Downwind
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Автор: Денис   
26.11.2009 16:36

DOWNWIND OPTIONS

The tactical options for a team downwind are dependent upon the relative positions of the boats, the strength of the wind, the variability of the wind (in speed and direction) and the performance characteristics of the boats.

The leading boat has the option of choosing which side of the course to sail, at least initially, and can round the top mark with a 'bear-away' set (taking the right side of the course), or a 'gybe-set' (taking the left side).

The trailing crew could then split sides, by doing the opposite. This gains the trailing team some lateral separation which it can leverage into a gain if it finds either favourable pressure, or a beneficial wind shift.

In lighter wind, the boats will set asymmetric spinnakers, which force the teams to sail higher angles (closer to the wind) and make it more difficult for a trailing boat to 'blanket' the leader, with its windshadow. At those higher angles, the apparent wind angle is so far forward, a team needs to get forward of bow to bow to affect the wind of the other boat.

In stronger winds, with symmetrical spinnakers, the boats sail more directly towards the leeward mark, and the trailing boat will be more likely to throw its windshadow on the leader if it is within a couple of boatlengths.

In the following example, the trailing boat Blue, has followed Yellow around the mark. By not doing a 'gybe-set', Yellow has decided the favourable wind is on the right side of the course.

At position '1', Blue can gybe first, taking the left side of the course, wait and gybe at the same time as Yellow, in hope of getting bow forward enough to affect the wind Yellow gets, or switch sides by continuing on if Yellow gybes.

In this example, at position '2' Blue gybes first, and Yellow immediately follows to prevent Blue from gaining any significant separation on the left side of the race course.

These 'simultaneous gybes' are an excellent opportunity for superior crew work to gain your team a few metres.

At position '3' Blue gybes a second time, and Yellow again responds in kind immediately, protecting the right side of the race course.

When Blue gybes in position '4' Yellow follows and is in a strong position. Blue would need to make a massive gain to be able to gybe and cross in front. From this position, Yellow can sail Blue down to the port gybe layline, before turning for the mark, and leading Blue around the leeward mark.

Crew work and equipment reliability are critical on the downwind leg. Gybing in light wind with the asymmetrical spinnaker is risky, as there is always a chance of the sail getting wrapped on the forestay or torn on a spreader. In stronger winds, the sail itself is at risk of tearing, and a small defect can quickly result in a tattered sail. The spinnaker pole too is under tremendous strain, and any small mistake can manifest itself in a broken pole very easily. Although it often appears to be easier sailing, with the boat relatively flat compared to the upwind legs, sailing an America's Cup Class boat downwind is no time to relax.

While a trailing boat can often make a gain on the downwind leg, it is much more difficult to convert that into a clear lead change. A team that makes a pass on the run has done a magnificent job.

 


PROPER COURSE

This is a situation that occurs with some frequency in the America's Cup, usually when a trailing boat makes a gain on the downwind leg.

In this case, Yellow has made a gain, and established an overlap position from clear astern. Under Rule 17.1, Yellow can not sail above its proper course. While there is some degree of subjectivity in this, the Umpires will be watching Yellow very closely.

It is important to note that Yellow isn't the only one burdened by Proper Course here. Rule 17.2 also restricts Blue from sailing below its proper course

As the boats approach the layline, Yellow's proper course is to gybe for the mark, and under the Rules, must do so. However, the further past the layline that Yellow can sail, the more difficult it will be for Blue to establish the inside overlap that would allow it to round the mark in the lead. As the boats approach the layline, Blue will be making loud and constant appeals to the Umpires that Yellow is sailing them too far without gybing. Yellow must temper its desire to punish Blue, with the reality that the Umpires are about to punish them.

Proper course is a very difficult call for the Umpires to make, but Yellow must take care that it doesn't test the Umpires too aggressively here.

Yellow is only forced to gybe if the original overlap it established was from clear astern. If it was Blue that originally made the gain from astern to becoming overlapped to windward, then Yellow has luffing rights under Rule 11 and is free to sail Blue past the mark.


DOWNWIND PENALTY

Taking a penalty turn downwind (defined as sailing more than 90-degrees off the wind direction) requires a team to tack when executing the turn. In addition the spinnaker must be taken down such that the head of the sail is below the gooseneck (where the boom meets the mast). Rule C7.2, C7.3 and C7.4 are applicable.

In America’s Cup boats, taking a penalty turn downwind is less common because of the time required to drop and re-hoist the spinnaker. The exception of course is at the finishing line, where there is no need to re-hoist the spinnaker or build up speed again.

In position 1, the genoa is hoisted. In position 2, the spinnaker comes down as per a normal mark rounding. The boat takes its penalty turn around the pin end of the finishing line, which makes it easier to judge where the line is. The worst scenario is making the penalty turn to early and finding the boat stalled coming out of the penalty turn but still needing to sail for the finish line. Blue also is given rights as the inside boat at the finishing line as soon it is on a downwind course.

 


 

BEAR AWAY SET

The easiest approach to the windward mark, from a crewman’s perspective, is to tack on the port tack layline with nearly two minutes of sailing left before reaching the mark. This allows plenty of time to get the spinnaker ready, put the spinnaker pole on the mast, sneak the spinnaker part of the way up, and be calm and confident when arriving at the mark.

Of course, for any number of tactical reasons, this rarely happens. And the Port tack approach has and element of risk if the opposition is close and approaching the mark on starboard tack.

When the boat arrives too late on the layline, there is not enough time left to complete all the procedures, and so the spinnaker hoist is slower.

1 - The spinnaker pole is clipped on to the mast and the spinnaker sheets are attached.

2 - The pole is raised.

3 - The spinnaker halyard is partly raised and the spinnaker is ‘pre-hoisted’ as high as the second spreader on the mast.

4 - The boat bears away for a full speed hoist. When there is a starboard tack boat approaching on the starboard tack layline, Rule 10 applies.

Finally, the headsail is dropped as soon as possible and the crew signal that they are ready to gybe whenever the afterguard feels it necessary.

 


 

TACK SET

The tack-set is a harder manoeuvre for the crew, and occurs when the boat approaches the windward mark on starboard tack and must tack around the mark. The foredeck team begins to set up for the manoeuvre. The first job is to put the pole on the mast.

As the boat tacks around the mark, the genoa sheet is released for the tack, the spinnaker halyard is hoisted and the spinnaker pole is raised up the mast as well.

From a tactical position, this can be a strong manoeuvre as a starboard tack boat maintains rights all the way to the mark.

 


 

GYBE-SET

If the wind has shifted to the left during the windward leg, it may be advantageous to gybe immediately upon rounding the windward mark. This may also be the case if a trailing boat is trying to achieve a measure of separation from a leading boat that has executed the more common bear-away spinnaker set.

The gybe-set is a more difficult manoeuvre, and slower than a bear-away set.

The pole is typically set on the mast while on starboard tack.

As the boat bears away around the mark, the helmsman continues turning through a gybe. The spinnaker is hoisted in the ‘gybed’ position as the boat bears away and the spinnaker pole is raised as soon as the genoa gybed across the boat. The spinnaker is usually slower to fill, as it sheltered by the mainsail until the turn is complete and the pole is raised.

Источник: 32nd America's Cup Official Website