AU2004100379B4 - Breakdown Sit-on and Sit-in Plastic Paddle Boats - Google Patents

Description

AUSTRALIA

Patents Act 1990 INNOVATION PATENT SPECIFICATION

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John Carl SLATTERY PO Box E55, Corimal East, NSW, 2518 John Carl SLATTERY Paul A Grant and Associates PO Box 60, Fisher, ACT, 2611 INVENTION TITLE: Breakdown Sit-on and Sit-in Plastic Paddled-Boats The following statement is a full description of this invention, including the best method of performing it known to me:- 2 TITLE: BREAKDOWN SIT-ON AND SIT-IN PLASTIC PADDLED-BOATS TECHNICAL FIELD This invention relates to sit-on or sit-in moulded plastic paddle-boats that can be broken-down or separated transversely into at least two parts.

More particularly, the invention relates to rotationally-moulded or blow-moulded thermo-plastic breakdown kayak-like paddle-boats that are formed from polyethylene powder by rotational molding techniques or from drawn polyethylene tubing by blow-molding techniques.

BACKGROUND TO THE INVENTION Small boats that can be broken down into separate sections are well known.

They are easier to transport and store and easier to carry over portages than the same size boats which cannot be disassembled. Each section of such a boat is usually joined to its neighbour at a bulkhead so that each section is watertight and can be independently floated. Because of the added stress on the bulkheads and hulls, small breakdown boats are fabricated around stiffening frames, whether they have metal, FRP (fiber-reinforced-plastic) or moulded plastic hulls.

US patent 1,449,222 [1923] to Goethel disclosed a fabricated metal open breakdown dinghy having bow section with an aft bulkhead, a stern section with a fore bulkhead and a center section with both fore and aft bulkheads. The bulkheads are formed with tapered multiple tenons and grooves of dovetail section that run the full height of the bulkhead. Thus, if the assembled boat is turned upside down, the bow and stern sections can be slipped vertically upward with respect to the center section to effect disassemble the dinghy. The assembly of the dinghy from separate sections is, of course, effected in the reverse manner by turning the center section upside-down and slipping the inverted bow and stern sections into place. While the tapered joints provide vertical location of the sections when the boat is turned right-way-up and 3 floated, each pair of coupled bulkheads is also secured together by a pair of longitudinally-extending bolts located at or above gunwale-level.

US patent 3,822,427 to Ewart disclosed a similar breakdown dinghy to that of Goethel, except that it is fabricated from fiberglass reinforced plastic [FRP], the vertical dovetail joints of the bulkheads are not tapered and the sections are bolted together beneath the gunwale level (but above the normal waterline).

The boat can be assembled by lowering an inverted or upright bow or stern section onto an inverted or upright center section because the dovetail tenon and groove joints are not tapered. Ewart also discloses the use of bolted fishplate joints between sections along the keel.

The breakdown systems disclosed by Goethel and Ewart may be suited to fabricated metal and fiberglass construction using suitable stiffeners, frames or brackets, but they are not suited to practical rotationally-molded or blow-molded thermo-plastic dinghies or kayaks because of their much greater wall-flexibility.

If formed from, say polyethylene, by such conventional molding techniques, the bottom of the tenon joints would tend to spring open each time the craft bridges two waves, polyethylene being significantly less rigid than FRP for the same wall thickness. Not only would this quickly wear and fatigue the joints, but the flexing would make kayak difficult to handle. While this problem would be largely overcome by the use of bolted keel fishplates, as taught by Ewart, this method of joining is not suited to keel-less kayak-type paddle boats.

Futhermore, the use of multiple shear-bolts to join adjacent bulkheads is problematic in hollow-form kayaks where access to bulkheads is difficult and time-consuming during portage.

US patent 3,916,468 to Tetreault discloses a molded plastic Canadian-style (open) breakdown canoe that, like the Goethel dinghy, has multiple sections in which adjacent bulkheads are joined by multiple tapered dovetails. However, Tetreault discloses the use of dovetails that taper (narrow) from top to bottom and, therefore, require the canoe to be assembled by sliding upright end sections onto an upright center section. Tetreault also teaches the use of a 4 dovetail tongue-and-groove joint that terminates before the bottom of the canoe in a wedge-like tip. The wedge-tip assists in holding the bottom edges of the coupled bulkheads together and vertically locates one section with respect to the next. Tetreault also discloses the use of swing-hooks and pins to prevent the coupled sections from working loose.

While Tetreault does not state the plastic molding method employed, other than to indicate that 'suitable, mouldable plastic material' is used, the multilayer channel-section gunwales and the differing wall thickness of bulkhead and hull io strongly suggest sprayed FRP in a female mold. Low-pressure injection-molding of such large and complex components was probably beyond the capability of the plastic canoe industry in 1974 (when the Tetreault patent was filed).

I have found the breakdown canoe disclosed by Tetreault unsuited to blowmolded and rotationally-molded polyethylene canoes because of their relatively thin and flexible walls and the rather large dimensional tolerances involved during manufacture. Also, for kayak-style paddle boats, protruding swing-hook fasteners are undesirable, though quick and convenient to operate. Such fasteners can be easily disengaged inadvertently and are prone to catch on ropes and to injure persons. Moreover, I have found that multiple dovetail joints of the type taught by Tetreault can jam and wear because of the ingress of sand and other waterborne particles.

OUTLINE OF THE INVENTION From one aspect, this invention comprises a breakdown kayak comprising multiple hollow-form unitary sections, each molded from thermo-plastic material such as polyethylene by rotational-molding or blow-molding and each having a deck portion spaced from and above a hull portion and each having at least one transverse bulkhead formed integrally with the deck and hull portions, the bulkhead being shaped to form a single wedge-shape tongue or groove of a dovetail joint with a similar bulkhead of an adjacent section to effect releasable or demountable coupling of the sections.

The moulded sections will normally have a wall thickness of between 3 and mm and, therefore, be quite flexible. However, the integral moulding of the deck, hull, bulkhead and tongue or groove provides much needed stiffening of a thin bulkhead and such stiffening can be enhanced by ensuring that the tongue/groove extends vertically for at least 50% preferably between 66% and 75% of the height of the bulkhead and/or extends horizontally for at least preferably between 66% and 75% of the width of the bulkhead. I have found that these measures obviate the need for heavy wall sections or the addition of stiffening plates or frames in, on or around the bulkhead. This strength is further enhanced by the low oval cross-section of many kayaks, and by the rounded flatter and more rectangular section of many hollow-form sit-on paddle boats, such as surf skis.

Short, longitudinally extending metal straps may be used to secure the coupled sections together, the straps bridging the junction between adjacent bulkheads and being attached at each end to a section by bolts, screws or other suitable fasteners. Preferably, at least four straps are employed for each joint, two on either side of the deck above the waterline and two on either side of the hull below the waterline.

Rotational-molding is herein preferred as it is better suited to kayak production and is less technically challenging to rotationally-mold large-dimension hollow shapes having the requisite wall thickness for a kayak than to blow-mold them.

However, either rotational molding or blow-molding can yield the unitary hollowform structure required for each section of the kayak. It might be noted that, while hollow-form plastic kayaks can be injection-molded or vacuum-formed it is generally necessary to produce multiple parts by such techniques and to assemble them in some manner. This makes for a more expensive, complex and heavy paddle boat than the unitary hollow-form structure generated by 3o rotational or blow-molding.

The paddle boats of this invention are preferably formed from polyethylene having a density in excess of 900 gm/Itr and, preferably, in the range 935 955, 6 densities between 940 and 948 being preferred for rotational molding and densities between 940 and 955 being preferred for blow molding. With such materials light-weight hollow-form kayaks can be manufactured with wall thicknesses of between 3 and 6 mm, uniform wall thicknesses of between 3 and 4 mm being preferred for the hull portions and the bulkhead portions.

The term 'kayak' is herein used to designate any hollow-form, elongate, decked boat that is molded from plastics material and that a person can sit on or sit in and propel by hand-paddles. Thus, I mean 'kayak' to include: Sit-in Eskimo-style paddle boats that are fully decked except for cockpithole(s) that allow the paddler(s) to sit on or near the bottom of the hull while paddling, whether such kayaks are of the short, highlymaneuverable one-person whitewater sports type, the long multi-person sea-kayak type, or something in between, Hollow-form sit-on surf-skis and boards, with or without recessed or backed seat areas, foot-straps and the like that assist paddlers maintain their seated position, and Hollow-form sit-on canoes that are similar to sit-on surf skis except that they have relatively high, full-length, hollow-form gunwales or sides that that protect and locate the paddler(s), such canoes often having the superficial appearance, in profile, of low-sided non-hollow-form Canadian-style canoes.

It might be noted that sit-on kayaks that have recessed or walled seat areas usually provide for the drainage of these areas. This is often in the form of socalled 'kiss-offs' that are drainage passages running more or less vertically from the sit-on deck to the bottom of the hull. These passages also serve to reinforce and stiffen the hollow molded structure by tying deck to hull. Again, kiss-offs are much more readily formed in rotational-molding than in blow-molding.

7 The dovetail joint between section bulkheads is preferably formed by one large mating tongue and groove joint (of dovetail section) in which the single tongue/groove has an outer end and an inner end, the tongue/groove tapering (ie, narrowing in width) from the outer toward the inner end. Preferably, the length of the tongue/groove (measured from the outer to the inner end) is at least half of the corresponding dimension of the kayak section, and preferably, the width of the inner end of the tongue/groove is at least half of the corresponding dimension of the kayak section. Preferably, also, the entire inner end of the joint is wedge-shaped to assist in holding or locking the two sections together.

The outer end of the groove of the joint may open out at deck level and the inner end may be located near the bottom of the hull; that is, the groove/joint may 'face' upward. Alternatively, the outer end of the groove may open out at the bottom of the hull and the inner end may be located near the deck; that is, it may face downward. An upward facing joint offers slightly less turbulence when the kayak is being paddled at speed, but has the disadvantage that it is prone to collect sand. A downward facing has the important advantage that it does not collect sand.

The joint may be held together by the use of metal (preferably stainless steel) ties or straps that extend across the joint and are bolted at one end to one section and at the other end to the other section. Preferably, four ties are used, two on the deck above the waterline and two on the hull below the waterline. A recess is formed in each section to accommodate the respective end of each strap so that, when fitted, each strap is inset or recessed into the surface of the kayak section so that it (and preferably the heads of its fixing bolts or screws) do not project proud of the surface and present a hazard to the user or undue turbulence. This external positioning allows ready access to the bolts for rapid removal or insertion when the boat is being broken-down or assembled.

DESCRIPTION OF EXAMPLES 8 Having portrayed the nature of the present invention, particular examples will now be described with reference to the accompanying drawings. However, those skilled in the art will appreciate that many variations and modifications can be made to the examples without departing from the scope of the invention as outlined above. In the accompanying drawings: Figure 1, is a perspective view from above of a rotationally-moulded, hollowform, three-section, sit-in, sea-kayak that forms the first example of the application of the principles of the present invention.

Figure 2 is an enlarged perspective view of the joint between the center and stern sections of the sea-kayak of Figure 1, after the sections have been separated.

Figure 3 is a sectional elevation of the sea kayak joint shown in of Figure 2, the section being taken on plane 3 3 of Figure 1 with the sections joined.

Figure 4 is an enlarged section through a strap of Figure 1 taken on plane 4 4 of Figure 1.

Figure 5 is a perspective view from above of a hollow-form, four-section rotationally-moulded, sit-on, paddle-board kayak that forms the second example of the application of the principles of the present invention.

Figure 6 is an end elevation of one of the sections of the sit-on kayak of Figure Figure 7 is a sectional side elevation of the kayak of Figure 7 taken on section line 7 7 of Figure 6.

The sea kayak 10 of the first example (shown in Figure 1) is a one person kayak of three sections for easy storage in confined places and easy portage for one person. The three sections are a bow section 12, a mid-section 14 and a stern section 16, the bow and mid-section being joined by a large dovetail joint 9 and the mid-section and stern section being joined by a large dovetail joint 22. Joints 20 and 22 will be described in detail below.

Each section, 12, 14 and 16, is rotationally moulded separately from HDPVC in the manner known in the art to form a one-piece hollow body that includes an integral bulkhead shaped to form one half of the appropriate joint 20 or 22. Bow section 12 is a fully enclosed hollow body, except for a single hatch opening 24 in the deck 26, which is formed by incorporating a hatch-ring insert and plug in the rotational mould in a manner known in the art. The stern of bow section 12 is closed to form a bulkhead, generally indicated at 28, which forms one half of joint 20. It will be noted that bulkhead 28 is integrally moulded with deck 26 and the hull 29 of bow section 12 so that the panel of the bulkhead is thus fully supported around its entire periphery by deck 26 and hull 29 without the need for any joins or reinforcing frames.

Mid-section 14 is rotationally molded in the same manner but the rotational mould incorporates a large cockpit rim insert that creates an out-turned raised cockpit lip 30 in the deck 32 near the stern of mid-section 14, the cockpit hole 34 within lip 30 normally being formed by cutting out the blank created by the rotational moulding process. As is normal, cockpit hole 34 is just big enough to accommodate an adult in the seated position on the bottom of the hull of midsection 14. The rotational moulding methods for forming such rimmed openings are well known in the rotational molding art. Mid-section 14 has a bow bulkhead, generally indicated at 36, that forms the second part of joint 20 and a stern bulkhead 38 that forms one part of joint 22. Again, it will be noted that bulkheads 36 and 38 are formed integrally with the deck 40 and hull 42 so that they are fully supported around their entire peripheries by the deck 40 and hull 42 without the need for any joins or reinforcing frames.

Stern section 16 of kayak 10 is formed in practically the same way as described with respect to bow section 12, except that two hatches 44 and 45 are formed in its deck 46 instead of one, stern section 16 having a hull 47 that is formed integrally with the deck 46. Stern section 16 has an integral bow bulkhead 48 that forms the other half of joint 22. It will again be noted that bulkhead 48 is supported around its entire periphery by deck 46 and hull 47 with which it is integrally moulded.

Turning now to Figures 2 and 3, the components of joint 22 are shown in Figure 2 after mid-section 14 and stern section 16 have been separated, while Figure 3 is a sectional view of sections 14 and 16 joined, as in Figure 1. Joint 22 is a dovetail joint made up by a single large downwardly and inwardly tapering wedge-shape groove 50 in bulkhead 38 of mid section 14, the side edges 52 of io groove 50 being angled outward and forward to form the wedge-shape dovetail.

The bottom edge 54 of groove 50 is both angled downwardly toward its center 56 and downwardly towards the bow to impart a dovetail feature to bottom edge 54 as well to as sides 52. The remaining part of joint 22 is formed by shaping bulkhead 48 of stern section 16 in a complementary manner. Bulkhead 48 has a single large outwardly and forwardly protruding wedge-shape tongue 56 with side edges 58 that are angled rearwards and inwards, bulkhead 48 also having a bottom edge 60 that is angled downwards toward the center 62 and upwards toward the stern. The way in which the bottom edges of groove 50 and tongue 56 are shaped will be clear from Figure 3. It will be seen from Figures 2 and 3 (which are drawn roughly to scale) that the vertical dimension of the tongue/groove is over 66% of the height of the respective bulkheads and (ii) the width of the groove/tongue is greater than 66% of the width of the respective bulkheads. This feature provides significant strengthening of the bulkheads.

Finally, it might be noted that Figure 2 shows a seat 64 fitted in cockpit opening 34.

To secure sections 12, 14 and 16 securely in place after the joints 20 and 22 have been formed, four stainless steel straps 66 are secured across each joint, two on the top of the decks and two on the bottom of the hulls, each strap being fitted in its own moulded recess 68 (Figures 2 and 4) so that it does not stand proud of the surface of the kayak 10. [Figure 1 shows only the four straps 66 located on the tops of decks 26, 32 and 46). While straps 66 are not shown in 11 Figure 2, the recesses 68 in which they fit are shown, four on each side of the joint.

Figure 4 is a sectional detail of one of straps 66 fitted across joint 22 between decks 32 and 46 in its recess 68. Strap 66 is secured in place with four countersunk-head screws 70, each engaging an externally flanged and internally threaded insert 72 that is moulded into the respective deck wall, as shown. If desired, hexagon-headed, Allen-headed bolts or other suitable fasteners may be used instead of screws 70. It is desirable, however, for the io fasteners to be easily installed and removed with a simple tool such as a screw driver, socket wrench or Allen key by a kayaker in the field. Straps 66 hold the joints firmly together when kayak 10 being paddled as, otherwise, the bow and stern sections are likely to work upwards with respect to the mid section when traversing waves.

The second example of a kayak formed in accordance with the principles of the present invention is illustrated in Figures 5 7 and concerns a four-section siton paddle-board kayak 100 having a bow section 102, a first mid-section 104, a second mid-section 106 and a stern section 108. Each section is joined to the next by a double dovetail joint of the type disclosed in the first example, except that the dovetail is turned upside down so that only a straight joint crack is visible from above. This has the advantage that sand entering the joint will tend to wash out rather than pack-in, making the joint difficult to separate. Figure 6 is an end elevation of rear transom 110 of bow section 102 taken on plane 6 6 of Figure 5 (also shown in Figure It will be seen that wedge-like groove 112 tapers inwards and upwards and has a gabled top surface that rise to an apex 114.

It will also be seen from Figure 5 (which is drawn approximately to scale) that the width and depth of groove 112 is about 75% of the respective dimensions of bulkhead 110. The same applies to each of the other joints of paddle-board 100. As already noted, the integral moulding of decks, hulls, bulkheads, tongues and grooves, along with the dimensional features just mentioned are of great 12 importance in ensuring optimal joint strength when wall thicknesses approaching 3 mm are used in polyethylene.

The deck of each section of paddle-board 100 is recessed to form short side rails or gunnels. The recessed deck helps locate the buttocks of paddlers laterally and the gunnels provide a convenient hand grip when carrying the sections. In Figures 5- 7, the recess and gunnels of bow section 102 are indicated at 116 and 118 respectively, while the recess and gunnels of first midsection 104 are indicated at 120 and 122 respectively. Seat-like depressions t0 124, 126 and 128 are formed at the front or bow ends of first mid-section 104, second mid-section 106 and stern section 108, respectively. In fact, the deck recess 130 of stern section 108 is just large enough to accommodate seat depression 128. A first pair of foot straps 132 is attached to the recessed deck at the front of bow section 102, a second pair of foot straps 134 is attached to the recessed deck of first mid-section 104 just behind seat depression 124 and a third pair of foot straps 136 is attached to the recessed deck of second midsection 106 just behind seat depression 126.

Thus, as set up in Figure 5, paddle-board kayak 100 is suitable for carrying three paddlers, one seated on seat 124 with his/her feet in straps 132, the second seated on seat 126 with his/her feet in foot straps 134 and the third seated on seat 128 with his/her feet in foot straps 136. By removing second mid-section 106, and coupling stern second 108 to first mid-section 104, the paddle-board is set up for two paddlers. By removing both mid sections 104 and 106 and coupling stern section 108 to bow section 102, the paddle-board is setup for one paddler.

As is known in the art, a series of drainage holes 140 that double as strengthening pillars are formed in the recessed decks of sections 102, 104 and 106. Such holes, sometimes referred to as 'kiss-offs' in the art, are shown in section in Figure 7. Figure 7 also provides a sectional view of the joint between bow section 102 and first mid-section 104.

13 Finally coupling straps 142 of the type described in the first example are used to join the gunnels and the bottoms of the hulls of each section to the next, a gunnel strap is shown in broken lines at in Figure 7, the recesses adapted to house such gunnel straps are shown at 144 in Figure 6 and the recesses adapted to house the hull straps are shown at 146 in Figure 6.

It will be appreciated that, unlike the first example, one or both mid-sections of paddle-board 100 can be removed (after straps 142 have been taken off) by lifting them upward with respect to the bow and stern sections, when the board 'o is lying upright and flat. There is no need to turn board 100 upside down to effect its break-down.

It will be seen that the rotationally moulded kayaks of the examples offer substantial flexibility and utility without sacrificing joint strength because of thin bulkhead wall sections. However, may other different types of kayak can be made using the teachings of this specification without departing from the scope of the invention as claimed below.