How can Outeniqua sail towards the wind?

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Sail aboard our luxury yacht, Outeniqua, through the Knysna Heads

It seems wrong: the wind is coming from the east (or the west, or the south-east – you know what we mean) – but here Outeniqua is, sailing TOWARDS the east. How can she DO that?

 

First, a bit of vocab:

  • Downwind = when you sail in the same direction as the wind
  • Upwind = when you sail in the direction from which the wind is blowing.

 

Sailing downwind is easy (well, sort of): if you want to go in the same direction as the wind, you need only set your sails roughly perpendicular to it, and you’ll romp along beautifully for as long as the wind’s up yer tail.

 

But this isn’t always very efficient, because the wind has a mind of its own. It don’t always blow where you want it to.

 

This wasn’t too much of a problem for the ancients, of course. The Egyptians, Greeks, Romans, and such simply conquered a country or two, captured their men, and put them into the holds of their ships as slaves. Then when they wanted to proceed upwind, they rowed.

 

But you can’t do that with guests.

 

So when our skippers on Outeniqua want to travel against the wind, they have to use physics.

 

The sail as a wing

You’ve probably noticed that Outeniqua has a triangular mainsail that billows out into the shape of a vertical wing – and, in fact, it works in exactly the same way as an aircraft wing does to generate lift.

 

Except on a yacht, the lift propels things forwards instead of upwards.

 

When the wind fills the sail – but can’t push the canvas out of the way because it (the canvas) is fixed on two sides (to the mast and the boom) – it (the wind) is forced to change direction and must now begin to flow parallel to the sail.

 

This causes lift: thanks to Newton 3 (schooldays, remember? “For every action, there’s an equal and opposite reaction”) the equal and opposite force on the sail forces the yacht forward.

 

But, since the yacht is also influenced by the water under the keel – and the rudder bends the flow of water to influence her direction – the skipper can balance the force against the sail and the force against the keel to cause the boat to sail at almost any angle up to 45 degrees to the wind.

 

And, by zig-zagging across the wind, move the boat towards it!

 

It’s that easy.

 

Sort of.

 

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