghies.  In this case, we know  the adjacent  compass heading for the starboard tack and for the port tack. With this, we can determine, without any more instruments, whether we are in a lift or in a header. 

So far so good. But there is another aspect, we have to care for: Many boats/yachts, however, varies their optimum height with the wind strenghth. The VPS diagram gives you further information for the optimum tacking angles at different wind speeds. If these angles vary a lot, you must of course, adopt your compass headings for the main wind direction to recognize when the wind shift has crossed the average direction..

 

Downwind

In principle, when sailing downwind, everything is in reverse to how it is on the leg to the weather mark.  Because with modern boats, whether with Gennaker or Spinnaker, you never sail direct before the wind, also when sailing downwind we have the problem of choice.  Should we sail on starboard tack, or on port tack?  When should we gybe? With oscillating winds its as follows:  If we get a header we can bear away and sail a shorter route to the leeward mark as a result.  If we sail in a lift (i.e. higher than the average wind direction) we should gybe.  That means, in contrast to the upwind leg, where we should always sail in the lift, on the downwind we should always try to stay in the header.  However, there are still two important differences to the upwind leg to note: look where there is more wind.  In contrast to the leg to the weather amark, it pays to sail to where the next squall is, simply because if the squalls and the boat are both moving in the same direction that means you will stay in a squall for much longer than on a upwind leg and will profit much more from it.  The correct lane is not so important when going downwind as on the beat.  It is much more important that you stay in the areas with stronger wind for as long as possible. Because you sail significantly faster, it could be that although the wind conditions are constant, and the wind oscillates around the same amplitude that you will sail with oscillating wind on the upwind leg and find a constant wind shift on the downwind leg, simply because thanks to the  high speed as the wind swings back, you will already be on the next beat again.

 

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Consistent Wind shift

Windward leg

If your prediction is that the wind will shift consitently to one direction, you will unfortunately have to sail hard on the side on which the wind is turning.  The greatest difficulty on such a beat is to judge when you have reached the Layline.  In this case, the Layline isn't straight but, due to the constant wind rotation, a curve.   If you now tack below the Layline, you won't reach the windward mark, despite it going higher and higher in the direction of the windward mark.  Then, on the leg to the mark you would be sailing against the wind direction and lose many meters.  So in this case its better to tack several meters above the Layline, and then, in case you are too high up, open your sheet, hike as hard as you can and sail fast down to the windward mark.. This costs you only a few seconds and is a much better choice than tack too soon and have to make an additional tack at the mark, against the wind direction.

 

Downwind leg

 

In this case, we sail first to the side of the wind direction, e.g. if the wind is shifting to starport, we sail first on starboard tack. If the wind turns to port, we sail first on port tack.
If the wind strengths on both sides of the stretch are very different, it can be useful to make a detour and sail on the 'wrong side'.nach oben

Combination of both

Windward leg

Very often you find a combination of oscillating wind shift and consistent wind shift. The wind shows a continual rotation to one side, but this constant rotation is is overlapped by many small wind shifts on both sides.  This wind pattern is the hardest to recognise but the correct strategy for these conditions is relatively simple.  Basically you sail as if with a constant wind rotation.  As described in the chapter above, you sail in the direction in which the wind is blowing.    That means when the wind is rotating to the right you would generally favour the right hand side of the 'track', and by a rotation to the left, the left hand side.

The brief oscillating winds in the opposite direction to the main wind rotation can be made use of to tack and sail a short way in the other direction. That way you don't sail so extreme to one side, take longer to reach the Layline and the risk is not so high, if the wind developes different to our prediction.

Downwind leg

On the downwind course, follow the same rules as you would for a consistent wind shift.  Whether we make use of the brief counter wind shifts is very much dependent on the type of boat you have.  If we don't lose any time with our jibe, it will be worth not to make use of every little counter wind.  If we are quite slow when we jibe, we should ignore the little oscillating winds and focus on the main constant wind direction.  Naturally, we should never forget the main Downwind principle:  sail where the strongest wind is to be expected.

 

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No idea what kind of wind will be blowing

Upwind leg

How could that happen? Its not always possible to recognised a wind pattern from our wind records. Or, even more trivial: for some reason or other we didn't have time to make any wind calculations.  In this case, there's one simple ground rule; we always sail the route that brings us nearer to the weather mark.  The theory behind this ground rule is as follows; In case the race organisers have positioned the buoy exactly in the main wind direction, we'll always find ourselves in a Lift if we always sail the route that brings us nearer to the buoy.  Another advantage of this method is that we stay more in the middle of the course and not too close to the Layline.  That way, we have room to the laylines and can react to wind changes.

If the wind shifts consistent, but you haven't recognised that, there's nothing else you can do but to sail the last tack against the wind direction. But I'm guessing you won't be alone!
As you approach the windward mark, you would at some point have to abandon this tactic, otherwise the beats will become shorter and the number of tacks increase.

 

Downwind

If you don't know how the wind will cahnge direction on your downwind leg you have to try to stay always in the zones with the strongest wind gusts.   A good moment to jibe is always when the gusts are strongest.  This does raise adrenaline levels, at least when winds are strong, but does ensure that you stay as long as possible in the area where the wind is strongest.  If there are no special areas behind you with more wind, you simply follow the same formula as for the upwind leg.  We sail the route that brings us nearer to the buoy.  That isn't always the shortest route, but will certainly be the route that keeps us more in the centre of the course and therefore further away from the Laylines, which means more room for us to act and react. At least keep the losses within boundaries.

 

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