The mast and boom form the supporting structure for most sails. In sailboat mast design, wood, aluminium and carbon fibre are the materials used, aluminium being the normal choice. The standard sailboat [ mast section ] is elliptical, with an integral luff groove at its trailing edge.
The hollow spars are formed by extruding aluminium through a shaped die similar in effect to toothpaste from a tube in the extrusion mills. These extruded mast sections are then purchased by mast makers in a variety of profile ranges and fabricated into a mast, using design specifications. Some large spar sections are unable to be extruded; therefore they are fabricated from rolled panels and glued, welded or riveted into the desired shape.
Good sailboat mast design requires that the [ sailboat shrouds and stays ] are attached internally, using a developed captive T-bar and in-mast terminals to cut down the windage created by external tangs and toggles. On yacht masts, the spinnaker pole track is positioned on the leading edge of the mast with the boom gooseneck on the trailing edge.
On yachts, halyards, control lines and electric and electronic instrument cables are carried inside the sailboat masts with conduits in the mast ensuring that the halyards and electrics are separated. Moulded alloy or stainless steel sheave boxes are inserted into the mast at the head and halyard exit points.
The [ masthead ] contains mounts for wind instruments, the tricolour navigation light and the VHF aerial. The foot of the mast incorporates a number of pulley blocks dispersing the halyards and controls via turning blocks and rope stoppers.
Deck-stepped masts are usually mounted on an inverted 'T-shaped fitting while keel-stepped masts are chocked tightly at deck level with wedges, and a neoprene gaiter at deck level preventing water finding its way into the hull.
The masts and booms of small dinghies are wooden or alloy structures and single sailed boats usually have unstayed masts, with no supporting shrouds or stays. Boats for two or more people carrying more than one sail, have masts supported by standing rigging with a sailboat shroud at each side, and a forestay attached to the bow. Racing multihulls sailboats have a have a different mast design in the form of a wing, which accompanied by the sail create the overall aerofoil shape and construction is of laminated wood, aluminium and carbon fibre.
Slab reefing systems require specially fabricated end fittings. Outboard the reefing lines lead up from their correct seats on the boom through the reef cringles to pulleys housed in the boom end and inboard, the reefing lines run through quick-release stoppers.
The development of in-mast and in-boom reefing systems require larger shaped sections which accommodates the furled sail within an enlarged luff groove. With these reefing systems the sails are fitted with hollow-cut leeches because sail battens cannot be fitted.
Sailboat mast rigging hardware is all the equipment fixed to the deck and the rigging hardware attached to the deck is often the weak point. Aluminium craft have much of the gear welded directly to the deck where on other boats it is through-bolted and bedded down on a marine sealant. Fittings may loosen over time and sealant hardens and cracks. Make an inspection of deck fittings for movement, and tighten if necessary. Inspect the fitting and its fasteners for signs of corrosion.
Rigging hardware fittings and fasteners are made of stainless steel. Stainless steel resists rust because of a protective layer forming on the surface in the presence of oxygen. When a stainless-steel fastener is sealed from the air, corrosion may occur in small crevices. High-quality marine fittings are polished after welding removing surface irregularities. If rust is detected, maintain it by buffing up to remove the surface damage at the source of the corrosion.
Rigging hardware such as sailboat shrouds, forestays, and backstays are made of stainless or galvanized wire. Standing rigging needs little maintenance other than periodic checks for broken strands. If detected, replace the wire as any weakness compromises the reliability of the entire rig. Salt crystals accelerate crevice corrosion, especially where wire enters the end terminals.
Rigging screws should have toggles between them and the chainplates so there is free movement in any direction without bending. Inspect for any signs of hairline cracks indicating stress damage. If the standing rigging is over ten years old, consider a replacement even where there is no sign of defects.
Aluminium sailboat spars have anodized surfaces that eventually get roughened by salt crystals and contaminants in the air. Wash and finish the surface with a wax polish. Check them annually for corrosion around fittings especially where stainless steel fasteners are used and for hairline cracks. Inspect the mast-step area, mast spreader roots, and sailboat rigging attachment points.
Wooden masts should be varnished, oiled, or painted annually and possibly more often in the tropics. Check for splits in the wood and signs of rot. Carbon masts are painted with hard polyurethane and are checked and cleaned like aluminium.