Freedivers getting softer?

[Walrus]

Quite a few people have mentioned already that an angled fin can help you from spiraling or falling sideways in CB. I have been using a wateway fin which I love but do tend to fall sideways on a CB dive. Last year I did a national AIDA CB record but I was allowed to use a neckweight. This made gliding very easy and just kept you straight. Whilst training in Cyprus I had to use a weighbelt. I noticed the difference in stabillity. I had problems on some of my training dives. Kicking down further, ie keep kicking even where you can start to glide helped. I even set a new PB of 80m so was pretty stoked

Unfortunately on my competition dive wether due to nerves or something I didn't kick down for as long, then fell completely sideways. I had to start kicking again when I was quite deep so burned to much O2. Didn't have the sense to turn early and ended up DQing my dive. :waterwork

I realise some of this could be fixed with posture and kicking down further but I would prefer to be more stable to start with. Then there is a bit more room for error. Often my competiton dives are so much messier then what I do in training. I'm quite keen to try out an angled blade. Even one with Omer footpockets. Right now it's a hassle having to swap fins because I can't wear the WW for too long or it hurts my feet. I'm almost consdering going back to using bi-fins for competition as I never had problems with them.

Cheers,
Wal

 

[derelictp]

I mentioned the same (spinning and falling sideways) in my post and I used a WW M1MD back in -2001. That was the main thing that made me look for angled monofins.

When I started using angled monofins I found that I could relax MUCH MUCH more on the descent and at the 0-30m zone my speed was low (0,7-1,0).
My stremlining was better due to body positioning with angled blade that my descent speed was about 1,2m/s at 40m to target depth.

I have never had a squeeze (lucky me) and I progress very slow intentionally.

I am not shure but I think that we can deal with 1,5m/s too if the progression is slow, remember that the pressure change below 30m is very slow, to double the relative pressure from 30m we have to go to 70m.
I can go to 8m with empty lungs and that in 15 sec because I want to make it real slow. That is similar to starting at RV at 30m and going to 62-64 if I dont remember wrong (I have done the math's once). With my speed I would take this depth change in some 27-30 sec and that is not a short time if we compare with empty lungs to 7-8m or a FRC to 25-30m.

Good discussion

 

[rafacuatic]

I was using a WW mono for some time, then i modified the angle of the foot pockets and i improoved a lot in the way of using the up and down strokes ang gliding fase.Now the mono is easy to use in a perfect line and dont hurt my feet.
Rafa

 

[neshamah]

dolphin kick

A look at the dohpin kick. The dophin kick is very likely the most powerful of the all the swimming kicks. The entire body seems to contribute to the power of the drive, as the body and legs perform like a whip in building up great velocity of the feet . Unlike othere strokes where hip position is fixed,the hips move up and down in the dolphin kick. This hip mobility is a significant feature indeveloping power..

Because the arms pull together reather thatn alternately, there is no roll of the body. The kicking action is straight up and down. There is not diagonal component as in the kicking action for the crawl stroke, the kicks of the two strokes have the same basic features . Of course ,there is the obvious different that in the dolphin kick both legs move together, not alternately. The dolphin kick is fuller and more powerful, the increased range of the kick comming about through hip mobitily.

 

[neshamah]

dophin kick

Atually, there is some evidence that the upbeat can make a contribution to forward speed. Definitive studies are difficult to come by, and the matter may reamin in doubt for some time to come. However, the test of contribution to propulsion is basically simple. As we have stated, if you can get the feet moving backward faster thant the body is moving forward,there is a contribution to speed. Slow-motion movies of some fine swimmers suggest that this can be done. Among the top performers, especially those with good ankle flexibility, water pressure during the upbeat bends the ankle so that eh sole of the foot si facing backward , which coud not happen unless the legs were contritution to forward speed . Without such a contribution the ankle would flex in opposite direction so that eh toes would point backward, In any case , the upbeat should be carried out with the intention of making a contribution to forward speed.

At the downbeat the hips are high and the legs are straight . This position comes about naturally as a result of the downbeat. The legs are kept straitht as they start upward. It's important that there be no bend at the knees, because a bend would cause drag. Some loose -jointed swimmers can even gain from hyperextension, a "reverse bend" at the knees. The ankle flex so that the sole of the feet ar facing backward. This position of the feet allows the important backward push againg the water. The upbeat ends when the legs are about parallel to the surface of the water.

 

[tylerz]

I have noticed the tendency for the body to want to tip over on the descent when using a WW monofin, which I deal with by giving a kick to set me straight again. I assumed it was from poor form on my dive, such as looking down the line or uneven foot positions. However, to overcome this, others just let their weightbelts slide down their torso, to lower the center of gravity, using nylon belts.

I am curious if anybody has tried an angled fin that did not have a rail? I think this would be the true test to determine whether the tipping is to do with the angle or not. I am thinking about the hydrodynamics involved that might cause this to happen.

If you are familiar with ocean kayaks in the surf, or other such things, then you may see the parallel I am drawing. Our body, at the head and shoulders, cuts the water, thereby receiving the brunt of the force exterted on the water (or by the water). Whereas at all points past this, there is less force to hinder its movement. Therefore, with the weights around our hips, and the same gravitational force being applied, the hips have the freedom to accelerate beyond that of the head and shoulders, especially since the trailing legs and fin (with no rail) have a very low frictional drag, related to the rest of the body, towards the side of our body, being the direction of tipping. However, at greater, speeds the force exerted on the body past the head and shoulders will also be greater due to momentum of the water passing by (oops switched my frame of reference here, but it should be easier to understand). Therefore the gravitational force that would accelerate the legs and torso past beyond that of the head and shoulders, can not overcome the force of the water and the legs and torso would maintain trailing the body.

So, it would make sense to me that the rail offers a stabilizing of the tipping for a longer amount of time at slower speeds, because it creates a force that opposes the tipping. However, I do not understand how comparing the angled fin to non-angled, at the same speed, would be able to suggest that one is better to avoid tipping. Sumersaulting, yes, because if your non-angled fin is creating a force against the water then it will be in the opposite direction that one would be directed.

Ah! But saying that, I may have found a way that it would still happen, like in sailing. If their is a force at the front of the blade due to the fin receiving the water on its surface area, then the outlet of that force will be an attempt to pivot the body backwards. But this can not happen due to the force of the water acting on the back of the body from the momentum already created, therefore a squeeze occurs, where the force outlet is towards the direction of least resistance, being to one side. Tipping occurs.

Now, that being said, it is just a possibility that really depends on all the actual values of the forces and masses involved. So, the important thing to determine, is whether an angled fin with no rails, gives the same non-tipping advantage? I am going to go look at profiles of divers in the act with monofins.

Actually it would be interesting to do some test on the actual variances under controlled circumstances. Use various fins, but control the rate of descent with a weighted line, doing variable ballast dives. Using different fins, you should be able to determine at what speeds a fin is (in)effective and what the differences are in design. Problem is getting a hold of the various fins with the right sized footpockets.

 

[tylerz]

Peter,

Good point about the negative and FRC! I generally go much slower on such dives, but it would be interesting to see the rate of change that we safely achieve in such dives compared to a related deep inhale dive.

However, the point Peter Scott brought up, would suggest that is irrelevant. The theory (don't quote me) has to do with, on a full inhale or greater (dependent on the person), the blood is displaced from the core, and therefore is not readily available to pump into the alveoli during lung compression. Meaning our natural defense to fill space in the lungs, due to compressed air, will not occur as effectively. He speculates that after starting such a dive, the recovery during the dive, is a function of time and the drop in pressure as the inflated lungs shrink. Rate of descent is the determinant of these factors. This would imply a negative or FRC does not simulate these circumstances.

Good ideas!

Tyler

 

[derelictp]

Tyler

About angled mono without rails: The mono I use today is without rails but it has a FINIS footpocket on it.

Look at it http://www.nordicapnea.com/fins.html

All I can say is that the "tipping effect" is, in my opinion, mainly reduced by the angle and not the rails. I have used 9 different monos with an angle and some of them had rails and some not.

Another important thing to mention is that the "tipping-effect" is NOT totally eliminated by the angle, it's just demands MUCH LESS motions to keep the body straight down.

Remember; this is for my body and my technique.

About pressure changes/descent speed: I really dont have any more arguments about this. What Peter mentioned in his article makes sense to me too.

I just hope that I never squeeze my lungs.

Cheers