When a ship or boat leans over to one side, from the action of waves
or from the centrifugal force of a turn or under wind pressure or from
amount of exposed topsides, it is said to 'heel'. A sailing boat that is
over-canvassed
and therefore heeling, may sail less efficiently depending on
fundamental or opportunistic factors such as temporary nature of the
feature (e.g. wind gust), use (e.g. racing), crew ability, point of
sail, hull size & design.
When a vessel is subject to a heeling force (such as wind pressure),
vessel buoyancy & beam of the hull will counter-act the heeling
force. A weighted keel provides additional means to right the boat. In
some high-performance racing yachts, water ballast or the angle of a canting keel
can be changed to provide additional righting force to counteract
heeling. The crew may move their personal weight to the high (upwind)
side of the boat, this is called hiking,
which also changes the centre of gravity & produces a righting
lever to reduce the degree of heeling. Incidental benefits include
faster vessel speed caused by more efficient action of the hull &
sails. Other options to reduce heeling include reducing exposed sail
area & efficiency of the sail setting & a variant of hiking
called "trapezing". This can only be done if the vessel is designed for this, as in dinghy sailing. A sailor can (usually involuntarily) try turning upwind in gusts (it is known as rounding up).
This can lead to difficulties in controlling the vessel if
over-canvassed. Wind can be spilled from the sails by 'sheeting out', or
loosening them. The number of sails, their size and shape can be
altered. Raising the dinghy centreboard can reduce heeling by allowing
more leeway.
The increasingly asymmetric underwater shape of the hull matching the increasing angle of heel may generate an increasing directional turning force into the wind. The sails' centre of effort will also increase this turning effect or force on the vessel's motion due to increasing lever effect with increased heeling which shows itself as increased human effort required to steer a straight course. Increased heeling reduces exposed sail area relative to the wind direction, so leading to an equilibrium state. As more heeling force causes more heel, weather helm may be experienced. This condition has a braking effect on the vessel but has the safety effect in that an excessively hard pressed boat will try and turn into the wind therefore reducing the forces on the sail. Small amounts (≤5 degrees) of weather helm are generally considered desirable because of the consequent aerofoil lift effect from the rudder. This aerofoil lift produces helpful motion to windward & the corollary of the reason why lee helm is dangerous. Lee helm, the opposite of weather helm, is generally considered to be dangerous because the vessel turns away from the wind when the helm is released, thus increasing forces on the sail at a time when the helmsperson is not in control.
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| Boats heeling in front of Britannia Bridge in a round-Anglesey race 1998. |
The increasingly asymmetric underwater shape of the hull matching the increasing angle of heel may generate an increasing directional turning force into the wind. The sails' centre of effort will also increase this turning effect or force on the vessel's motion due to increasing lever effect with increased heeling which shows itself as increased human effort required to steer a straight course. Increased heeling reduces exposed sail area relative to the wind direction, so leading to an equilibrium state. As more heeling force causes more heel, weather helm may be experienced. This condition has a braking effect on the vessel but has the safety effect in that an excessively hard pressed boat will try and turn into the wind therefore reducing the forces on the sail. Small amounts (≤5 degrees) of weather helm are generally considered desirable because of the consequent aerofoil lift effect from the rudder. This aerofoil lift produces helpful motion to windward & the corollary of the reason why lee helm is dangerous. Lee helm, the opposite of weather helm, is generally considered to be dangerous because the vessel turns away from the wind when the helm is released, thus increasing forces on the sail at a time when the helmsperson is not in control.