From the standpoint of physics, I can’t quite comprehend how drafting in the swim works.
With cycling, it seems to me that the idea is that you’re literally hit with less air molecules, which of course are causing the force that causes the wind resistance. The air molecules bounce off the cyclist in front of you and you slide in behind before all those air molecules have time to reform around him.
In the swim though, is the same thing really happening? The speeds are FAR slower, and the water molecules have way more time to get around a swimmer. Yes liquid molecules are moving much slower than gas molecules, but still you’d think they’d move fast enough. Furthermore a horizontal swimmer has much less blocking ability than a semi-vertical cyclist. I just find it hard to believe that drafting behind a swimmer means hitting significantly less molecules.
I don’t deny that drafting works in triathlons (granted I suck too badly to ever get any use from it, but I’m curious from an academic standpoint). So what’s the deal?
Am I wrong in my whole analysis of drafting in general?
Am I wrong in my swimming analysis? Is it true that you really ARE hit with so many less water molecules that it’s significant?
Could there be a different mechanism for drafting in water vs. drafting in cycling? E.g., maybe the swimmer in front of you creates a forward moving current (or at least counteracts a current) that actually pulls you forward? (Granted this mechanism could work in cycling too, but maybe it’s more important in the swim.)
Lead swimmer displaces water that creates a wake - a small wave.
Tail swimmer gets on this little wave and “rides” it. It isn’t much, but enough to matter.
That’s my take on it, fwiw.
From the standpoint of physics, I can’t quite comprehend how drafting in the swim works.
With cycling, it seems to me that the idea is that you’re literally hit with less air molecules, which of course are causing the force that causes the wind resistance. The air molecules bounce off the cyclist in front of you and you slide in behind before all those air molecules have time to reform around him.
In the swim though, is the same thing really happening? The speeds are FAR slower, and the water molecules have way more time to get around a swimmer. Yes liquid molecules are moving much slower than gas molecules, but still you’d think they’d move fast enough. Furthermore a horizontal swimmer has much less blocking ability than a semi-vertical cyclist. I just find it hard to believe that drafting behind a swimmer means hitting significantly less molecules.
I don’t deny that drafting works in triathlons (granted I suck too badly to ever get any use from it, but I’m curious from an academic standpoint). So what’s the deal?
Am I wrong in my whole analysis of drafting in general?
Am I wrong in my swimming analysis? Is it true that you really ARE hit with so many less water molecules that it’s significant?
Could there be a different mechanism for drafting in water vs. drafting in cycling? E.g., maybe the swimmer in front of you creates a forward moving current (or at least counteracts a current) that actually pulls you forward? (Granted this mechanism could work in cycling too, but maybe it’s more important in the swim.)
Other?
I hate to disagree with Dave Luscan, but…
I don’t think it’s the number of air/water molecules that changes so much as their inertia: the air behind a cyclist is turbulent. Some of the molecules are moving forward to fill the low pressure area behind the cyclist, therefore they don’t require as much energy to move “out of the way.” I’m guessing that the actual low pressure area (“fewer molecules”) is pretty small and close to the cyclist. This can be seen by watching a motorcyclist wearing a t-shirt: the shirt is actually pushed forward/upward on the rider’s back by air filling in the low pressure area behind the rider.
In swimming, a body moves water out of the way as it goes forward. Water must fill in behind the swimmer, and this water does actually create a forward moving current that requires less energy to move “out of the way” for a trailing swimmer (there’s a scientific term for this, in terms of the drag this effect has on the swimmer). Good evidence of this can be seen watching a 50m sprint race: there is a wave that follows the swimmers into the wall that is not the wake.
My limited understanding of physics is that, at least at normal speeds and pressures, water and air behave basically the same as fair as drafting and drag are concerned. So, in simple terms, dafting in the swim “works” the same as drafting on the bike. The differences are ones of maganitudes of the effects based on the density differences between air and water.
Of course I’ve haven’t taken a physics class since high school so take this with a grain of salt
…Some of the molecules are moving forward to fill the low pressure area behind the cyclist, therefore they don’t require as much energy to move “out of the way.”
In swimming, a body moves water out of the way as it goes forward. Water must fill in behind the swimmer, and this water does actually create a forward moving current that requires less energy to move “out of the way”…
Ken, I think this is a great explanation in both cases! At least it seems very logical to me. Thanks!
I wish it were easier for me. I can’t do it well. I either smack into people or their pace is so fast for me (all but about 2% of anyone swimming is too fast for me) that trying to draft causes more anxiety and causes my stroke to go crazy trying to stay on the bubbles, such that I wear out nearly instantly. Maybe some day I’ll get the hang of it.
I wish it were easier for me. I can’t do it well. I either smack into people or their pace is so fast for me (all but about 2% of anyone swimming is too fast for me) that trying to draft causes more anxiety and causes my stroke to go crazy trying to stay on the bubbles, such that I wear out nearly instantly. Maybe some day I’ll get the hang of it.
i’m with you. my fastest im and him swims have been when i swam most of the time with no draft. i have not figured out how to find a draft that will pull me as fast as i would go myslef with the same effort. most probably, when i draft, i am not relaxed enough = i swim slower = am only able to draft a slower swimmer.
following bubbles isn’t that much fun in a race. actually, i find it kind of stressful. i don’t want to hit the other persons feet (well, not very often) but i don’t want to fall too far behind either. more tension. slower swimming.
Watch some surfing videos, it’s kinda like that. It is not necessarily easy, and you may have to change your pace quite often, depending on who you are trying to draft.
From the standpoint of physics, I can’t quite comprehend how drafting in the swim works.
With cycling, it seems to me that the idea is that you’re literally hit with less air molecules, which of course are causing the force that causes the wind resistance. The air molecules bounce off the cyclist in front of you and you slide in behind before all those air molecules have time to reform around him.
Drafting is a rather learned art.
In the pool it’s relatively easy. The person in front is following a lane rope or pool mark, you get on their feet and there’s no real problem. Apart from understanding that if you touch their foot, you are asking to go ahead at the next turn.
But OWS is far more tricky.
First there is no lane rope and people swim less than straight. The water quality is usually on the murky side, so all you see is bubbles half the time and they are all over the pace. So bumping into disembodied feet is a whole new experience.
I have had only one good drafting race in about 30. And yes sometimes it’s easier to just swim your own race. But you can get lucky.
It gives about a 15% advantage (please don’t ask for real facts) and that is a lot over 3800m. As much as 10 minutes if you do the math. For the not so great swimmer that’s a 1:06 versus a 1:16. Worth learning, but not worth fretting about if you don’t find the right pair of feet.
By the way you don’t have to be on their feet. For all those who watched the US Olympic relay swim, you will see that just behind the shoulder is also pretty good.
Of course if you have a foot fetish, well what can I say!
Fairly new to tri’s so this question may seem obvious to some…
Do athletes team up to take advantage of the drafting effect? Can a rabbit sacrifice him/herself in the swim to help his/her teammate?
Swimmers understand how big an effect drafting is during training sessions. Simply get on the feet of a faster teammate and ride their wave through a 1000 or 1500. Amazing how little energy you have to use if done properly.
And yes, that 400 Relay in Beijing Olympics shows the effect that drafting has even at the highest levels of the sport.
In any big triathlon get in the middle of a group. When you reach a buoy where there is a 90 degree type turn, notice how if you dont adjust you will get way off course. In IM WI I experienced this. Swimming with a strong group and not doing much swimming. We got to the first buoy, the group turned left and within two strokes I am a solid 10 yards farther. The current just pushed me.
I coach swimming youth and high school swimming and have the opportunity to draft off anyone. I have gotten quite good at it. Just a few weeks ago I was doing a set of 10x100s on about 1:20 with a strong 14 year old girl. First 9 I got a good draft off this 90lb 5’1 monster. Last one I held it til about a lap and a half left. Shes pretty tired and I just blow past her. Of course I did exactly what I tell my kids not to do at practice – be a sand bag sally. being somewhat out of shape…I had tons of energy to make the pass in about 4 strokes.
In any big triathlon get in the middle of a group. When you reach a buoy where there is a 90 degree type turn, notice how if you dont adjust you will get way off course. In IM WI I experienced this. Swimming with a strong group and not doing much swimming. We got to the first buoy, the group turned left and within two strokes I am a solid 10 yards farther. The current just pushed me.
I coach swimming youth and high school swimming and have the opportunity to draft off anyone. I have gotten quite good at it. Just a few weeks ago I was doing a set of 10x100s on about 1:20 with a strong 14 year old girl. First 9 I got a good draft off this 90lb 5’1 monster. Last one I held it til about a lap and a half left. Shes pretty tired and I just blow past her. Of course I did exactly what I tell my kids not to do at practice – be a sand bag sally. being somewhat out of shape…I had tons of energy to make the pass in about 4 strokes.
Good to see that you are utilizing your students expensive training time to your own benefit. We’ve got a very selfish coach here Slowtwitchers.
It was actually a reward in our summer rec league. I told them if we achieved a best time percent of 75% in our meet vs the worst team in the league that I would swim a practice with them.
In my experience there are three things that always motivate swimmers in “non-key” meets
Candy
Coaching the coach
Swimming with the coach
I dont make enough for #1
I dont want to reward swimmers in a short season (6 weeks) with missing training time
I can swing this as the other coaches handle the workout.
It was actually a reward in our summer rec league. I told them if we achieved a best time percent of 75% in our meet vs the worst team in the league that I would swim a practice with them.
In my experience there are three things that always motivate swimmers in “non-key” meets
Candy
Coaching the coach
Swimming with the coach
I dont make enough for #1
I dont want to reward swimmers in a short season (6 weeks) with missing training time
I can swing this as the other coaches handle the workout.
