cool_hardware52:
Apparently I have failed to make my point. Air Balance can be a problem, even when prone, if the wing is too wide. Narrow profile wings, (nobody makes a narrower wing than I do) work because when in normal use, i.e. horizontal at depth, filled to ~25% or less the "side pontoons" will not be tacoed above the tank, they are along side it. This means when prone there will also be air in the top arc If there is air in the top arc, and you vent from the left OPV the balance will occur through the top arc, you can't stop it.
With a "too wide horseshoe" the air in the side pontoons is well above the top arc, and some degree of heads up will be necessary to shift gas. This is not my "position" it's simple physics.
Doubles are different beast. On our single wings we use the roughly triangular space between the plate and the tank, our singles wings inflate almost all the way to the center. This keeps the "bubbles" at the same leve as the top arc. Can't do that with doubles. With doubles the tanks contact the plate right down the outside edge of the plate, no space left between the tanks and the plate, i.e. all the inflation must be outside of the tanks. This alone dictates a wider wing and precludes having the top arc filled when prone.
The second reason is volume vs overall profile. Doubles wings need more lift than singles, and this means wider profiles. However if you stick some of that volume in a bottom connection, you can makes the sides slimmer, i.e. less drag. Remember that almost never is awing fully inflated except at the surface, or if you have total DS flood. This means "hidding" some of the necessary lift under the bottom of the tanks has little effect in normal use.
You sure about that?:05:
Regards,
Tobin
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When I dive with a RecWing, it is with doubles. Since I use the OPV as a dump valve, I reach back with my hand and I can feel the air bubble in the bladder as I cup the OPV. I have examined both sides and my air pockets are very small (maybe two or three fists on each side at the start of the dive). They are located in the bottom portion of the bladder (I am mostly horizontal), and are above the plane of the bp with no air leading to the front arch. The OPV is conveniently right on top of that bubble, and I do not need to reposition any to release some of that air. I can't think of any reason why I wouldn't want to do that (other than the balance issue which can be addressed with another dump).
To vent via the inflator hose, I must go slightly heads up (or, at a minimum, not heads down), I must hold the inflator above the height of the bubble, and the effort, albeit modest, is significantly more involved than releasing via the OPV in the original position. Furthermore, in the absense of a conduit connecting the sides at the bottom, if I don't restore my head down position while parallel to the surface, I can trap more air in one side than the other.
I will admit though, since the RecWing has a wider profile near the bottom, and the air pockets are above the plane of the backplate, I would be required to go more head down to pass air between the sides even if the wing was a donut, and I would still need to remain parallel to ensure equal transfer. Given the constaints, my hopes for achieving donut freedom with doubles idoesn't look promising. Not a big deal though, as the imbalance isn't a major issue, although I did find the dual dumps on the Zeagle very convenient to nudge that balance when the opportunity to vent came about while my activities were favoring a head down posture.
Apparently I have been comparing apples to oranges: I dive the OxyCheq 30# with singles and indeed the taco effect is not present and the bottom arch contains air when I am slightly head down. Given that the air flows freely from side to side (again, very small amount of air in the bladder), I never need to adjust head up/down to transfer air from one side to the other: I merely lean and the air moves. I still think this bodes well for donuts for singles where the top and bottom crossovers are similar and the air is at a level to take advantage of the path without imposing a horizontal or head higher position. Although your singles wings are indeed a very narrow profile, I am still not convinced that the donut would not provide an advantage when the air bubble does not make it across the top arch (slightly head down posture) but could make it across a bottom arch. Without testing it though, I cannot qualify the strength of that advantage, and I apologize for using my RecWing/doubles experience for that purpose (it was not my intent to compare apples to oranges).
Am I the only person opting for the simplicity of dumping via the OPV? OPV failures are never an issue above that of nuisance, and they are very simple mechanisms to maintain. I often go heads down slightly when I need to vent just because its often easier to get the bubble under the OPV than to get the bubble to the inflator. Not that the inflator method is hard (I do it often enough), just requires a specific action that is more involved than heads down pull chord. Additionally, I often check for the presence of the bubble before venting from the OPV (my hand is right there anyhow): near the end of the dive that bubble is getting very small. It sure appears bladder manufacturers are aware of this use given the migration of the OPV location to a location that is optimal for bottom venting (at least for the Zeagle Ranger, DiveRite RecWing, and OxyCheq donut that I have experience with).
