Sit-on-top, sit-inside kayak and method of producing the same
A method of forming a positive-buoyancy watercraft as a seamless, one-piece hollow body with a cockpit including a seat and a recess for a user's legs is disclosed and claimed. Watercraft and other structures formed by the method are also described and claimed.
The invention relates to rotation-molded structures. More specifically, the invention relates to a method of forming a partially-enclosed cockpit in a one-piece molded structure such as a watercraft.
BACKGROUNDSmall watercraft such as kayaks, dinghies, paddleboards, surfboards and the like can be manufactured using a rotational molding process similar to that described in U.S. Pat. No. 3,202,745 issued to Ringdal, where a thermoplastic powder or granules are placed in a hollow mold and the mold is heated while being rotated and/or rocked around several axes. The plastic powder or granules coat the inner surface of the mold and fuse together to form the desired object, where the outer surface of the object bears features that are the negative of the inner surface of the mold.
Since articles molded by this process are hollow, they are naturally buoyant. Furthermore, by selecting suitable plastic materials and quantities, strong and durable watercraft may be formed. However, the molding process restricts the possible shape of hulls formed because of the way the product must be removed from the mold. Molds are typically constructed in two pieces (e.g. top and bottom) that are clamped or bolted together during casting. The hull cannot have protrusions or indentations that restrict its removal from the mold. For example,
A kayak is a small, maneuverable boat fashioned after a craft used by indigenous people in the Arctic regions of North America and Greenland. The pilot sits inside a traditional kayak as shown in
A sit-inside kayak can be formed by rotation-molding a blank and then cutting an opening for the cockpit, and a sit-on-top kayak can be formed by rotation-molding a hull with depressions. However, it has not been possible to form a positively buoyant, sit-inside kayak by rotation molding because the cockpit of such a kayak is an indentation that restricts its removal from the mold.
SUMMARY OF THE INVENTIONA positive-buoyancy watercraft can be formed as a seamless, one-piece hollow body with a cockpit including a seat and a recess for a user's legs by rotation-molding a casting material in a mold that is divided into at least three sections.
BRIEF DESCRIPTION OF DRAWINGSEmbodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean “at least one.”
Dashed line 375 shows the location of a third cross-section, 380. This section shows how the perimeters described with reference to cross-section 325 may change as the section line approaches the place where the outer hull and inner cockpit join together (near coaming 310). There are still two continuous perimeters 330 and 335, but they are tangent along a portion of their circumferences (see circled areas indicated as 385). The inside of cockpit 305 and hollow hull interior 340 are visible in section 380, also.
The size and shape of the hull may be adapted to the intended user and use. For example, a more-pronounced keel may enhance the vessel's stability and tracking, while a rounder bottom may improve its maneuverability. A flat or square transom 390 may provide a place to mount a rudder for steering or a motor for propulsion. A coaming or splash guard 310 may be formed around the cockpit, and indentations or recesses 315 formed on the deck may provide storage spaces. An opening 320 may be made in the deck to afford access to the hollow interior of the craft, but such an opening should be covered with a watertight hatch cover to prevent water from entering. A round or oval opening can be sealed effectively with a flexible covering that is held in place by elastic tension. A round opening can also be sealed by a threaded hatch cover that screws into a corresponding threaded hatch frame. A rectangular opening (or more generally, an opening that is neither circular nor oval) may require a rigid hatch cover that is held in place by a locking mechanism such as a rotating cam or latch.
Since the kayak is formed as a molded, continuous surface enclosing an interior volume, it has a natural positive buoyancy. Even if the cockpit fills with water, the craft will not sink. In fact, channels or “scuppers” 345 (visible in
If desired, a second or even third cockpit can be formed in the continuous surface to accommodate additional passengers, or a single, wide cockpit (with, for example, a plurality of seat depressions arranged across the beam of the craft) can be constructed.
The watercraft described with reference to
Element 470 is a third portion of the mold, which is inserted through opening 460 during the casting process. The outside of this portion of the mold contains features that are the negative of features found inside the partially-enclosed cockpit of the finished watercraft. For example, protrusion 480 will form seat indentation 365, and protrusions 490 will form footwells 370. Mold portion 470 may be hollow, as shown, or solid; the inside area 499 of this portion does not contribute directly to the formation of the watercraft. However, thermal or other effects may make hollow mold portions to perform better.
Note that the top 410 and bottom 440 portions of this mold are shown as material removed from solid, rectangular blocks. This is a simplification for explanatory purposes only; a practical mold would probably contain only enough material outside the inner surface to give the mold adequate stiffness, strength, and thermal properties. It is the inner surfaces of top 410 and bottom 440 molds sections that form the outer surface of the watercraft's hull (in contrast, the outer surface of mold section 470 forms the inner surface of the partially-enclosed cockpit). As is known in the art, smooth or textured (rough, pebbled, ridged, etc.) surfaces can be formed by rotation molding if appropriate negatives of those features are formed on the mold surfaces.
Now, the mold is heated and rotated and/or rocked about several axes (540) to melt and distribute the casting material on the inner surfaces of the mold. Once the mold has been heated and rotated for a sufficient time, it is allowed to cool (550) (while continuing to rotate and/or rock, so that the melted casting material does not settle at the bottom of the mold). Then, the first, second and third sections of the mold are separated from each other (560) and the cast watercraft may be removed. If spacers were used to form scuppers, these may need to be disconnected from the mold before the mold pieces are separated. The spacers can be removed after the boat is removed from the mold, leaving channels from the cockpit sole to the bottom of the hull. Finally, plastic flash, mold marks and blemishes may be trimmed from the watercraft (570), and openings for hatches cut, holes for deck rails and accessories drilled, and so forth. (580).
In embodiments with multiple cockpits, the top portion of the mold may have several openings, into each of which a mold part like the third portion described above may be inserted. In some embodiments, the first and second mold sections may form the left and right sides of the watercraft, rather than the top and bottom surfaces. (In other words, the mold line between the first and second sections will be vertical rather than horizontal.) When this type of mold is used, the opening to receive the third section of the mold may be divided between the first and second sections, as shown at
The applications of the present invention have been described largely by reference to a specific example of a one-piece, seamless, hollow, sit-inside kayak. However, those of skill in the art will recognize that similar inherently-buoyant watercraft with partially-enclosed cockpits can also be produced by variations of the method disclosed herein. Furthermore, the favorable strength-to-weight ratio, durability, and relative ease of manufacture of rotational-molded items suggest additional applications for the three (or more) piece molding process described herein.
Claims
1. A structure comprising:
- a seamless, one-piece, hollow body containing a cockpit formed therein, the cockpit to include a seat and a recess for a user's legs; wherein
- a section of the body taken perpendicular to a point on a line parallel to the user's legs discloses two continuous perimeters, a smaller of the two perimeters contained within a larger of the two perimeters.
2. The structure of claim 1, wherein the smaller of the two perimeters is completely contained within the larger of the two perimeters.
3. The structure of claim 1, wherein the smaller of the two perimeters is tangent to the larger of the two perimeters along a common portion of a circumference of the smaller perimeter and a circumference of the larger perimeter.
4. The structure of claim 1 wherein the hollow body comprises a watercraft with an elongated shape.
5. The structure of claim 4, further comprising:
- a plurality of scuppers to drain water from the cockpit.
6. The structure of claim 4, further comprising:
- an opening in a deck of the watercraft, the opening to be covered with a hatch cover.
7. The structure of claim 4, further comprising at least one of:
- a recess formed on a top portion of the hollow body;
- a coaming formed on the top portion of the hollow body; and
- a keel formed on a bottom portion of the hollow body.
8. The structure of claim 4 wherein a rear portion of the body forms a flat, substantially vertical transom.
9. A watercraft comprising:
- an elongated, molded, continuous surface enclosing an interior volume; and
- a partially-enclosed cockpit;
- wherein the surface forms two lateral sides of the cockpit, a sole of the cockpit, and a deck covering a portion of the cockpit.
10. The watercraft of claim 9, wherein the surface is formed as a single unit.
11. The watercraft of claim 9, further comprising:
- at least one channel to connect the sole of the partially enclosed cockpit with an outer surface of the watercraft, wherein
- one end of the at least one channel is below a waterline of the watercraft in the watercraft's standard orientation.
12. The watercraft of claim 9, further comprising:
- a covered hatch to provide access to the interior volume through the continuous surface.
13. The watercraft of claim 12, wherein the covered hatch is oval in shape, the watercraft further comprising:
- a watertight hatch cover constructed of an elastic material, the hatch cover to seal to the hatch by elastic tension.
14. The watercraft of claim 12, wherein the covered hatch is rectangular in shape, the watercraft further comprising:
- a watertight hatch cover constructed of a rigid material, the hatch cover to seal to the hatch by a locking means.
15. The watercraft of claim 12, wherein the covered hatch is circular in shape, the watercraft further comprising:
- a watertight hatch cover constructed of a rigid material, the hatch cover to seal to the hatch by a screw means.
16. The watercraft of claim 9, further comprising:
- a second partially-enclosed cockpit,
- wherein the continuous surface forms two lateral sides of the second cockpit, a floor of the second cockpit, and a deck covering a portion of the second cockpit.
17. A method of forming a structure comprising:
- securing a first section of a mold to a second section of the mold;
- placing a casting material into the mold;
- inserting a third section of the mold through an opening in the mold;
- securing the third portion of the mold so that the casting material cannot escape from the mold; and
- simultaneously rotating the mold and heating the mold to melt and distribute the casting material.
18. The method of claim 17, further comprising:
- placing at least one spacer between the third section of the mold and one of the first section of the mold and the second section of the mold.
19. The method of claim 17, further comprising:
- inserting a fourth section of the mold through a second opening in the mold; and
- securing the fourth section of the mold so that the casting material cannot escape from the mold.
20. A mold comprising:
- a first section to form a first portion of a surface of a watercraft;
- a second section to form a second portion of a surface of the watercraft; and
- a third section to form a third portion of a surface of the watercraft, wherein
- the first and second sections are to be secured together;
- when the first and second sections are secured together, an opening to an interior of the mold remains; and
- the third section is to be inserted into the opening and secured to the opening.
21. The mold of claim 20, further comprising:
- a protrusion in the first section to form a recess in the first portion of the surface of the watercraft.
22. The mold of claim 20, further comprising:
- a protrusion in the third section to form a seat depression in the third portion of the surface of the watercraft.
23. The mold of claim 20, further comprising:
- a spacer to be inserted between the third section and one of the first section and the second section, wherein
- a fastener to connect the spacer to the third section is accessible when the sections of the mold are secured together.
Type: Application
Filed: Dec 8, 2005
Publication Date: Jun 14, 2007
Inventor: Warren Aitken (Gardena, CA)
Application Number: 11/299,075
International Classification: B63B 35/71 (20060101);