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
What about extending your reach and, in the case of that Dutch star (Inga de Bruijin?) growing your fingernails as long as possible? What about pointing your toes when you kick? Is hull length only a matter of length? Does the bill of a sailfish or marlin, for instance, extend its hull length even though the bill comes down to a pencil point tip?
if so, I would think shortish people with exceptionally long arms could be as long in the water as tall people with short arms.
Also, if there a point where being too long starts to hurt speed?
For what it's worth: Wikipedia-- In the United States the highest percentile of height given by the FAA is the 99th percentile, which is 75.2 inches (191 cm) or 6 ft 3 in.
I'm having trouble drawing conclusions here.
Here are the conclusions I made:
1) Allen has way too much time on his hands. :notworthy:
2) I'm 5'1" tall; therefore, I'm screwed. :doh:
Anna Lea
My conclusions:
1) I am about 5'11", so I am lucky.
3) My time for a 100 is close to that time. Does this mean I am maximizing my drag/effort/speed ratio? Or should I be able to go faster if I learn to swim "taller"
3) How can I swim "taller"? Or does this relate to strength, technique, pure athletic ability, etc?
Front quadrant swimming is one way to swim tall I guess. Ian Thorpe swims this way, even though he's already 6'5.
Thanks for the post Allen, interesting.
I assume this hull speed calculation is something that comes from boat hulls. Since swimmers are not boats, does it apply at all? If it does apply does it need a different formula than is used for boats? It sure seems to me that it would.
Does the body extension really help???
The propulsion only commences from the catch to where we finish the stroke.
I think we are falling into a trap if you think you are going to get faster by having the so called longer vessel. Even though I try to have a longer vessel but is a longer, but very bloated vessel.
Allen- I think, sometimes, you over complicate swimming. Don't get me wrong your obersvations are well thought out, but, at some point you just got to swim. A lot of swimming is just having a natural feel for the water I don't think it can be taught IMO
Some people are naturals, no doubt. But I thought technique was something that could be improved and honed. There was a recent article in the NYT on this issue contrasting swimming and running. The author opined that running efficiency could not be taught, but swimming efficiency could -- because swimming (unlike running) is such a technique-dependent sport.
I didn't really get too much of what Allen the Scientist was saying, and I'm too tired to try, so I guess I'm banking on the less wave drag via SDK theory. I'm starting to think that SDKs are slightly more important in 100 sprints than 50s though.
The "swim tall" question has been vexing me.It seems to me that if your arm extension forward is disrupting your bow wave it is making your "length at the waterline" longer and hence increasing your hull speed.
Allen- I think, sometimes, you over complicate swimming. Don't get me wrong your obersvations are well thought out, but, at some point you just got to swim. A lot of swimming is just having a natural feel for the water I don't think it can be taught IMO
