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Getting The Most From Gusts - by Ben Morris

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Why do some yachts seem to accelerate in gusts and others simply stagger along, screw up to windward and end up two or three boat lengths behind in the blink of an eye? 

To examine this issue I will describe the simplest situation of a yacht sailing on a square reach in a gentle breeze that receives a gust from the same direction.  To examine this I need to talk about real wind and apparent wind - sorry!  Look at the graphic below. 

The yacht is now sailing with the apparent wind slightly forward with the sheets pulled in a little tighter than would be the case if the wind was at right angles to the yacht.

If a gust from the same direction now reaches the yacht the wind velocity is much greater than the yacht velocity and the apparent wind will now move back almost to the original direction at right angles to the yacht.  So what happens?

If no changes are made immediately by the skipper then the sail will stall at the leading edge as the wind will be unable to turn the sharp corner around the back of the sail.  This has three effects.  The first is that the forward drive of the sail will decrease slowing the yacht.  The second is that the heeling force on the sail will increase causing the yacht to heel.  The third is that the yacht will experience a sudden increase in weather helm causing the yacht to head up into the wind thus spilling the wind out of the sails and losing all drive and speed.  As well the skipper will probably attempt to compensate for the sudden change in direction by moving the helm vigorously which in the conditions will simple cause it to stall, create drag and not steer it at all.  Every action (or inaction) then causes the yacht to slow down!

So what does a smart skipper do?  The skipper will have seen the gust coming using indicators such as boats nearby suddenly heeling, the water surface will become rougher in the direction of the wind and their own boat beginning to heel.  The skipper will immediately let the sails out from the green position towards the red position or beyond and steer the yacht slightly away from the wind.  As the leading edge of the sail is now in line with the wind direction, the wind will stay attached to the sail and generate more forward drive with the greater wind velocity but not generate too great a heeling force. The change in heading will place the wind slightly behind the beam where the gust can now blow the yacht even faster and even further reduce the heeling force.  As the yacht goes faster with less heeling, the rudder becomes much more effective and steering is not a problem - in fact the rudder become far more sensitive and will have to be treated gently!  It hasn't finished yet because the nature of gusts are that they gradually die away so the skipper will be bringing the yacht back onto course and gradually pulling the sails back in as the gusts fade and the apparent wind moves forwards again. It is often during this last section that the yacht seems to accelerate and get that two or three boat length advantage!

Of course there is always that gust that is too strong even for the best laid plans so survival is the order of the day then.  Let the sail right out until the heeling is controlled, the steering becomes effective and the yachts stays pointing in the right direction.  Easing the sails back in will enable you to  determine how much drive you can get yet still not end up on your side.

You need to practise these manoeuvres as they really do make a significant difference!  As soon as I see or hear skippers saying that their rudder has lost grip in the gust or they can't control the yacht in the gust I know they haven't done those two key things, ease the sails and bear away from the wind gust

Even tho this discussion deals with yachts on a reach, the same ideas apply equally well from beating to broad reaching.  It's a little different for a yacht on a square run because really there is no where to run other than to keep going down wind.  So how do you cope with this?

Luckily as the yacht is running away from the wind, the speed of the yacht is already subtracting speed from the wind so the apparent wind is already less and corresponding gusts are also less strong.  Like before as the speed of the yacht increases the effectiveness of the rudder increases so small movements of the helm can cause quite large direction changes so use small movements on the rudder stick.  How often have you seen yachts going downwind in a gust swing wildly from port to starboard and back again as the skipper pushes his helm from one extreme to the other?  Once the wind has reached a critical speed the nose of the yacht is pushed deeper into the water increasing the drag, slowing the yacht and increasing the apparent wind thus pushing the nose in deeper etc etc.  How to cope with this?  One way is to swing the nose slightly from side to side.  The curve on the side of the hull near the stem will impart a lifting force as it moves sideways so this may help.  You can always cry yeeaaaaahh! as you go screaming downwind to end in a submarine dive.  It won't help the yacht but it might make you feel better.

Remember gusts are there to help you - you must get the most from the gusts, more than the other guy anyway.