Ocean waves are mesmerizing to watch and listen to; and on days when waves are at their mightiest, they provide us with one of the planet’s best shows. If you’re prone to seasickness, even gently rolling swells can cause you to wish you had chosen a different pastime; if you are an adventure seeking surfer, then you might drop everything just for the chance to get in one perfect ride. The motion of the ocean is endless and always changing, and the more time you spend watching and learning, the better your chances of choosing the perfect time to dive.
Waves, Wind and You
Waves are formed when the wind pushes against the water’s surface while the water’s tension and the pull of the earth’s gravity work together to pull the water back into its place. There are three factors that determine how large waves grow to be; they include wind speed, how long the wind blows uninterrupted, and the distance of open water across which the wind blows, which is also known as the Fetch. Strong, steady winds create waves that grow in size; the greater waves grow to be, and the longer the wind blows, the more intense wave activity becomes, and the less you might enjoy diving, due to surge that can inhibit visibility and cause you to expend a great amount of energy.
Waves all have crests, troughs, and wavelengths, and their height is determined by the distance from the bottom of the trough to the tip of the crest. Wave periods, which are measured in seconds, are determined by the amount of time it takes an entire wave to pass a set point, from one crest to another. So, for example, a period of five feet at twenty seconds indicates that every twenty seconds, another wave crest five feet high will pass a set point.
As waves move away from the wind, they begin to take on an orderly motion, forming swells that carry energy along while leaving the water in the water column behind. Water molecules orbit in a clockwise oval shape as swell and waves move up and forward; so long as there is no current, you’ll do the same as the molecules that surround you – simply bob up and down, and maybe move from side to side a bit while floating on the surface.
As you head into deeper water, the motion of the waves can be felt less, until you are about half as deep as the waves are long. If you have ever ducked beneath a swell or breaker to wait for it to pass, then you have experienced this phenomenon. If surface swells are twenty feet long, you’ll no longer be able to feel them once you reach a depth of ten feet.
It is important to remember that waves are not as orderly as artists often depict them to be; next time you are flying over water or looking down onto the water’s surface from a high cliff, notice the way that waves come in from different directions, at different speeds; and notice that they often vary in height. Oceanographers have spent vast amounts of time studying this phenomenon, as well as studying rogue waves, and have calculated that one of every 23 waves will be twice as high as the average height of waves surrounding it, with one in 1,175 being over three times the average height, and one in 300,000 coming in at a stunning four times the average height, meaning that some of the largest waves in the world are well over 100 feet high. Luckily though, such monsters are rare.
Diving when waves are small and regularly sized will permit you to enjoy a fairly predictable dive, so long as you are at a site where current does not present much of a challenge. The more you dive, the easier understanding waves becomes – just one more reason to enjoy diving on a regular basis.
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Things I've never considered b4.