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Sail Trim and Stability

Balance of a Sailing Boat

There are three ways in which a boat may react when one sails under reaching conditions with the tiller held straight:

She may turn towards the wind (luffs) and one must pull the tiller (put the helm up) to keep the balance. In this case the boat is carrying weather helm.

She tends to bear away and one must push the tiller away (put the helm down) to keep the balance. The boat is then carrying ‘leehelm’.

She stays on course even if one does not touch the tiller – this is called a balanced boat.

For maximum efficiency, the boat has to be balanced under all points of sailing; otherwise the force exerted on the rudder to keep it on course will act as a brake. In practice, it is almost impossible to obtain a perfect balance under all points of sailing and wind conditions. Generally speaking, a good boat, reaching with medium wind force, has slight weather helm and one must exert a slight pull on the tiller.

Let us now examine the settings and how they may influence the balance and thus the speed of the boat.

Centre of effort of sails and centre board

The centre of effort of the sail Cv is the effective point of the combined pressure of the wind on the boat (jib, main sail, superstructures). It is located approximately at the centre of gravity of the sails’ surface. Its location depends on the setting of the sails and the impact of the wind.

The centre of lateral resistance, Cd, is the effective point of the combined pressure exerted by the water on the hull and the centre board. It is located more or less at the centre of effort of the part of the boat under water.

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