Polytarp sails refer to sail

Sail

A sail is any type of surface intended to move a vessel, vehicle or rotor by being placed in a wind—in essence a propulsion wing. Sails are used in sailing.-History of sails:...

s constructed from rectangular polyethylene

Polyethylene

Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...

 tarpaulin

Tarpaulin

A tarpaulin, colloquially tarp, is a large sheet of strong, flexible, water-resistant or waterproof material, often cloth such as canvas or polyester coated with urethane, or made of plastics such as polyethylene. In some places such as Australia, and in military slang, a tarp may be known as a...

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 thick (1 mil is .001 inches) and weighs about 6–8 ounces per square yard—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. "Canopy grade" white polytarps, on the other hand, have a weave of 12 x 14 or 14 x 14. Increasingly, white polytarp is used to construct mainsail

Mainsail

A mainsail is a sail located behind the main mast of a sailing vessel.On a square rigged vessel, it is the lowest and largest sail on the main mast....

s, jib

Jib

A jib is a triangular staysail set ahead of the foremast of a sailing vessel. Its tack is fixed to the bowsprit, to the bow, or to the deck between the bowsprit and the foremost mast...

s, and mizzens, while the lightweight polytarp materials are reserved for making spinnaker

Spinnaker

A spinnaker is a special type of sail that is designed specifically for sailing off the wind from a reaching course to a downwind, i.e. with the wind 90°–180° off the bow. The spinnaker fills with wind and balloons out in front of the boat when it is deployed, called flying. It is constructed of...

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 sprits, lugs, gaffs, gunters, lateens, 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.