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
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Out of curiosity, when you switched to a more front quadrant stroke, did you delay your catch or speed up your recovery?
Btw, front quadrant doesn't work by moving your center of buoyancy forward, it works by shifting your center of gravity forward, closer to your center of buoyancy. In the static case, if they are both in the same place you will be stable. With your arms at your side your center of gravity will be below your center of buoyancy (toward your feet) and a rotational force will be created (for example buoyancy pushing up at your chest and gravity pushing down at your hips will cause your legs to sink).
The basic explanation for hull speed is that the faster the speed the longer the wave length. At very slow speeds you create little ripples that are closely spaced, as you speed up the distance from peak to peak increases and for a boat, as the speed increases the distance from the bow wave to the following wave increases, first to the point where the rear of the boat is traveling on the second peak, and then eventually the back of the boat will be in the trough with the bow in the peak of the bow wave, so you are effectively powering yourself up the back of a wave, which takes a lot more power. The longer the hull the greater the speed you can travel before your stern falls into the trough so the greater your hull speed is. Sticking a pole on the front of a boat (extending your arm in front of you in swimming) will only increase your hull speed if it moves the bow wave (and following wave) forward, which is not the case with a swimmer extending an arm forward under the water. Extending your arm will however make you more streamlined.
Out of curiosity, when you switched to a more front quadrant stroke, did you delay your catch or speed up your recovery?
Btw, front quadrant doesn't work by moving your center of buoyancy forward, it works by shifting your center of gravity forward, closer to your center of buoyancy. In the static case, if they are both in the same place you will be stable. With your arms at your side your center of gravity will be below your center of buoyancy (toward your feet) and a rotational force will be created (for example buoyancy pushing up at your chest and gravity pushing down at your hips will cause your legs to sink).
The basic explanation for hull speed is that the faster the speed the longer the wave length. At very slow speeds you create little ripples that are closely spaced, as you speed up the distance from peak to peak increases and for a boat, as the speed increases the distance from the bow wave to the following wave increases, first to the point where the rear of the boat is traveling on the second peak, and then eventually the back of the boat will be in the trough with the bow in the peak of the bow wave, so you are effectively powering yourself up the back of a wave, which takes a lot more power. The longer the hull the greater the speed you can travel before your stern falls into the trough so the greater your hull speed is. Sticking a pole on the front of a boat (extending your arm in front of you in swimming) will only increase your hull speed if it moves the bow wave (and following wave) forward, which is not the case with a swimmer extending an arm forward under the water. Extending your arm will however make you more streamlined.
