The downwind leg gives you the chance to exploit the same wind shifts you utilized going upwind , but with more dramatic results, When sailing downwind , the sails do not produce any lift. In fact, it is their drag that moves the boat forward. Only when the boat heading changes from dead downwind will flow develop to generate lift. This lift combined with the drag causes the boat to accelerate (cause and effect). The helmsman can initiate this cycle of cause and effect by merely heading up slightly. As always, there is a trade off between extra speed generated and extra distance sailed. Above a certain wind speed, the heading that produces the best speed downwind drops off drastically so that at that point you should head directly at the mark.
Before rounding the mark you should decide which way you want to go and when you will jibe. You should ask the following questions:
1) What has the wind been doing (oscillating or persistent shift)?
2) Has one side of the course been favored and why?
3) Is current a factor?
4) Where is the rest of the fleet and can you stay out of their wind shadow?
Sailing direct to the mark is usually slow. Therefore you should sail on a broad reach and back and forth. Your course is one that snakes back and forth across the rumb line. It may look inefficient but it achieves the greatest average velocity toward the mark. A fast course is to sail slightly above a downwind course. When the boats starts to slow, head up to keep the apparent wind forward.
Sail trim downwind:
The mainsail provides the speed so ease the sheet out as far as possible. The vang should be fairy tight but some twist is desirable, so ease the vang slightly and trim mainsheet so top telltail flows.
Course to be sailed:
Under 3 knots of wind:
Sail directly downwind.
3 to 10 knots of wind:
Sail 40 degrees above dead downwind.
IO to 14 knots of wind:
As the wind increases, sail gradually from 35 ° down to 15 ° above
dead downwind. Sail off in puffs and up in lulls.
Over 14 knots of wind:
Sail direct to the mark.
Polars are a graphics display which shows the optimum boat speed for every wind speed. They are used in the following manner. Assume your target speed is 3.87 knots in 8 knots true wind speed. If you are sailing at 3.58 knots you are obviously slow and you should head up until you reach your target boat speed. If you are sailing at 4.21 knots you are obviously sailing too fast and you should bear off and sail toward the mark until the boat loses momentum and you assume your target speed.
Don't wait until you round the mark to decide which way you want to go.
Instead of sailing on a lifted tack as you do when you are sailing upwind, you sail on a HEADED tack downwind. This is more of a research than a run.
There are two types of wind shifts - OSCILLATING and PERSISTENT
Sail on a headed jibe first or the opposite of the upwind counterpart. If you are lifted, you should jibe to get back on the header. This will cut down on your sailing distance to the mark. A lift can be determined by your compass. Another way to determine a lift is when the spinnaker calls for the pole to go back or is easing on the sheet. You are being lifted so jibe the boat. Do not sail to the layline too early. Sail the long jibe first. To determine which is the longest jibe first - recall the weather leg. If you sailed the longest beat on starboard, then start the port tack on the run downwind. Another way to determine the longest jibe is to check the compass course on each jibe. When you encounter a down wind header you are actually sailing from more wind to less wind as a drop in wind speed is what is causing the header. Use your excess speed to bear off to leeward and you will be sailing closer to the mark. A conservative approach is to sail direct to the mark. A short term response is to come back up before your speed drops off significantly.
A persistent shift goes only in one direction. You should sail away from the shift and jibe short of the layline. It is important to understand the reasoning behind each tactic and mentally visualize the situation in your mind. You can then apply the information and make the proper decision. You are sailing away from the shift in order to jibe onto a header tact. By sailing away from the shift you can also jibe to a closer reaching angle. If the spinnaker trimmer is asking for the pole to come back you are sailing in the correct direction. Jibe before the layline and sail a header tack to the mark. If the spinnaker trimmer is asking for the pole to go forward then jibe immediately.
The most important skill in sailing down wind is to be able to react to the wind shifts and the ability to look for and find more wind.
In a persistent wind shift always sail away from the shift which results in the best reaching angle.
In a shifting wind sail toward the shift which results in more wind.
WHAT IS THE IMPACT OF A DOWNWIND SHIFT?
If your boat speed is 6 knots and you are sailing a 2 mile course 40° above DOW and encounter a 10° wind shift you will sail this leg 3 minutes faster if you change your heading 30°. What is the significance of three minutes in two miles? It's 90 seconds a mile! If the fleet ignores the wind shift and sails at 50°, you gain over them will be 8 minutes!
HOW DO YOU FIND WIND SHIFTS?
After you round the mark you should get on a headed tack immediately and note your wind angle, boat speed and compass course. You should be sailing the reciprocal of the course sailed on the weather leg or parallel to the boats sailing on that leg. Upwind and downwind are opposite but mirror images of each other. Sail at an angle where the boat feels comfortable and appears fast. The big question is "am I gaining or losing?" Again, upwind you tack on headers and sail on lifts. Down wind you jib on lifts and sail on headers.
Once on the headed tack you should attack those ahead of you. Sail down on them and chase them to the sides of the course. When they jibe, jibe inside them which pushes your wind shadow on top of them.
Down wind, the primary goal is clear air for defense and speed. Your mast head fly will point to clear air. A boat 8 to 10 boat lengths away can disturb your air. If your mast head fly is pointing directly at a boat then you are in his disturbed air.
TO PROTECT TO THE RIGHT?
Bear off slowly until boats converge and then head up which will allow you to pop into clean air.
TO PROTECT TO THE LEFT?
Head up until the other boat jibes and the head off.
When sailing upwind, the difference between high and slow and low and fast is 10 degrees. Down wind, the difference is 25 degrees and the opposite of upwind - low and slow and high and fast.
Helm should be neutral. There should be no heel angle.
Telltails on the main are not much help as there is no attached flow. The flow is stalled but, telltails on the shrouds are useful.
Watch the competition. If you are high and fast but the competition is low (more to the mark than you) and slow then sail lower.
If your behind, locate the center of disturbed air and blanket the boat that is ahead. You can tell when this is effective by noting their mainsail first and then their spinnaker. The spinnaker will collapse or behave strangely. If you are ahead, and the boat behind blankets you, you should immediately head up or jibe. If you are sailing in more wind, don't jibe but merely head up.
HOW FAR IS HEAD UP AND HOW FAR IS HEAD DOWN?
There is a narrow band beyond which there is diminishing return. A boat may move faster but will move farther from the mark or it will move slower but move closer to the mark. Most boats make their best speed when headed closer to the mark.
A sample scenario would be to round the mark and sail a compass course direct to the mark. Note the boat speed. Assume it is 5 knots. Come up 20 degrees and note the boat speed. The boat speed has to increase 5% to break even and to justify the extra distance sailed. If you are not going faster than 5.25 knots your progress to the mark (VMG) is slow. The solution is to sail low and slow but more directly to the mark.
Look for better wind.
If there was a favored side going upwind then sail to that side when going downwind.
In light air:
Look for open lanes.
In medium air:
Do not hesitate to jibe. The jibe angle is wider as the boat sails higher. The width of the grove between high and fast and low and slow is 25 degrees.
In heavy air:
Sail either higher and faster or lower and slower as it has little effect on VMG. Sail The course that is most direct to the mark.
Look backwards for puff and lulls:
Position yourself down wind on a puff.
In dying wind:
Work for position to keep clear air and keep clear of the crowds.
- Maximize WAG with the best combination of downwind angle and speed.
- In oscillating shifts -jibe on the lift.
- In persistent shifts - sail on lifted tack first.
- In a combination of oscillating and persistent shifts- sail on the lifted tack first and jibe on the lift.
- Avoid the laylines.
- More wind or a favorable current are reasons to violate rules 2,3 and 4.
- Sail for more wind and fall off or jibe to stay with it. Remember that jibing does not have as significant an impact on speed as does tacking.
- Keep clear air.
- Avoid corners.
- Crew position in light to medium air is forward and boat should be kept level.
- With jib and main only you should sail wing and wing and more or less directly at the mark. Sail slightly "by the lee" with slight windward heel. Run off in puffs and reach up in lulls. Put your wind shadow on the bow of the boats ahead of you.