Sailing Theory & Background
Points of Sailing
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In order to make communication easier, there is a name for each direction of sailing, and they are all expressed relative to the wind. As we have seen during the earlier AY Courses there is one area, in which it is impossible to sail, which we call the No Go Zone (see Diagram below).

We have also already seen during the Level 1 Basic Principles of Sailing Yachts that a sail works best at only one angle to the wind. To find that position simply sheet in until the sail just stops flapping along the luff, and then it follows that every time you alter the boats course, you will have to adjust the setting of the sail.

Try to think of this as moving the boat under the sail and it will soon become a natural action.

No Go Zone

By trying to sail closer to the wind you will find that you have to pull the sails in harder, until you reach the stage when, even though they are pulled in tightly, they still start to back. This is the limit of windward sailing, the edge of the "No-Go" zone into which it is impossible to sail.

Basic Aerodynamic Theory - How a sail works?

Without going into too much detail, the easiest way to understand the aerodynamic theory of how a sail works is to think of it as a wind deflector.

The force, which the wind exerts on the sail, can be split into two components - lift and drag. It is the lift which provides our motive power, whilst the drag tries to heel the boat over and push it bodily sideways through the water.

The overall effect of drag on the boat will vary according to its heading relative to the wind. Firstly, drag will push the boat directly away from the wind. If you are running, this does not matter, but when reaching or beating it must be resisted by using the centerboard. Drag is clearly most detrimental when you are beating, which is why the centerboard is lowered fully for this point of sailing.

By lowering the centerboard, we may reduce or even eliminate the sideways movement or leeway, which the boat makes, but we cannot eliminate the drag that causes it. Instead, the force is all translated into trying to tip the boat over.

Helmsman and crew sitting out to balance the boat and keep it flat resist this heeling. Again, it should be clear that the need to do this will vary according to the wind strength and direction.

From all of this, you can see that the crew have to work together to adjust sail trim, balance and centerboard to get the most from the boat on any point of sailing. Don't worry if it seems complicated at first; it will soon become natural.

Basic Advice on Sea Sailing

If your AY Course is at a school, club or Yachting Center on the sea or in an estuary, you will have to deal with tides and waves from the start. Even if you learn to sail inland, it will probably not be long before you want to savoir the extra dimension which coastal yachting has to offer.

The basic difference between inland and coastal sailing is the enormous influence of the tide. It can affect where you go, when you can go there, how long it will take and how wet the journey will be.

Tides & Tidal Sequence

Tides are caused by the gravitational pull of the moon and, to a lesser extent, the sun. The difference in height between successive high and low tides is known as the Tidal Range. This difference produces a flow of water around the coast, called a Tidal Stream. When the tide is rising it is said to be flooding and when it is falling it is said to be ebbing.

Local Tide Tables

Information about what the tide is doing at any time can be found from Tide Tables, which give the predicted times of high and low water and the range of the tide for each day of the year. These predictions are based on information printed for Standard Ports. Tables can be obtained from chandlers or Chart Agents and are in several Nautical Almanacs.

Springs and Neaps

When sun, earth and moon are all in a line (at new moon and full moon) the combined effect of the sun and moon causes the particularly big tides, which are called springs. In between these times, at the first and third quarters of the moon, the sun and the moon are at right angles to each other and their smaller combined pull effect causes smaller neap tides. Spring tides are both higher and lower than Neap tides.

Ebb and Flow

When the tide is rising it is said to be flooding and when it is falling it is said to be ebbing

Relationship between Tidal Streams and Wind

The direction of the tidal stream can be observed by;

1. Boats at anchor or at a single mooring riding with the bow facing the stream.
2. Buoys leaning away with the stream and water "piling up" against the buoys,
3. Water swirling around a post or uncovered object.

It is also useful to know that tidal streams flow faster in:

1. Deep waters or channels
2. The third and fourth hours of the ebb and flood
3. Off headlands

It must be remembered that if such tidal streams are constricted or obstructed in any way by headlands or an uneven sea bottom, tidal rips, eddies and overfalls can occur with turbulent seas. Especially if the wind direction opposes that of the tidal stream. Rough water can also be expected over a harbor bar, due to the combination of wind, tide and depth.

Relative Speed with / against current

When planning a day's yachting in tidal waters, first look at the tide tables. It ought to be obvious that with a favorable two-knot tide, a yacht of four knots will be effectively three times as fast as when it is battling against the tide. Yet it is common to see boats struggling home against a tide as darkness falls. The right use of the tide will enhance any day's sailing. Get it wrong and you could be in for a miserable time and a long journey home.