How to swim during a swimrun race – Be smarter, faster and save energy – Use a pull-cord!

In the early days of swimrun, very few used a pull-cord of any sort, whereas today this equipment has become standard in team swimrun racing. Its main purpose is to help pull the weaker swimmer during the swims but despite this great benefit, some teams still opt for racing without one. This is totally fine, but the options should be weighed carefully, because you might gain several benefits from using a pull-cord.

A standard pull-cord
A standard pull-cord

Ok. So, to use or not to use that is the question?

Well, both are of course ok. If you’re a strong swimmer with good technique and ‘presence’ in the water, e.g. buoyancy position, navigation and adaptation to waves and currents, where your team mate has the same capacity, you probably don’t need it. In this case, the option would be to use a cord only for the sake of helping each other during the running stages. However, if swimming is not the teams strongest discipline, it’s recommended that you go for a pull-cord.

The pull-cord serves many purposes

How to swim, what pull-cord to use and how long it should be, is an ongoing debate in the young swimrun community. It’s also a matter of careful testing because finding a good position behind the lead swimmer when being pulled can be somewhat of an enigma. Excitingly enough, science might just have found a way to give us crucial insight into how a swimmer should position oneself in relation to other swimmers, or a team mate for that matter, in order to swim as efficiently as possible, with and without the use of a pull-cord.

The study in question, Beaumont et al (2017, read more below), set out to evaluate the hydrodynamic drag during the swimmer’s displacement to determine the best position for the second swimmer (draft swimmer). They did this by using advanced mathematics (the Reynolds-averaged Navier–Stokes equations, if you are interested) in a computer model to simulate turbulent flow around a theoretical lead swimmer.

Now, imagine that when swimming you find yourself in a constant state of ‘catching’ a wave, just like in wave surfing. The sense of being pushed down-forward while swimming, gaining extra speed, without really having to fight for it. In aero- and hydrodynamic terms this would mean always catching the moment, the sweet-spot, between the up-force (up-wash) and down-force (down-wash).

Catching the the sweet-spot

Getting this right would mean swimming in a constant down-hill state. And how nice wouldn’t that be, to swim faster AND save energy at the same time! This surfer type wave momentum can also be created behind objects moving across water, first explained by Lord Kelvin, hence the name Kelvin wake pattern. If you find yourself behind, or on the side of the lead swimmer, in a perfect position on an emerging Kelvin wake, you can actually be able to rest while swimming.

Wake patterns in the water

But which position is the best one?

The results from the simulations in the study show that the best position for a second swimmer is found to be directly behind the lead swimmer close to the toes, and very close to the side in current conditions, then with the head positioned somewhere between the lead swimmer’s shoulder and hip. Swimming without a pull-cord or in an individual race trying to positioning oneself like this, will of course put extra pressure on the second swimmer trying to find an optimal way to sync with the rhythm of the lead swimmer. But if one manages to do this, the sweet-spot position will offer great value given the supplied free speed and saved energy. But just as the sweet-spot will grant you this, missing it can also mean swimming ‘up-hill’ which would deplete your energy reserves in no time. So it’s a tricky matter.

Computer simulations

Then what about using a pull-cord to find the sweet-spot?

When adjusted correctly, a pull-cord will help the second swimmer into the sweet-spot position and to remain there without spending too much effort. As the results of the study suggests, the pull-cord should be as short as possible, keeping the second swimmer just behind the toes or to the side of the lead swimmer pending the conditions.

A good way to figure out if you’ve hit the sweet-spot is to swim behind an equally strong swimmer, where keeping up at full speed shouldn’t be a problem at all. Most likely you’ll find yourself swimming too fast, which will force you to adapt your swimming technique accordingly e.g., stroke frequency and strength, breathing and so forth. Likewise, when swimming on the side of the lead swimmer, that you have to reduce your speed to ‘keep-up’. Should you fall behind, the beauty with the pull-cord is that it will help keep you in place. But finding the perfect length of the pull-cord is a matter of careful testing in varying conditions.

During this year’s ÖtillÖ, many teams would have benefited from this knowledge when swimming the strong currents of the ‘Pig-Swim’.

Strong currents & wrong displacement of the 2nd swimmer

Below you’ll find a few pointers on what to think of when swimming with or without a pull-cord:

  • If you keep touching the feet of the lead swimmer, try to widen the entry of your stroke
  • Adjust your swim direction by focusing on the pull-cord underneath the water. Looking above water will slow you down and disrupt your rhythm
  • If swimming on the side, remember to breathe inwards toward the lead swimmer to maintain speed and position (gap)
  • If possible, synchronise your stroke rhythm with the lead swimmer to avoid colliding arms
  • If racing individually or without a cord, don’t rely solely on the lead swimmer’s navigation skills. Always double-check yourself
Breathe inwards (Pic from Swim Smooth)

To find a proper pull-cord is quite easy and can be bought in a regular boat store or any of the many swimrun shops out there but:

  • Remember to always use a pull-cord which is flexible
  • Sometimes when swimming in waves it can be beneficial to use a slightly longer cord so you don’t crash into each other between the waves
  • A longer pull-cord is suggested if you also aim for running with it, especially in varying terrain.
  • A long pull-cord stand a greater chance of getting entangled in races with many racers and narrow entries and exists
  • The technical swimrun-nerds have 2 lengths on 1 single pull-cord i.e., 1 short for swimming and 1 long (fully extended) for running.
Crowded entries and exits can entangle a long pull-cord
Crowded entries and exits can entangle a long pull-cord

But as we always say here at WoS, the less gear the better and remember that racing is as much about being smart as it is about being fast!

Good luck

/The WoS Team

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NEW TO SWIMRUN OR LOOKING TO ADVANCE YOUR SKILLS?

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Preliminary numerical investigation in open currents-water swimming: Pressure field in the swimmer wake

Fabien Beaumont, Redha Taïar ∗, Guillaume Polidori

A b s t r a c t

The drafting in swimming is a sports practice usually used during the open water race of triathlon. Indeed, it is well known that swimming drafting behind or close to the lead swimmer induces a reduction in drag, once the draft swimmer is located in the low pressure field of the lead swimmer’s wake. For this purpose, in order to determine the best position for the draft swimmer, a preliminary perfect knowledge of the lead swimmer’s wake is necessary in presence or not of currents. The present preliminary study focuses this point before developing further analyses on reducing drag and enhancing performance in drafting by considering both lead and draft swimmers. In this work, the computational fluid dynamics (CFD) method was used in order to evaluate the hydrodynamic drag during the swimmer’s displacement in presence of currents. The standard k- ω turbulence model was chosen to predict the resistance forces with currents-negative ( α=0 °: aligned posi- tion of the swimmer’s body relative to the main flow direction) and cross-currents (angle of incidence of the swimmer’s body relative to the main flow direction, respectively 10 and 20 °). The analysis of the CFD results have shown that the best position for a draft swim- mer was found to be directly behind the lead swimmer (close to the toes) and very close to the side of the lead swimmer when drafter’s head is between shoulders and hip level of the leader.