Canoe/Kayak: Hydrodynamics

The canoe and the kayak are both ancient forms of watercraft that have been adapted for a variety of purposes in modern times. In prehistoric times, both canoes and kayaks were used in cultures throughout the world for both hunting and transportation; the primary modern adaptations for both versions are recreational and athletic pursuits.

Until recent times, kayaking was regarded as a subset of canoeing; today kayak racing and canoe racing are separate athletic disciplines, each with its own status at international and Olympic competitions. The chief reasons for treating the two sports as one arose from the similarities in basic design and means of propulsion. While the fundamental concept of an open water craft propelled by human power delivered by paddles is common, the design of each craft, the characteristics of each as it is powered through the water, and the technique in which the paddle is moved through the water differ dramatically between the kayak and the canoe.

Hydrodynamics—the characteristics of any craft as it moves through water—is a branch off of the physical science known as fluid mechanics. Hydrodynamics are contrasted with hydrostatic mechanics, the movements and characteristics of a craft that is stationary in water. A number of variables will be assessed in determining the optimal hydrodynamics of any boat, including the speed and the nature of the water through which the craft will travel, the pressure placed upon the hull, and the purpose for which the craft will be used.

It is a generally held principle of boat hydrodynamics that the speed of a boat will be a function of the amount of power delivered, and the amount of resistance created by the water as the hull of the boat passes through it. It follows that the longer and slimmer the hull of a craft, the generally less pronounced the effect of friction will be. As the weight of the canoe is spread over a greater hull length, the hull will draw less water, and thus the craft will generally be less stable. Hydrodynamic research regarding the most efficient canoe hull designs suggests that 90% of the drag, or friction, on the boat is the water, while the remaining 10% is created by the hull and the paddlers moving through the air above the water.

The sport of canoeing has created different competitions that take place in different conditions; small, very sleek canoes that are used to race on calm, sheltered water (flat-water); canoes that are used for competition in fast-flowing, often obstacle-strewn rivers (whitewater); and long-distance racing involving large crews paddling larger, heavier boats (dragon boats). In sprint canoe racing, the most important hydrodynamic consideration is generating maximum speed. Given the short distances traveled in a race (Olympic canoe races range from 500 m to 2,000 m), and the very calm water in which the hull sits, a long, narrow hull is used and the stability of the craft is a secondary concern.

In whitewater conditions, the primary hydro-dynamic considerations are stability and maneuverability; the paddler is required to both maintain balance while the canoe is subject to strong current and river flow, as well as move quickly to avoid river obstacles such as boulders or other obstructions. For these reasons, a whitewater canoe will be shorter, wider, and more durably constructed than a racing canoe (white-water canoes are usually constructed of Kevlar or a similar synthetic, flexible compound). The shorter axis of a racing canoe makes it easier to turn.

Dragon boat racing and other forms of long-distance canoeing involve competitions that occur in large or open bodies of water, often with boat crews of 20 paddlers. Dragon boats, so named in reference to the origins of the sport in Hong Kong, are much longer and heavier than other canoes, as the stability of the boat is paramount to race success. Dragon boats are usually constructed with a keel, a device extending from the hull running along the axis of the craft. The keel increases the stability of the dragon boat—where a keel would impair the hydrodynamics of both a racing and whitewater canoe, it is essential in a craft that, fully loaded for racing, may bear a weight in excess of 4,000 lb (1,800 kg).

Kayak racing has similar competitive distinctions, each of which affects the desirable hydrodynamics of the kayak. Kayaks are generally longer, narrower, and sleeker in design than canoes by virtue of the position of the paddler in the kayak; this design thus reduces the paddler's center of mass to a point lower than can be achieved in a canoe. Further, the double paddle used by a kayaker is a more inherently stable and efficient method of propulsion, as power is generated in equal amounts on each side of the hull.

The desirable optimum characteristics of a sprint race kayak are similar to those in canoeing: a long, narrow hull with a premium on reduced friction. Whitewater kayaks, sometimes referred to as slalom kayaks, are much shorter, with the primary focus on maneuverability. A whitewater kayak paddled by an expert can be taken through very rough, fast-flowing currents, with the double paddle permitting the hull of the craft to be readily spun in 180° changes of direction where necessary. For longer distances over open water, the sea kayak is utilized. Sea kayaks are built as either one- or two-person crafts, slightly wider and heavier given the prospect of rough waves.

Unlike a canoe, the shape of the kayak hull permits the paddler, with practice, to right the hull from a submerged position. This maneuver is known as the "Eskimo roll." As a comparison, if a canoe becomes submerged or otherwise swamped, it must be emptied or the craft will sink.

Just as there are different hydrodynamic considerations for a canoe or kayak depending upon the nature of competition, related issues arise in determining what shape of paddle should be employed to achieve maximum effect. When the generation of speed is the primary consideration, most canoeists employ a bent shaft paddle, constructed with the blade at an angle to the shaft that will keep the blade perpendicular to the water and maximize power. Whitewater racers use paddles that have a shorter, squarer blade, as the nature of the sport will require the paddler to take numerous quick strokes. Distance canoeists often employ paddles with longer, narrower blades, to balance the desire to generate power and the fact that the paddler may make thousands of repetitive strokes.

Kayak paddles require similar considerations. The kayak paddle carries the additional consideration of its aerodynamic properties, given that the paddle is above the head of the kayaker for a portion of every stroke, exposing the blade to the flow of air created by the kayak, as well as any wind. Kayak paddles are constructed with this consideration in mind. They have a thin handle and thin blades to make the paddle more aerodynamically efficient.

see also Canoe/Kayak; Environmental conditions and training; Rowing: Hydrodynamics.