Following the leader could help swimmers race to victory

Triathlon swimmers

Researchers at the University of Strathclyde have found that following the leader in a swimming race could save competitors up to 63 per cent of wave drag.

Investigators analysing the forces affecting competitive swimmers found that like ducklings who swim in formation and benefit from the waves generated by the leading mother duck, swimmers ‘ride the waves’ in the same way.

The study ‘Steady hydrodynamic interaction between human swimmers’ calculated the wave drag of a lone swimmer in open water, and again in the wake of one or two leading swimmers.

They found that by swimming closely to the leaders, a swimmer could save energy and that by following two side-by-side leaders, could double that reduction in wave drag.

Mother duck

Ducklings following mother duck

Lead author of the research paper, Dr Zhiming Yuan, said: “It’s the phenomenon you see in the swimming formation of ducklings when a group follow their mother duck in a single-file line or V-shape.

We believe that competitive swimmers are very sensitive to the drag, and they are able to position themselves in the drag-reduction positions behind a lead swimmer, thus conserving energy.

“A lead swimmer could generate waves - so-called Kelvin waves behind them – which have crests and troughs.

“When a followers head and shoulders are in the trough, while the hip and legs are in the crest, they are surfing - or riding - the waves.

“In this wave-riding, the waves could push them moving forward and therefore saving energy, so the follower could use the waves generated by the leader as a propulsion force to save energy. “

Swimmers with less experience in strategy, or who are less sensitive to the drag change, may actually make it harder for themselves by inadvertently positioning themselves in the drag-increase region behind a lead swimmer where they have to expend more energy.

Improve performance

In competitive swimming where victory can be measured in seconds or even in hundredths of seconds, reducing the drag could improve performance.

Dr Yuan, a lecturer of Hydrodynamics in the Naval Architecture, Ocean and Marine Engineering Department at Strathclyde, says that the best position is determined by both the swimming speed and whether it’s open water or a swimming pool.

He added: “In an open water race, the best position is right behind the leader and the drafter can get the benefit from the leader up to a distance of 60cm. In long course racing, the strategy of riding waves could have significant impact on swimmers.

“When the competition is in a swimming pool of 10 lanes separated by ropes, the benefit still exists but the drafter can only receive about 30 per cent of the benefit, compared to open water, as the rope will absorb most of the wave energy.

“But if the swimmers are well trained, they can follow the leaders in the right position to save energy at the beginning and in the last few seconds, could overtake the leader to win.

“So we believe the swimmers could win the race in a ‘smart’ way.”