WO1995010447A1

WO1995010447A1 - Improvements in the structural composition of chest-type surfboards

Info

Publication number: WO1995010447A1
Application number: PCT/IB1994/000310
Authority: WO
Inventors: Bernd Martin Reidl; Gordon Sydney Berry Gray
Original assignee: Inducel Ltda.
Priority date: 1993-10-15
Filing date: 1994-10-12
Publication date: 1995-04-20
Also published as: AU7821494A; BR9304020A

Abstract

An improved structure for a chest-type surfboard (bodyboard) comprises a plurality of elongate members (3) extruded from expanded polyethylene structural foam. The members (3) are then joined laterally to one another by means of a thermal fusion bonding process which compacts the expanded polyethylene, thus forming, at the laterally adjoining walls of the members (3), a corresponding number of rigid films (4) oriented at right angles to bending stress applied to an upper or a lower surface of the joined members (3), thus acting as girders having their greater direction of strength opposing the bending stress. A thermally laminated skin (2) is disposed on both upper and lower surfaces of the joined members (3), forming a 'sandwich' assembly which is subsequently subjected to complementary operations of coating the top, the bottom, and the side edges, as well as surface finishing and the other customary operations. The 'sandwich' assembly shows improved rigidity and elasticity with no increase of weight over conventional chest-type boards because the density of the foam forming the elongate members (3) is about 20 Kg/m3, less than in conventional boards, while the density of the foam forming the skins (2) is about 140 Kg/m3, much greater than that of conventional boards. The average density is, thus, in the region of conventional boards (36-42 Kg/m3).

Description

IMPROVEMENTS IN THE

STRUCTURAL COMPOSITION

OF CHEST-TYPE SURFBOARDS

BACKGROUND OF THE INVENTION

1. Field of the Invention

It is a matter of general knowledge that chest-type surfboards, more commonly known as bodyboards, are enjoying increasingly widespread use which includes use by persons of a much wider age spectrum. This utilization is justified by a series of different factors, among which a particularly significant one is that it permits participation in an extraordinary sport such as surfing, while in a prone position, gliding over an ocean wave.

From the viewpoint of structural composition, these bodyboards are generally fabricated of light, flexible materials; that is, plastic materials which do not absorb water and which impart both buoyancy and safety of use in the event of accidental wave-induced impact of the board with the user.

Expanded polyethylene is the construction material of choice for these bodyboards, it being a lightweight, closed-cell material which is both flexible and weather-/salt water-resistant.

2. Description of Related Art

Despite the above-mentioned positive characteristics, expanded polyethy¬ lene does not offer sufficiently high mechanical strength to endow the board with long life, mainly because the user executes all of the maneuvers while gripping the board's edges with his hands. This gripping results in excessive wear and tear which the mechanical strength of polyethylene foam is not adequate to resist.

In this regard, it should also be pointed out that, within the present state- of-the-art of bodyboard fabrication, a sufficiently high modulus of elasticity has not yet been achieved to permit the board to withstand this maneuvering stress, exerted, for example, in projecting the athlete/board combination from the crest of a wave for execution of aerobatics. It is recognized, naturally, that considerable effort has been expended to obtain a better modulus of elasticity in the board. Examples include the installation of fiberglass longerons in its structure, coating its lower and upper surfaces with substantially rigid materials such as high density polyethylene, increasing the upper coating thickness with foam of greater density, coating the edges of the board with high density polyethylene films, and many others.

While these techniques increase the board's modulus of elasticity, as intended, they still leave a lot to be desired since, at the same time, they increase the total weight of the board, thereby negating part of the initial benefit.

Furthermore, it should also be recognized that the innumerable variations of maneuvers executed by the user generate cumulative strains in the board's structure so that, with the passage of time and frequency of these mechanical stresses, the board undergoes a substantial loss of its original rigidity as a whole. This phenomenon might even lead to the appearance of furrows or bends at the points of the board which are subjected to external stress.

In other words, with the passage of some time, chest-type surfboards made of expanded polyethylene frequently lose or, to put it more accurately, suffer a diminution in their initial modulus of elasticity, thereby considerably hampering smooth execution of maneuvers. This renders their use inadvisable or even unsuitable for the maneuvers of competitive events.

Under these circumstances; that is, in view of all the foregoing considerations, it would be highly desirable to obtain a chest-type surfboard having a high modulus of elasticity without incurring a concomitant increase in its total weight, and which would maintain its rigidity over a prolonged period.

OBJECTS OF THE INVENTION The precise object of this invention is a chest-type surfboard, of the type whose inner portion is in the form of expanded polyethylene plates or blocks, obtained by extrusion. This board, however, has a new and improved structural composition for the said inner part; a structure which is quite simple from the essential point of view, but highly ingenious and practical and, more importantly, is capable of leading to the objectives sought above.

It is thus a purpose of this invention, in one aspect, to improve the expanded polyethylene surfboard by increasing its modulus of elasticity without increasing its total weight. Additionally, and in another aspect, the invention comprises an improved expanded polyethylene surfboard which, in addition to having improved mechanical strength, ensures an adequate and prolonged elastic behavior, facilitating execution of maneuvers by the user.

BRIEF DESCRIPTION OF THE DRAWINGS The objects and features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages, may best be understood by reference to the following description, taken in connection with the accompanying drawings. Figure 1 is a side view;

Figure 2 is a plan view partially cut away to show the inner portion of a chest-type surfboard, equipped with the improvements under consideration; Figure 3 is a perspective view of the elements comprising the inner portion of the surfboard illustrated in Figures 1 and 2;

Figure 4 is a plan view of the said surfboard, already duly assembled; and

Figure 5 illustrates the cross-section A- A indicated in Figure 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventors of carrying out their invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the generic principles of the present invention have been defined herein specifically to provide a chest-type surfboard having improved rigidity and elasticity.

As illustrated in the figures described above, the chest-type surfboard for which the structural composition improvements were planned, the object of this invention, is of the type consisting essentially (Figures 1 and 2) of an expanded polyethylene structural inner portion 1 , with a thermally laminated skin 2 on its surfaces, both upper and lower, forming a "sandwich," this assembly subse¬ quently being subjected to complementary operations of coating the top, the bottom, and the side edges, as well as surface finishing and other customary operations. In order to obtain the maximum rigidity for the surfboard type in question, the improvements per se, which are the object of this invention, are comprised essentially of the fact that the structural inner portion 1 of the surfboard is constituted of individual longitudinal members 3 (Figure 3), naturally made of expanded polyethylene, but joined laterally to one another by means of a thermal fusion bonding process which compacts the expanded poly¬ ethylene, thus forming, at the laterally adjoining walls of the members 3, a corresponding number of rigid films 4 oriented at right angles to bending stress, thus acting as a girder with their greater moment of resistance opposing a primary source of bending stress applied to the board.

Once the structural inner portion 1 of the surfboard has been built, the lamination of the skin 2 to both its upper and lower surfaces is likewise accomplished by a thermal fusion bonding process, also using expanded poly¬ ethylene, but with a substantially greater density than that of the structural inner portion 1, specifically the skin density is about 140 Kg/m³, as opposed to a structural inner portion 1 density of about 20 Kg/m³.

For a better understanding of the above data, it should be noted that the inner portion of a conventional surfboard, built in accordance with the state-of- the-art, is typically comprised of an expanded polyethylene body or structure, in the form of a uniform plank and having a density of 36 to 42 Kg/m³, this body being subsequently covered with expanded polyethylene having a density of 100 Kg/m³ on the top and with a nonexpanded polyethylene film on the bottom.

Despite the fact that the structure of the improved surfboard of this invention has a lower density (20 K/m³) than that (35 to 42 Kg/m³) of the conventional board structure belonging to the state-of-the-art, the greater rigidity of the board of the present invention is explained precisely by the fact that it is a structural "sandwich" with individual elements which, after being bonded laterally to one another, form a film of greater density in the position of their greater moment of bending resistance.

As to the density of the skin 2 of the improved board in question, it is approximately 140 Kg/m³; that is, significantly greater than that of the ordinary inner structures.

Meanwhile, in spite of this high density of the skin 2 of the board in question, the corresponding increased weight is offset by the rather low density (about 20 Kg/mg³) of the individual elements comprising the structural inner portion, so that for essentially equal weights of the inner part, the modulus of elasticity of the inner part of the board according to this invention is significantly greater.

It should also be pointed out that once the inner portion of the improved surfboard in question has been produced as described above, it will be subjected to complementary operations and/or phases of covering the upper and lower surfaces and lateral edges, as well as to surface finishing of the chest- type surfboard itself, which naturally may be either smooth or otherwise, and applied in one or more coats, as well as having a number of other differentiating details.

Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiment can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.

Claims

1. An improved structure for a chest-type surfboard of the type essentially constituted with an inner portion (1) of expanded polyethylene, with a skin (2) thermally laminated on its surfaces, both upper and lower, forming a "sandwich," which is subsequently subjected to complementary coating operations of the bottom, top, and side edges, as well as surface finishing; wherein the improvements comprise: a structural inner portion (1) of the surfboard comprising individual longitudinal elements (3), made of low density expanded poly¬ ethylene, bonded laterally to one another by means of a thermal fusion bonding process, thereby resulting in compaction of the expanded poly¬ ethylene and subsequent formation of, at the laterally adjoining walls of the members (3), a corresponding number of rigid films (4), acting as girders with their greater moment of resistance, oriented at right angles to applied bending force when the board is in use; and a skin (2) of expanded polyethylene of a substantially greater density than that of the inner portion (1), the skin (2) laminated by a thermal fusion bonding process to both the upper and lower surfaces of the inner portion (1).

2. An improved chest-type surfboard comprising: an inner portion of low density expanded polyethylene foam, the inner portion comprised of: a plurality of individual, longitudinal elements of expanded poly¬ ethylene foam disposed in lateral contact with each other to form a plank; and a plurality of rigid polyethylene films formed between said longitudinal elements by a thermal fusion process so that said rigid films are oriented substantially at right angles to an upper and a lower surface of the plank; an upper skin of expanded polyethylene foam, of substantially higher density than said inner portion, said upper skin bonded by thermal fusion to the upper surface of the plank; and a lower skin of expanded polyethylene foam, of substantially higher density than said inner portion, said lower skin bonded by thermal fusion to the lower surface of the plank.

3. The surfboard of Claim 2, wherein the inner portion has a density of less than about 25 Kg/m³ and the upper and lower skins have a density greater than about 120 Kg/m³.

4. The surfboard of Claim 2, wherein the inner portion has a density of about 20 Kg/m³ and the lower and upper skins have a density of about 140

Kg/m³.

5. An improved chest-type surfboard comprising: an inner portion of low density expanded polyethylene foam having a density of about 20 Kg/m³, the inner portion comprised of: a plurality of individual, longitudinal elements of expanded poly¬ ethylene foam disposed in lateral contact with each other to form a plank; and a plurality of rigid polyethylene films formed between said longitudinal elements by a thermal fusion process so that said rigid films are oriented substantially at right angles to an upper and a lower surface of the plank; an upper skin of expanded polyethylene foam having a density of about 140 Kg/m³, said upper skin bonded by thermal fusion to the upper surface of the plank; and a lower skin of expanded polyethylene foam having a density of about 140 Kg/m³, said lower skin bonded by thermal fusion to the lower surface of the plank.

6. An improved chest-type surfboard comprising: an inner portion of low density expanded polyethylene foam, the inner portion comprised of: a plurality of individual, longitudinal elements of expanded poly- ethylene disposed in lateral contact with each other to form a plank; and a plurality of rigid polyethylene films formed between said longitudinal elements by a bonding process so that said rigid films are oriented substantially at right angles to an upper and a lower surface of the plank; an upper skin of expanded polyethylene foam, of substantially higher density than the inner portion, said upper skin bonded to the upper surface of the plank; and a lower skin of expanded polyethylene foam, of substantially higher density than the inner portion, said lower skin bonded to the lower surface of the plank.

7. A method for constructing an improved chest-type surfboard comprising the steps of: extruding elements of low density polyethylene foam to at least a desired length of the surfboard; thermally fusing the elements together side by side to form a plank with relatively rigid areas of polyethylene film at the junctions of the elements and oriented at substantially right angles to an upper and lower surface of the plank; cutting the plank to approximately the desired length of the surfboard; and thermally fusing a skin of polyethylene foam of substantially higher density than the foam of the elements to the upper and the lower surface of the plank.

8. The method of Claim 7 wherein the cutting step follows the step of fusing a skin rather than the step of fusing the elements.