Sloop

:For the warships of the 1800s to World War II, see Sloop-of-war.

Rationale behind the sloop rig

When attempting to build an efficient ship, an important consideration must be kept in mind. This is the question of whether the ship will need to sail predominantly down-wind (i.e. with the wind behind the boat) or up-wind (with the wind blowing into the boat from the prow). Sloop rigs are specifically designed to optimise upwind sailing.

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It is, however, clear that the most difficult direction to sail a (sailing) ship is upwind. Sailing to windward (known as sailing close-hauled) requires some specific design features. Firstly, to make a good upwind sailing ship, the sail must be as vertical as possible to maximise the wind's energy in the sails.

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Two forces act on a sailing ship to deviate it from vertical. Firstly, the weight of the rig itself will tend to pull the sailboat over in one direction the moment the ship departs from the vertical. Secondly, the force of the wind acting on the sails makes the mast behave like a lever. The first effect can be counteracted by reducing the weight of the rig itself. Therefore, the sloop rig weighs quite a bit less than other rigs because its simple design requires fewer ropes and sails.

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In terms of counteracting the shear introduced by the wind blowing against the sails, a keel is attached to the hull of the boat. A particular sail-plan will have an optimal set of keel shapes and sizes which will reduce the effect of the wind.

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When sailing upwind, it is also important to minimize the drag of the wind on the sail and rig. A major cause of drag of the sail is a vortex of turbulent air generated by the top of the mast and sail. Secondary causes are non-optimal aerodynamic shapes of masts, stays and control lines. The sloop minimizes the tip-vortex's drag by making the sail high and narrow, maximizing the amount of sail for the same sized tip-vortex compared to a square-rigged or gaff-rigged ship. Also, the simplicity of the rig reduces the drag induced by control lines, masts and booms.

Related Topics:
Vortex - Turbulent

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