Something about wave formation on the surface that it creates extra drag. Moving about under water of course creates drag too but can be less resistant with shape and movement like with SDK where currents roll of the body's surface.
I think most mammals go under water for acceleration, just watch Phelps.
Thanks all for the comments, and thanks to Steve for the great article (just starting to read, but at first look at the pictures of the marine mammals, I like to be the Florida manatee :D).
Water surface tension and wave formation make a lot of sense. I wonder if the wave formation factor applies more to good swimmers than the bad ones, because a good swimmer can make "good" underwater waves for himself, while for someone who can't swim well, he can't move much anyway, whether on surface or underwater. Does this sound like a reasonable conjecture? :rolleyes:
Cutting down resistance.
I have been experimenting with my breakout from a dive or turn on freestyle. The first stroke being a two arm butterfly stroke. Then leaving the one arm at my side to get back into regular crawl. I have noticed a 0.5 time improvement in my times per length. Now maybe this is because I am overweight. It makes me pop out of the water like I used to in the old days when I did my deep dive. After I pop out I seem to have a better body position for swimming.
Two things Matt Mann told me in 1952. He said "You must learn to swim down hill, and when you dive in or when you exit a turn you must pop up out of the water."
Now I have a question: why, then, in freestyle, one should not have the head completely immersed in water, but keep the water level at about the hairline? Is it because it would be hard to turn to surface to breathe? So if one doesn't breathe, would it be faster to bury the head underwater?
When doing head-up breaststroke, I feel I'm faster than the regular breaststroke (head popping up and down)--never timed, so I don't know, though I spend more strokes in head-up. Maybe it's just because I can see the scenes passing by? :rolleyes: Or maybe I wasn't swimming the regular breaststroke right (my feet tend to be out of water) :(
One way to think about wave drag is in terms of the force needed to lift all the water in the wave that is above the normal surface level. Water is heavy and it takes a lot of energy to lift all the water in a large bow wave.
Here's an interesting tidbit. If the body of a swimmer doubles the depth (sinks) as they swim, it would take eight times the power or effort to maintain their speed (peak). So when you body sinks (even a little bit) and as you increase your speed, frontal resistance is killing your speed.
As Matt Mann told me many years ago, Swim Down Hill is to get the body up on top of the bow wave and swimdownhill. This was his theory of popping out of the water after a turn or dive and get on top of the bow wave.
Others have a different idea of what swimming down hill is.
I agree with the discussion on hydrodynamic resistance for swimming primarily being made up of form resistance and wave drag.
Another interesting article can be found at:
www.swimalberta.ca/.../morphology_and_hydrodynamic_resistance_in_young_swimmers.pdf
One other thing to consider might be for all the physiological power your body is capable to put out, what is the most efficient. I see the challenge as trying to tune the insweep/recovery/breath to minimize the up motion and get momentum energy moving forward.
Thank you Allen for the good points. Your square vs. cube comparison prompted me to an observation (maybe?) that beginners usually work on the form drag, while advanced swimmers work more on the wave drag?
One reason I do head-up breaststroke is to avoid the unknown stuffs in the pool :cool:
Edit: Thanks scassady--just saw your reply. Thanks for the article--going to read it.
