A buddy and I were recently discussing what is the benefit of extending one's arms above the head or in front of the head (if swimming horizontally).
It is easy to think that fluids are doing things that they are not because intuition is often wrong when considering objects moving through fluid media.
One might assume that the extended arms in some way "Prepare the Way" for the rest of the body, by grooming the flow prior to the rest of the body's entry. In that case one might think that the effect is similar to tailing a truck on the highway as they did on mythbusters to achieve better fuel economy. One might also assume that there is a streamlining effect which is achieved. Instead of pushing the shoulders and head into the water first the hands part the water and in that way the difference is like that between the shape of a moving van and that of a Ferrari.
I understand the advantages of putting a boat tail on something like a rifle bullet, on the leading and trailing shapes of submarines and on aircraft. It didn't seem to me though that extending the arms would provide the type of pressure management that those things impart because the legs are kicking behind the diver; the trailing shape is doing a lot of shape changing in the case of stereo kicking where extended arms also help (not just during monofinning).
Perhaps some or all those factors come into play. At the velocities that we move at, in water, I'm skeptical that streamlining or any of those other factors do much. I do a fair amount of computer analysis with some pretty spendy thermal-fluids software but I couldn't pin down why putting the arms above the head offered an advantage.
I felt certain that viscous drag was the culprit and tried lots of swimming with my arms plastered to my sides to try to decrease the wetted area. It made very little difference.
I finally had to concede that extended arms does increase efficiency. I used to be a deny-er of that and swam for years with my arms at my sides. Some new buddies though recently shamed me into increased shoulder flexibility and once I started getting some form I had to admit that it does make things a lot easier. I am now even willing to pay the penalty of straining a bit to keep them out there because of how noticeable the efficiency gain is.
I asked a buddy of mine who is a PhD thermal/fluids guy. He doesn't just have the credentials but also a demonstrated ability in terms of both the mathematics and where the rubber meets the road...literally since he's done lots of work on dragsters and other performance vehicles as well as aircraft and in the space program. He's saved my ass a lot of times.
His feeling was that gains one feels by extending the arms are due to an effect similar to what is known as hull speed which governs the dynamics of a displacement hull ship moving through water. By extending the arms, the length of the body is synergistic with the wave created by the diver moving through the water.
I thought the community might like to kick this around a bit.
It is easy to think that fluids are doing things that they are not because intuition is often wrong when considering objects moving through fluid media.
One might assume that the extended arms in some way "Prepare the Way" for the rest of the body, by grooming the flow prior to the rest of the body's entry. In that case one might think that the effect is similar to tailing a truck on the highway as they did on mythbusters to achieve better fuel economy. One might also assume that there is a streamlining effect which is achieved. Instead of pushing the shoulders and head into the water first the hands part the water and in that way the difference is like that between the shape of a moving van and that of a Ferrari.
I understand the advantages of putting a boat tail on something like a rifle bullet, on the leading and trailing shapes of submarines and on aircraft. It didn't seem to me though that extending the arms would provide the type of pressure management that those things impart because the legs are kicking behind the diver; the trailing shape is doing a lot of shape changing in the case of stereo kicking where extended arms also help (not just during monofinning).
Perhaps some or all those factors come into play. At the velocities that we move at, in water, I'm skeptical that streamlining or any of those other factors do much. I do a fair amount of computer analysis with some pretty spendy thermal-fluids software but I couldn't pin down why putting the arms above the head offered an advantage.
I felt certain that viscous drag was the culprit and tried lots of swimming with my arms plastered to my sides to try to decrease the wetted area. It made very little difference.
I finally had to concede that extended arms does increase efficiency. I used to be a deny-er of that and swam for years with my arms at my sides. Some new buddies though recently shamed me into increased shoulder flexibility and once I started getting some form I had to admit that it does make things a lot easier. I am now even willing to pay the penalty of straining a bit to keep them out there because of how noticeable the efficiency gain is.
I asked a buddy of mine who is a PhD thermal/fluids guy. He doesn't just have the credentials but also a demonstrated ability in terms of both the mathematics and where the rubber meets the road...literally since he's done lots of work on dragsters and other performance vehicles as well as aircraft and in the space program. He's saved my ass a lot of times.
His feeling was that gains one feels by extending the arms are due to an effect similar to what is known as hull speed which governs the dynamics of a displacement hull ship moving through water. By extending the arms, the length of the body is synergistic with the wave created by the diver moving through the water.
I thought the community might like to kick this around a bit.
