Where are your hands?

[andrsn]

Re: Back to physics class

Originally posted by groats
The most efficient form is the one that looks like a raindrop and not the long and slim form, so extended arms are hydrodynamically less effective than arms behind.

Dive often, joe

Actually, this is not really the case(with all due respect, Joe). I think people put their arms at their side for a more comfortable posture and to conserve oxygen(by not having to support your arms).

Optimizing speed in water is more about maximizing laminar flow. And... this comes when the maximum diameter of the object is near the back third(with rear propulsion). However, this does follow the requirement that the body has a length to height ratio of about 5. The best example of this is the Tuna. But, as the length to height ratio increases, the maximum diameter moves forward. But, in contrast to a raindrop, the best reduction in turbulence comes from a piercing point at the front. This minimizes eddy currents and creates a laminar flow.

So, I think being able to conserve that much more oxygen outweighs the loss in speed due to the drop in arms/hands. So then conclusively, the raindrop shape is not the most hydrodynamically efficient, but for some, it may be the most effective.

Sorry to sound like a lecture, but I had a few Ocean Engineering courses that covered this stuff.

Cheers,
Anderson

 

[Jason Billows]

My 2 cents...

I think that many people don't like the hands over head position for two reasons: lack of shoulder flexibility and/or their wetsuit being too tight. I have experimented with both styles and found the hands over head position to be much more efficient for me.

This is also the position Kirk Krack taught in the last two workshops I took with Performance Feediving and I have quite a bit of faith in his expertise.

My only exception to using this position is in the last 10 to 15 meters of my dive, depending upon buoyancy. As I near the surface, I drop my arms, relax and float to the surface. This depends upon your buoyancy though. It's a nice, relaxed way to end your dive and prepare yourself for proper breathing on the surface.

Jason Billows
Ottawa, Canada

 

[Alun]

by my side, always...

arms down, elbows gently tucked in with palms flat on my hips/legs... for descent and ascent

 

[ivan]

hi

Alun I guess you are using fluid googles and a nose clip, or can you equalise without hands

cheers

 

[Alun]

yes, goggles. i do the same when wearing a mask - but with one hand on my nose during the descent. ascent is obviously no different.
actually i've noticed a significant difference in sinking speed between those two scenarios... having your arm up across your chest and up to you face seems to cause a big increase in drag, comapred with both arms by the side... something like 0.1-0.15m/s difference.
i recently tried doing a constant weight dive without fins- just to 25m. but i noticed that i could sink even faster like that... obviously the monofin causes some drag also, because it's hard to get your legs *and* the fin straight, but when doing constant weight without fins - you're perfectly streamlined with your legs straight... so you sink even faster - that's what i've found anyway.

alun

 

[ivan]

hi

A NO FINS dive to JUST 25M !!!!!

Thats impressive

cheers

 

[Alun]

no way.... diving to 50-60m with no fins, like David and Topi.... now *that's* impressive!!

 

[ivan]

hi

What about that guy Stig avall severison (spelling) he did 150m dynamic no fins, wonder what he could do in ocean.

cheers

 

[neshamah]

you should try the unassisted

I think freedivers should test the unassisted--i din't knok how good it is-until i did it for the first time-is very funny as a friend of mine says---and this has helped me a lot-even when using my fins. ..because in unassisted you more energy and capatiy.


saludos ..


Daniel.

"thanks to God who has done great things for us"
"Gloria aquel que es poderoso en hacer las cosa mas grande que lo que entendemos"

 

[neshamah]

i like this subject

i like this topic----that's the next --to see What stig will do in the ocean...he has a good technique for swiming too....that's the most importan in the unassisted..the idronicamica and the posicion of the boby

 

[Shellback]

Relax

I got back into freediving about ten years ago...but i must admit infrequently due to location. I got some really good advice from a very good diver/coach named David Sipperley.

He suggested finding a balance between streamlining in the water column and reducing all unneccessary effort to conserve O2.

David suggested placing the hands relaxed but flat on the lower abdomen near the groin. Also become concious about relaxation of all muscle groups not associated with swimming...basically the arms, sholders, neck, and upper back. this made a great difference for me.

I agree with Cliff about the safety issues of having the arms up "as you near the surface". I also know you get a greater glide with the arms forward in a pool when you kick off, but gliding in a pool horizontally is different going vertical.
i think a useful issue is becoming aware of your "typical" kick-and-glide measurement, both horizontally in a pool and vertically in the ocean or a lake.
How many kicks does it typically take you to cover a certain distance? How many kick to a 50 meter pool? How many kicks to a 25 meter vertical position? Is it different going down or coming up? The information can save your neck. Literally.
If you know your depth and you are asending, approximately how many kick to the surface? Stick that arm up with in a safty zone distance from the surface.

On the kick....with good form...there is an apparent "sweet spot" for forward motion related to the effort it takes to create the forward motion. David mention to try 3-4 powerful strokes to get up to speed, then back off just a bit to find the optimun cruising speed. It will vary with fin, strength, and that streamlining in the water column......but it will be more efficient and require less effort, leaving more air. Experiment. Relax more.

Shellback