UK: Effective Specification Drafting - The Case Study Based on A WindSurfer Patent (continued)

Last Updated: 15 December 2003
Article by Paul Cole
This article is part of a series: Click Effective Specification Drafting - The Case Study Based On A Windsurfer Patent for the previous article.

Technical features – I – identification of a single novel feature

In most cases the applicant will require the broadest available Protection17, and for that purpose it will usually be appropriate to file main  independent claims based on a single novel feature that introduces an advantage and hence is arguably inventive.

Initial attention was focused on the unsupported pivoted mast that was held upright by a user to sail the board. Embodiments of the pivot could have a  single axis, two axes or three axes. On the premise that it is best to start with the minimum difference from the known prior art, i.e. the Sailfish/Sunfish sailboards, it would have been logical at the initial filing stage to cover pivoting about a single axis. One starting point statement of invention could therefore have been based on a board having a sailing rig including firstly an unsupported mast  pivotally attachable to the board for movement about at least one axis and secondly hand control means for grasping by a user for positioning the mast. The US versions of the Windsurfer patent preserve the broadest definition of the invention as originally filed, and refer to "wind propulsion means pivotally associated with the body means and adapted to receive wind for motive power."  The word pivotally in the above statement covers all three possibilities for the number of pivot axes. From this definition, it would have been possible to reconstruct a technical problem, treating the Sailfish/Sunfish sailboards as closest known prior art, of providing a sailboard whose control demands new skills and that provided a greater sensation of speed and excitement.

The inventors might have objected to such a broad statements of invention based on their experience with their unsatisfactory Skate prototype in which the mast and sail were pivoted only for movement in a fore and aft plane. In that prototype, heeling movements of the sail were transmitted to the board  and made it impossible for the user to stand on the board, so that Skate was never sailed. However, the patent attorney could have replied that Skate used a surfboard hull and was therefore of low roll stability. If the inventors intended to cover other sailing craft, their heavier and deeper hulls might provide sufficient roll stability for control from a standing position. Part of the task of the patent  attorney is to seek protection covering versions of the invention that use only some features of the preferred embodiment, thereby sacrificing some but not all of the benefits obtainable. Limiting the claims to multi-axis pivoting at the initial filing stage would have been unwise because of the risk that a third party would find a way of making single-axis pivoting practical.

In the disclosed embodiment pivoting the mast in the fore and aft plane appeared to be the most important because it facilitated steering. Providing an additional axis for pivoting the mast in a plane transversely of the hull prevented heeling forces on the sail from being transmitted via the mast to the hull which  though advantageous was arguably less critical. Permitting the mast to rotate about its axis relative to the hull becomes advantageous where the sail is attached to the mast by a sock and is stiffened by battens so that the actions of pulling the sail in or letting the sail out tend to rotate the mast. In the prototypes where the booms are pivoted to the mast and the sail is wholly of flexible cloth the mast  rotation feature may be a non-critical refinement. One useful subsidiary claim could therefore have specified that the sailing rig was pivotally attachable to the board for movement in at least a plane aligned with the fore and aft direction of the board, with the supporting advantage that the hand control means could be used to steer the board towards or away from the apparent wind by manual  adjustment of the mast position in said fore-and aft plane18. Further subsidiary claims could have introduced the second and third pivot axes, with their associated advantages being explained in the description.

Technical features – II – arcuate booms

Arcuate for the shape of the booms provides an example of the use of an unexplained structural definition where a functional definition would have been more effective. The meaning of arcuate became critical in the UK infringement proceedings because it provided the only available distinction from another prior  sailing craft19 that had been found by the defendants. It used a split boom formed from straight pieces of wood that became curved to some extent when the craft was being sailed. The only purposes disclosed in the patent for the arcuate booms were to provide a grip for the user and to hold the sail taught. Straight booms achieved these purposes equally effectively. The Court refused to take  notice of the fact that the booms were shaped and curved so that the sail would take up an aerofoil shape because such a requirement was neither discussed in the specific description nor a feature of any dependent claim, and the fact that the feature might be discerned by inspection of the drawing was not persuasive.

Structural claims often suffer from the problem that they are narrow and easily circumvented, especially when they introduce a geometrical feature. In the US, the classic case is Winans v Denmead20 , where the patentee claimed a railway truck for transporting coal. It had a coal hopper of inverted frustoconical shape to give a relatively small base that could extend below the frame of the truck and between its axles to give a low centre of gravity. The defendant’s truck was similar, except that their hopper had the form of a hexagonal pyramid i.e. it  had a number of straight walls instead of the required single curved wall. The resulting infringement controversy reached the US Supreme Court before it was finally resolved in the patentee’s favour. In the UK, the classic case is Catnic v Hill & Smith21 in which the patentee claimed a vertical wall in a lintel structure and the alleged infringement had a wall inclined at a few degrees to the vertical.  Again, the resulting infringement controversy was litigated as far as the House of Lords, and infringement was established only on the basis of a widened or "purposive" construction of the claim language. That language cannot be regarded as successful if infringement can only be established on appeal to the highest court in the relevant jurisdiction. In the case of the Windsurfer patent, it  was foreseeable that third parties might design a split boom arrangement in which the booms were spaced to give the sail sufficient space to take up its natural aerofoil shape, but that were not arcuate. An example appears from Fig. 9 which is taken from a third party patent22 that formed part of the Windsurfer licensing package considered by the EU Commission. If an unauthorised third  party had adopted such a triangular boom structure, there would have been no literal adoption of the arcuate claim language, and proof of infringement on the basis of a widened "purposive construction" of that language would have been difficult.

Technical features – III – body means

The reference to "body means" in claim 1 of the UK patent is not further  qualified in any of the subsidiary claims. In the description the hull is merely referred to as a "surfboard" without further explanation. It therefore appears that the inventors or their attorneys were of the opinion that the board either was not novel or differed from known sailboards only in such minor details as to provide no contribution to the invention. That was also the opinion of the German Patent  Office, which after being notified about references disclosing wishbone rigs and about the Darby sailboard allowed a claim to the rig but refused a claim to the rig/board combination on the ground that the board contributed nothing novel.

Windsurfer had a policy of granting licenses to manufacture boards only  on condition that they were supplied together with rigs. The EU Commission objected to this policy on the ground that a patent should not be used to restrict competition in the boards which were not covered by the claims of the German patent, and their objection was upheld on appeal to the EU Court23 . The same view about the separate novelty of the board and other components was taken in proceedings for infringement of the corresponding Canadian patent24 , where the Federal Court of Appeals said:

"No one has never alleged in this case infringement by the components of the invention. They are acknowledged to be old. The invention is the combination of the old components or elements…" 

Whenever a product based on a new combination of components is  developed, the starting position of an attorney should be that the individual components are likely to be novel, and that although they may resemble similar components in existing products, they will have been modified for use in the new combination. The attorney should therefore seek out such modifications and ensure that his findings are described in the specification and claimed  appropriately. If the attorney does not include the necessary information in the specification, then a Patent Office or Court has no alternative but to reach an adverse conclusion about the novelty of the components, as happened in Canada in Windsurfer.

If the Windsurfer prototype boards existing at the time of US or international filing had been described in more detail, patent offices and courts could not have treated their novelty, at least over the Sailfish/Sunfish sailboards, so dismissively. For example, the Windsurfer prototype boards were shallower than and less than half the weight of Sailfish/Sunfish sailboards, and it would  have been easy to specify permitted depth and weight ranges that would have covered most boards likely to be useful in Windsurfing but were different from the Sailfish/Sunfish boards. Implicit in the above discussion is density, which could also have been discussed with advantage because it was important in surfboard design, where there had been a quest from the 1940’s onwards for low-density materials to give better performance and manoeuvrability, first balsa  wood and subsequently sheathed structures based on a foam plastics core. Such constructions were not conventional for sailing craft hulls. The completely closed board structure with a smooth uninterrupted top surface formed without a recess defining a recumbent control position and the absence of fittings for supporting a rudder are further differences that could have been specified.

Starting from the Sailfish/Sunfish sailboards, it is arguable that it was not obvious to reduce the weight and thickness of the hull, to form a closed structure with a smooth top surface and to omit provision for rudder steering without awareness of the Windsurfer concept. The Windsurfer prototype boards also  differed from surfboards because that they had a central aperture for a centreboard that was required to enable to board to be sailed upwind. What would have been the motivation for a skilled person to form a centreboard opening through a surfboard (but not to provide for steering by means of a tiller) unless he was aware of the Windsurfer concept? It is submitted that there was  scope for adding useful dependent claims directed to board design features and thereby distinguished over the Sailfish/Sunfish prior art. The extent to which such subsidiary claims would have distinguished effectively over the Darby sailboard is debatable. However, claims directed to hull weight and density and to the sheathed plastics foam construction characteristic of surfboards and important for  manoeuvrability would have been novel and might have provided additional room for arguments in favour of inventive step.

Technical features IV – features of the sail

At the time when the Windsurfer was invented what did the skilled person have to do to adapt a Bermuda rig for use with a sailboard having an unstayed hand-controlled rig?

In general designers do not start from first principles, but take an existing design and modify it for the new requirements that it has to meet. Of the various rigs for a small sailing craft, the Bermuda rig was the most efficient and by far the most popular and it would have provided the most logical starting point. In such a rig (Fig. 1), the main sail had the general form of a right angle triangle with its two shorter sides forming the luff and the foot of the sail respectively attached along the mast and the boom and with its hypotenuse forming the leech. The problems that confronted the inventors was how to provide for effective hand control of the mast and rig, how to facilitate that control from a standing  position, and how to achieve good power while keeping the centre of effort and hence the heeling moment of the sail relatively low.

The solution adopted for the Windsurfer prototypes was to provide a sail in the form of a right angle or scalene triangle with its longest side forming the  luff and attached along the mast, and with its two shorter sides forming the leech and the foot and with the clew located at the junction between them. The sail was controlled by a wishbone boom attached to the mast at its forward end between the tack and the head of the sail at a position corresponding to chest height and attached at its aft end to the clew. This arrangement had two practical  advantages. Firstly the region of the sail that extended below the booms provided power with only slight increase in the heeling moment. Secondly it provided protection against uncontrolled upward movement of the booms caused e.g. by strong wind forces on the sail. Upward movement of the booms can only take place if the lower region of the sail stretches. That region is resistant to stretching  because the tack is attached to the mast and its clew is attached to the booms by an outhaul which is tensioned by the user when the boat is rigged for sailing. The booms therefore assume a relatively stable position relative to the mast, which facilitates control of the rig and avoids the need for a kicking strap.

The contribution of the sail shape and in particular of that part of the sail which extended below the booms was recognised both in Windsurfer’s granted  German patent and in their reissued US patent25 . However, in the UK patent sail shape features were not claimed and their advantages were not described so that they could be of no help to the patentees in their UK infringement proceedings. The patent attorney might reasonably have taken the view that it was inappropriate to specify that the sail had to be strictly triangular26 . He could have distinguished the Windsurfer sail shape from a conventional Bermuda sail shape by specifying that the luff of the sail was longer than the leech or the foot, that the foot was rearwardly and upwardly inclined, and that the booms were attached at their forward ends to the mast at a spacing above the foot and at their aft ends adjacent where the leech joins the foot.

Additional claims could have referred to the pocket formed along the luff of the sail, and the forward-facing cut-out partway along the pocket to allow the booms to be attached to the mast. These features have remained in Windsurfers from the initial prototypes to the present day, but neither of them was claimed or  remarked on as contributing ingeniously to the development of a practical rig.

If an explanation of the problems that the inventors had faced and the reasons for the selections that they had made had been included in the specification together with appropriate claims, the UK courts might not have  been so easily persuaded that the Windsurfer rig was a simple step from Darby’s kite rig, because the evidence on this point gives a strong impression of impermissible hindsight27 . It should be noted that the German Patent Office decided that the rig was patentable following third party oppositions based on the Darby disclosure.

Human activities – I – direct or contributory infringement?

It is important to consider the form that an invention will take when it is sold and to ensure so far as possible that there are claims that are literally infringed by the sale of the product in that form. If that precaution is not taken, the patentee may have to rely on the doctrine of induced or contributory infringement, which is more difficult to prove than literal infringement and under the laws of the UK and other EPC contracting states does not cover products supplied for export in disassembled form.

The claims of the UK Windsurfer patent provide an example where such  forethought was apparently lacking. For practical reasons, the sailing rig of a small boat is dismantled and stowed when the boat is not being sailed, and Windsurfer users follow this practice. In the prototype shown in the patent (Fig 4), the sailing rig can be detached from the board, the boom can be detached from the mast, and the sail can be detached from the mast and boom. However,  the main claim included the words connected, attached and held taught which can only refer to the sailing craft when fully rigged and ready for use. The point passed without comment in the UK because the Court of Appeal did not need to discuss infringement in its opinion, but in proceedings for infringement of the corresponding patent in Canada28 , the Federal Court of Appeals held for the above reason that was that there had only been induced infringement. Expression of the relationships between the parts in terms of conditional words (e.g. connectable) or purposive words (e.g. for connection) coupled with a statement in the description that the invention included the sailing craft both when  dismantled for storage and assembled for use could have avoided this problem.

Human activities II – claims to components and spare parts

An assembled Windsurfer and its components can be regarded as a distributed invention29 where both the assembly and the individual novel components are patentable provided that the appropriate claim format is used. In the Windsurfer case, it would have been most advantageous to claim:

  • The assembly of the board and rig (claim 1).
  • A sailing rig for use in the assembly of claim 1 and having [defined novel rig features] (arguably patentable over both Sailfish/Sunfish and Darby).
  • A sail for use in the assembly of claim 1 and having [defined novel sail features] (arguably patentable over both Sailfish/Sunfish and Darby).
  • A board for use in the assembly of claim 1 and having [defined novel  board features] (arguably patentable over Sailfish/Sunfish; more difficult to distinguish effectively over Darby).

The for use in language in the preamble to a claim for a component of a distributed invention defines how the features of the claimed component relate to  corresponding features of other components. It both provides clarity for the language of the component claim30 and helps to support the inventiveness of the component by reference to the inventiveness of the distributed invention considered as a whole. Claims to structures that differ from the prior art in only slight and apparently insignificant details can often be successfully prosecuted in the for use format if they can be identified as components of a distributed invention. If the Windsurfer application had been under prosecution before the EPO under current practice, there should have been no difficulty in obtaining  grant of claims covering the sail, sailing rig and sailboards as individual components based on the Sailfish/Sunfish prior art known to the patentees at the time of filing and prosecution, although claims to the board might have proved vulnerable having regard to the disclosure of the Darby reference.

Selection of the drawings

The granted patent has only a single sheet of drawings, and they provide scant details of either the new sailing craft or the way in which it is operated. In particular:

  • A drawing like Fig. 4 above of a person sailing the new board would have increased the impact of the patent and made it possible to see at a glance why the design features of the sailing rig were selected and what their purpose was. In particular the reasons for the unusual sail shape, the  selected height of the booms and the flat top surface of the sailboard would have been apparent by inspection.
  • A drawing showing the components of the Windsurfer prototype in disassembled state would have supported claims covering the board in disassembled form.
  • The diagrammatic perspective view of the hull was inadequate, and there should have been at least a plan and a perspective view (see Fig. 5), and at least one sectional view. If there were significant changes in hull profile along its length or internal construction (e.g. to react load from the mast and centreboard) then additional views were needed showing how  the section and internal construction changed with position.
  • A plan showing the actual shapes of the split booms instead of the fragmentary views in the patent.
  • When filing in the UK and in other countries outside the USA, drawings of the Big Red prototype which had been the most successful and included significant changes compared to the Old Yeller prototype should  have been included. It is dangerous to omit description of improvements made during the priority year because, although these may seem minor at the time when updating the specification is being considered, subsequent events may demonstrate their importance.

Detailed description

The specific description should not be a mere wooden statement of structure and function but should

  • support the claims;
  • support arguments for the inventive character of the main claims and of the important subsidiary claims; and
  • provide an enabling disclosure.

Following the decisions of the US courts in Markman and Festo, best  practice nowadays is to include in the specific description definitions of the various terms used in the claims. The Windsurfer case demonstrates the wisdom of this practice for the UK and Europe also. For example what is the meaning of surfboard, which appears in the description and should have been the subject of an independent claim? To answer that question involved study of existing  surfboards, identification of their distinctive constructional and hydrodynamic characteristics, and consideration of which of those characteristics had been incorporated unchanged into the Windsurfer prototypes and which had been modified. If this information had found its way into the description, it would have been available to answer the question whether the Darby board was truly a  surfboard. For example would the Darby board have been an acceptable article of merchandise in the 1960’s in a shop in California selling boards to surfers, or would customers have rejected it? In the latter case what would have been the basis of their rejection? A definition of a surfboard based on the investigation referred to above might have provided a basis for answering these questions, potentially to the advantage of the patentees. But as previously explained,  without such a definition, the UK courts were unwilling to attach any importance to the belated attempt of the patentees to limit their claims to a California surfboard hull. 

In the present case, at least one prototype had been designed and made  before the original US application was filed and additional prototypes had been made before the UK and other foreign applications were filed. There was no reason to suppress constructional and dimensional information, which turned out to be more important than had been appreciated at the time of filing and could have supported patentability. For example, the sail area of the Windsurfer  prototypes was greater than that of the kite sail of the Darby sailboard, the height of the mast was greater which tended to increase the heeling moment, and the rig was of greater aerodynamic efficiency, implying greater control forces. There was room for argument whether it was obvious from the Darby publication that these changes to a more powerful rig were possible, but that argument became  available only if the relevant figures had been provided in the specification, and the fact that the prototypes had out-raced the best previously known sailboards had been commented upon. The prototypes can be regarded as experiments that gave favourable results but went unreported, which was to the disadvantage of the patentees.  

Where adoption of a particular feature involves choices amongst alternatives, reasons for the selection should be given and the associated advantages should be identified. For example, the specification states that the booms were located about 4ft above the board when the mast was upright, but  the reason for the distance selected was not explained. It becomes immediately apparent if a drawing like Fig. 4 is included. However, the visual image would have needed to be reinforced by a written explanation that the boom height had been selected for comfortable and convenient control from a standing position, and that a height range of e.g. from 3 to 4.5 ft would be convenient for most adult users, with about 4 ft being preferred.

There may be arguments that the disclosure was insufficient, both from the standpoint of the new sailing craft as a whole and from the standpoint of the very limited board disclosure. One addressee of the specification would be a potential boat builder with skills in aerodynamics and hydrodynamics. However, was it legitimate to disregard skilled amateur boat builders with ordinary  practical skills of the kind who routinely built sailing craft from plans and descriptions in magazines? There was a striking lack of detailed information and directions about sizes, sail area, board construction, materials and the like. Why should the information in the specification be less than that which would enable an amateur boat builder to make a workable sailboard straightforwardly from the  disclosure in the specification or which the inventor James Drake included in his 1969 lecture, very shortly after the end of the priority year? If this had been a European patent, a patent attorney acting for a potential opponent should have considered making an objection of insufficiency based on (a) undue experimentation and (b) non-availablilty of a suitable board.  

At the priority date of the patent, surfboards for use with fore-and aft-rigged sails were not available for purchase because the product was new, the patent did not contain a reference providing detailed instructions about how such boards should be made, there was no specific starting point disclosed for the  design of a suitable board, and no established methodology for adapting a surfboard to accept a sailing rig and dagger board. The design problems of surfboards had received considerable attention but surfboards for use with sails were new and their design problems had not been addressed. Under the jurisprudence of the EPO Appeal Boards, any deficiency in disclosure can only  be remedied by reference to the common general knowledge of the skilled person at the priority or application date, and the body of qualifying information that is available to remedy a deficiency in disclosure is therefore relatively small31 . An argument concerning non-enablement would not have been certain of success, but it was clearly feasible. That fact should provide a warning to those dealing with engineering or electronic inventions that they should treat "black boxes" and parts shown symbolically or diagrammatically with appropriate caution: it is  important to check that the part concerned is genuinely available to the skilled person and is not an undisclosed starting material that the inventor does not know where to obtain or how to make. 

Post-grant amendment

 It is prudent prior to litigation to consider amendment of the patent to shed unwanted claim scope that is of no commercial significance but can give rise to unnecessary criticisms, and to ensure that the claims are in the strongest possible form. The most cost-effective way of making such amendments in the  UK is by application to the Patent Office. Windsurfer may have been in a position where that route was effectively blocked by the likelihood of third party oppositions to the amendments, but they nevertheless had the option to apply to amend by application to the Court at the outset of the infringement proceedings. As explained above, neither option was attempted and amendments were only  considered when it had become too late. 

Since sailing surfboards were the only commercial embodiment, why did Windsurfer persist in covering a wide technical field that was not of commercial value and exposed them to unnecessary risk? Why not limit all the claims to  wind-propelled watercraft having body means in the form of a surfboard? Why not also define more positively the shape of the sail, and in particular the region located below the booms? Such amendments would not necessarily have produced a different result, but they would almost certainly have made Windsurfer’s case more focused and persuasive.  

Under the current round of reforms to the EPC, there will be a new procedure for voluntary post-grant restriction of the claims of a granted European patent by application to the EPO. Review of European patents for potentially desirable amendments can be expected to become part of the pre-litigation  routine. It should also be a routine task for important patents because, at least under UK law, the owner of a patent that is only partly valid is at a considerable disadvantage, especially once he has become aware of the need to amend his patent and delays in doing so.


It will be apparent that if a patent is to be of any value, it has to be written with at least a full understanding of the technical background known to the inventor(s) and a full technical understanding of the further developments that he  inventors have contributed. Shortcuts in ascertaining the technical facts produce specifications with critical details omitted and either an unenforceable patent or disproportionate expenditure of effort and cost in remedying the deficiency. Judges have the recurring characteristic that they treat ill-prepared documents dismissively and patent specifications are no exception, as the recent US  Supreme Court decision in Festo demonstrates. Unfortunately a recurring characteristic of inventors is shortage of funds at the time when patent specifications have to be written, but if they impose undue budgetary constraints on their attorneys they risk foregoing their rights.

Characteristics of effective patent attorneys which have been highlighted by the present study include:

  • Enquiring and persistent minds that prompt them to insist on knowing, for example, what are the significant differences between a sailboat hull and  a surfboard (which at first sight look quite similar) and to investigate the history of surfboard and sailing craft development until answers are forthcoming. 
  • Powers of observation that enable them to focus on differences between the invention and the prior art and to notice, for example, that the triangular Windsurfer sail is attached to the mast along its longest edge,  whereas a conventional Bermuda sail is attached along one of the shorter edges, and then to ask whether this difference might be significant.
  • Analytical skills that provide a structured law-based framework within which the description and claims can be written. The technical problem approach of the EPO goes far towards providing this framework, and its  development by the EPO Appeal Boards is arguably the most valuable contribution to the development of patent practice over the last two decades.
  • A realistic and practical approach, identifying the interests of the applicant that need to be protected. For example, in Windsurfer, the  highest priority was to protect the invention for surfboards where it originated, and it was foreseeable that the licensing programme would need to cover individual components. Defining an invention by a set of claims is not a mere academic exercise between a patent examiner and an attorney, but is a real-world task that requires the claims as granted to be  legally and commercially effective. Safeguarding the commercial interests of clients is, of course, the major purpose of our existence as an independent profession.


1 United States v Adams, 383 U.S. 39 (1966), US Supreme Court.

2 The CIPA Journal, 32, 320 and 379 (2003)

3 Windsurfing International Inv v Tabur Marine (Great Britain) Ltd [1985] RPC 59

4 James R Drake, "Windsurfing a new concept in sailing", AIAA (American Institute of Aeronautics and Astronautics) lecture, 26 th April 1969, Marina Del Ray, California Yacht Club, 26 th April 1969, downloadable from

5 Sailfish/Sunfish series then being produced by Alcourt, Inc. of Waterbury, Connecticut.

6 A reader of the UK Court of Appeal decision gains the impression that the Darby sailboard could be dismissed as a device of only marginally satisfactory performance. Early film of a Darby sailboard in use can be downloaded from, and shows that in fact it was manoeuvrable and performed well, although on the evidence not so well as the Windsurfer.

7 See

8 James R Drake, supra, ref. 4.

9 See also US-A-3487800 and the successfully re-issued patent Re 31167 in which the original claims were replaced and much additional prior art cited including references describing wishbone booms and the Popular Science Monthly article concerning the Darby sailboard. In addition to litigation in the UK, corresponding patents in Canada and Australia were also litigated and grant of the corresponding German patent was opposed.

10 T 24/81 Metal refining/BASF

11 Proving that the idea of producing the claimed invention is known or obvious is a major step towards proving invalidity. In Texas Iron Works’ Patent [2000] RPC 207, the defining moment was when the technical expert giving evidence on behalf of the patentees admitted that the idea of making the claimed invention was obvious, since this became an undisputed fact. The task of proving lack of inventive step then required evaluating the various difficulties in implementation that he had identified and showing that each of them was either non-existent or easily overcome by a skilled person. The patent was revoked by the Patents County Court for lack of inventive step, and that decision was affirmed by the Court of Appeal.

12 At this stage, of course, a reference to the earlier Darby board would have been difficult to find because Darby’s article appeared in a general interest scientific magazine and not in a specialised yachting magazine.

13 Supra

14 T 570/91 AE PLC/Pistons

15 See the discussion in Windsurfer [1985] RPC at p. 71 line 48 to page 72 line 2.

16 James R. Drake, article (supra)

17 Occasionally this is not the case e.g. where a consortium of applicants seeks protection for a common agreed standard but do not wish to protect subject matter outside that standard.

18 This definition would have covered the Bermuda rig and all other fore and aft rigs. A question that the patent attorney might routinely have put to the inventors was whether moving the rig fore and aft was the only way of steering the sailboard, or whether other steering movements were possible e.g. moving the rig transversely of the board. That discussion might well have identified the kite rig as an alternative to the Bermuda rig since the inventors had started with the idea of attaching a kite by a line to the surfboard and had gone on to consider standing the kite at one end on the surfboard which was close to the Darby arrangement. Darby’s kite rig when tacking was steered by moving the mast obliquely and when running was steered by moving the mast from side to side.

19 Sailed by an individual called Peter Chilvers, then 12 years old, during 1958 at Hayling Island, on the south cost of the UK. The hull of the Chilvers sailing craft is not described in the judgment, but it seems to have been a conventional dinghy hull originally steered by a rudder. It will be recalled that the Windsurfer patent had no claim that distinguished a surfboard hull from such a conventional dinghy hull.

20 See US Patent 5175 issued 26 th June 1847 and 56 US (15 How.) 330 (1853); the case is discussed in Peter D. Rosenberg, Patent Law Fundamentals, Clark Boardman Company, Ltd, New York.

21 [1982] RPC 183

22 GB-A-1551426

23The patent in question was the equivalent DE-B-1914602; see 83/400/EEC: Commission Decision of 11 July 1983 relating to a proceeding under Article 85 of the EEC Treaty (IV/29.395 - Windsurfing International), Official Journal L 229, 20/08/1983 pp. 0001 – 0021 which explains the technical problem identified by the German Patent Office for the above patent and gives the text for the main claim in its final form; for the appeal see Windsurfing International Inc. v Commission of the European Communities, Agreements prohibited by Article 85 of the EEC Treaty, Case 193/83, [1986] ECR 611. Both of these decisions are available on the Internet.

24 Windsurfing International Inc v Trilantic Corporation (Pic Sports Inc) [1985] 8 C.P.R. (3d) 241

25 See the corresponding US Re 031167 at column 3 lines 48-52 and claim 20.

26 Modern Windsurfers do not use strictly triangular sails. Their masts are no longer straight but are formed with strong rearward curvature. The sails are more nearly four-sided with the fourth side being defined by a short horizontal region at the head of the sail leading from the mast head to the leech. However the family descent from the original triangular sail of the Windsurfer prototypes is visible.

27 The only expert witnesses in the UK proceedings who had read the Darby article at the time when it was published (a Mr. Ellison) said in his evidence that the obvious thing to do to improve performance was to fold Darby’s sail in two and wrap it round the mast, holding the sail taught by a boom on either side, see the Court of Appeal judgment at p. 70. Mr Ellison was arguably trivialising the difficulties that a designer would in reality have faced, and his knowledge of the answer enabled him to propose a superficially simple but unrealistic route to the solution. A designer wishing to improve Darby’s kite rig would not naturally have adopted as his starting point an unconventional rig of predictably poor performance, but instead would have started with the familiar and efficient Bermuda rig. He would immediately have realized that it was not self-evident how to adapt that rig for a surfboard hull. The more you understand about the forces in the Windsurfer rig, and the way in which control is achieved, the cleverer the rig design of the Windsurfer appears.

28 Windsurfing International Inc v Trilantic Corporation (Pic Sports Inc, supra)

29 See EPO Appeal Board Case T 1194/97 Philips. Such inventions are also referred to as "plug and socket" or as "bow and arrow" cases.

30 T 1194/97 Philips supra.

31 T 0171/84 Redox Catalyst/Air Products   

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