need advice on swimming and bouancy

[Charlie99]

DIR Tec Diver once bubbled...
WIth your knees bent and your legs from knee down in veritical position, you are not affecting your streamlining or trim in any way, actually increasing it. Your head and shoulders break the water causing a slip stream around and over your body.

It's funny that the ONLY drag test numbers I can find on the web are on the OMS website, showing how the bungeed wings ARE less drag than non-bungied, yet the DIR mantra is "bungied wings are high drag".

Have you ever seen an Olympic swimmer going through the water with his body forward, but lower legs vertical?

When you scooter, do you also keep your legs in the bent position?

Next you will be telling me that LP104 doubles have less drag than an AL80.

 

[DIR Tec Diver]

Charlie,

You can not compare olympic swimming with diving, however olympic swimmers do not break the slip stream, as I already mentioned causes increased drag and resistance.

OMS wings ARE NOT more streamlined or efficient in the water, that is an absolute lie by OMS and has been proven over and over. The reason that they are the only ones to publish numbers is to try and justify their extremely poor design and configuration. That is fact not fiction.

Yes when scootering the legs are still bent, but not as much as when swimming as the weight of the scooter in front demands that your legs are not as bent. That is called proper trim. Think of a see saw. The more you put out on one side the more you have to compensate on the other side to achieve balance.

 

[DA Aquamaster]

I agree that a good and efficient frog kick is very hard if not impossible to beat in terms of speed and efficiency. I am routinely critised when diving with buddies as I am too fast, and this is with a set of doubles compared to their singles. It is said I move through the water like a seal even with all the extra stuff and only an occassional kick.

"Normal" divers have trouble figuring that out. What they do not look at is that the my "stuff" is well streamlined as is my body position and that a good frog kick involves a majority of the time in a coast/glide phase where you are maintaining very low drag. Assuming your fins are correctly oriented on the outstroke, you are also presenting relatively little drag when preparing for another kick - much less than you would think at first. This does have some of my dive buddies thinking that their force fins and split fins are perhaps not everything they thought they were or the last word in speed and efficiency.

However, I have a problem with the whole slip stream idea. Water is 800 times denser than air and you may introduce some turbulent flow but you are not going to get a noticeable aquadynamic slipstream effect with a diver at the speeds involved. With the speeds and distances involved it just is not going to happen.

I do agree with what you are saying overall though as again, the extra drag added by raising your legs a bit at the knee will be more than offset by reduced drag at the fins. Given the limited angles normal humans are capable of obtaining at the ankle, a bit of bend in the knee is needed to keep the large area of your fins streamlined. Many newer fins and in particular many split fins try to compensate for this with fins that droop a lot at the tip compared to the angle of your foot, but are still not as efficient as a fin well suited to a frog kick.

 

[DIR Tec Diver]

Very good post aquamaster. You hit the nail on the head

 

[Boogie711]

You could learn a lesson from Uncle Pug and others on this board when it comes to telling people about gear configuration and diving style. And this is coming from a diver who isn't DIR, but would perhaps one day like to be!

Let me say that I do now own, nor do I like, OMS wings. But for you to say that "that is an absolute lie by OMS and has been proven over and over" is just atrocious!

I'll call you on that. OK - please show me 'over and over' where OMS is lying. Find me objective third party data. Please provide me with some evidence.

After all, isn't DIR being open minded? Well - I'm being open minded. Right now, you're not.

It's statements like this that give DIR a bad name. And that's not fair to DIR in and of itself.

 

[DIR Tec Diver]

I think you are being a bit too sensitive and over reactionary.

One good source of test data is available by George Irvine. Of course now you say that he is impartial, but I beg to differ. He goes with what works and has no problems telling people when it does not work. His testing of everything down to drag, resistance and speed differences between different canister lights is incredible. These kinds of tests and that kind of data is at a level I have never seen by any manufacturer.

From a safety aspect bungeed BCDs have no place in diving. Sorry if that upsets you to be so strong a statement, but that is just life. The pressure that the bungees put on the wing not only will empty it in the event of a puncture giving you 0 buoyancy and lift as a result, but if you try to orally inflate them, it won't work. I am not trying to be mean, nasty or "atrocious", just practical and straight forward.

I have no problems with you, and it's ok to go after me, I don't take it personally and usually that is when some of the best info comes out, so no problems. Being open and objective is one thing. Bowing down to be politically correct and sanitizing everything is another.

 

[Boogie711]

Please understand - I AGREE with you. But you cannot expect to run around and say things like "XXX are a bunch of liars" without having evidence to back you up - because then that would make you just as bad, wouldn't it?

And by the way - if you're trying to preach DIR to the non-disciples, using George Irvine as a source probably isn't your best approach.

 

[Charlie99]

DIR Tec Diver once bubbled...
One good source of test data is available by George Irvine. Of course now you say that he is impartial, but I beg to differ. He goes with what works and has no problems telling people when it does not work. His testing of everything down to drag, resistance and speed differences between different canister lights is incredible. These kinds of tests and that kind of data is at a level I have never seen by any manufacturer.

The pressure that the bungees put on the wing ...., but if you try to orally inflate them, it won't work. I am not trying to be mean, nasty or "atrocious", just practical and straight forward.

Is this test data on streamlining published somewhere. I couldn't find any at GUE, Halcyon or WKPP websites. As I have before, the ONLY drag/streamlining info I have seen is what has been published by OMS. While you may laugh at the crudeness of using a moored boat's propwash to generate a current in which to test drag, it's the one and only report along these lines.

On rec.scuba, there is a guy that is coordinating a senior project for some engineering students and they are doing drag testing of various BCs. He has been trying unsucessfully to get some Halcyon gear for evaluation.

As to bungied wings not being able to be orally inflated ---- do you have anything to support that. This is yet another myth, along with the other bogus statement of "You can inflate them on the surface, but you can't inflate them at depth because of the increased pressure".

http://www.omsdive.com/faq-bc.html#faq-bc

p.s. I agree with the statement that it is better not to have the bungies due to the possible problem of deflation after a puncture, but that valid statement often gets buried along with the other b.s. that gets thown around about drag and oral inflation.

 

[Charlie99]

DA Aquamaster once bubbled...
I do agree with what you are saying overall though as again, the extra drag added by raising your legs a bit at the knee will be more than offset by reduced drag at the fins. Given the limited angles normal humans are capable of obtaining at the ankle, a bit of bend in the knee is needed to keep the large area of your fins streamlined. Many newer fins and in particular many split fins try to compensate for this with fins that droop a lot at the tip compared to the angle of your foot, but are still not as efficient as a fin well suited to a frog kick.

The key words are "raising your legs a bit at the knee". For optimum streamlining you shouldn't be bending your knees any more than is needed to get your fin blades horizontal. Making your knees bend at right angles to put your lower legs vertical just increases drag.
As I posted yesterday, I use a modified frog kick that uses mostly the ankles. I keep my toes pointed so that my fin blades (original U.S. Diver Blades) are straight back and horizontal during the glide phase. My knees are only very slightly bent and my fins are probably about even with the center of my tank.

A few months ago the group on the boat were talking about identifying divers underwater. A couple people laughingly said that I was easy to spot since every time they looked at me I wasn't moving any body parts, but was somehow flowing through the water. That's the advantage of a frog kick

 

[Upwelling]

thanks everyone for the good info, there is a lot to think about here...although I got a bit lost when peopel started talking about the DIR stuff