I was asked on the SDK thread about my past posts on speed and height.Here is a more complete explanation.There are 2 main forms of drag affecting swimmers:form drag and wave drag.Wave drag only occurs at the surface so it is not a factor when swimming underwater.Lack of wave drag is why SDK can be so fast even though it is less propulsive than full stroke.
Form drag is from how much water you push in front of you and pull behind you. Improved streamlining decreases form drag.There are many things we can do to decrease form drag:good body position,shaving down,technical suits,losing weight,etc.For a given shape form drag resistance increases as the square of the velocity.
Wave drag comes primarily from pushing your bow wave. There is very little drag from this until you exceed your "hull speed" at which point you are climbing up on your bow wave.At this point resistance goes up as the cube of velocity so it rapidly becomes the primary resistance.
The formula for hull speed is:hull speed(in knots)=1.34times the square root of the length at the waterline(in feet)(for a swimmer that is the height)This is why longer boats(and taller swimmers) are faster.
For example I'm 5'8" (or 5.67 ft) so my hull speed is 3.19 Kt.A knot is 1 nautical mile per hr or about 1.67 fps so my hull speed is 5.32 fps.This is doing 50 yd in 28.19 sec.Going faster than that requires disproportionally more power than going slower than that(at the surface).
What can you do to decrease wave drag?You can be tall(or at least swim tall),you can stay underwater,or you can swim slower.Obviously swimming slower is no help in a sprint,but it does mean that even pacing will use less energy than going fast for part of the race.
Here is a table I calculated of height and hull speed
Height Hull Speed(feet per sec) Time for 50 yd
5' 5 fps 30 sec.
5'3" 5.12 fps :29.29
5'6" 5.24 fps :28.62
5'9" 5.36 fps :27.98
6' 5.47 fps :27.42
6'3" 5.59 fps :26.83
6'6" 5.71 fps :26.26
"Hull speed" is an issue for any object that is moving through the water, regardless of shape; all things being equal, the fastest ships tend to be the longest ships. The formula for 10-meter racing sailboats gives designers the flexibility to make trade offs between sail area (power) and hull length (reduction of resistence) - and you may have noticed that most 10-meter boats have roughly the same hull length because designers want to get the most from the benefits of faster hull speed. The analogy of boats to swimmers, however, does not apply to the "speed boats" - they exceed their hull speed by hydroplaning, and humans cannot attain such speeds because they cannot generate enough power or leverage on the water to drive themselves forward out of the water. The lesson for swimmers: swim low in the water (and ignore what the coaches taught me a long time ago, which is to keep your head high - instead, keep your hips high), pay attention to that "front quadrant stuff" (it's as valid in breaststroke as freestyle). A couple months ago I began to experiment with "front quadrant" ideas after looking over this book:
www.amazon.com/.../unitedstatesmast
I noticed I needed fewer strokes to get across the pool - I think that was because of lower resistance, not more power, as my underwater stroke changed little. That book encouraged that notion, as did this one:
www.amazon.com/.../unitedstatesmast
Meanwhile, someone noted the effects of the irregularities of shape in the human body. These, it appears, further heighten the resistance as a result of the eddy currents and boundry water. The purpose of a technical suit is to mitigate this resistance. The problem with "bobbing" is that this also heightens eddy currents. The "new" wave-style breastroke is designed, in large part, to reduce the resistance in the leg recovery that come from dropping the knees in the old "flat" style. Meanwhile, boat designers have been able to improve speed by altering hull and keel designs, for example, but those alternatives are less available to swimmers.
Here's one simple way of looking at this:
swimming.about.com/.../offsite.htm
"Hull speed" is an issue for any object that is moving through the water, regardless of shape; all things being equal, the fastest ships tend to be the longest ships. The formula for 10-meter racing sailboats gives designers the flexibility to make trade offs between sail area (power) and hull length (reduction of resistence) - and you may have noticed that most 10-meter boats have roughly the same hull length because designers want to get the most from the benefits of faster hull speed. The analogy of boats to swimmers, however, does not apply to the "speed boats" - they exceed their hull speed by hydroplaning, and humans cannot attain such speeds because they cannot generate enough power or leverage on the water to drive themselves forward out of the water. The lesson for swimmers: swim low in the water (and ignore what the coaches taught me a long time ago, which is to keep your head high - instead, keep your hips high), pay attention to that "front quadrant stuff" (it's as valid in breaststroke as freestyle). A couple months ago I began to experiment with "front quadrant" ideas after looking over this book:
www.amazon.com/.../unitedstatesmast
I noticed I needed fewer strokes to get across the pool - I think that was because of lower resistance, not more power, as my underwater stroke changed little. That book encouraged that notion, as did this one:
www.amazon.com/.../unitedstatesmast
Meanwhile, someone noted the effects of the irregularities of shape in the human body. These, it appears, further heighten the resistance as a result of the eddy currents and boundry water. The purpose of a technical suit is to mitigate this resistance. The problem with "bobbing" is that this also heightens eddy currents. The "new" wave-style breastroke is designed, in large part, to reduce the resistance in the leg recovery that come from dropping the knees in the old "flat" style. Meanwhile, boat designers have been able to improve speed by altering hull and keel designs, for example, but those alternatives are less available to swimmers.
Here's one simple way of looking at this:
swimming.about.com/.../offsite.htm
