Sails and sailcloth.

The three constructions

Yacht, the German sailing magazine, and Sailtrader both divide sailcloth into woven fabric, laminate and membrane.

Yacht says woven cloth suits cruising boats, daysailers and inland boats, and names performance cruising and racing as the usual home for laminates.

Woven polyester in more detail

Sailtrader explains that the crimp where yarns cross is what lets woven cloth stretch. Chemical treatment and heat shrinking reduce it, but woven cloth still holds shape less well than laminate. North Sails dates Dacron as a sailcloth to the 1950s.

UK Sailmakers defines three yarn terms worth knowing: tenacity (breaking strength), modulus (resistance to stretch) and denier (yarn thickness). As a sailmaker's claim, it calls modulus the critical figure for cruisers. It also says crosscut sails, built from horizontal panels, use fill-oriented cloth, while radial sails hold shape better but need cloth strong in more than one direction. Cloth is made for high-aspect (tall, narrow) or low-aspect (short, wide) sails, and UK Sailmakers says a mismatch shortens sail life.

A sailmaker writing in Cruising World recommends low-aspect Dacron for tropical sun, after a high-aspect main built from thinner yarns was ruined by UV. The author also rates high-tenacity polyester clearly better than lower grades, and reports a crosscut Dacron main lasting about seven years and 45,000 nautical miles with its shape nearly intact.

Molded sails

North Sails describes its 3Di sails as spread-filament tapes molded in three dimensions into one composite with no Mylar film. Sailtrader says 3Di is about 70% fibre and 30% resin, and argues that with no film there is nothing to delaminate. North Sails' description of 3Di as the world's fastest and most reliable sails is the manufacturer's own claim.

Fibres

Yacht summarizes the main fibres used in performance cloth:

• Aramid (Kevlar, Technora): strong and low-stretch, though Kevlar is vulnerable to kinking and UV.
• Vectran: sits between polyester and aramid.
• Dyneema: UV-stable, but creeps under long, heavy loads.
• Carbon: very low-stretch but brittle. Sailtrader adds that carbon sails should not be left to flog, and that Dyneema is often blended in to improve flex life.

How long sails last

Sources do not agree on a single figure for Dacron. Sailtrader reports owners getting more than 20 years. SpinSheet says a family sailing about 150 hours a year can expect about 10 years from a premium polyester cruising sail, while charter fleets get two to three years (roughly 1,500 to 2,500 hours) and treat about 2,000 hours as worn out.

What wears them out:

• Sunlight. SpinSheet calls UV the biggest environmental threat to sails, and the Cruising World sailmaker calls it the top cause of sail failure in tropical cruising.
• Flogging. SpinSheet says half an hour of flogging in a squall can do as much harm as 50 hours of normal sailing.
• Thread. The Cruising World author found standard UV-stabilized polyester thread broke down within two to three years in full tropical sun, while PTFE thread held up far better. Stitching often goes before the cloth.
• Salt and moisture. SpinSheet says these build up between a laminate's layers and degrade it.

SpinSheet advises covering sails left in the sun and getting new covers with new sails, since old canvas loses its UV protection. For roller-furling sails, UK Sailmakers notes that some have a UV strip sewn along the edge, and recommends a UV-resistant cover on the exposed leech and foot when the sail is furled.

Mainsails

Battens support the roach, the area outside a straight line from head to clew. North Sails makes these claims about the options:

• Full battens suit a large roach and are typical on multihulls and boats without a backstay. They reduce flogging, stack neatly on the boom and suit lazy jacks, but can make reefing harder in strong wind. North Sails says boats over about 30 ft need low-friction cars at the front of each full batten.
• Partial battens are enough for a small roach on a boat with a backstay, though the cloth can fatigue at the inner end of each pocket.

Quantum Sails describes two furling mains. An in-mast main rolls up inside the mast, has no horizontal battens, is roughly 20 to 25% smaller than a conventional main and must be cut flat with little roach; its leech tends to curl. An in-boom main rolls onto a mandrel inside the boom and keeps full battens and roach, but needs more care when lowering. UK Sailmakers agrees that some sailors find in-mast mains less efficient and that in-boom furling keeps a more traditional shape.

Headsails

A jib is a headsail; a genoa is a jib larger than 100% of the foretriangle whose leech overlaps the main (Wikipedia). UK Sailmakers explains the sizing: LP is the shortest distance from clew to luff, and the percentage is LP divided by the boat's J measurement, so a 135% genoa on a boat with a 10 ft J has a 13.5 ft LP. It notes that "No. 1" simply means the largest genoa aboard, and that 135% is the most common size for its furling cruising genoas, which use a foam luff pad to hold shape when partly rolled (a sailmaker's claim).

Downwind sails

North Sails says a symmetric spinnaker flies from a pole, is better at deep angles but harder to rig and douse, while an asymmetric tacks to a fixed pole or bowsprit, reaches better and is the one it recommends for cruising. Symmetric sails are named S1, S2 and so on, asymmetrics A1, A2.

Sail Magazine's 2008 cruising guide gives working ranges: a symmetric from about 65 to 75 degrees apparent to dead downwind, an asymmetric from about 45 to 135 degrees, and a Code 0 (a flat, roller-furled reaching sail) from about 35 to 45 degrees forward to 115 to 125 aft in 5 to 10 knots. It ranks the Code 0 easiest to handle and the symmetric hardest. A sock or snuffer is a fabric tube with a ring at one end: it stops the sail filling while it goes up and gathers it back in for the drop (Wikipedia). Sail Magazine recommends nylon for cruising spinnakers because it absorbs gust loads.

How to use these sails is covered under sail trim and sailing downwind.