History of Sailing Yacht Masts, Rigging and Sails: 1900-Present day.
by James Gilliam
The design, construction and materials of masts, rigging and sails have changed greatly over the course of the 20th century. From solid wooden masts built from a single tree to carbon fibre sections aerodynamically tested, super light and super strong. For sails there have been developments from natural materials such as cotton, which had a tendency to rot and stretch when wet, to new materials such as North sails 3DL sails using Vectran, carbon fibre, Kevlar and exotic films and glues. This report will be looking at the history of these developments and the technological advances necessary for these developments.
The Rig is the powerhouse of a sailing boat. Through the development of new rig materials and technology efficiency and reliability of the rig can be increased. This leads to yachts becoming faster. In the second half of the 19th century yacht racing was borne as a sport. Initially events such as the America's cup were started, this type of racing lead to the development of measurement and handicap rules. Thus begun the development of racing boats to push the boundaries of these rules. Significant improvements in performance could be found by the development of better rigs. Since the beginning of this century there have been a number of developments in materials and manufacturing, from the use of cotton sails and wooden spars at the turn of the century to the Carbon rigs and cuben fibre sails found aboard the new breed of yachts.
Before investigating the developments in rig technology it is necessary to investigate what the objectives are for developing the technology are. The aims include:
- Weight (as light as possible)
- Resistant to environmental damage
The aim of the designer and manufacturer is to find a compromise between all the aims above with the materials and technology available.
New technologies and materials are usually seen first in the development classes, such as the international 14's and international moths. These technologies tend to trickle down into other classes with time. In yachts new developments are usually first developed and tested for yachts competing in the top of the sport. The most expensive and radical developments are found in America's cup yachts. This has been a source of most new technological developments sine the cup first started in 1851. Technological developments are slow to become accepted in the one-design classes, the requirements for a one design class is for a equally matched yacht and also to keep the costs down of buying and maintaining the yachts is an important consideration in the choice of materials and construction of the rig.
Mast materials and manufacturing.
There have been 3 main developments in the materials used masts. The main developments happened in the following order: wooden, aluminium, and composite mast materials. Although at present all these materials are still used in yachts and dinghies but only carbon fibre is used in high performance racing machines.
Wood was the most common material used in masts in the beginning of the 20th century. It does have some major drawbacks:
- It is not a light material, especially in comparison to modern composite masts.
- Greatest strength is achieved by using a single length of wood.
- Prone to rot if it is not treated correctly.
The problem of greatest strength coming from a single length of wood became important at the beginning of the century in Britain. During the industrial revolution vast areas of woodland were destroyed, for various reasons such as building of ships and for firewood. This meant that the wood required to make masts became harder and therefore more expensive to come by.
Wooden masts had been in use for many thousands of years and proved itself as a reliable means of carrying sail. Things changed in the 20th century as boats began to be built solely for speed and racing. The cost of labor and cost of materials compared to the final wooden mast is no longer economic.
Aluminium masts in dinghies were 1st seen after the Second World War. They were tried in the development class dinghies such as the international moth and the international 14. There was a relatively cheap supply of aluminium standard foil sections from the aerospace industry, which were tried out in these development classes.
At present aluminium masts are the most common for most cruisers and a large number of racing classes. Aluminium was used in the 30's for large yachts, such as the J-class "Shamrock V". She used
The size of the mast that needs to be constructed will largely determine the manufacturing method employed. For simple dinghy masts and small cruisers a standard extruded mast section is commonly employed, these are made by extruding aluminium through a mould. The mast is then chopped to its desired length and the fittings are attached. This is the cheapest form of aluminium mast since it does not require the use of expensive machinery and moulds. The design and manufacturing methods used to make extruded aluminium masts has changed little since the 70's however it is still by far the most popular type of mast that is in use today.
For higher performance and larger masts the same system can be employed, Only that a triangle is cut out of the top of the mast ant the space is bent and welded together. The resulting shape has a tapered top enabling the mast to bend more.
The latest development in aluminium masts is the use of Alustartm. This is an aluminium alloy developed for the marine industry. With a 20% increase in the strength of the alloy over other marine grades the plate thickness used can be reduced, therefore reducing the weight of the mast. It keeps its corrosion resistance, bend ability and weld ability of other aluminium alloys in its group. This alloy is available in plate form with which aluminium plate masts are constructed. These masts are said to be stronger and lighter than extruded aluminium masts, although as yet no comparisons of strength have been found.
Carbon fibre masts:
Carbon masts began to be used in the early 90's, initially in the America's cup and Admirals cup yachts. In the decade since their first use carbon fibre is still not as widely used as one might think.
Through the use of carbon fibre a mast can be manufactured which is lighter and stiffer than an aluminium mast. This can significantly improve the performance of the rig. There are 2 main manufacturing methods employed in the construction of a carbon mast. The first is to use a standard section mould to produce a uniform section throughout the length of the mast. This is the cheapest type of carbon mast as the moulds used to make the standard section can be used more than once. They can be built as "one-offs" for a particular yacht. This type is more expensive since a mould has to be constructed to the specifications of the mast, this mould can usually only be used once. The main problem with carbon is the additional cost of the materials and the increased labour involved. A typical carbon mast will be approximately 7 times the cost of an aluminium mast.
Through the use of modern computer technology, such as CFD (computational fluid dynamics) and FEA (Finite element analysis) the precise loads on the mast can be calculated. Therefore a carbon mast can be built with increased strength in the direction of the principle loads. For optimum sail shape the bend of the mast is very important, it flattens the sail, since a carbon mast can be manufactured with precisely controlled orientation of fibres it is possible to create a mast which has the correct bending characteristics. This is an important advance in technology, complement this with new sail technology and they form a superior aerodynamic shape that could ever be achieved with an aluminium mast and polyester sails. The use of CFD can also determine the flow around the mast and on the more powerful programs the interaction of the sails and the standing rigging can also be taken into account.
Carbon fibre is an extremely well suited material for the manufacture of masts. It offers high strength with low weight, complex shapes can be produced and they have also proven to be reliable. There have been problems with carbon masts recently. The development of carbon masts for IACC yachts have shown that when a carbon mast fails (usually due to under engineering the mast or failure of another rig component leading to the failure of the mast) splinters of carbon fibre are produced and can cause harm to the crew or the boat.
Comparison of mast material:
It is difficult to compare like for like in masts. This is because the strength on the mast is largely dependant on the second moment of area of the mast section. Since the 3 mast materials will use different section shapes it is hard to compare. The other main consideration of mast material is the amount of windage induced by the mast. This windage can be reduced through a combination of reducing the width of the mast and making it a more aerodynamic shape. This is easy to achieve with carbon as the strength of the mast section is easier to create with different second moments of are fore and aft and sideways. Greatest strength and stiffness is required in the side direction and less is required fore and aft. This means that for a wooden mast there is going to be a surplus amount of wood in the fore and aft direction, which in turn means increased weight.
Future mast technology:
Since the introduction of Carbon masts there has been little further work done on alternative materials. There is however continuous development in the design of the masts to get the most out of the material.
Further developments in masts could come from the use of new matrix materials and new fibres. Fibres such as PBO could be used to increase the properties of the mast. The properties of any composite material can be greatly improved through the use of better, more advanced manufacturing methods. The most obvious being the use of an autoclave, which consolidates the laminate much better, resulting in a stronger lighter laminate.
Un-stayed rigs and fixed wing rigs:
Un-stayed rigs have been around for many years, the most successful examples of these are the Laser I and the Topper dinghies, which were developed in the 70's. They have very simple easy to handle rigs. The benefit of a rig such as this is that there is reduced parasitic drag due to the lack of shrouds and stays.
The main company, which manufactures this type of rig commercially, is Aerorig. This type of rig is confined mostly to cruising yachts and is rarely found aboard a racing yacht. This is due to a number of reasons, the most obvious being the simplicity of the rig, which does not provide for a good enough test of sailing skill. This factor however does mean that it is well-suited rig for a cruising yacht. Fig 1 shows the largest un-stayed rig manufactured to date, the mast is 60m tall (197ft). The benefits for this vessel is that the rig is well balanced and can be handled by a single person.
The technological advances in materials and new understanding of how composite materials behave under load have been crucial in the developments of these rigs.
The first noticeable fixed wing rig is to be found on the water speed record boat Yellow Pages.
Standing rigging materials.
Twisted strand stainless steel wire standing rigging:
This is a common type of standing rigging used aboard most yachts and dinghies. It is corrosion resistant, strong, flexible and cheap. As far as I can ascertain this type of standing rigging has been in use for the majority of the latter half of the 20th century. Although there would be small advances in the quality of the steel and the manufacturing process. Its drawbacks are that it is relatively heavy for its given strength and does stretch to some extent. Therefore there have been developments to find stronger, more stretch resistant and smoother standing rigging.
Twisted strand wire comes in a variety of different configurations. The most common forms are seen in Fig 2 & 3. Different arrangements of the individual strands have a large impact on the properties of the rope. Fig 5. shows the relative modulus of elasticity of 2 different types of wire rope. Stainless steel rope 1x19 has around twice the modulus of elasticity of wire rope 7x7. This is an indicator of how properties change with different configurations of strands.
There have been some developments in twisted strand standing rigging to reduce the diameter far a given strength. Such as the Dyform twisted strand wire. (Seen adjacent). It also offers reduced drag akin to the rod rigging. Dyform offers a 30% increase in breaking strength compared to traditional 1x19 wire. The cross section shows how the specially shaped wires fill a greater proportion of the strand cross-section. There is also a smoother surface on the Dyform compared to standard wire rope, this decreases the parasitic drag of the standing rigging.
Rod standing rigging:
It is hard to determine when rod rigging was developed for yachts; I believe that is developed in the 80's as an alternative to twisted wire rigging. The aim of which was to create a stiffer rig to increase performance. This has largely been achieved and rod rigging is increasing in popularity. It is increasingly being seen in large cruising yachts and is used by most medium to high performance racing boats. There are a number of different materials that are used for rod rigging. The most common seems to be Nitronic 50TM, this is a high grade of marine stainless steel. Other types include cobalt, carbon and Kevlar rod rigging.
Comparative analysis of different standing rigging:
The modulus of elasticity is given by the following formula:
S=(P L) / (A E)
Where S = Elongation of a loaded wire
P = Applied load
A = Cross sectional area
E = Modulus of elasticity
Figure 5. Shows the comparative stiffness of the different standing rigging types available. It clearly shows how most rod materials are nearly twice as stiff as wire rope materials. Soft Kevlar rope does not appear to have very good properties compared to rope or metal rods, this is because the soft KevlarTM is primarily used for backstays where high strength and moderate stiffness are the main requirements.
Breaking strength is the first consideration when choosing what type of standing rigging. It is the maximum load the wire/rod can carry without breaking. Generally rod is approximately 20% stronger than wire of the same diameter.
Fatigue is an important consideration. So long as the attachment points are made in such a way as to allow small changes in angle of attack then there will be fewer problems with fatigue failure. Wire is more sensitive to fatigue because the individual strands rub together. Rod however is sensitive to surface damage, which can lead to fatigue cracking. This is where the wire has the advantage, when wire fails through fatigue the strands fail one by one and it is therefore easier to spot and to remedy. Rod on the other hand fails without warning and the signs of initial cracking are almost impossible to detect by visual inspection.
Elongation of the loaded wire/rod increases proportionally to the load and length, and inversely to the Cross sectional area and modulus of elasticity. It has a large impact on the overall efficiency of the rig. As long as the load is within 70% of the ultimate breaking load then there is no plastic deformation. Less elongation has the effect of producing a stiffer straighter rig. This results in a reduction in the weather helm, although this is not much normally around 2-3%. Also the lesser the mast falls of to leeward the straighter it is and the more resistant it is to bending.
The wind resistance of the shrouds and stays increases with increasing diameter. Rod for the same strength as wire has a smaller diameter and also a smoother surface therefore producing less drag.
Sail materials and technology
These were in common use throughout the world. The material is cheap and easy to manufacture. Cotton, being a natural fibre, has poor resistance to rot, UV light and water absorption. These qualities made it unsuitable cloth sailcloth for high performance racers. These qualities steered the sailcloth industry to consider new materials and to develop new methods of manufacture in order to increase the resistance to environmental and mechanical damage.
Laminated and composite sail cloth.
The latest advances have been in laminated sails, like the North sails 3DL (3-dimensional laminate) cloths. These cloths have the fibres orientated in line with the principle loads. This enables the sail to be made lighter and stronger than standard polyester or even conventional laminated sails. There is a wide range of cloths available from polyester fibre laminated sail-cloth for use on cruising boats up to cuben fibre laminated clots which are used in IACC yachts and other high performance yachts (like VO60's and open 60's). The more one pays for the cloth the stronger, lighter and better resistance it has to stretching.
The main advantage with using laminated cloth is that the sail will hold its shape better and for longer than a polyester weave. Fig 6 shows the main reasons why laminate cloths are superior to woven. In a laminate cloth there is virtually no crimp. This means that the cloth produced is stronger and more resistant to stretching.
Fig 7. Shows how a laminate is arranged, in this case the spectra scrim is the primary load carrier, the Mylar film is what holds the spectra fibres in place and offers protection to the spectra, the polyester taffeta back is for the abrasion resistance and offers a high level of overall protection to the laminate. This arrangement is the common form used for cruising cloths. The reason being that it is a heavier more durable laminate than what is used for racing boats.
A disadvantage, which the laminated cloths have in common with the other cloth types, is the damage that is done to the sail from UV rays. This is common to most types of cloths. New films for the laminating process are being developed to combat UV rays but none has yet achieved a cloth, which is totally resistant to UV rays.
In the beginning of the 20th century the most common sailcloth's were made with cotton or flax. Cotton, being a natural fibre, has poor resistance to rot, UV light and water absorption. These qualities made it unsuitable cloth sailcloth.
Nylon was one of the 1st man-made fibres to be used for sailcloth. The chemical formulation and general properties of nylon have changed little over the intervening years. It is a cheap, durable and relatively resistant to UV light, good flex-fatigue resistance and shows middle of the road strength properties. However Nylon is mostly restricted to use in spinnakers due to its poor stretch resistance. Even for spinnakers it is not the ideal material as it can absorb as much as 3% its own weight in water.
The most important development occurred in the mid 1950's when polyester sailcloths were developed. Until the 1980's the only widely used sailcloth was woven polyester (or Dacron, Dupont's trade name for their polyester yarn). Dacron is a very durable sailcloth and is resistant to mould and water absorption. Dacron is also very durable making it an excellent sailcloth.
Woven sail clots have an inherent problem with its stretch resistance. Some yarns pass over and under one another. Over time as load is applied these yarns attempt to straighten out, this results in the fabric stretching. This is commonly referred to as crimp. This lead to the development of laminated cloths where the fibres are laid is straight as possible.
A further development of polyester occurred in the 90's with the development of PentexTM. A derivative of polyester which 2 and a half times the elastic modulus of traditional polyester. Which makes for sailcloth which is more resistant to stretch and holds its shape longer.
In the mid eighty's sail makers began the development of laminated sails. These were to be developed for America's cup yachts and over top end racers. The reason these were developed was that the resulting laminate is lighter, stronger and more stretch resistant.
Comparison of modern sail cloths:
Figure 9 
New manufacturing methods:
In the end of the 80's and the beginning of the 90's there were developments in the sail making industry to make sails which would hold their shape better and be lighter and more durable. The results of this work were 3 different solutions, namely:
- North sails 3DL system
- Sobstad Genesis system
- And UK sail makers Tape-Drive® system
North sails use large moulds mounted on hydraulics, these moulds can change shape to the desired shape of the sail. Then with a combination of robots and people suspended over the mould laminate films and fibres are laid down, consolidated and heated with an infrared lamp. The fibres are laid in a precise manner by a robotic arm, which lays them along the lines of principle loads. The resulting sail is extremely light and holds its shape much better than a sail made by stitching fabric together. The drawback of this method is that the capitol investment in the machinery and technology needed is huge. There is currently only one manufacturing centre for 3DL in the world, located in the US. There is doubt on whether north sails can keep manufacturing these sails, as there is a bitter dispute with Genesis about Patent issues. North sails were accused of breaching Patent and copyright law with the use of 3DL and if Genesis gets its way then North Sails will be forced to discontinue production.
The Genesis system is similar to the North sails system, the difference being that they don't use a large moveable mould like the 3DL system. Figure 10 is a representation of the types of sail cloth available. The 3DL in fig 10 clearly shows how the fibres run in the direction of the loads. The black cross weave on the bottom 3 sail clots in figure 10 are simply dyed fibres to make the sail look better.
The latest development in sail technology was the Introduction of Cuben fibre. This was given its first major test aboard "team adventure" which was the Giles-Olier super cat, which took part in "The Race" in 2000. There were no major problems with the sails as the Cat powered its way round the world. At the start of the race there were light winds it could be sent then that the Cuben Fibre sails were performing very well. Team adventures speed was higher that that of her sister ships which were using older tried and tested sailcloth's. In the same race the super cat "Playstation" used a new suit of Cuben fibre. These were not as successful as aboard "Team adventure" this was put down to the factors of safety, which the "Playstation" designers used, was not nearly as much as "Team adventures". There is no doubt that Cuben Fibre will become widely used for sails in the future, its only drawback at present is its prohibitively high cost. As its usage in the marine industry is increased this price will fall.
Cuben fibre is a combination of different fibres the precise fibres that they use has not been disclosed. At the time it came out people assumed it was some new exotic type of fibre similar to carbon fibre, this is not the case. It is manufactured in a unique process whereby large panels are laid up with as many as 7 different layers of yarn. This is lightly bonded to a Mylar substrate, which is in turn heated and pressurised in an autoclave until the layers become one. The resulting sail produced is extremely light, waterproof and has unequalled strength and stretch resistance. The laminate has the feel of heavy plastic, this means that sail repairs are easy to carry out; patches can be made up and glued on with a hot glue gun.
There has been an increase in the last decade of the use of full batten systems. These systems enable the sail designer to make the final sail conform to a better aerodynamic shape. The recent development in composite technology has enabled battens to be manufactured, which were both light strong and flex correctly. Noticeable increases in speed can be seen with the use of full batten systems compared to normally battened sails.
Vectran is a fibre the US navy developed. The US navy wanted a fibre to listening devices behind submarines. The requirements for the fibre were for the length of the tow to be constant and one, which could withstand adverse conditions. The result of the research was Vectran. It is a liquid crystal polymer, which shows similar initial properties to the commonly used grades of Aramid. Flex fatigue resistance is much higher than Aramid fibres; its UV resistance is slightly lower. However it is considerably more expensive than Kevlar. Current applications for this cloth are in endurance events such as the Volvo ocean race.
PBO was developed in the late 90's and was heralded as the new wonder material. It has higher stretch resistance than any other material, except carbon, and very high initial strength. It has one major drawback, poor light resistance. Research showed that the fibres were damaged by visible light and therefore that led to further developments in film technology to combat this problem. At present this cloth is reserved for use in high-end racing such as the America's cup and grand prix racing.
The improvements in sails in the next few years are going to be in the mixture of fabrics which complement each other and go into making better sails.
Windsurfers were developed in the 60's by 2 southern Californian surfers in the 60's. The first windsurfers hit the water in 1968 and since then they have become very popular. Some say there are more windsurfers on the planet than and other sailing craft. This is due to the small cost, simplicity and small size.
The general design of the windsurfer, or sailboard as it used to be known, has changed little since its original design. The changes have come about in the development of new materials and new manufacturing techniques. The way in which a windsurfer rig is different to a dinghy or yacht rig is through the use of a universal joint connecting the mast to the board. This means that the rig is held up by the sailor and the rig is able to tilt in any direction. This enables the windsurfer to be steered by tilting the rig.
Modern windsurfers have carbon-Kevlar masts and fully battened laminated sails with a large amount of aft mast rake. These rigs are used with high tensions along the leech; this gives the most efficient foil shape and keeps the sail more stable. With these new technological developments in windsurfer technology they have been able to set the wind-powered water speed record of 45.34 Knots.
The latest development in windsurfer technology is the "DynawingTM". Developed in the late 90's with the aid of computer design and testing a highly efficient sail has been produced. This is a so-called soft wing sail; it is more efficient than a traditional sail as it conforms to a better aerodynamic shape and virtually eliminates the drag induced by the mast. This results in greater lift and reduced drag.
There are not very many avenues for further development of windsurfer technology. There will be however gradual improvement in the materials and manufacturing techniques that are used to make windsurfers. Future changes in windsurfers could come in the form of some of the same laminate technology that has been used in dinghy and yacht sails.
Running rigging introduction:
At the beginning of the 20th century the choice of running rigging was very limited. Hemp rope and other natural fibres were all that was available. In the 30's Nylon and other man-made fibres were being developed. This led to a revolution in the rope industry. Man made fibres were less prone to environmental damage, less stretch, lighter, stronger and less water absorption. These new fibres enabled rigs, which could be tensioned up more it also reduced weight aloft. Since the introduction of these man made fibres in the first half of the century technology has moved on and the properties of the ropes have been gradually improving.
Modern rope is usually an exotic fibre, Kevlar is commonplace, sheathed a flexible rope fibre. The fibre core is for load carried and the sheath is in place to protect the internal fibres. It is common practice aboard high performance dinghy's (such as 18ft skiffs) to remove the sheath from the rope and to use only the load-carrying core. This reduces the weight aloft and decreases the pitching moment of the mast. The drawback of this is that the rope will need to be replaced more often and the rope must be checked for damage more often. There is a vast amount of different types of rope available today. Each has its own properties, which suit certain uses. For instance for a halyard a lightweight low stretch rope is needed or an anchor rope where a cheap material is used and also floats in water.
Overview of principle properties of rope materials:
- Most elastic of all fibres
- High strength and stretch
- Minimal strength loss when exposed to sunlight
- Ideal for use where stretch absorption are important, such as in dock and anchor lines
- Highest strength Aramid fibre
- Very low stretch
- Subject to fatigue if cycled over small radius
- Does not creep under normal loads
- Black version has superior resistance to UV degradation
- Ideal for low stretch rigging, such as halyards
- Low stretch fibre
- Very good abrasion resistance wet or dry
- Excellent weathering characteristics
- Spun polyester is fuzzy, filament polyester is smooth
- Good choice for running rigging requiring moderate to low stretch, good durability and a nice feel
- Often referred to as Dacron, a DuPont trade name
- Light weight and no stretch
- Very susceptible to UV degradation
- Melts under high friction
- Very high strength and very low stretch
- Light weight; will not absorb water
- Low melting point, susceptible to friction
- Very slippery
- "Creeps", gets longer under sustained load
- Ideal for low stretch running rigging requiring light weight
- Liquid Crystal Polymer fibre
- Very high strength
- Extremely low stretch
- Zero creep
- Low water absorption
- Good resistance to "Flex Fatigue"
- Ideal for low stretch running rigging on competitive race boats and mega-yachts
There have been many major developments in rig technology over the last century. The most significant being the transition from natural materials to man made materials. The development of aluminium rigs, polyester sail-cloths and polyester ropes have proved to be the most important developments of the 20th century, they have enabled rigs to be mass produced making sailing a more affordable pastime. The developments have come about from the shift in use of sailing rigs, which occurred in the early part of the century. The use of sailing rigs for the transportation of goods and fishing declined rapidly and in its place recreational boats began to appear and the need for speed came about, leading to the developments discussed.
The benefits of all the developments, which have happened in the sailing and windsurfing industry, is that there is now a vast number of options available to builders and owners. The decisions on what material and construction to be used for all aspects of the rig are based on cost, performance, reliability, durability and a host of other factors.
I believe that major new developments in rig technology are going to be a long time coming. The technology that has so far been developed has plenty of room for improvement. There is a theoretical limit to how efficient the rig is as a whole. The advancements in technology in the last century have brought designers closer to this maximum value of efficiency.
References and bibliography:
Principles of Yacht Design - Lars Larsson and Rolf E Eliasson 2nd edition 2000 By McGraw-Hill Companies
Boat Data Book - Ian Nicholson 4th edition By Adlard Coles Nautical
Yachting World - May 2001 pg 78-82
Yachts and Yachting - April 13th 2001 pg 52-58
Sailing Today - February 2000 pg 44-48
Web sites used:
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