How do surfboards work

A surfboard can grip the wave because when some of the water moving up the wave face hits the bottom of the surfboard it flows around the soft, inside rail of the board.

In the vast majority of cases, this is what holds your board into the wave, not your fins as most people think more on that another time. As far as physics is concerned, water is actually very sticky, so when it flows along a surface it will follow the curves, and this attraction is what gives the board grip.

A great example of this is to hold a spoon under a running faucet — if you hold it upside down the water flows along the curved surface and actually sucks the spoon into the waterflow. In the case of a rounded object in water i. This means that thicker, softer rails, riding on smaller, slower waves will have much more hold in the wave face than a thin rail at high speeds. Now, while some of the water that flows up the wave, wraps around the inside rail and holds the board in the wave face, the rest, the majority of it in fact, hits the bottom of your surfboard, and is directed along the length of your surfboard to exit out through the tail.

Concave or channeled bottom contours are designed to redirect as much water as possible along the board and out past the fins, whilst convex bottoms shed water out towards the rails so are slower down the line, but facilitate easier turning as they transition from rail to rail more readily. The importance to generating speed of redirecting as much flow as possible along the length of your surfboard rather than shedding it off your rails is why locking in your inside rail and taking a high line is such an important habit to form.

The illustration above shows a cross section of a wave with surfboards in three possible scenarios. The first surfboard is in trim on a highline across the wave, and is creating as much lift and thrust as possible because the bottom of the board is perpendicular to the flow of water up the face of the wave.

Place a support under your center of mass and you can rest in balance. Buoyancy This is an upward force created by the still water pushing up on the board and is known as a hydrostatic force a force exerted by a liquid at rest.

The water exerts its force on every part of the board that it touches, yet the buoyant force acts as if it were pushing up on the board just at the center of buoyancy, which is the center of mass of the water displaced by the board. When Archimedes, a mathematician of ancient Greece, discovered the mathematics of buoyancy while bathing, he became so excited that he jumped out of the bath and ran naked through the streets shouting "Eureka!

No acceleration means no net force. Note, however, that you can be moving at a constant velocity even when the acceleration is zero; acceleration produces changes in velocity. Balance The most important thing for a beginning surfer to learn about is balance. If the downward force of gravity and the upward force of buoyancy are in line, they add to zero and things are stable. Slide backward on your board, though, and the downward force of gravity moves behind the upward buoyant force.

When these two opposing forces get out of line, the board will experience a torque, or twisting force. When you move backward, the torque twists the board so that the nose begins to go up and the tail begins to go down.

The more area of the surfboard is in contact with the water, the more friction drag will exist and, the slower the surfboard will be; 3. The greater the rocker, the greater the drag force; 4. The greater the velocity or speed, the greater the lift; 5. Bottom shapes with concaves and channels produce an upward force or lift; 6. Wave faces flow and move in orbital fashion and create lift; The Variables of Surfboard Shaping 1. More surfboard area means more planing potential, less sinking and bogging; 2.

The elements of a template are total and half-length, nose shape and width, outline curve, location of the wide point relative to the center, width, tail shape , and width; 3. More curve in the outline means easier turning; 4. Longer boards provide faster paddling, greater risk of nose-diving, and more effort required in turning; 5. Wider surfboards plane better in dead or slow wave spots; 6. Wider boards turn easier at slow speeds but have poorer rail-to-rail transitions; 7. Wider templates have poor hold in the wave face at high speeds on the rail; 8.

Wider surfboards are stiffer; 9. Rounder noses provide more lift and buoyancy but create form drag; Pointed noses suffer less "baseball bat effect" and are easier to hold in rail turns; Pintail surfboards have an extremely low surface area and high holding power; Square tail surfboards have high planing area and looseness; Thicker boards have greater buoyancy and have easier paddling; More thickness in the middle of the board means difficulty to lean on the rail; Thicker tails are looser at slow speeds; More rocker means easier turning, harder paddling, and slow speeds in a straight line; More rocker means less nose-diving; Vee bottoms create less lift and are slower than flat bottoms in neutral position; Vee bottoms allow for easier rail-to-rail transitions; Single concaves create more lift and speed and are harder to turn; Double concaves keep the rails free and are looser and faster; Harder rails plane very well but have a stiff, less smooth response to turning; Soft rails are slower but provide better hold in subtle turns; Tucked under edge rails balance the characteristics of hard rails and soft rails; Greater fin area means better holding power; Streamlined fin foils have higher holding power; Asymmetrical side fin foils provide better directional holding power; Greater fin height creates greater resistance to rail-to-rail turning; Further forward fin placement will loosen up the board;