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The waterline length refers to the part of the kayak hull that meets the water’s surface. If the kayak has a long sloping bow and/or stern, its waterline length will be shorter than its overall length. Waterline length is a critical element in establishing the maximum speed of the kayak. The greater the waterline length, the greater its potential for a top-end speed.Kayaks are displacement hulls—that is, they move through the water rather than skim across its surface as a planing boat does. The top speed of a displacement hull is determined by the waves it creates. At maximum speed, the hull creates a wave at the bow and at the stern with a trough in the middle. Since a wave of a given distance between crests travels at a particular speed, the hull can only be as fast as the wave it creates, known as the wave of translation. Increases in speed are possible but only with dramatic increases in the energy applied to propelling the hull forward.Waterline beam: This refers to the maximum width of the hull area that meets the water’s surface. Since most kayaks have rounded or sloped sides, the waterline beam is usually less than the overall maximum beam. The waterline beam also has an impact on the efficiency in converting effort into speed. Narrower beamed boats have less distance to push the water aside and therefore create less resistance to forward motion.The beam also has an impact on stability: The wider the boat, the more stable it will feel when you’re sitting with the kayak on an even keel.Draft: The vertical distance between the surface of the water and the deepest part of the hull.Prismatic Coefficient: The prism refers to a shape that has a cross-section identical to the widest part of the immersed hull and a length equal to the kayak’s waterline length. The prismatic coefficient, or PC, is the ratio of the displacement of the kayak to the volume of the prism. A kayak that displaces 45% of the volume of the prism has a PC of 0.45. The PC is useful as a measurement of how fine or full the ends of the kayak are.A kayak with a high PC has more volume in its ends. This increases the wetted surface, creating more drag from friction between the hull and the water. This is a significant factor in the efficiency of the hull at low speeds. At high speeds, the full ends create a long wave of translation, so a kayak with a higher PC has a potential for a higher top speed (for the application of a given amount of effort).

In 1986, Sea Kayaker magazine established a standard for reviewing kayaks that has never been equaled. The reviews included measuring the hull to provide a basis for an objective assessment of performance characteristics. The number crunching may be confusing for many readers, but it is worth making an effort to understand the various terms involved.The information presented here on Sea Kayaker’s web site is intended to augment the information provided by the reviews published in Sea Kayaker magazine. Here you’ll find a list of the terms used in our numerical assessments of the kayaks we review. We also have supplement for each kayak review (starting with those published in the June 2004 issue) that includes tables of measurements, computer-calculated hydrostatics and metric conversions.For the full kayak reviews, please visit the Sea Kayaker store’s Back Issues area to order specific issues of Sea Kayaker.

MEASUREMENTS
(These are taken for each kayak reviewed in Sea Kayaker.)Length overall: The length of the kayak from bow to stern, not including the rudder if present.Beam: The maximum width of the kayak.Volume: The space occupied by the entire kayak including the cockpit’s interior space as if closed off by a cockpit cover.Cockpit size: The width and length measured inside.Cockpit heights: Measured to the inside, at the lower edge of the coaming.Height of the seat: Measured at the lowest point. The height of the seat is a significant factor in the kayak’s stability. With a foam seat or a foam pad, a bit of compression is allowed for.Weight: The weight of the kayak as measured by Sea Kayaker. The weights we list often differ from the “target” weights given by the manufacturer because of variations in the construction of individual kayaks.

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Performed correctly:
1. Start by placing your forearms and toes on the ground.
2. Push off the ground, resting on your toes and elbows. Ensure your back is straight, and parallel to the floor.
3. Hold this position for 30 – 60 seconds, keeping your back straight and parallel to the floor.
4. Take a 1 minute break, and repeat 3-4 times.

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