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Allen Stark
November 10th, 2007, 03:49 PM
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

rtodd
November 10th, 2007, 08:09 PM
Interesting stuff. Can you expand on what conclusions can be made?

I'm having trouble drawing conclusions here.

ALM
November 10th, 2007, 08:18 PM
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

stussy96
November 10th, 2007, 09:26 PM
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?

jim thornton
November 10th, 2007, 10:32 PM
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 (http://en.wikipedia.org/wiki/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.

bobbyhillny
November 11th, 2007, 02:28 AM
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.

Allen Stark
November 11th, 2007, 11:05 AM
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.

geochuck
November 11th, 2007, 04:04 PM
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.

knelson
November 11th, 2007, 08:17 PM
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.

Its a slow show
November 11th, 2007, 10:05 PM
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

The Fortress
November 11th, 2007, 10:14 PM
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.

gull
November 12th, 2007, 08:55 AM
The hull speed formula applies to displacement-type vessels like a keeled sailboat, which can only exceed that speed when hydroplaning. A catamaran, which has two planing hulls, can beat a keeled sailboat with a much longer waterline length, as Dennis Conner convincingly demonstrated when he defeated New Zealand in the 1988 America's Cup.

Perhaps a swimmer is better characterized as "semi-displacement" or "semi-planing."

jim thornton
November 12th, 2007, 09:30 AM
If I were to somehow attach myself in parallel with a fellow swimmer, say, Amanda Beard, and in so doing create a kind of human catamaran, would the two of us go faster than the fastest of us (her) could go alone? This is assuming no odd rudder effects being generated by catamaranization.

gull
November 12th, 2007, 09:44 AM
It's not the rudder, Jim, it's the length of your mast.

jim thornton
November 12th, 2007, 11:16 AM
I was assuming Amanda and I were swimming freestyle, not backstroke. To be honest, I think both "rudder" and "mast" overstate things considerably in my particular case. "Slightly enlarged dermal denticle" might be more accurate, though I suppose Amanda, given her Olympic greatness, might inspire more.

Sorry. Did not mean to steer this in non-swimming related directions.

Back post haste to form drag!

Steve Ruiter
November 12th, 2007, 12:58 PM
I don't know a lot of the science behind hullspeed, but I do sail and am familiar with the concept. The hull speed formula cited is an empirical approximation that apparantly works for the typical configuration of displacement hulled boats. The exact geometry of the hull certainly matters, so the application of this concept to particular hulls and extending it to the human body would be less exact.

My understanding of hull speed is that the additional power required to go faster is some sort of exponential curve which "jumps" or becomes much steeper at hull speed. Its not that you cannot go faster than hull speed (planing hulled boats do it), but it takes a lot more power to do so. The marginal return on effort becomes less.

Sailing home in rough seas yesterday, and watching my GPS, I noticed a few things that can be learned from sailing and applied to swimming:

- Splashing is a waste of energy
- You move fastest when your center of gravity is moving in a straight line (i.e. not bobbing up and down)
- You move fastest when your propulsive force is not varying and you maintain momentum.
- Always put your beer in a gimballed cupholder

Steve

jim thornton
November 12th, 2007, 01:10 PM
And when your beer is moved from its gimballed cupholder to the skipper's digestive system, you care less, one way or the other, about how fast your hull is moving.

Allen Stark
November 12th, 2007, 07:14 PM
You are right that hull speed calculations are not exact for the human form.Really the main points are that being tall is an advantage on the surface but not underwater.Also that resistance increases rapidly above hull speed,but it is,of course possible to go faster.

knelson
November 12th, 2007, 11:56 PM
Really the main points are that being tall is an advantage on the surface but not underwater.

I'm not sure I buy this. When there is no free surface involved, such as swimming underwater, you can use classical aerodynamics more readily. A long, thin airfoil (wing) will produce less drag than a short, fat airfoil. I think a tall person has an advantage both on top of and under the water.

geochuck
November 13th, 2007, 09:25 AM
A long vessel with an empty tank does not move well through the water. I also like front wheel drive and a full tank. (Full tank is conditioning) A thing I have not been able to accomplish for a long time.

It is a drag for sure. The old hull no longer speeds.

Allen Stark
November 13th, 2007, 01:29 PM
Kirk,I'm not sure about the effect of length on underwater drag.In your example the key words may be fat and thin,not long and short.It would seem to me that with 2 swimmers of equal girth,the shorter swimmer would have less form drag by virtue of lees surface area,but I'm not sure.

Kevin in MD
November 13th, 2007, 03:12 PM
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.

Not to mention that the formulas undoubtedly were put together for steady state situations, not ones where the bow wave is dirsupted about twice per second. I suppose it remains to be demonstrated whether there is anything we can do with our entries to change the amount of wave drag we encounter. Maybe the folks doing computational fluid dynamics will look at this one of these days.

craiglll@yahoo.com
November 14th, 2007, 04:19 PM
This always makes my head spin. Isn't drag always going to occur when you move forward. Opposite and equal and the "L" effect.

also, I'm always so surprised to see how much peole actually do look like a hull of a ship when they are swimming.

knelson
November 14th, 2007, 05:16 PM
This always makes my head spin. Isn't drag always going to occur when you move forward. Opposite and equal and the "L" effect.

Yes, drag will always occur. If you are at a constant velocity (which, of course, you never are when swimming) then your drag is equal and opposite to the force you are creating to move you forward (your kick and pull).

The bottom line is the more you can minimize your drag the faster you will go.

Its a slow show
November 14th, 2007, 08:59 PM
This is getting boring. Learn to race and don't over complicate things. Enjoy!! Allen your getting to serious and I suggest you just let it go and race.

Allen Stark
November 15th, 2007, 05:14 PM
I agree this thread is getting boring and should just drift away to the second page.Streamlining is not boring though.Streamlining is "free" speed.I am always looking for the easiest way to go the fastest.:bouncing:

inklaire
November 15th, 2007, 08:10 PM
I agree this thread is getting boring and should just drift away to the second page.Streamlining is not boring though.Streamlining is "free" speed.I am always looking for the easiest way to go the fastest.:bouncing:

Not boring at all. Keep thinking and talking, please. :)

david.margrave
February 22nd, 2008, 01:17 AM
I came across this while searching for front quadrant. I was messing around during warm-down and tried swimming with no kick at all, to see how much my legs dragged with different stroke techniques. I tried front quadrant style and normal style, and my legs were dragging noticeably worse with normal stroke. The whole idea of front quadrant swimming is to move your center of buoyancy forward for a large part of your stroke cycle, right?

I haven't tried front quadrant in workout sets yet, but plan to, to get a feel for whether it works for me or not. It seems like the 'catch up' drill is probably a good way to develop technique.

rtodd
February 22nd, 2008, 09:04 AM
Good point.

I think front quadrant swimming allows the weight of your arms to help balance out the weight of your legs and create a flatter streamline profile. This helps in distance when your kick is less activated. Thorpe was the master.

LindsayNB
February 22nd, 2008, 09:38 AM
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.

david.margrave
February 22nd, 2008, 10:44 AM
Out of curiosity, when you switched to a more front quadrant stroke, did you delay your catch or speed up your recovery?


I guess I delayed my catch, spent more time with my arm extended in front. I may not be doing it correctly, but I hope to develop this technique and use it for distance races.

james lucas
February 22nd, 2008, 11:35 AM
:drown:

james lucas
February 22nd, 2008, 11:44 AM
"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:

http://www.amazon.com/exec/obidos/ASIN/0736031804/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:

http://www.amazon.com/exec/obidos/ASIN/0736037772/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:

http://swimming.about.com/gi/dynamic/offsite.htm?zi=1/XJ/Ya&sdn=swimming&cdn=sports&tm=58&gps=48_1295_1020_574&f=00&tt=14&bt=1&bts=0&zu=http%3A//www.svl.ch/svl_swim_like_a_fish.html (http://swimming.about.com/gi/dynamic/offsite.htm?zi=1/XJ/Ya&sdn=swimming&cdn=sports&tm=58&gps=48_1295_1020_574&f=00&tt=14&bt=1&bts=0&zu=http%3A//www.svl.ch/svl_swim_like_a_fish.html)

geochuck
February 23rd, 2008, 10:39 AM
Maybe we should apply some of these techniques to our swimming http://www.youtube.com/user/jimsquad

Chris Stevenson
February 23rd, 2008, 02:47 PM
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.

This is conjecture on my part, but I believe you have stated the primary effect of the suits: changing and maintaining the shape of the "hull," not buoyancy or even friction. What this implies to me is:

-- there may be very little difference between suits
-- the effect will be significantly greater for a muscular or, um, flabby swimmer
-- the effect is greatest on dives/pushoffs and underwater work, the effect will be less in LCM than SCY/SCM and may almost disappear in an OW swim.

Again, I have no data to back this up, just my own feeling after using the FSII suit for the first time last year.

geochuck
February 23rd, 2008, 02:50 PM
I just saw that the Canadian Swim team at the Olympics are going to swim in the NASA designed swim wear.

david.margrave
February 25th, 2008, 11:03 PM
We did 16x100s on 1:30 (yards) this evening, and I'm pretty confident that the front quadrant technique, which I've adopted for distance sets, is more efficient. It's actually noticeable when I get it right, I don't tire as quickly. Keeping one arm extended for a bit longer time in front is part of it, but for me the key was realizing that my other hand was dwelling too long at the end of the stroke/beginning of recovery, and change the timing a bit so I don't hesitate there, but immediately recover.

I had my coach watch and he says I've got the technique correct with the arms, but I need a more consistent kick. I've heard conflicting information on this, some people say kick is more important with front quadrant technique, other people say it's less important. If we set aside the fact that it is normally used on distance events, and just compare front quadrant and normal techniques, which if any does kicking play a more important role in? Maybe there is no answer, it's just another extension of the whole kicking debate.

geochuck
February 25th, 2008, 11:50 PM
A lot of front quadrant swimmers use a 2 beat kick, so how important is the kick in their case.

I also believe the finish low on the thigh but a clean exit is important.

I also call myself a front quadrant swimmer and I use a six beat kick.

I am also a sprint swimmer converted to a distance swimmer, converted back to a sprinter.

What is the difference for me to sprint or swim distance. Very little. I kick hard in a sprint and turn over faster. In distance everything is controlled but it is the same stroke. I ease up on the kick, and every stroke is very similar to the sprint but I turn over slower.