The Science Bit: Basic Sailing Theory
Author: Peter Aitken and Tim Davison
Basic sailing theory -including why the boat moves and a bluffer's guide to the main points of sailing
From The Mirror Book by Peter Aitken and Tim Davison
Quick links in this article:
The basic set up
How the boat moves
How can I steer?
How can I stop?
How can I tell which way the wind is blowing?
Point of sailing: reaching, beating and running
The basic set up
Take at look at this picture, you will see that:
· The helm ( the person who steers the boat) sits on the windward side of the boat.
· The helm always holds the tiller in his aft (back) hand. He steers with the tiller.
· The helm always holds the mainsheet in his forward (front) hand.
· The mainsheet adjusts the angle of the mainsail to the centreline of the boat.
· The crew uses his weight to help the helm prevent the boat heeling.
· This means sitting to windward in strong winds, to leeward in light winds.
· The crew generally holds the jibsheet in his aft hand.
· The jibsheet controls the angle of the jib to the centreline of the boat.
· The jib and mainsail are roughly parallel.
The force pushes the boat forwards and sideways. 
The forwards push propels the boat. The sideways push is counteracted by water pressure on the centreboard. The helm’s and crew’s weight counteract the turning (capsizing) effect.
The further you lean out, the more leverage you get – this is called ‘sitting out’ or ‘hiking.
If the sails are pulled in, forces A and B will be almost at right angles to the boat: the sideways force is maximum and the centreboard needs to be pushed right down to counteract it. 
If the sails are let out, the forces point forwards: there is no sideways force, so the centreboard can be pulled up
How can I steer?
When a boat is sailing straight and upright the water fl ows past the rudder undisturbed. When the rudder is turned, the water is deflected. The water hitting the rudder pushes it, and the back of the boat, in direction C. The bow turns to the left
In short, pulling the tiller towards you turns the bow away from you, and vice versa.
How can I stop?.JPG)
It is the wind in the sails that makes a boat go forward. To stop, take the wind out of the sails either by letting out the sheets or by altering course towards the wind (Figure 4.5).
How can I tell which way the wind is blowing?
Everything in sailing is related to the wind direction. You can tell which way it’s blowing by the feel of it on your face, by the wave direction or by using a burgee. Remember, the burgee points to where the wind is going.
Points of sailing
Look at Figure 4.6 below. There are three points of sailing:
Reaching – the boat sails across the wind.
Beating – the boat sails towards the wind.
Running – the boat sails with the wind behind.
Reaching
The boat in photo 2 below is reaching. It is sailing at right angles to the wind, which is blowing from behind the helmsman’s back. The sails are about halfway out and the centreboard halfway up.
Beating
If you want to change course towards the wind, you must push the centreboard down and pull in the sails as you turn (photo 3). You can go on turning towards the wind until the sails are pulled right in. Then you are beating.
If you try to turn further towards the wind, you enter the ‘no-go area’. The sails flap and the boat stops. To get from A to B, the only way is to beat in a zigzag fashion (see Figure 4.7). At the end of each ‘zig’ the boat turns through an angle of 90°. This is called a tack. The boat turns ‘through’ the wind – the sails blow across to the other side and the helmsman and crew must shift their weight across the boat to balance it.
Running
From a reach, you may want to change course away from the wind. Pull up the centreboard (not more than three-quarters up) and let out the sails as you turn. You can go on turning until the wind is coming from behind the boat. Then you are running (photo 4 above).
If you turn more, the boat will gybe. The wind blows from the other side of the mainsail, which flicks across to the other side of the boat. Push the centreboard down before the gybe, and shift your weight as the boom comes across.
Article taken from The Mirror Book- Mirror Sailing From Start to Finish by Peter Aitken and Tim Davison
Copyright 2008 John Wiley & Sons
