Dual hull kayak

The invention relates to dual hull kayak, with a one piece elongate moulded body of a continuous outer membrane enclosing an internal cavity. The kayak body has two lateral side walls and a concave bottom wall joined laterally with a bottom edge of each side wall to define two laterally spaced apart parallel pontoons each with a downwardly pointed keel. The top wall of the kayak body is joined laterally with a top edge of each side wall, to complete the hollow body. The top wall together with the bottom wall define a bridge platform spanning a central longitudinal tunnel between the pontoons. The pontoons support a top portion of the tunnel above the waterline. The top wall has a recessed open cockpit with a self-draining floor, side gunnels, and front and back cockpit walls formed into transverse reinforcing ribs. The simple easily moulded structure is very stable against lateral tipping, whereas conventional kayaks and canoes are very unstable laterally. The dual pointed hull also provides directional stability for straight line padding even by novices. Conventional kayaks or canoes are very difficult to master by novices who often paddle in a zig zig pattern and require a significant degree of skill to paddle in a relatively straight line. The sharp dual hulls reduce drag due to reduced wetted surface. The dual hull kayak is so stable laterally that it can be used as a diving platform and can be remounted by a swimmer from the water without tipping or overturning. Conventional kayaks or canoes require expert level skill to accomplish the same re-entry task. If desired the kayak can be inverted and the tunnel shape of the bottom wall provides a rigid water slide for children, water rescue cradle or can be adapted for use as a suntanning lounge. The kayak body includes bow eyelets and is rigid enough to be safely towed with a tow rope behind a motor boat.

TECHNICAL FIELD 
The invention is directed to a sit on top dual hull kayak of one piece 
hollow molded construction providing superior lateral stability, straight 
line padding, minimal wetted surface and self draining recessed open 
cockpit. 
BACKGROUND OF THE ART 
Human powered watercraft have historically been used for transport and 
hunting, however, modern uses more likely involve sport and recreation. 
The traditional design of canoes and kayaks is often repeated in modern 
forms of fiber glass or molded plastic. The traditional design involves a 
single hull which has the advantage of being quickly maneuverable. 
Especially in the case of sport kayaking, it is important that the kayak 
can be rotated about a vertical axis very rapidly to enable the paddler to 
maneuver around rocks and other obstacles. Traditional designs of canoes 
also include a single hull originally for transporting cargo, although in 
modern use, canoes are generally used for recreational activities. In both 
cases, the traditional design of kayaks and canoes is relatively unstable 
and the passengers must maintain balanced to avoid unintentionally tipping 
themselves into the water. 
Another disadvantage of traditional canoe and kayak designs is the need to 
develop a technique for paddling in order to direct the watercraft in a 
relatively straight line. Novices and children often have great difficulty 
in propelling canoes and kayaks in a straight line and tend to zigzag 
across the surface of the water as they switch paddling from one side of 
the watercraft to the other. 
While kayaks are generally smaller in size than canoes and produce as 
little wetted surface as possible, traditional canoe designs present a 
relatively large hull and develop significant water resistance or drag. 
A further disadvantage of kayaks and canoes of traditional design is the 
inability of persons to re-enter the canoe or kayak after entering the 
water. In the case of the kayak, it takes great strength and practice to 
move from an overturned position to an upright position after the kayak 
tips. This is a technique practiced by expert kayakers and in general, 
novices and inexperienced paddlers have great difficulty in re-righting 
the kayak. 
In the case of canoes, they generally include a buoyant float at both ends 
of the canoe to prevent it from sinking. Once a canoe has overturned and 
the passengers are floating in the water, it is very difficult to re-right 
the canoe and enter the canoe without tipping it over again. There are 
techniques for doing this especially when two persons are involved and can 
balance each other's weight, however, this is a very difficult maneuver 
beyond the ability of novices and children. 
Traditional designs of kayaks and canoes remain popular because they are 
relatively inexpensive and simple to build and maintain. Despite the 
disadvantages of lateral instability and paddling difficulty, they remain 
popular mainly due to their simplicity of operation and well known methods 
of use. In contrast for example, motorized boats require fuel, generate 
noise and demand a higher level of care and attention to operate. 
Watercraft propelled by human arm or leg power are popular in that they 
are useable by a wide variety of people and are environmentally friendly. 
Despite the above preferences for human powered watercraft, there are 
significant disadvantages in that kayaks and canoes of traditional design 
are extremely difficult to balance and quite often passengers are tipped 
over into the water unexpectedly. Even persons who know how to swim well 
are required to wear lifejackets due to the possibility of unexpected 
tipping and injury as the passenger collides with the boat or rocks, etc. 
in the water. The single hull design of kayaks and canoes enables the 
passenger to rotate and maneuver the personal watercraft very easily, 
however, this also results in a disadvantage where it requires significant 
skill and practice to propel a kayak or canoe in a relatively straight 
line. Long kayaks, due to the difficulty in turning them, often include 
foot pedals with cables to control a rear rudder. 
The prior art is replete with various designs of human powered watercraft 
reflecting the popularity of this form of transport and recreation. 
Especially in recent times kayaking and white water rafting are becoming 
more popular as an adventure recreational activity and there is a desire 
to produce safe and practical new designs. Of particular interest are 
plastic or fiberglass molded bodies. These have the advantage of superior 
buoyancy due to an enclosed air filled cavity, ease of repair and the 
ability to use mass produced molding techniques common to the plastics 
industry. 
Typical hull shapes include a generally semi-circular hull, rectangular 
hull and catamaran dual hull shapes. While a semi-circular hull has a 
comparatively moderate draft and drag, it has low stability. A rectangular 
shaped hull with the same bouyancy has greater stability and less draft, 
however, the wetted surface is higher resulting in higher drag. A dual 
hull catamaran concentrates the bouyancy and weight in the lateral hull 
areas resulting in relatively high stability with low drag due to the 
smaller wetted surface. The draft of a catamran hull is relatively high 
due to the pointed dual hulls. 
A design of a molded kayak watercraft is shown in U.S. Design Pat. No. 
341,351 to Arcouette. The Arcouette design includes a molded plastic body 
generally of the shape of traditional kayak but with an open cockpit. The 
Arcouette design includes a rear keel which projects into the water and 
impedes rapid rotation. The whole shape of the Arcouette is a traditional 
rounded single hull with a slightly concave mid bottom portion. This 
single hull, as in the case of traditional canoes, presents a relatively 
large wetted surface and results in increased drag and water resistance. 
Although the hull shape is relatively wide, the smooth rounded shape 
results in a boat which is easily tipped laterally as in the case of 
traditional kayak and canoe designs. 
It is well known that superior lateral stability is obtained by a catamaran 
design or dual hull. Also, included in this art are watercraft which 
include outrigger floats to increase lateral stability and prevent 
unintentional tipping. For example, U.S. Pat. No. 5,649,498 to Zigurs and 
U.S. Pat. No. 5,189,974 to Masters present two dual hull kayaks or kayak 
catamarans to increase lateral stability and impede overturning. As in a 
traditional catamaran, these designs involve two parallel boat hulls tied 
together with an upper flexible platform or braces. Such designs are 
fairly large and are meant to be operated by two or more persons. They are 
large and heavy and may require a lifting apparatus or dismantling prior 
to transport. 
U.S. Pat. No. 3,150,386 to Bastien provides a kayak watercraft with 
removable outriggers and floats to improve lateral stability. This type of 
design does nothing however, to enable the user to paddle in a straight 
line but merely provides some resistance to overturning at the cost of 
increased drag when the outriggers contact the water surface. This type of 
kayak is clearly unsuitable for white water, however, may be suitable for 
recreational use on relatively calm waters. The increased weight due to 
the outriggers and complicated assembly severely restrict commercial 
viability. 
Examples of dual hull multi-person catamarans are common. Examples are 
provided in U.S. Pat. No. 2,918,031 to Gunderson which provides a common 
motor boat with a catamaran style hull. U.S. Pat. No. 2,666,406 to Babcock 
describes a dual hull catamaran speed boat with a conventional two hull 
base spanned by a platform bridge to support the passengers. Between the 
dual hull is a tunnel which in the case of a speed boat, has the advantage 
of compressing air and lifting the speed boat to plane on the water 
surface. Of course, all catamarans due to the buoyant mass on the 
laterally outward areas of the hull, substantially increase lateral 
stability against tipping. Motor boats and sail boats which include a 
catamaran hull also have superior straight line directional stability 
compared to traditional hulls, however, at the cost of decreased 
maneuverability. 
It is an object of the present invention to combine the advantageous of a 
catamaran hull with a single molded plastic or fiberglass personal 
watercraft application. 
It is a particular object of the invention to enhance the enjoyment of 
traditional kayak and canoe personal watercraft with improved directional 
and lateral tipping stability of a catamaran design. 
It is a further object of the invention to utilize the conventional methods 
known and understood widely in respect of hollow molded plastic boats to 
produce a unique double hull kayak in a cost effective and efficient 
manner. 
It is a further object of the invention to produce a hull with reduced 
wetted surface and resulting drag. 
DISCLOSURE OF THE INVENTION 
The invention provides a dual hull kayak, with a one piece elongate moulded 
body of a continuous outer membrane enclosing an internal air filled 
cavity. The kayak body has two lateral side walls and a concave bottom 
wall joined laterally with a bottom edge of each side wall to define two 
laterally spaced apart parallel pontoons each with a downwardly pointed 
keel. The pontoons support the central portion of the kayak or the bridge 
platform above the water surface. 
The top wall of the kayak body is joined laterally with a top edge of each 
side wall, to complete the hollow body. The top wall together with the 
bottom wall define a bridge platform spanning a central longitudinal 
tunnel between the pontoons. 
The top wall has a recessed open cockpit with a self-draining floor, side 
gunnels, and front and back cockpit walls formed into transverse 
reinforcing ribs. The sharp dual hulls reduce drag due to a reduced wetted 
surface. The hollow body is very light and the passenger is supported in a 
recessed self draining open cockpit on a raised bridge platform above the 
water surface. 
The simple easily moulded structure is very stable against lateral tipping, 
whereas conventional kayaks and canoes are very unstable laterally. The 
dual pointed hull also provides excellent directional stability for 
straight line padding even by novices. Conventional kayaks or canoes are 
very difficult to master by novices who often paddle in a zig zig pattern 
and require a significant degree of skill to paddle in a relatively 
straight line. 
The dual hull kayak is so stable laterally that it can be used as a diving 
platform and can be remounted by a swimmer from the water without tipping 
or overturning. Conventional kayaks or canoes require expert level skill 
to accomplish the same re-entry task. An overturned canoe or kayak of 
traditional design can represent a life threatening danger to children or 
novice users even if lifejackets are worn due to the risk of head impact 
injury and hypothermia. 
The stable dual hull design of the invention substantially reduces the risk 
of tipping, and enables users to easily re-enter the kayak from the water. 
These features increase the safety of use and increase overall enjoyment 
of the boating experience. 
If desired the kayak can be inverted and the tunnel shape of the bottom 
wall provides a rigid water slide for children or water rescue cradle. The 
kayak body includes bow eyelets and is rigid enough to be safely towed 
with a tow rope behind a motor boat. 
Further details of the invention and its advantages will be apparent from 
the detailed description and drawings included below.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
With reference to FIG. 1, the invention provides a simple design for a dual 
hull kayak having a one piece elongate molded body of a continuous outer 
plastic or fiberglass membrane enclosing an internal air-filled cavity. 
The internal air-filled cavity provides excellent buoyancy. The smooth 
molded exterior reduces water resistance. Mass production in various 
colours provides efficient low cost production using known molding 
technology. 
The details of construction are illustrated in sectional FIGS. 4 and 5. The 
dual hull kayak body has two lateral side walls 1 and a concave bottom 
wall 2. The bottom wall 2 is laterally joined with the bottom edge of each 
side wall 1 to define to laterally spaced apart parallel pontoons 3 which 
each enclose a volume of air for buoyancy and lateral stability. Each 
pontoon 3 has a downwardly pointed keel 4 and the pontoons 3 support the 
top of the concave bottom wall 24 above the water line. 
The depth of the submerged keel 4 and the semi-cylindrical tunnel formed by 
the concave bottom wall 2 improve directional stability and enable even a 
novice paddler to propel the dual hull kayak in a straight direction. The 
depth of the keel 4 also provides resistance against lateral drift when 
encountering lateral winds. As clear from FIG. 5, the relatively large 
volume of air contained within each pontoon 3 provides excellent lateral 
stability and buoyant force. This buoyant force in the pontoons 3 resists 
tipping and enables a user to re-enter the dual hull kayak from the water 
surface without overturning the kayak. 
As shown in FIGS. 4 and 5, the kayak includes a top wall 5 joined on its 
lateral edges with a top edge of each side wall 1. The top wall 5 includes 
an open cockpit 6 with a floor 7 and gunnels 8. The front cockpit wall 9 
is shown in FIG. 4 as an upwardly extending reinforcing rib 9 and the back 
cockpit wall 10 also comprises a transverse reinforcing rib 10 upwardly 
extending from the top wall 5 in the shape of a seat backrest 10. 
As indicated in FIG. 5, the top wall 5 including cockpit 6, combined with 
the concave bottom wall 5 defines a bridge platform spanning a central 
longitudinal tunnel between the pontoons 3. The bridge platform and 
transverse ribs 9, 10 provide stable support and join the pontoons 3 
together into an integral body structure. 
The one piece molded body of the kayak provides a continuous outer membrane 
comprised of the bottom wall 2, side walls 1 and top wall 5 to enclose and 
contain a relatively large volume of air within an airtight internal 
cavity. The bulk of the air is contained within the pontoons 3 in order to 
provide a buoyant force laterally extended outwardly from the center of 
gravity of the kayak and seated passenger. As a result, the invention 
provides a kayak with superior lateral stability in comparison with 
conventional kayaks and canoes. As well the one piece molded construction 
utilizes conventional technology for molding and manufacturing resulting 
in significant cost efficiencies in production. 
Several further details of the design shown provide significant 
advantageous as follows. In order to accommodate vertical stacking of like 
kayaks, the illustrated embodiment shows an upper edge 11 of the seatback 
rest 10 with a profile that mates the bottom wall tunnel 2. During 
manufacture shipping or storage, the vertical stacking of the kayaks will 
reduce overall height allowing three or four kayaks to be nested and 
stacked upon each other. 
Also, as indicated in the drawings, the back rib 10 or seat back 10 
includes a central paddle storage slot 12. In the embodiments shown, the 
front rib 9 also includes a central paddle storage slot 13. 
With reference to FIGS. 1 and 4 particularly, the cockpit floor 7 includes 
a drain hole 14 communicating with the tunnel defined by concave bottom 
wall 2. The cockpit floor 7 includes a recessed drainage channel 15 which 
is inclined towards and communicates with the drain hole 14. The cockpit 
floor 7 also includes recessed transversed foot rest channels 16 which in 
the embodiment shown also feed into the recessed drain channel 15 and 
provide recesses into which the user may insert heels to adopt a 
comfortable seated position. 
As shown in FIGS. 1 and 5, at least one cockpit gunnel 8 includes a 
longitudinal paddle storage groove 17. A conventional kayak paddle 
includes a long cylindrical handle with offset paddles at both ends. The 
paddle storage groove 17 is concave and includes two hooks 18 to assist in 
retaining the paddle handle in the groove 17 while the user is seated 
within the cockpit 6. 
With reference to FIGS. 1, 2 and 3, the kayak includes two bow eyelet 
handles 20 which provide an elongate opening large enough for an adult 
hand to pass through between the top and bottom walls 5 and 2. The eyelets 
20 also enable a rope to be tied to the kayak securing the kayak to a 
motor boat or dock structure. 
Also included, as shown in FIGS. 3 and 2, is a stern handle 21 which in the 
embodiments shown comprises a transverse rod which spans between the 
pontoons 3 rearward of the seatback 10. The top wall 5 and bottom wall 2 
form a rear platform 22 which can be used for storage and provides a 
platform to assist the user in re-entering the kayak by grasping the stem 
handle 21. The platform 22 also increases structural strength of the 
kayak. The bow 23 is moderately upswept to reduce the possibility of 
submarining the bow 23 when riding or surfing waves. 
Although the above description and accompanying drawings relate to a 
specific preferred embodiment as presently contemplated by the inventor, 
it will be understood that the invention in its broad aspect includes 
mechanical and functional equivalents of the elements described and 
illustrated.