The basic mechanics of sailing
I will attempt here to describe the mechanics of sailing vessels - what makes a yacht go.
Preamble
Sailing and yachts mean different things to different people and range from ultra-light, ultra-fast dinghies, to heavy-weight square riggers. (My preference is for long keeled, wooden built gaff-rigged yachts from the 1940's - they are so in-tune with the sea that they feel alive, but I digress...). However, regardless of their form, a sailing ship must harness the wind in order for it to move.
So, how do they do it?
Well, regardless of the type of vessel, there are a few key elements which go towards producing forward motion in the desired direction:
Sails
Obvious perhaps, but there are many different types of sail, supported in many different types of rig. These can be loosely categorised into two main types:
- Downwind rigs
These are the simplest of sail configurations, the most familiar of these being the square rigged ships seen in countless pirate movies. It is simple to see how these ships achieve forward motion, basically presenting the sail to the wind as a simple parachute or bag and using the wind to blow them along. A characteristic of this type of rig is that the wind must always be behind the mast and that the ship will never be able to exceed the speed of the wind.
- The 'others'
In this context, the 'others' refers to 'foil' type rigs which rather than just using the parachute priciple, present the sail to the wind as an aerofoil, generating power from the lift of the sail. These sails come in a variety of shapes and sizes, but all use this principle of aerodynamic lift.
Crucially, it is these foil type sails which allow the ship to sail into the wind.
At first this may seem an impossibility, but by presenting the aerofoil to the an oncoming wind,
lift will be generated in the sail which is transferred down the mast and generates
forward motion. In practice, a ship can point no closer than 45 degrees into the oncoming wind, as at this point the sail will be
sheeted in such that it lies along the centre line of the boat and at lesser angles it will lose its efficency to the point where the foil
collapses. Of course there is a trade-off in terms of efficiency of power generation in the sail depending on its angle to the wind, with the most efficient (and therefore fastest) being with the ship at 90 degrees to the wind and the sail trimmed slightly back from 90 degrees (a so-called 'beam reach'). At this angle, a modern yacht's speed can easily exceed that of the wind.
So how can the boat travel into the wind without just being blown backwards?
This highlights another characteristic which will apply to any sailing vessel. This is that, unless the wind is directly behind the boat, there will be a tendency for the wind to just push the boat directly downwind (which may not be the desired direction of travel). This phenomenon is called 'leeway'.
In order to counter this, the boat must somehow resist this leeway and turn the force into forward motion. To do this the boat uses:
The keel
The keel basically protrudes from the bottom of the ships hull and places a resistance in the water which slows the rate of downwind travel of the boat.
Of course, keels can take as many forms as sails and range from nothing more than the hull shape of the boat, to 3m deep aerofoil sections with a depleted uranium weight at the tip.
Given that the keel will be travelling forwards through the water, use can be made of this motion and modern keels usually have an aerofoil shape which uses the lift of the keel to further reduce leeway.
Keels also have another important job, which is to reduce the tendency of the wind to push the boat over (known as 'heeling') and to this end are usually made of lead or other heavy material so as to maximise this resistance to heeling.
It is this triangle of forces resulting from the wind, the lift of the sail and the resistance to leeway generated by the keel which combine to produce forward motion.
Of course one final component which should not be neglected is our control of direction which uses the:
Rudder
The rudder hangs from the stern of the boat into the water and can be rotated along its axis, producing a sideways force which pivots the boat about its keel, thus allowing us to steer.
The rudder is connected to a steering device which could be a simple bar attached to the top of the rudder - a 'tiller' or possibly via a mechanical linkage to a conventional 'wheel'.
Footnote
In the above, I have presented the very basics of sailboat mechanics. It is of course quite possible to go into far greater detail and there are many resources available which further describe the subject.
Source: My head really - if you spot errors, inaccuracies or ommisions, please msg me