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Up a creek without a paddle? Fluid dynamics can help!

Lose your paddle whilst out canoeing or paddleboarding and you would probably feel a bit stuck.

But gunwale bobbing – essentially bouncing your craft at one end with a particular rhythm – can propel your canoe or paddleboard through the water, at speeds of up to a metre per second.

Professor Neufeld gunwale bobbing on the River Cam

Scientists, including Trinity Fellow Professor Jerome Neufeld, have uncovered the science behind gunwale (pronounced gunnel) bobbing in the first hydrodynamic model of this method of forward propulsion.

Their research offers the possibility of a competitive edge for serious canoeists and perhaps rowers – and some fun on the water for the rest of us.

It was during just such a moment – on a lakeside holiday north of Toronto – that Professor Neufeld was inspired to investigate the fluid dynamics of gunwale bobbing.

With my family were playing about on boards and canoes and it turns out if you jump on the back of paddleboard or a canoe you generate your own wave field and if you jump at the right frequency you can drive your own forward velocity.

Holiday fun

Wave energy we are familiar with, whether it’s tidal power, coastal erosion or leisure pursuits on the sea. But wave fields can also be created on flat bodies of water such as rivers and lakes.

You can see this in the wakes created by ducks, motorised boats and canoes, explains Professor Neufeld.

That wave field carries energy from the swimming duck, or the motorised boat or canoe off into the distance. Some of that energy you can use to drive your own forward velocity.

He explains how a wave fields work: either bobbing up and down on a canoe or pitching it side to side would generate a symmetric wave field that radiates energy, but it wouldn’t drive you forward.

What you really need is both – by combining a heaving motion and a pitching motion you can arrange to push down on the slope of your last wave and surf it forward at metre per second velocity.

You can watch Professor Neufeld without a paddle gunwale bobbing his canoe down the Cam in a new short film. Of course this isn’t normal practice for canoeists, who are not advised to give up their paddles.

But as they paddle they do generate their own wave.

So the question is for Olympic canoeists, for rowers, are they able to harness that energy in the wave they are shedding behind them to gain 1 – 3 per cent extra efficiency to go that little bit faster?

There is a serious side to the research by Drs Graham Benham, Olivier Devauchelle, and Professor Stephen Morris, which is published in Physical Review Fluids 2022: it tells us how to use the energy already present in water waves.

Professor Neufeld says:

Of course, the research also points to a fun way to observe and interact with the fluid dynamics of everyday life, and perhaps cool down while enjoying the science of water waves.

Professor Jerome Neufeld

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