''Polytarp sails'' refer to

sail A sail is a tensile structure—which is made from fabric or other membrane materials—that uses wind power to propel sailing craft, including sailing ships, sailboats, windsurfers, ice boats, and even sail-powered land vehicles. Sails may ...

s constructed from rectangular

polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including bo ...

tarpaulin A tarpaulin ( , ) or tarp is a large sheet of strong, flexible, water-resistant or waterproof material, often cloth such as canvas or polyester coated with polyurethane, or made of plastics such as polyethylene. Tarpaulins often have reinforced ...

s. Home boat builders often favor these synthetic ''sheet'' sails because the materials are inexpensive and easy to assemble into functional, durable sails.

Construction method

The usual construction method involves * laying out the tarp material, * measuring the sail dimensions, * creating baselines from corner to corner, * placing double-faced carpet tape around the sail outline with sufficient rounding on selected edges to shape the sail, * placing a reinforcing rope along the inner edge of the tape, and * folding the taped overlap back over the rope to create the sail shape. The sail can be strengthened by adding reinforcing material to the corners and stitching around the edges of the sail. Adding grommets to the corners and edges will allow the sail to be attached to the mast and spars. Because these grommets are placed through doubled material and behind the reinforcing line inside the sail edge, the resulting attachment points have tremendous strength.

Grades and specifications

The most attractive, durable polytarp sails are usually made from a heavier white polytarp material. Generally, polysails are made from white ultraviolet-protected (UV-protected) material that is 12–16 mils (0.30–0.40 mm) thick (1 mil is .001 inches) and weighs about 6–8 ounces per square yard (200-270

gram The gram (originally gramme; SI unit symbol g) is a Physical unit, unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram. Originally defined as of 1795 as "the absolute weight of a volume of pure wate ...

s per

square meter The square metre ( international spelling as used by the International Bureau of Weights and Measures) or square meter (American spelling) is the unit of area in the International System of Units (SI) with symbol m2. It is the area of a square w ...

) —about twice the weight and thickness of the common colored tarps which usually have no UV protection. The weave density of polyethylene strips in the inner layer determines the quality of the material. Common tarps have a weave of about 6' x 8' (1.8 x 2.4 m). "Canopy grade" white polytarps, on the other hand, have a weave of 12' x 14' (3.6 m x 4.3 m) or 14' x 14' (4.3 m x 4.3 m). Increasingly, white polytarp is used to construct

mainsail A mainsail is a sail rigged on the main mast of a sailing vessel. * On a square rigged vessel, it is the lowest and largest sail on the main mast. * On a fore-and-aft rigged vessel, it is the sail rigged aft of the main mast. The sail's foot ...

jib A jib is a triangular sail that sets ahead of the foremast of a sailing vessel. Its tack is fixed to the bowsprit, to the bows, or to the deck between the bowsprit and the foremost mast. Jibs and spinnakers are the two main types of headsail ...

s, and

mizzen The mast of a sailing vessel is a tall spar, or arrangement of spars, erected more or less vertically on the centre-line of a ship or boat. Its purposes include carrying sails, spars, and derricks, and giving necessary height to a navigation ligh ...

s, while the lightweight polytarp materials are reserved for making

spinnaker A spinnaker is a sail designed specifically for sailing off the wind on courses between a reach (wind at 90° to the course) to downwind (course in the same direction as the wind). Spinnakers are constructed of lightweight fabric, usually n ...

s. Polysail is the term given to any sail made of polytarp material and not just the white polytarp material.

Common sail types

Polytarp is used to construct nearly every type of sail. However, the material is best for traditional sail types such as

sprit The spritsail is a four-sided, fore-and-aft sail that is supported at its highest points by the mast and a diagonally running spar known as the sprit. The foot of the sail can be stretched by a boom or held loose-footed just by its sheets. A spr ...

s, lugs, gaffs, gunters,

lateen A lateen (from French ''latine'', meaning "Latin") or latin-rig is a triangular sail set on a long yard mounted at an angle on the mast, and running in a fore-and-aft direction. The settee can be considered to be an associated type of the same o ...

s, junk sails, and jib-headed sprits. They are not suitable for sails that depend upon being highly tensioned, such as the marconi or Bermuda types of triangular sails.

References

{{Reflist Sailing rigs and rigging