Help with Doubles

[tbone1004]

I was told (by someone vastly more experienced than myself) that the bungees are useful to maintain balance. I.e. if you roll to one side, the bungees help to prevent all the gas in your wing from going to that one side.

yeah they lied to you. Not possible to control the bubble. If you think about it the bondage wings have equal pressure on both sides of the wing, so when you roll over, you still have an imbalance of pressure just like you would if they were unbound. Goes against physics....

 

[stuartv]

yeah they lied to you. Not possible to control the bubble. If you think about it the bondage wings have equal pressure on both sides of the wing, so when you roll over, you still have an imbalance of pressure just like you would if they were unbound. Goes against physics....

So, you're saying that a balloon under water will have the air collect on the high side of the balloon?

Isn't a wing with bungees on it like a balloon? I.e. the bungees create surface tension that a wing with no bungees doesn't have?

Obviously, if there is not enough air in the wing to cause the bungees to come under tension, then the bungees aren't going to affect anything. OTOH, if the air in the wing fills the wing up to just under the point where the bungees start to have tension (when the wing is horizontal and in trim), then if you roll to one side and the air all tries to go to the high side of the wing, the bungees will resist that and force some air to stay in the low side of the wing. Which is why my earlier post said

the bungees help to prevent all the gas in your wing

. Because they HELP. And it's to prevent ALL the air from going over to one side.

No?

Also, is it not the case that, when you get all (or most) of the air over in one side and then you roll back to horizontal, it's common to still be a little imbalanced until you roll a little back the other way? In that case, won't the tension of bungees (mostly) force the air back into the other side of the wing, equalizing pressure between the two sides, when you get back to horizontal, without you having to roll a bit in the other direction?

 

[tomfcrist]

Ahh Stuart...a wing with bungees cannot be compared to a balloon. Maybe if the entire wing was elastic instead of being a big floppy bag, SOME of what you just said would be SOMEWHAT correct.

But just for fun. If you attached a ballon to a solid object underwater and rolled the object one way or the other...would the balloon move? Or would it stay tightly secured in the exact position you attached it?

 

[tbone1004]

yes a balloon will bias towards the top and the pressure differential is inversely proportional to depth. If you have bungees on each side it will expedite the balancing of the air once you get back to horizontal, but that is it, and is only true with bondage style wings like the old OMS. The Dive Rite style does little except help control the shape of the wing when it is deflated. The thin bungee they use doesn't have enough tensile strength to resist much. With the Nomad and Rec wing, the tabs are on the outside to help restrain them for use with singles or lighter weight bottle configuration, but do not confuse that method of bungee with the bondage wings.

 

[KevinNM]

I bought the cheap dive gear express doubles wing. Feels roughly like the Halcyon wing I used in class, but fit in the budget last month. I plan to replace it if I ever go to an actual tech course, but it works today.

I would try pulling tight the waist belt once you are in the water and horizontal. At least that was the solution to my issue with this in class.

 

[divad]

I can't intuitively fathom how a bungied wing could not be less efficient than a non-bungied wing. It doesn't make sense.




If the bungie is stronger than water pressure, it should trap air. If its weaker, at some point, it won't do anything but try to trap air at a lesser depth. What's is the point?

 

[stuartv]

If you have bungees on each side it will expedite the balancing of the air once you get back to horizontal

Okay, good. So there is some potential benefit. Note the keyword "potential".

... but that is it, and is only true with bondage style wings like the old OMS. The Dive Rite style does little except help control the shape of the wing when it is deflated. The thin bungee they use doesn't have enough tensile strength to resist much.

If the DR bungees are providing tension when the wing is deflated, then they must be providing even more tension when it is inflated. I'm sure they are not ideal springs, but, as long as they aren't stretched to the limit of their elasticity, being stretched twice as long should yield ROUGHLY double the tension, right? So, how can it be that they would provide no help in equalizing the sides of a wing when horizontal?

And, for that matter, the pressure differential at, just say for example, 100' between the high and low sides of a wing (when the diver is on his side) isn't that great. A DR Classic is 26" wide, so, call it 2'. That's 4 ATA on the high side and 4.06 ATA on the low side (if I've done my maths correctly). That's 1.5% greater pressure at the bottom than at the top. You're saying the bungees are short enough to control the wing when it's empty. With 5 or 6 (looking at a picture of a DR Classic) lengths of bungee pulling across the "tube" (attempting to compress) on the high side, you're saying that would make no noticeable, practical difference in how much air is in the high side versus the low side (as compared to the same wing with no bungees)? When it's only fighting a 1.5% pressure differential?

---------- Post added October 13th, 2015 at 09:55 PM ----------

I bought the cheap dive gear express doubles wing. Feels roughly like the Halcyon wing I used in class, but fit in the budget last month. I plan to replace it if I ever go to an actual tech course, but it works today.

I would try pulling tight the waist belt once you are in the water and horizontal. At least that was the solution to my issue with this in class.

Just curious: What class are you taking where you're diving doubles, that is not "an actual tech course"?

 

[Centrals]

Just curious: What class are you taking where you're diving doubles, that is not "an actual tech course"?

Twin tank diving is NOT technical. I would have thought any tec diver or aspired tec diver should know about it.
PSAI twin tank diver, the "F" course of GUE and UTD, there might be one from BSAC(not sure).

 

[MMM]

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[KevinNM]

Just curious: What class are you taking where you're diving doubles, that is not "an actual tech course"?

GUE doubles primer. Where I demonstrated an amazing lack of flexibility in my left shoulder, but I'm marginally able to reach the valve now with the right selection of undergarment and doing thing just right.