The Tall Triangle

Remove the gaff from the sail we have just examined. Hoist a triangular mainsail’s head towards the masthead and retain its luff along the mast. The boom still spreads the lower edge, and the sheet still controls the boom. The upper outer spar and its moving mast connection have gone.

This is the familiar Bermuda rig, also called Bermudan or Bermudian rig. Here the name identifies the triangular mainsail supported directly by the mast. It does not tell us how many masts a vessel has, what other sails it carries or what its spars are made from. Those properties can combine in several ways.

The triangle used in our opening chapters was already an example of this support form. We can now understand what it asks of its equipment, and why choosing it was a consequential change for yachts previously carrying a gaff.

Give the mast the upper corner

In the gaff rig, throat and peak occupy separate upper corners, and the gaff holds the head edge between them. In this triangle, the head is one corner at the top of the luff. The sail’s leech runs from that head to the clew. Cloth that formerly spread beneath the gaff’s outer portion has no equivalent upper beam carrying it.

The peak bridle and peak span no longer distribute a hoisting pull along that beam. Its peak purchase no longer raises the moving outer support, and its peak downhaul no longer brings that support down. The throat’s travelling jaws or saddle also disappear from this upper connection. These are particular jobs removed with the gaff, rather than a general disappearance of sail controls.

The mainsail halyard now supports the head through its reinforced attachment. Slides or a retained luff rope transfer loads along the mast while permitting the sail to rise and fall. The track, groove or other chosen attachment must support that long edge and allow its intended movement. The mast’s bend changes the boundary against which the sail takes shape; the clew, sheet and lower-edge controls still affect the cloth.

A gaff can spread a broad upper portion beneath a relatively short mast. To retain a chosen sail area as a narrower triangle, the designer must provide more height. This is a comparison of specified geometry: a small triangular sail could of course fit on the shorter mast if the extra area were given up.

Height brings the sail head farther from its lower support. A longer mast must resist bending and compression over its supported lengths, while stays, shrouds and spreaders provide the restraints already examined. The extra height, changing attachment locations and altered sail forces must be considered together. Removing the gaff reduces one collection of loads; it does not determine the new mast’s loads by subtraction alone.

Measure the surface being compared

The span of a supporting or lifting surface is its extent between the ends being considered. For the simple upright triangular sail in this comparison, take the vertical distance from the level of its foot to its head. That is the dimension across which we distribute the sail’s area. State the endpoints: total mast length, exposed sail height and the effective aerodynamic extent of a complete rig need not be the same measurement.

Aspect ratio relates this span to the sail’s area. In the aerodynamic convention used here, it is span squared divided by area. Both measurements belong to the same surface: metres squared in the numerator and square metres of sail in the denominator, leaving a ratio without units. A long narrow surface has a higher aspect ratio than a short broad one of equal area.

Consider two hypothetical right-triangular outlines, with vertical luffs and horizontal feet. One is 6 metres high with a 4-metre foot; the other is 8 metres high with a 3-metre foot. Each encloses 12 square metres. Their aspect ratios under this convention are 6 × 6 ÷ 12 = 3 and 8 × 8 ÷ 12, about 5.3. We have changed the area distribution while retaining the area itself.

These are flat geometric outlines, not measured sails under load. Curved edges, mast rake and three-dimensional flying shape require an appropriate measurement convention. The working span used in an aerodynamic model can also account for the surface’s surroundings. A designer cannot always put total mast height into this formula and obtain a useful description of the yacht’s sail system.

Follow the flow around the end

A real sail has a finite span. The pressure difference across it helps drive flow around its ends, and the resulting trailing wake changes the local direction of flow at the surface. Producing lift in this three-dimensional flow adds a force component along the incoming air’s direction. This contribution is induced drag.

It differs from drag associated with surface friction and separated flow. It accompanies the production of lift, so reducing roughness alone does not remove it. In a simplified comparison with the same sail area, total lift and airspeed, and comparable efficiency of loading across the span, increasing span reduces induced drag. That is one aerodynamic reason to consider a taller, narrower sail. NASA’s finite-wing explanation states this conditional relationship.

The lift-to-drag ratio, often written L/D or L:D, compares the lift force with the drag force for a stated condition. Recall that lift is perpendicular to the apparent airflow and drag is parallel to it. If a hypothetical sail produces 600 newtons of lift and 60 newtons of total drag, its lift-to-drag ratio is 10. Retain the same lift while reducing drag to 50 newtons and the ratio becomes 12. The denominator includes all the drag counted in that comparison, not just the induced part.

That force ratio is different from the geometric aspect ratio. A change to one can affect the other, but neither number is a boat speed. The direction of the apparent wind decides how lift and drag contribute to driving and sideways forces. The underwater surfaces and hull then have their own responses.

A yacht also places the sail beside a mast and above a deck and water surface, often near other sails, in wind that varies with height. Twist and camber change the loading. The taller surface may reduce one aerodynamic loss while increasing heeling leverage, support demands or the drag of its associated mast and rigging. The useful result belongs to that complete arrangement and sailing condition.

Build a long spar from wood

A wooden spar carries its loads through timber, with the grain arranged chiefly along its length. A solid mast cut from one suitable length depends on finding timber with the necessary dimensions and sound, suitably aligned grain. Its cross-section then has to supply both bending stiffness and resistance to the compression imposed by the rig.

The builder need not find one piece of timber for the whole mast. A built-up mast joins several pieces into one working member, with bonded or fastened connections transferring load between them. The finished length and section can exceed what any individual piece supplies. In a bonded wooden example, long pieces form the walls, and joints are distributed so that they do not all interrupt the same section. The adhesive connections must make those walls act together.

Those walls can surround an empty centre. A hollow wooden mast puts timber around the outside of its section while omitting some central material. In bending, material farther from the middle experiences more of the lengthening or shortening we examined in the mast chapter. Keeping material out towards the perimeter can therefore provide useful bending stiffness for a given mass.

Hollowing a fixed outer section also removes some stiffness and load-carrying material. It is not a free increase in strength. The useful design comparison changes dimensions and wall thickness to meet a stated requirement. Thin walls can buckle locally, joints can fail, and a concentrated fitting can crush or split an inadequately supported region. The empty centre has to remain part of a connected structural design.

The 1926 re-rigging of Vagrant II gives built wood a dated application. A contemporary newspaper described her new tall mast as hollow, assembled from more than a hundred bonded pieces, with joints staggered along its length. A modern-looking sail arrangement was being supported by carefully joined timber. The account’s word “laminated” describes that construction; it does not tell us that the adhesive was a modern epoxy.

Mast construction and mast segmentation are separate choices. A pole mast has no separately stepped upper mast: its main working length forms one continuous spar. It can be built from joined pieces or sections. Calling it a pole mast therefore describes its arrangement, without promising that it was cut from one tree or made from one material.

Form a metal section

An aluminium alloy combines aluminium with other elements to obtain useful material properties. The particular alloy and its processing affect strength, corrosion behaviour and fabrication. Alloying is not a promise of an equally large increase in elastic stiffness: resistance to permanent damage and resistance to elastic deformation are different properties.

An aluminium mast commonly begins as a long hollow section made by extrusion. The manufacturer forces workable metal through a shaped die, whose opening establishes the section. The emerging length can include the hollow wall and a sail groove as features of one profile. Subsequent shaping, treatment, joining and fitting turn that section into the finished spar.

Seldén’s documented process takes these extruded alloy sections through tapering and other manufacturing operations. Its company history places aluminium-mast manufacture in the 1960s. Instead of selecting and joining timber to obtain the section, the builder starts with a repeatable profile from an industrial process. That profile still needs local reinforcement and suitable fittings to carry loads into its wall. The extrusion supplies the starting shape, not a complete mast.

Hold fibres in a rigid shape

A carbon mast uses carbon-fibre reinforcement in a bonded structural material. Fibres placed along the spar can contribute strongly to its lengthwise response. Fibres arranged at other angles help carry loads in those directions and transfer forces around the section. Resin holds the reinforcement in place and transfers load between fibres and layers.

Carbon can also reinforce a sail along its load paths or in membrane construction. There the fibres follow useful tensile routes in a flexible sheet. A mast needs a three-dimensional section, suitable wall thickness and reinforcement that also withstands bending, compression and local attachment loads. Carbon can contribute to both, but the surrounding construction makes one a flexible sail and the other a rigid spar.

Epoxy is one family of resins used for bonding and fibre composites. With the specified hardener, the resin undergoes a chemical reaction which changes it from a workable mixture into a solid network. This process is cure. It depends on formulation, mixing and conditions; the surface becoming firm does not by itself establish that every intended property has developed.

The cured epoxy is a thermoset. Its linked structure has formed irreversibly, so heating it does not simply return it to the original workable mixture. Some epoxy systems cure at ordinary workshop temperatures. A particular mast-making process may instead require controlled heat and pressure to obtain its intended material quality.

Seldén describes winding resin-impregnated carbon fibres at selected angles around a rotating mandrel, the temporary form establishing the spar’s inside shape. Heat and pressure in an autoclave, a pressurised processing vessel, consolidate and cure that assembly; the mandrel is then removed. Fibre placement, resin, consolidation and cure together produce the load-bearing wall. A poor bond or unsuitable fibre direction can defeat otherwise promising ingredients.

These processes developed at different dates from the sail geometry. Southern Spars dates its own first carbon spar to 1990, while Seldén reports concentrating its carbon production in Britain from 2002. Neither date is the invention of carbon spars, and both come long after the wooden-masted triangular yachts discussed here. Bonded timber, aluminium and carbon remain available answers with different manufacturing, inspection, repair and cost demands.

Compare a material, then its finished mast

Two material measures help explain the interest in saving mass. Specific stiffness relates a material’s elastic stiffness measure to its density. For a simple lengthwise elastic comparison, that measure is the modulus: the applied stress divided by the resulting strain. A high value means comparatively little elastic change for the stated stress. Dividing it by density lets the material comparison account for how much mass occupies a given volume.

Specific strength instead divides a stated strength measure by density. The strength might be the stress at which a chosen failure or permanent-deformation limit is reached. The limit and direction must be specified, especially for timber and fibre composites. One quantity concerns elastic deformation; the other concerns reaching a limiting load condition.

Neither material ratio has yet described a complete mast. Its stiffness and strength also depend on section shape, wall thickness, length, support spacing, joints and fibre or grain direction. A favourable ratio alone cannot promise less bending, greater load capacity or lower weight in the finished spar. Those results depend on the demand and the structure built to meet it.

Return to the mast’s foot. The heel bears into its mast step through a surface suited to the new section. In a hollow spar, local structure must deliver wall loads to that seating without simply crushing the end. Changing from a solid timber heel to a thin metal or composite wall therefore changes the connection detail even when its place aboard remains the same.

Farther up, the partners must spread their lateral bearing into the new wall without crushing it. The collar must fit the changed section and its permitted movement; the boot seals around that working contact.

The existing mast bury sets the separation of these support reactions. A replacement spar has to work with that geometry or receive a redesigned support. In a tabernacle, the heel fitting and pivot must also transmit the revised loads through the intended lowering movement.

The material has changed, but the mast still delivers its loads to the hull through those contacts. A stiff spar needs sound bearings. A strong wall needs appropriate restraint against buckling, both along its supported length and locally near openings and fittings. The completed mast, its attachments and the yacht beneath it work together.

Account for mass at height

Weight aloft is the weight of material carried high above the hull: mast, standing rigging, fittings, sails and the lines or spars accompanying them. Its height matters to the yacht’s weight distribution and motion.

With other masses fixed, moving part of the load upwards raises the combined centre of gravity. When the boat heels, gravity acting on the displaced high mass contributes a turning effect. The changed distribution also alters the yacht’s resistance to angular acceleration: material farther from a chosen rolling or pitching axis must travel farther for the same angle of movement.

Reducing mast mass can therefore have consequences beyond the weighing scale, depending on where that mass was carried and what replaces it. A heavier support system or additional equipment can use some of the saving. Removing the gaff and choosing a taller mast changes the whole rig; the new combination is not automatically lighter aloft.

Put the developments in time

The Bermuda name preserves a regional history older than these modern materials. John Hardie’s 1671 account, reproduced in the second volume of J. H. Lefroy’s history in 1879, describes triangular sails on local boats; the accompanying representation has two raking masts. A James Bell Heyl photograph catalogued as about 1870 records Bermudian boats with triangular mainsails and sails ahead of them. These are evidence of earlier local arrangements. They do not establish a continuous chain into every later triangular yacht rig.

American yacht accounts were using Marconi rig by 1919. The Herreshoff Marine Museum connects the nickname with the tall masts and wires of contemporary wireless stations. The name refers to that resemblance and period usage; it assigns no sailing-rig invention to the radio pioneer. Here Bermuda identifies the broad support form, while Marconi remains useful when a particular historical source calls its change by that name.

The Star class makes the work behind one such change unusually traceable. In 1919, Moria tried a Marconi rig against four gaff-rigged Stars. Five sailors exchanged boats during the trial, and the new arrangement failed to establish an advantage. The class permitted it in 1920, but no other boat adopted it that year. A permissible idea still needed a convincing working arrangement. Star class history, 1922.

During 1921, leading Long Island Sound boats converted while trying straight and bent wooden masts, different spreaders and different shroud arrangements. They could reuse the existing mainsail. The practical question was therefore how to support and set familiar cloth after removing the gaff, with sailors learning from successive combinations. The class’s contemporary account reported favourable results from that developing arrangement.

The taller, narrower Star sail came later. The decision for 1930 paired a taller mast with a shorter boom while retaining roughly the same area; sailmakers and the designer continued refining the result. This was the geometric exchange we calculated earlier, applied within a class whose trials, rules and shared experience made a coordinated change possible. Neither stage depended on aluminium or carbon spars. The first changed the support of existing cloth; the later one changed how the area was distributed. Star design and development history.

Other yachts did not all respond alike. In his 1928 Sailing Craft account, Lewis Kleinhans reported successful Marconi conversions among the New York Fifties that retained their single principal mast, but unsuccessful experiments among the New York Forties. He tentatively connected the latter result with extra sail, heavy-weather heel and the two classes’ nearly equal beam despite their different lengths. This is a period interpretation, not a controlled proof, but it records contemporaries encountering different outcomes from a similar proposed change.

The gaff continues to offer area beneath a shorter mast, with the option of a separately handled topsail. Its extra spar and controls can remain worthwhile where that geometry, handling practice, repair skills or a documented vessel’s character suits the purpose. The tall triangle’s usefulness grew through spar construction, support hardware, sailmaking and practical experience. The familiar outline rests on all that work, with several material and construction choices still available.

We have so far changed the support around the sail’s outside. A further arrangement puts repeated supporting members across the surface itself. Those battens can carry portions of the cloth, receive the sheet’s pull at several heights and gather with the sail when it is lowered. One sail can become a stack of supported panels.