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How to play oscillating shifts


Want to know the best way to lower your elapsed time around the race course? It's not sanding your bottom, buying new sails or practicing with your crew. No, the best way to increase your VMG is to play the windshifts better. And best of all, the wind is free! By nature, the wind is usually oscillating, or shifting back and forth, around an average wind direction. This shiftiness can be caused by vertically unstable air, thermal effects or offshore wind patterns. Sometimes the oscillations are very obvious and regular; other times they're subtle and confusing. In any case, the fastest sailors are those who are able to correctly identify and take advantage of the shifts. Here are some questions to ask yoursell';

Are the windshifts primarily oscillating or persistent?

This may be the most fundamental and crucial decision of your entire race. Before you play any shift as oscillating, make sure it's not really persistent. This requires good historical tracking of the wind pattern, both before and during the race.

What is the median wind direction!
Once you've identified an oscillating breeze, you need to find the "median." A phasing breeze will swing back and forth between extreme right and left shifts. You can generally get the median by averaging the.se two limits. (Don't worry so much about the timing of shifts, since this is erratic and difficult to track under even the best conditions.) You'll then use this number to make critical decisons about which tack to stay on during the race. Make sure you always have a median in mind during the race. You may need to revise it as you go, but don't forget it.

In what phase is the wind right now?

By having a median in mind, you will always know whether the wind is in a left or right-hand pliase. At any moment in a race you should be able to identify the wind phase, since this will have a large impact on your strategy and tactics. If you lose track of the median or phase, a nearly foolproof fallback is to sail the tack on which your bow is pointed closer to the next mark.

Follow this basic strategy.

When sailing upwind in an oscillating breeze, your goal is to sail on the lifts. By staying on the lifted tack as much as possible, you will sail the shortest distance toward the next mark. In general, .stay near the middle of the other boats and the course. Once you get close to the laylines, or to the fringes of the lleet, you lose your ability to play each shift to the fullest.

 

The secret to windshift success

One of the best questions to ask about oscillating winds is when you should tack. We've all heard about "tacking on the headers," but what does this really mean? Should you go as soon as you start to get headed, wait until you've sailed into the maximum header, or tack somewhere in between?

To find the answer, let's go to our secret laboratory (below) where wind velocity is perfectly steady, and the wind oscillates as predictably as a pendulum. We start off with two boats sailing upwind bow to bow. One of them (the purple boat) will tack each time it gets headed to the median wind direction. The other (black) will continue until it reaches the maximum header and then tack. Which will come out ahead? Here's how it goes:

 

A Both boats start off on port tack, sailing in a port-tack lift.

B The wind trends slowly to the right until it readies its median direction (^!35°). At this point Purple tacks to starboard and Black keeps going.

C As the wind continues phasing to the right, Purple is more lifted on starboard tack, while Black is headed more on port. Finally the wind reaches its farthest right oscillation (355°), and Black tacks.

D Now the wind starts shifting back toward the left. When it reaches the median (335°),  again, Purple tacks from starboard to port. Black remains on starboard tack and is slowly getting headed as she sails toward Purple.

E As the wind continues phasing toward its far-left oscillation, Purple is maximum lifted and crosses Black by over a boatlength. When the wind hits 315°, Black tacks onto port.

F Now the wind starts going right again (this predictable stuff is boring!). When it hits the median, Purple tacks again to starboard and Black continues almost two boatlengths behind.

 

What did we learn? It's better to tack at the median than it is to wait until you reach the maximum header. Why is this true? One quick glance at the courses of the two boats shows that Purple has sailed a more direct course to windward. This is the goal when racing in an oscillating breeze - to take a shortcut by sailing the closer tack to the next mark. In fact, one flung you can see about Purple is that whenever the wind is to the left. of median (purple shading in wind graph), she is on port tack. When it's to the right of median (grey shading), she's on starboard tack. That's the fastest way to go upwind in shifts.



David Dellenbaugh, former starting helmsman for America3, publishes Speed&Smarts, a monthly newsletter of how-to information for racing sailors. For subscription information call: 800-356-2200. To order a new subscription, click