The invention relates to a method for monitoring the rigging of a sailing vessel, according to the preamble of claim 1.

US-Bl-6, 543, 296 discloses a method in which the force on a stay is measured by means of a strain gauge, which is arranged in a turnbuckle. The elongation measure by the strain gauge is an indication of the force that is applied to the turnbuckle.

A disadvantage of this known method is that only the force which occurs in the turnbuckle is being measured. Although one may assume, that the force applied to the stay is equal to the force in the turnbuckle, this does not give a reliable indication of the behaviour of the stay itself. As a result, it is possible that a stay may break without the measured force in the turnbuckle having given any indication of a possible break.

Such a break occurs, for example, as a result of a local narrowing, or wear, of the stay arising, for example, from varying loads over a prolonged period of time, or a peak load in the past, this narrowing forming a relatively weak spot and thus breaking at a lower load than expected. A similar effect can be observed when the stay is damaged locally on its exterior, for example because another part of the sailing vessel has hit the stay or has rubbed against it. It is also possible that the stay undergoes plastic extension (creep) when subjected to load for a prolonged period of time. This is not detected by the prior art method either. Furthermore, relatively large yachts are generally not equipped with turnbuckles, so that the known method cannot be applied on these vessels.

It is an object of the invention to provide a method for monitoring the rigging of a sailing vessel, which at least partially eliminates these disadvantages, or at least to provide a usable alternative.

In particular, it is an object of the invention to provide a better indication of changes in the stay itself.

This object is achieved according to the invention by a method according to claim 1. The method according to the invention comprises monitoring the rigging of a sailing vessel, by measuring the elongation of at least part of a stay.

Measuring the elongation on the stay itself gives an insight into the actual behaviour of the stay. This makes it possible to detect when an elongation of such magnitude occurs that there is a likely risk of the stay breaking in the short or long term.

Surprisingly advantageously, the decrease of the elasticity of the stay can be monitored as well. Such a decrease may occur as a result of wear. By measuring the elongation of at least part of the stay, it can be observed when a higher elongation occurs at a similar load.

In particular, the elongation of substantially the entire stay is measured. This offers the advantage that every elongation of the stay is measured, even that at any random local position on the stay.

Expediently, the method comprises a step for converting the measured elongation data into a force. As long as no local or permanent extension of the stay occurs, the elongation of the stay, in combination with its modulus of elasticity and cross section, can be converted to a value for the force applied. This has the advantage that an insight is gained into the force which is applied to the stay during use.

In one embodiment, the method further comprises a step for storing the measured data and any calculated data. By storing these data, it is possible to analyse the load of the stay over a prolonged period of time, for example by looking at peak loads and cyclic loads.

In one particular form, the method furthermore comprises a step for checking a security feature, followed by the reading out of the stored data. In this manner, the data are protected from unauthorised users and can only be read out by users who are entitled to do so.

In one variant, the method comprises a step for transmitting the measured data and any calculated data from the sailing vessel to an on-shore receiving unit. A receiving unit of this kind can be located, for example, at an insurance company, a classification society, a government institution or

an agency which processes data for use in calculations for designing new rigging. The measured and any calculated data can be used on shore to determine whether irresponsible risks are being taken on board the sailing vessel.

In particular, the transmission of the measured data and any calculated data takes place in a wireless manner. This makes it possible, for example, to keep up with the loads that are currently occurring, or have occurred over a recent period, on board the sailing vessel.

More particularly, the transmission of the data takes place periodically and automatically. In this way, the receiver virtually continuously has a current overview without being dependent on an action on board the sailing vessel and without a continuous wireless connection being required.

The invention also relates to a stay, provided with elongation-measuring means, according to claim 9. By providing the stay itself with elongation-measuring means, the actual behaviour of the stay can be monitored.

In particular, the elongation-measuring means comprise an optical fibre, in particular a glass fibre. An optical fibre of this type is suitable for measuring the elongation over a relatively great length, such as occurs when measuring the elongation over a substantial part of a stay.

In another embodiment, the stay comprises a strand into which the optical fibre is incorporated. As a result, the optical fibre is integrated with the stay, as it were, which means that a complete correlation is established between the elongation behaviour of the stay, including the local behaviour, and the optical fibre.

In one variant, the stay comprises a first fastening element at a first end and a second fastening element at a second end. The elongation-measuring means extend between the first and the second fastening element. This results in a surprisingly simple way of arranging the elongation-measuring means on the stay. In addition, this ensures that the elongation is measured over substantially the entire length of the stay.

In one embodiment, the stay comprises a plastic cable.

Plastic has the advantage that it can be relatively lightweight while at the same time being able to absorb relatively large

loads.

Expediently, the stay is sealed against the environment over substantially its entire length by means of a cover. A cover of this type protects the stay both against damage, including wear, from parts of the sailing vessel and against the effects of external factors, such as sunlight and seawater.

In particular, the elongation-measuring means are inside the cover. This offers the advantage that the elongation- measuring means are likewise protected against external influences.

In an embodiment, the outside of substantially the whole cover has an absorption coefficient for sunlight of less than 0.8. Such a cover reflects a substantial amount of sunlight and thus reduces the warming up of the stay. This may extend the life of the stay.

In particular, the cover is constructed substantially from a metal. A metal cover has good properties in protecting the stay, and can have a reflective surface.

The invention furthermore relates to a measuring device for monitoring the rigging of a sailing vessel according to claim 19. The measuring device comprises elongation-measuring means which are designed to be fastened to a stay.

In one embodiment, the measuring device furthermore comprises a data connection which connects the measuring means to a processor unit.

In particular, the data connection is designed to pass through the mast of the sailing vessel. This offers the advantage that the data connection is less vulnerable and does not have to be passed along the railing of the sailing vessel.

Further preferred embodiments of the invention are defined in the subclaims.

The invention also relates to the use of data, which have been. obtained by means of the invention, for analysing the rigging of a sailing vessel, according to claim 24. The advantage of analysing this data is that an estimate can be made of whether the stay may break within a certain period of time, so that the stay can be replaced in time. In addition, it is possible, if the stay has broken, to analyse how this happened.

In particular, the data is used in designing the rigging of

the sailing vessel. This can be the rigging for the sailing vessel on which the measurements were carried out or rigging for other sailing vessels. This offers the advantage that the design can be based on the real behaviour of the rigging.

One embodiment of the invention will be explained in greater detail with reference to the attached drawing, in which: Fig. 1 shows a diagrammatic view of a large yacht; Fig. 2 shows a longitudinal view of a stay; Fig. 3 shows a cross section of the stay according to Fig.

2 along line III-III ; Fig. 4 shows a side view of the end of the stay according to Fig. 2; Fig. 5. shows a cross section of an alternative stay; Fig. 6 shows a flow diagram of a method according to the invention.

Fig. 1 shows a cross section of a large yacht, also known as a superyacht, which is denoted in its entirety by reference numeral 1. A mast 3 is positioned on a hull 2. In addition, the sailing vessel 1 is provided with rigging 4 which comprises several stays in addition to the sails and sheets (not shown).

Because of the symmetry between the starboard and port sides, the stays on only one side of the sailing vessel 1 will be described. Attached to the mast 3 is a crosstrees 5 which extends substantially at right angles to the mast 3 in the transverse direction.

A vertical stay 6, also referred to as V1, runs from the deck, on the outside of the hull, to that end of the crosstrees 5 which is remote from the mast. A diagonal stay 7, also referred to as D1, also runs from the deck, on the outside of the hull, to a point along the mast 3 near the mounting point of the crosstrees 5. A second vertical stay 8 and a second diagonal stay 9 run from the crosstrees 5 to a subsequent crosstrees (not shown). The number of crosstrees and thus the number of pairs of vertical and diagonal stays depends on the height of the mast and the maximum length of the stays. One last stay runs from the uppermost crosstrees (not shown) to the top of the mast. The mast 3 can also be provided with a front and/or rear stay. In addition, the yacht 1 can be provided with several masts, which can each be provided with a plurality of stays.

The stays 6,7, 8 and 9 comprise elongation-measuring means, which are shown and described in greater detail with reference to Figs 2-4. The stays and other components of the rigging which have not been shown can also comprise elongation- measuring means.

Fig. 1 furthermore shows a measuring device 10, comprising elongation-measuring means of the stays, as well as a processor unit 11, a processing and storage unit 12, a presentation unit 13 and alarm means in the form of a horn 14. The elongation- measuring means of stays 6 and 7 are connected to the processor unit 11 by means of data connections 16. Fig. 1 diagrammatically shows that a plurality of such data connections can be present for elongation-measuring means at various stays and any other measuring points on board the vessel 1.

The raw measurement signals are converted into digital signals in the processor unit 11 by means of a so-called analog/digital converter. The processed measurement signals are transferred to the processing and storage unit 12. The processing unit 12 is provide with a memory, wherein the material properties of the stays, such as the modulus of elasticity and cross sections, can be stored, as well as a computer program, for converting the processed measurement signals into force values. The forces calculated in this way are compared with the pre-set standard values. Depending on the ratio between the calculated values and the standard values, information is generated for the user. Thus, the presentation unit 13, which is a computer monitor in Fig. 1, but can also be a display of coloured LEDs, can indicate for each stay whether this stay is subjected to a safe, heavy, dangerous or very dangerous load by means of colours. When a potentially dangerous value is exceeded, an alarm signal can also be triggered by means of the horn 14.

The measured and calculated force and elongation values are also stored in the processing and storage unit 12. In addition, data about the sailing behaviour can be stored in this unit 12.

To this end, the processing and storage unit 12 is connected to an on-board computer 17. This on-board computer receives, inter alia, navigation data (speed and course) from a log 18, or a GPS-system (not shown), acceleration data from an x-y-g-meter 19

in the mast 3 and data relating to the force and direction of the wind from an anemometer. The anemometer has not been illustrated in the figure. The figure does, however, illustrate the connection of the on-board computer, via the x-y-g-meter 19, to the anemometer further up in the mast 3. The x-y-g-meter 19 measures the acceleration in the longitudinal (x-) and transverse (y-) direction.

The measured and/or calculated data can be transmitted in a wireless manner by means of a transmitter unit and an aerial 20. In the example shown, the transmitter unit is integral with the processing and storage unit 12, but it can also be a separate transmitter unit, such as a transmitter unit which is already present on board for other purposes. If such an external transmitter unit is used, it is supplied with data from the processing and storage unit 12 and is coupled to an aerial 20. The wireless transmission of the load data measured on board can also be used separately from the other aspects of the invention, and offers itself advantages over the prior art.

Fig. 2 shows a longitudinal diagrammatic view of a stay 21.

This stay 21 can be one of the stays 6,7, 8,9 illustrated or another component of the rigging 4. The part of the stay 21 which substantially absorbs the forces comprises a plurality of plastic fibres 22, in particular poly (p-phenylene-2,6- benzobisoxazole) (PBO). PBO has the advantage that it can carry very large tensile strain, with a relative low mass. The stay 21 can be fastened to the deck of the hull 2, the crosstrees 5 and/or the mast 3 by means of two fastening elements, a first fastening eye 25 and a second fastening eye 26, using a tenon- mortise joint. The stay 21 extends between both fastening elements 25, 26, in a substantially straight line.

The plastic fibres 22 are wound around the two fastening eyes 25,26 with their longitudinal direction running parallel to the longitudinal direction of the stay. The wound fibres form an endless loop, as it were, comprising a first fibre strand 27 and a second fibre strand 28. As it is an endless loop, the first strand 27 and second strand 28 are in fact one and the same, but in a cross section, such as the cross section along III-III (Fig. 3), there appear to be two strands, forming a plastic cable 29. Due to the plastic material used and because

the fastening elements 25,26 have been incorporated in the loop of plastic fibres 22, a stay of this type has good strength properties. These properties of the stay 21 can also advantageously be applied separately from the other aspects of the invention. Such an elongated tensile strain element can further be used in different areas than as a stay, e. g. as a suspension cable of a suspension bridge.

The fastening eyes 25 and 26 are provided with receiving elements 30 and 31 for an elongation-measuring means, such as an optical fibre, in particular glass fibre 32. The glass fibre 32 extends from the first receiving element 30 on the first fastening eye 25 to the second receiving element 31 on the second fastening eye 26. A connecting cable 33 runs from the first end of the optical fibre 32, at the location of the first fastening eye 25, which cable can be operatively connected to a data connection 16 (Fig. 1).

The stay 21 is provided over its entire length with a metal cover 39 comprising a metal tube-like cover, or sleeve 40. The metal sleeve 40 surrounds the strands 27 and 28 of plastic fibres 22. The metal sleeve 40 ends in the vicinity of the fastening eyes 25 and 26. The metal cover 39 furthermore comprises a first end piece 41 and second end piece 42. These end pieces 41 and 42 are slidably connected to the metal sleeve 40 in a watertight manner using a rubber sealing ring or flexible cement 43 and 44, respectively. The connection of the covers 41 and 42 to the metal sleeve 40 is slidable in order to prevent the metal cover 39 from being pulled to pieces if the fibres 22 stretch under load.

On account of the watertight seal, no seawater or other undesirable external influences can act on the plastic fibres 22. In addition, the metal cover 39 protects the plastic fibres 22 against the effects of sunlight and against wear and lateral load from other parts of the vessel, such as the boom and the rigging 4. Viewed in cross section, the metal sleeve 40 is oval in shape, with the longer axis of the oval cross section extending substantially in the longitudinal direction of the vessel 1. The oval cross section is advantageous from the point of view of aerodynamics as well as strength. A boom of the vessel which swings against the stay can exert a considerable

lateral force on the stay. On account of the orientation of the cross section of the metal sleeve 40, the latter will absorb such a force in its strongest direction.

The metal used for the cover 39 is preferably stainless steel, as this is able to withstand the effects of salt water and gives the stays a lustrous appearance. However, it is also possible to use other metals, metal alloys, anodised metals and coated metals, as well as covers made of other hard or rigid materials, such as hard plastic, or covers made of flexible plastic.

Preferably, the cover 39 is reflecting. With reflecting, it is meant that a substantial part of the sunlight is radiated back. Preferably, the absorption coefficient is less than substantially 0.5. This reduces the warming up of the stay, compared to a coloured, or white cover. With a metal cover, a very good reflecting surface can be obtained by polishing the surface. This results in an absorption coefficient of substantially 0.08. The absorption coefficient of non-polished, slightly oxidised metal, is substantially 0.3. A cover with such an absorption coefficient is still preferred over a white painted cover, which has an absorption coefficient of substantially 0.8.

With a cover of another material than metal, a metal layer can be vacuum metallised on the outside of the cover, in order to obtain a reflecting surface. A metal layer, e. g. a metal foil, or a vacuum metallised layer, can also be provided on the inner surface of a transparent sheet, which is applied to the cover. In this way, the metal layer is protected by the transparent sheet.

A preferred alternative cover (not shown) comprises a shrink-sleeve, comprising a wear-resistant plastic material, such as Teflon (poly (ethylene tetrafluoride) ). The Teflon shrink-sleeve is resistant to ultra-violet light, and has a thickness of 0.3 to 1 mm, depending on the amount of shrink. The shrink-sleeve can be made reflective, by adding a metal, or metal coloured, filling. More preferably, the cover further comprises a black shrink-sleeve, which surrounds the plastic fibres 22. The Teflon shrink-sleeve surrounds the black shrink-

sleeve. Such a combination increases the light-thightness of the shrink-sleeve.

The use of a cover of one of the above described types, in particular a reflecting cover, around a stay made of plastic fibres can also offer advantages compared to the prior art, separately from the other aspects of the invention. A metal cover, or a cover with a reflecting surface, can also advantageously be applied around other types of elongated tensile strain elements, such as around a suspension cable of a suspension bridge. When applied as a suspension cable of a suspension bridge, the metal cover protects the suspension cables against vandalism, and lateral impact, e. g. resulting from a collision, as well.

An alternative stay 121 is shown in cross section in fig.

5. In side view, this alternative stay 121 may appear comparable to that of the first embodiment, as shown in fig. 4. Plastic fibres 122 form strands 127,128, of a plastic cable 129. An elongation-measuring means, such as an optical fibre 132, extents over substantially the entire stay 121. The optical fibre 132 is incorporated in the strand 128. To this end, the optical fibre is wound along with the plastic fibres, in this example half a turn (once from the first fastening element to the second fastening element), but it can also be wound along a number of times. By packing the plastic fibres 122 sufficiently tight, the optical fibre 132 will behave as if it were part of the plastic cable 129, i. e. is integrated with the plastic cable 129.

The stay 121 is provided over its entire length with a cover 139 comprising a sleeve 140. The cover 139 furthermore comprises a first end piece 141 and a second end piece (not shown).

The method according to the invention is described below, referring to the above described embodiment, as well as to the flow chart of fig. 6, which diagrammatically shows a method for monitoring the rigging of a sailing vessel. An elongation of a stay 21 is measured (step 201), as follows. A light pulse, for example a laser light, is generated in the optical fibre by a light source (not shown) at regular points in time. This light pulse propagates from the first end of the optical fibre 32, at

the location of the first fastening eye 25, to the second end of the optical fibre 32, at the location of the second fastening eye 26. At this second end, the light pulse is reflected and travels back in the opposite direction. At the location of the first fastening eye 25, or at another known point along the glass fibre 32, the light pulse is detected by a light detector (not shown). The detection time between the light pulse being generated and the reflected light pulse being detected is a measure of the current length of the stay 21.

The stay 21 may stretch under load. Since the optical fibre 32 extends from the first fastening eye 25 to the second fastening eye 26, the elongation of the stay 21 translates into a lengthening of the optical fibre 32. The distance to be travelled by the light pulse consequently becomes greater and thus so does the time until, the reflected light pulse is detected. The difference between this time and the detection time in the load-free state is a measure of the elongation of the stay 21. The length or elongation data obtained in this way are transmitted to the processor unit 11 (step 202) via the connecting cable 33 and the data connection 16, and there they are converted into digital data which can be processed further in the processing and storage unit 12.

In an alternative measuring method, the elongation of the optical fibre 32 is measured, by a wavelength selective mirror, such as a Bragg Grating, which is present in the optical fibre 32, and reflects light with a specific wavelength. Such a Bragg Grating (not shown) is made by illuminating the core of the optical fibre 32 with a pattern of intense UV laser light. Such UV light damages locally the structure of the optical fibre 32, changing the local refractive index. Depending on the pattern that is applied to the optical fibre 32, and its material properties, light with a specific wavelength will be reflected, while light with substantial other wavelengths will propagate mostly uninterrupted.

The wavelength of the light that is reflected will further depend on the temperature and the stretch of the optical fibre 32. By sending light into the optical fibre 32, with a range of wavelengths, it can be derived from the wavelength of the reflected light what the stretch of the optical fibre 32 is. Of

course, the range of emitted wavelengths is chosen, such that the wavelengths that may be reflected by the Bragg Grating under the potential stretch and temperature conditions, are within this range.

A preferred method for observing the reflected wavelength, comprises emitting narrowband light pulses with mutual different wavelengths one after another. As it is known how long it takes before a reflected light pulse returns, it is only necessary to detect what time the reflected light pulse is received. This can be done by a simple photodiode detector. From this time, it can be derived which light pulse was reflected, and thus it is known what the wavelength of this pulse was, without actually having to measure this wavelength.

An alternative method for observing the reflected wavelength, comprises emitting a light pulse with a broad spectrum, and subsequently analysing the wavelength of the reflected light. This analysing can be done by a spectrometer, or a sloped optical filter.

The area of the optical fibre 32 with the Bragg Grating can be any area along the optical fibre 32, between the first and second fastening eye 25,26. As the optical fibre 23 stretches and shrinks homogeneously between the first and second fastening eye 25,26, such a measurement is a reliable measure of the elongation of the whole optical fibre 32, and thus of substantially the whole stay 21. This is an advantageous difference with a local measurement on the stay 21 itself, as the stay 21 could actually have a stretch behaviour which various over the length of the stay 21.

The second embodiment, as shown in fig. 5, may be used different from the embodiment as described above. If the stay 121 of this second embodiment does not stretch homogeneously, this may result in a corresponding local stretching of the optical fibre 129. This means that a measurement with just one Bragg Grating is not a reliable measure for the total elongation. However, it is still possible to measure the total length of the optical fibre 132, by sending a light pulse from the first end of the stay 121, which is reflected at the second end, and measuring the time between sending and receiving the reflection.

An advantageous use of the second embodiment, uses an optical fibre 132, and measuring equipment, that makes it possible to detect the local deformations of the optical fibre 132, resulting from a local deformation of the stay 121. Such a detection may be based on a multitude of Bragg Gratings along the optical fibre 132. These Bragg Gratings have different paterns, and are therefore sensitive for different wave lengths, which makes it possible to detect which Bragg Gratings is deformed, and thus in what area the optical fibre 132 is deformed.

In a variant, the local deformation is detected on basis of the local narrowing of the optical fibre 132, resulting from a local elongation.

It is also possible to calculate the force (fig. 5, step 203) which is applied on the stay from the elongation data obtained in one of the manners described above. The measured and/or calculated data are stored (step 204).

Over the course of time, creep may occur, which means that the stay 21 becomes longer by being acted upon by a load over a prolonged period of time, which elongation remains even when the load is removed. As a result, the processing unit 12 will detect a lengthening of the stay which on average increases slowly. The processing unit 12 can compensate for this elongation by determining the average length of the stay 21 over a large number of load cycles and comparing this with the average length over a large number of load cycles at any point in time in the past. The processing unit 12 can also compensate for the creep effect at a point in time when the rigging is subjected to steady-state load. Thus, a user can give a calibration command when the sailing vessel is anchored in a harbour or the processing unit can detect automatically that the vessel is stationary because no acceleration is detected by the x-y-g- meter 19.

Furthermore, the processing unit 12 can compensate for the effects the temperature has on the material properties of the optical fibre 32. To this end, a heat sensor 50 is connected to the processing unit 12. A heat sensor of this type is not required if a reference wire is provided for each stay 21 in the form of an additional optical fibre which is wound up and

arranged in a housing near to the connecting cable. A reference signal is passed through the reference wire in a manner similar to the light pulse in the elongation-measuring optical fibre 32 at the stay 21. As the reference wire is affected by the temperature in the same way as the elongation-measuring optical fibre 32, the required temperature compensation can be determined.

Preferably only standardised information is presented to the crew on board. Standardised means that the user can see the extent of the load for each individual stay. In this context, for example, a scale can be used which runs from"safe"to"very dangerous". The load level"very dangerous"in that case means that the respective stay is about to break. The load level below this level, for example the level"dangerous", can mean that a varying load at this level over a prolonged period of time will likewise lead to the stay breaking. An acoustic alarm signal can be emitted by the horn 14 if a pre-set load level of one of the stays is exceeded.

In order to prevent misuse of the stored data, only a user who logs on using a specific security feature, which is checked (step 205) can read out the data (step 206). Such a security feature can, for example, consist of an alphanumeric code which is to be keyed in by the user, a digital code, which is stored in a readout unit (not shown), or biometric features of the authorised user or users.

An interested party on shore, for example an insurance company or classification society, can be provided online or periodically with the obtained data, e. g. the measured elongation data, the calculated forces, and/or other data, such as the data about the sailing behaviour. These data can be used to determine whether the crew are acting in a responsible manner when subjecting the rigging 4 of the vessel 1 to load. As long as the data show this to be the case, any damage that might arise is covered by insurance. However, it may be part of the policy conditions that if a specific load level is exceeded by a certain degree and/or with a certain frequency, this will result in any damage to the rigging, the remainder of the vessel and/or the crew no longer being covered.

The calculated and/or measured data can be transmitted

wirelessly (step 207) in a continuous manner, i. e. online, or periodically (step 208) by a transmitter and the aerial 20. In this case, use can be made of any (satellite) communication equipment which is present on board. Alternatively, the data can also be read out from the processing and storage unit 12 when the vessel is in a harbour and/or when the vessel has suffered damage and is in a repair dock, for example, or at the bottom of the sea. In the latter case, it is advisable to ensure that the entire processing and storage unit 12, or a storage unit separate from the latter, is enclosed in such a manner that it is able to withstand the effects of seawater and high pressure.

This may be similar to the manner in which so-called black boxes on board aeroplanes are equipped.

The stored elongation and force data can also be used by designers of yachts to optimise the dimensions of the rigging of sailing vessels. Such data can be used, for example, if the rigging of an existing sailing vessel needs to be replaced.

These data can furthermore be generalised so that they are also suitable as design data for new sailing vessels to be constructed.

Various variants of the exemplary embodiment shown are possible, which are all within the scope of the invention. Thus, the elongation can be measured over a shorter part of the length of the stay, for example using a strain gauge. This may be desirable for stays which are known to have a relatively weak spot. In the case of so-called rod rigging, for example, this is the transition from the rod-shaped stay to the bump which is used as fastening element. In such variants, the elongation- measuring means are arranged on the stay itself.

In addition, several alternative elongation-measuring means are possible for the illustrated and described glass fibre, such as other types of optical fibres, a metal elongation wire, or telemetering in which a transmitter is provided at the first end of a stay and a receiver at the second end of a stay (or vice versa). As a further alternative, a reflector may be provided on the second end of a stay and a detector at, or integrated with, the transmitter. Suitable telemetering means of this kind may include a laser, infrared source or acoustic signal (including a radar).

The elongation-measuring means can also be provided on the outside of the cover, for example if there is not sufficient space available inside the cover. Likewise, it is possible to use an elongation-measuring means which gives information on where the greatest elongation on the stay occurs. This can be provided, for example, by means of an optical fibre cable which is wound along inside a strand of fibres. A type of optical fibre which is suitable for this purpose becomes narrower at the location of a relatively large elongation. The position of this narrowing is detected as a portion of the light pulse is reflected at the location of the narrowing.

The elongation-measuring means can also be attached to the stay in alternative ways, for example by means of a mechanical connection, welding, soldering or by adhesive means. Although it is advantageous to provide all stays with elongation-measuring means, the invention already offers advantages if the elongation-measuring means are applied in one stay, or in similar rigging components.

The tube-like cover can be designed with different cross sectional shapes. The sleeve can be round, triangle, square, or multiple cornered. The cross sectional shape can also be formed by straight and curved sections.

The fastening means can be of a different design, for example in the shape of a projecting part, which is received by a complementary aperture in or near the crosstrees, the deck or the mast.

This invention is not limited to super yachts. Any vessel with stays and/or similar rigging components can apply the invention according to the attached claims.

Thus, the invention offers the possibility of measuring the actual behaviour of the rigging of a sailing vessel and to prevent damage by using the measured data. In addition, the measured data can be used to analyse the loads and cases of damage retrospectively, both for assessing the insurer's loss and for optimising the future designs of ships. The measured data can be transferred to the shore without time delay or periodically by means of wireless communication, but can also be read out afterwards by duly authorised users.

In addition, the invention provides strong and relatively light stays which are well protected against external influences and have a lustrous appearance.