Gybing effectively Edit
It's rare for the downwind leg's CNM to be exactly 180 degrees from TWD and even when CNM and TWD are 180 degrees apart, any wind shift will tilt the balance in favor of either left side or right side of the course. Change tack to the favored course but realize that you lose boat speed during each gybe. This loss is more pronounced in a lighter wind than in a heavier wind. (Basically you can sail at larger TWA in a heavy wind than in a light wind.) In very shifty winds you should aim to minimize the number of gybes for your fastest time to the mark. Of course if you judged the favored side of the course badly then this could mean that you have sailed a much longer course through the water to get to the mark. Your best instrument readout for optimal downwind performance is VMG, so optimize VMG over HDG but never sail outside the layline.
- Over-stand the windward mark but under-stand the downwind mark!
To initially build up boat speed (i.e. accelerate) after a gybe, you will need to sail a few degrees closer to the wind in order for your boat to present a larger area of sail to the wind (and therefore draw more power). A 3 degree difference in course can mean the difference between taking 15-20 seconds to recover to maximum boat speed versus just 5 seconds! For those ~5 seconds you are not sailing the optimal heading (course through the water) but you will discover you've more than made up for that with boat speed. Of course you return to the HDG that maximizes VMG once you have gathered boat speed.
Avoiding a lee boat Edit
Since there are two schools of thought on achieving the fastest time to the downwind mark you'll find most fleets are divided between skippers steering as deep as they can sail (largest TWA) without sacrificing too much VMG and those skippers steering for maximum VMG. A few others will sail for maximum BS. Either of the second two groups of boats will typically be sailing a much longer course through the water. What this means is that if such a boat is on your lee (downwind of you) then you may be forced to sail their chosen course rather than your preferred course to the mark.
Therefore, always watch for the signs of a collision course using the same technique as described for the upwind leg. If another boat is sailing at smaller TWA than you and you believe there is risk of colliding then act early to avoid her by sailing astern of her because although you lose some boat speed while doing so (i) you will usually make up for that loss by avoiding a penalty situation and (ii) by sailing deeper (to pass astern) you are sailing a shorter course through the water. (Note that this same option is not available on the upwind leg because your sails will luff and rapidly lose power if you sail more directly into the wind.)
- It is never a good idea to try to sail across the bow of a lee boat on the same downwind tack as you. You are putting your keep-clear boat at the mercy of the skipper of the right-of-way boat. If they decide to head up a little then you will have earned yourself a penalty!