THERMOPLASTIC BOTTOM INFLATABLE BOAT

Abstract: A boat formed from a hull bottom (1) of thermoplastics material and side skirts (2) in the form of tapered inflatable tubes. The side skirts (2) are fastened to the hull bottom (1) by flexible adhesive tape or other continuous flexible mechanical fasteners so that there are no hard fastenings or frames to cause stress concentration in the thermoplastic hull bottom (1).

Description: THERMOPLASTIC BOTTOM INFLATABLE BOAT TECHNICAL FIELD - This invention relates to a boat and has been devised i particularly though not solely as a design for a small • 5 boat which can be simply manufactured using mass production techniques. BACKGROUND ART In the past 30 years small boats have generally been constructed from two major materials, namely glass 10 reinforced plastics (fibreglass) and sheet aluminium. Small fibreglass boats have the disadvantage that they are heavy and therefore difficult to handle requiring high power and fuel for their propulsion, they are manufactured from materials which are arguably 15 carcenogenic, they are flammable, suffer from osmosis and are difficult to repair when damaged. Aluminium boats are expensive due to the base cost of the material, are noisy in use due to wave pounding, suffer from dents and cracks in use and are prone to electrolysis. 20 Both fibreglass and aluminium small boats are labour intensive to manufacture and are expensive to transport to point of sale in bulk quantities. Neither fibreglass nor aluminium boats are particularly stable due to the design limitations imposed by the economic use of these 25 materials. A third type of small boat presently in the market is the inflatable or semi-rigid inflatable craft which has the ά advantage of being immensely stable and, because they can be deflated, are relatively easily transported. The main 30 disadvantage and limiting factor of inflatable craft is that many are made by hand and are particularly expensive. If the craft are fully inflatable they usually do not ride very well in rough water as the hull bottom is relatively flat and pounds when it hits waves. If the craft has a rigid hull (semi-rigid inflatable craft) , the hull is rigid and heavy and loses any ease of transport advantages of the fully inflatable craft. The flexible skirt and rigid hull are physically at odds with each other. In prior art craft with inflatable tubes the tube surrounds both sides and the bow (and in some craft the stern as well) . This has a number of disadvantages: (1) cost is greatly increased because of the number of seams and angles and wasted fabric offcuts; (2) there is great room for error in construction; (3) the bow of the craft may have excessive bouyancy when travelling through waves (causing destructive stress in the centre of the craft and impact shock to the passengers) . Attempts have been made in the past to overcome the labour intensive, and therefore expensive, method of manufacturing small boats by roto-moulding boats from various plastics materials. This method has never been very acceptable in the market place as the final product is heavy, very limited in design range and does not have a very long servicable life. Once again the end product is bulky and difficult to transport in large quantities to the point of sale. DISCLOSURE OF THE INVENTION Accordingly, in one aspect, the present invention provides a method of constructing a boat comprising the steps of: (a) forming a hull bottom from thermoplastics material; (b) providing side skirts in the form of inflatable tubes; and (c) securing the side skirts to the hull bottom. Preferably the thermoplastics material comprises sheet acrylic material or co-extruded acrylic and other thermoplastic material. Preferably the hull bottom is vacuum moulded from the sheet thermoplastics material. Alternatively the hull bottom is injection moulded from thermoplastics material. Preferably the step of securing the side skirts to the hull bottom comprises bonding by way of flexible acrylic adhesive tape or glue. Alternatively the side skirts are secured to the hull bottom by mechanical fasteners such as brackets, zip fasteners, or hook and loop tape (e.g. Velcro T.M.) Unlike conventional craft which are built excessively rigid, stiff, strong and subsequently heavy to withstand the destructive forces of the marine environment, a boat constructed according to the method of the present invention is made entirely from lightweight, energy absorbing materials and is constructed in such a fashion that any impact encountered on any part of the craft will be dissipated throughout the craft. The entire craft flexes on impact ensuring a softer, safer ride and greatly minimising the possibility of sustaining damage. This unique and novel feature is obtained by use of all flexible materials and adhesives, no frames or rigidising floors and no hard fastenings. As the craft is so light in weight, destructive, inertia forces are substantially less than in conventional craft. Preferably the flexible adhesive tape comprises double-sided adhesive tape running the full length of all contact points. Preferably the adhesive tape is the type of product manufactured by the 3M Company under the general product range known as "Very Strong Bond" tapes. Typically the hull material is a Rohm and Hass product, manufactured in the USA and marketed in Australia by BTR Nylex as 2000XT. Alternatively the hull bottom is moulded from polycarbonate or Lexan material, or some other suitable thermoplastics material. In one form of the invention the hull is fabricated by laminating two hull shells together one inside the other, bonded by flexible energy absorbing adhesives. Preferably the hull bottom incorporates an integrally moulded transom portion upturned between the side skirts at the aft end of the hull bottom. Preferably the transom portion is reinforced by laminating a second layer of sheet thermoplastics material to the transom and the hull bottom in the region of the transom, using flexible acrylic adhesive tape. Alternatively the transom portion is reinforced by bonding an injection moulded plastics reinforcing member to the transom. Preferably the side skirts are circular or oval in section and tapered in configuration from a smaller section nearer the bow to a larger section nearer the stern. In a further aspect the invention consists in a boat comprising a hull bottom formed from- ' thermoplastics material and side skirts in the form of inflatable tubes secured to the hull bottom. BRIEF DESCRIPTION OF THE DRAWINGS Notwithstanding any other forms that may fall within its scope, one preferred form of the invention will now be described by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a plan view of a boat according to the invention; Fig. 2 is a side view of the boat shown in Fig. 1; Fig. 3 is an underside view of the boat; and Fig. 4 is a rear view of the boat. MODES FOR CARRYING OUT THE INVENTION In the preferred form of the invention a small boat (typically 3 metres in length) is constructed from a hull bottom (1) formed from thermoplastics material to which are secured two side skirts (2) in the form of inflatable tubes, generally circular or oval in section and tapering from a smaller section (3) nearer the bow (4) of the boat to a larger section (5) nearer the stern of the boat. The boat also incorporates structurally stiffening through a flexible and impact absorbing topside cowling (7) over the bow portion. Both the hull bottom (1) and the topside cowling (7) are formed from thermoplastics material and preferably from sheet acrylic material. The hull bottom is typically either ther o-formed by vacuum moulding from sheet stock or alternatively is injection moulded. A typical material is the Rohm and Hass product manufactured in the USA and marketed in Australia by BTR Nylex as 2000XT. The topside cowling is bonded to the hull bottom along join lines (8) by the use of a double-sided adhesive acrylic tape, and similarly the inflatable side skirts (2) are preferably bonded to the hull bottom using similar tape. To facilitate the bonding of the side skirts to the hull, the outer edges of the hull are turned outwardly to form suitable bonding flanges (9) as can be clearly seen in Fig 2. Alternatively the side skirts may be fastened to the hull bottom by continuous mechanical fasteners such as extruded plastics mouldings used in conjunction with hook and loop fastening tape (e.g. Velco T.M.) or zip fasteners. It is important that the fastening be substantially continuous so as to avoid any hard spots or stress points which would crack or split the thermoplastic hull bottom. The inflatable side skirts (2) can be formed from any suitable material but are preferably formed from plasticised PVC. The ends of the inflatable side skirt tubes are typically completed by crimping or bonding, and at the forward end of the tubes, the crimped portions are attached inside the topside cowling (7) . At the rear of the ' hull bottom (1) , the sheet thermoplastics material is upturned to form a transom (10) which can similarly be provided with end flanges (11) , bonded to the inflated side skirts (2) by way of double-sided tape or other flexible adhesive. The transom may be reinforced to take an outboard motor by laminating a second layer of sheet thermplastics material to the transom, and to the hull bottom in the vicinity of the transom, once again using double-sided adhesive tape. Alternatively the transom can be reinforced by other methods such as bonding an injection moulded plastics reinforcing member to the transom in desired locations. It is a particular feature of a boat constructed as described above that there are no "hard" fastenings or fixtures anywhere in the boat. All of the materials and bonding methods used in the construction are flexible or semi-rigid so that the end result is a boat which forms an energy absorbing module able to flex and give with impact in use and which is therefore extremely strong and robust. It has been hitherto regarded as impossible to use sheet thermoplastics material for building boats as the material has a bad tendency to crack or craze anywhere that it is clamped or hard fastened using conventional boat building techniques. The material has therefore hitherto been discarded as unsuitable for boat building. The present invention stems from the realisation that thermoplastics material (and preferably sheet acrylic material) could be used for boat building if there are no hard fastenings or fixtures, and the present method of construction by continuous bonding was developed. Numerous other unique advantages acrue from this construction method. The end product is not only extremely tough but has a number of other unique advantages. Prime among these is the fact that the craft can be mass produced as a number of separate components (hull bottom, topside cowling, and side skirts) , large quantities of the individual components stacked by nesting and transported in a compact configuration to the point of sale. In this manner a very large quantity of boat components can, for example, be packed into a standard shipping container. At the point of sale or distribution, it is a simple assembly operation to bond together the hull bottom, topside cowling, and inflatable side skirts, to form the completed boat. To this end it is envisaged that the double-sided adhesive tape would be pre-applied to the hull bottom (and/or the topside cowling) in the appropriate areas before packaging for shipment. It is a further feature of the boat according to the invention, that the hull bottom can be made from a transparent acrylic material providing a wide underwater viewing area through the bottom of the craft. This is not only a unique marketing advantage but has practical applications for divers, .marine salvage operators, etc. The use of inflatable side skirts provides maximum stability of the craft, maximum buoyancy, and positive flotation should the craft fill with water or capsize. The skirts can be constructed and designed specifically to carry- comprehensive advertising material which makes the boat suitable as a mass advertising medium. The configuration of the side skirts, being tapered from the back of the craft to the front of the craft uniquely achieves a narrow, strong transom to compensate for flexibility in the acrylic hull which is important as the motor-mounting on the transom must be reasonably rigid but not at the expensive of the energy absorbing characteristics of the hull. The tapered tubes also give substantial buoyancy where it is most needed, ie in the position of the motor, fuel and occupants. The skirts, uniquely extend substantially past the transom resulting in greatly enhanced fore to aft stability. The engine, and passenger payload becomes more central in the craft preventing the transom "digging in", cavitation and the craft flipping over backwards if hit by a wave. Similarly, the craft has greatly enhanced stability in the event that it is dethrottled rapidly. The persuing bow wave cannot advance over the boat flooding it. Rather, the stern lifts due to its large bouyancy. The boat manufactured according to the invention enjoys extraordinary low weight achieved through the non-inclusion of frames, the use of a lightweight skirt material to provide buoyancy and the lightweight of the sheet acrylic used for the hull bottom and topside cowling. This low weight gives advantages of, low displacement, substantial reduction in motor size for speed, significant fuel savings, greatly reduced destructive inertia forces through wave impact or hitting solid objects, ease of handling, greater manoeuvrability and responsiveness, and a very low centre of gravity and therefore increased stability. The craft is also constructed of "radar invisible" materials which are highly energy absorbing. By increasing material thickness the unit can be made bullet proof. These features combined with its stackability, ultra lightweight and its ability to be four colour screen printed in "camouflage" make the craft ideally and uniquely suited to military purposes.

Claims: CLAIMS : - 1. A method of constructing a boat comprising the steps of: (a) forming a hull bottom from thermoplastics material; (b) providing side skirts in the form of inflatable tubes; and (c) securing the side skirts to the hull bottom. 2. A method of constructing a boat as claimed in claim 1 wherein the thermoplastics material comprises sheet acrylic material. . A method of constructing a boat as .claimed in claim 1 wherein the thermoplastics material comprises co-extruded acrylic and other thermoplastic material. 4. A method of constructing a boat as claimed in any one of the preceding claims wherein the step of bonding the side skirts to the hull bottom comprises fastening by way of flexible acrylic adhesive tape or glue. 5. A method of constructing a boat as claimed in claim 4 wherein the flexible adhesive tape comprises double-sided adhesive tape running the full length of all contact points. 6. A method of constructing a boat as claimed in any one of the preceding claims wherein the hull bottom is fabricated by laminating two hull shells together one inside the other, bonded by flexible energy absorbing adhesives. 7. A method of constructing a boat as claimed in any one of the preceding claims wherein the hull bottom incorporates an integrally moulded transom portion upturned between the side skirts at the aft end of the hull bottom. 8. A method of constructing a boat as claimed in claim 7 wherein the transom portion is reinforced by laminating a second layer of sheet thermoplastics material to the transom and the hull bottom in the region of the transom, using flexible acrylic adhesive tape. 9. A method of constructing a boat as claimed in claim 7 wherein the transom portion is reinforced by bonding an injection moulded plastics reinforcing member to the transom. 10. A boat comprising a hull bottom formed from thermoplastics material and side skirts in the form of inflatable tubes secured to the hull bottom. 11. A boat as claimed in claim 10 wherein the hull bottom incorporates an integrally moulded transom portion upturned between the side skirts at the aft end of the hull bottom. 12. A boat as claimed in claim 11 wherein the transom portion is reinforced by laminating a second layer of sheet thermoplastics material to the transom and the hull bottom in the region of the transom, using flexible acrylic adhesive tape. 13. A boat as claimed in any one of claims 10 to 12 wherein the side skirts are circular or oval in section and tapered in configuration from a smaller section nearer the bow to a larger section at the stern.

Inventors: GRUHN AMANDA LYNN, HARMAN JAYDEN DAVID, GRUHN, AMANDA, LYNN, HARMAN, JAYDEN, DAVID
Applicants: TANK & PIPE WELDING PTY LTD, TANK AND PIPE WELDING PTY LTD
Application year: 1991
Main classification: B63B7
IPC codes: B63B5, B63B7