Drafting Off The Bow Wave

Drafting Off The Bow Wave

Courtesy of WOWSA, Huntington Beach, California.

Captain Tim Johnson explains about bow waves, the waves that form at the bow of a ship when it moves through the water.

A swimmer is a displacement vessel. The bow waves has forward movement and lateral movement. The lateral movement combined with the forward movement vectors the wave to move at an angle related to the direction of the swimmer based on speed, water density, depth, and a few other factors.

The depth, or properly called draft for a boat, will create a better wave. Anyway just like a wave at the beach, the one or two inches that pile up are just not pushed forward, but draw water from in front of them to build up. This causes the slight draw the leading swimmers feel in a pack.

When a swimmer is mid-body is the wake, the spreading of the lead swimmer’s bow wave has moved far enough laterally to be sensed by the trailing swimmer now coming alongside. At some point, the swimmer is perfectly positioned to take maximum advantage of the bow wake. As for the proper term, he’s surfing the wave. If you’ve watched boats, the wave that is launched cannot extend beyond the length of the vessel that creates it. The wave lifts up at the end of the swimmer.

Efficient swimming is when a swimmer cruises in the wave they’ve created. That takes a bit of work to launch the wave and the wall comes much too soon. Swimmers will find it even more efficient swimming if they cruise at the right speed in the wake of the lead swimmer off to the side away from the eddies caused by the kicking. I would venture to guess the lead swimmer’s kick creates swirls; the more swirls, the more drag.

Porpoises surf off the wave of boat’s bow waves because it is easy swimming. Slowing down, they are lifted up and using gravity, they can fall down the front surface. They love speed because their swimming speed is combined with the boat speed; they just have to catch it. I’ve done the same thing with a dinghy surfing off a bow wake and kept up with a much larger boat going faster than my 6 horsepower outboard could possibly propel the dinghy. I’ve also dropped a dinghy’s bow into the water and by staying in the wake bumped the boat speed up twice as fast as usual

Food for thought for those competitive swimmers in the open water.

Copyright © 2014 by World Open Water Swimming Association
Steven Munatones