Estimating Wave Height for Canoes and Kayaks

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Grand Marais, MN straddles the boundary between two worlds. To the north, canoeists explore the many lakes and portages of the Boundary Waters Canoe Area Wilderness and to the south, kayakers navigate the big ocean-like water of Lake Superior. If one adventurer from each crowd paddled in the same water and waves, expect to hear different reports of how big the waves were later in the pub. In my experience, I’ve found most paddlers have no idea how to report the size of a wave, and this comes from a lack of education and a reference point.

Measuring Wave Size

The measurement of a wave is typically given in height and period. The height of the wave is measured from the bottom of the trough to the top of the crest, and the period of the wave is the length of time it take for the next crest to pass a point that the previous crest just passed. The period could also be defined as the length of the wave in seconds. Paddlers should give wave size in both to accurately describe the difficulty or thrill of paddling that sea state.

One of the common errors paddlers commit when telling the size of the wave is to use a length measurement of the period of the waves. I’ve heard paddlers describe the waves as huge, because they were x feet. When questioning them further, what they’re describing is the length of the wave along the side of the kayak or canoe. This provides an easy reference, because if the boat is 18′ and the wave runs half-way along the boat, it is 9′ long. The problem with this measurement is that the wave height could vary significantly, and a larger (higher) wave will mean a steeper wave for the same length. Paddling in 1′ waves that are 9′ long is a much different experience than paddling in 3′ waves that are 9′ long. Generally speaking for the same wave height, shorter periods are harder to paddle in.

Kayaker surfing on a 1' wind wave. — Kayaker surfing on a 1′ wind wave.

The other most common error is in estimating the wave height. Most of the time, paddlers over estimate the wave height while they are in the boat. In the excellent Sea Kayak: A Manual for Intermediate and Advanced Sea Kayakers, Gordon Brown lists a nice standard rule for sea kayakers and canoeists, “If you have a distant horizon the waves are less than one metere. If your horizon is the crest of the wave immediately in front of you, the waves are over a metere.”

Using this rule, you’ll know that if you can see the horizon, the waves were less than 3′. If you can’t, they were over 3′. To refine the rule further, when under 3′ if you lose sight of just your partner’s boat when they’re in the trough of the wave, then the waves are 1′. If you lose sight of your partner’s shoulders and just their head is visible above the crests of the waves, then the waves are 2′.

Estimating wave height on overhead waves is much harder. To get a reference sit on the floor in the kitchen and look to the top of the refrigerator. Most refrigerators are 6′ tall, so if the wave looks like a refrigerator coming at you, then it’s probably 6′ tall.

An Easy Reference

I suggest that when talking about the size of the waves, paddlers should use references like surfers do. Surfers often say ‘waist high’, ‘head high’, ‘shoulder high’ and ‘over head.’ In a paddler’s case, these terms are ‘shoulder high’, ‘over head’, and ‘double overhead.’ For most people these terms will result in a more accurate description of the waves that they were in.