How to Understand Wave Shape and Tides for Surfing

Surfing is glorious fun, but to tame the beast one must understand both wave shape and tides significantly for safety reasons, among other things.

Wave shape can vary drastically from day to day at the same spot. Swell size, speed, and direction; tides; currents; curve and shape of the shore; and kelp and wind conditions all affect shape. Every surf spot has a unique set of variables that affect wave shape.

Areas with long, gradual rises from deep to shallow water usually result in what's known as a peeling wave. A peeling wave breaks easily down the face or front side of the wave, spilling or toppling over. It appears to crumble or peel along its length and is generally the most forgiving type of wave.

Breaks with a more abrupt change from deep to shallow water usually result in what's called a tubing wave. A tubing wave breaks from top to bottom as the swell peaks more quickly and pitches the crest down the wave face. This type of wave creates a hollow tube or barrel section. The term hollow is used to describe this concave and steep wave face shape. The term sucky is also used to describe wave conditions that are hollow and breaking in shallow water. And when waves break all at once along their entire face, they are referred to as closed out.

Tides are related to the moon's cycles and occur in all bodies of water, but they're most prominent along the coast. In most places the tide rises and falls twice a day. The maximum and minimum levels of the rise and fall are called high and low tide, respectively. It takes roughly six hours for rising water to reach high tide and approximately another six to reach low tide again. This sequence is called the tidal cycle and is repeated every twelve hours and twenty-five minutes. The amount of change in the water level during the cycle is known as the tidal range. During the first and last quarter of the moon's cycle, called a neap tide, there is minimal difference between high and low tides. When there's a full or new moon cycle, known as spring tide, there's a bigger difference between high and low tides.

Most surf shops provide a book listing the times that high and low tide will occur each day for the entire year. This can help you plan your surfing sessions, as changes in water depth at the points where waves break can significantly alter the shape of the wave.