Up a creek without paddle? Researchers suggest 'gunwale bobbing'

If you stand up in a canoe, you'll most likely end up in the water. You can jump up and down on the sides of the canoe to get to the drink. You can move yourself along by as much as one meter per second if you get the balance right.

In bobbing, a canoeist stands on the sides of the canoe and jumps up and down, moving the boat forward by surfing the waves.

After an initial period of instability before finding its rhythm, the canoe achieved a cruising speed that satisfied a balance between the thrust generated from pushing downwards into the surface of the waves and the resistance caused by drag On stand-up paddle boards, the technique can be used.

Stephen Morris, a professor in the department of physics in the Faculty of Arts & Science and co-author of the study, says that people have enjoyed gunwale bobbing for a long time, but no one has ever explained how it works. We have figured out how balance can be sustained by using long-standing linear wave and oscillation theories.

The University of Cambridge, Oxford University, and the University of Paris collaborated with Morris to create a theoretical model to describe the wave field produced. They compared the data from the gunwale bobber crossing the body of water in a canoe with waves created when its two ends pitch up and down.

When a canoeist's body pitches forward and backward in equal measure, the waves generated cause the vessel to oscillate back and forth with no net motion. The vehicle gains a net thrust when a person jumps up and down out of phase with one end of the vessel.

The technique could propel a canoe at a steady speed of up to one meter per second, comparable to the speeds observed for gunwale bobbing with real canoes.

Understanding gunwale bobbing could be useful in water sports. It might be possible to maximize rowing strokes so the boat interacts with the waves it creates in a way that pushes it forward.

More information: Graham P. Benham et al, Gunwale bobbing, Physical Review Fluids (2022). DOI: 10.1103/PhysRevFluids.7.074804