Questions concerning Backplates.

[danvolker]

I am wondering about the how of these pinch flats...My 18 pound halcyon gets NO special care from me, and has not since 1997. At the end of dive, I drop it in my dive bag, usually plate on bottom...but not always....it gets hosed when I get home and hung on a hook by the cam bands till I want to use it again..

I do NOT have integrated weights on the kit...aabsutely dont believe in them....maybe tbe mass from something like that is causing your punctures

?

 

[stuartv]

I am wondering about the how of these pinch flats...My 18 pound halcyon gets NO special care from me, and has not since 1997. At the end of dive, I drop it in my dive bag, usually plate on bottom...but not always....it gets hosed when I get home and hung on a hook by the cam bands till I want to use it again..

I do NOT have integrated weights on the kit...aabsutely dont believe in them....maybe tbe mass from something like that is causing your punctures

?

I didn't have integrated weights on it, but I did have 2 x 4# weights in trim pockets on the cam bands. With a 6# plate, that means 14 pounds, total (plus wing and rigging and 1 or 2 lights). That's assuming it happened during a tank change. Otherwise, it would have just been all that less the 8 # of weight in trim pockets.

No doubt it was operator error on my part. And I'll blame it on (almost) losing my balance on a heaving boat. But still my fault.

Also, being as old as it is, maybe DSS was using thinner bladder material back then?

 

[cwoco]

I wonder if Tobin does consider that the scenario I painted out benefits from having a donut wing or right dump valve, and has decided that the disadvantages are not worth it. Or if he considers it to be of completely no benefit as he seems to represent sometimes - that the donut wing is just there to placate divers who want all the doodads and gizmos.

 

[cool_hardware52]

I wonder if Tobin does consider that the scenario I painted out benefits from having a donut wing or right dump valve, and has decided that the disadvantages are not worth it. Or if he considers it to be of completely no benefit as he seems to represent sometimes - that the donut wing is just there to placate divers who want all the doodads and gizmos.

The reality remains that for gas to transfer across the lower arc of a donut wing one needs to be almost completely heads downs. As the gas volume in the wing drops this becomes more and more true.

Gas *always* moves to the high point of a wing. Even in a donut wing gas is still bound by the laws of physics. The lower arc of a donut wing in between the bottom end of the cylinder and divers rear end. It is undesirable for wings to extend below the bottom of the cylinder, and with normal cylinders they do not. The center of the lower arc will only be the highest point it the diver is vertical or near vertical heads down.

Ya, it's really that simple.

We won't be adding a 2nd dump. All BC's need at least one OPV, to prevent rupture. Adding another OPV to solve a skills deficit is not a path DSS will be choosing anytime soon.

As I've said before we offer both Horseshoes and donuts. Getting the capacity correct almost always trumps shape. Donuts aren't evil but they aren't a magic wand either.

There will never be a substitute for planning ahead WRT to buoyancy.

Tobin

 

[TSandM]

There will never be a substitute for planning ahead WRT to buoyancy.

Yup!

The i3 system that Aqualung has was an attempt to create an equipment solution to this problem -- multiple dumps and all of them opened by the same lever, so that the diver didn't have to think about where the air was in order to get it out. It was a clever idea, but the execution was clumsy and fraught with eventual malfunctions.

It is interesting that virtually all manufacturers of wings use a single OPV on the left-hand side (rarely on the right). And a lot of wings are horseshoes. The manufacturers (Tobin among them, but not at all alone) must feel that this problem is manageable. After all, they're the ones who are going to get sued if someone ends up embolizing because they couldn't get air out the left-hand rear OPV . . .

 

[tbone1004]

cwoco, while I agree mostly with Tobin and his experience is far greater than my own, I do prefer donut wings for single tanks BUT and this is a very very important but, I use STA's and that extra inch does allow the gas to transfer a bit faster when in a slightly head down attitude. Now, the reason I prefer donut wings is because when I bought my last singles wing, I got a screaming deal on a Halcyon Eclipse and wasn't going to spend a colossal amount of money for something that I use for MAYBE 2 dives a year? I think I've put 10 total dives on it, 6 of which were for rescue training where doubles were frowned upon. I dive singles so infrequently that it just doesn't make sense for me to switch to anything else. That set gets loaned out more than it gets used by me so I'm not going to put any more money into it. As of right now I sold the eclipse due to getting a free Dive Rite Travel wing which is nice because I can use it on my transpac that I use occasionally for doubles use and that wing has yet to get in the water. On the transpac though it is held even close to the plate than on a DSS style rig and it just limits the capacity of the wing so no advantage to it on there.

 

[ams511]

I am wondering about the how of these pinch flats...My 18 pound halcyon gets NO special care from me, and has not since 1997. At the end of dive, I drop it in my dive bag, usually plate on bottom...but not always....it gets hosed when I get home and hung on a hook by the cam bands till I want to use it again..

I do NOT have integrated weights on the kit...aabsutely dont believe in them....maybe tbe mass from something like that is causing your punctures

?

Does your 18lb Halcyon have a bladder? I am pretty certain it doesn't.

 

[Dr. Lecter]

Does your 18lb Halcyon have a bladder? I am pretty certain it doesn't.

Even the bladderless old Halcyon wings can be pinch-flatted, because all it takes to make them leak is disrupting the nylon weave enough to tear the relatively thin coating on the inside of the bag. I have an 18lb batwing with an ugly aquaseal repair at the bottom left corner thanks to that problem...though at least the design makes patching them easier and more reliable than trying to patch a urethane bladder.

 

[cool_hardware52]

cwoco, while I agree mostly with Tobin and his experience is far greater than my own, I do prefer donut wings for single tanks BUT and this is a very very important but, I use STA's and that extra inch does allow the gas to transfer a bit faster when in a slightly head down attitude. Now, the reason I prefer donut wings is because when I bought my last singles wing, I got a screaming deal on a Halcyon Eclipse and wasn't going to spend a colossal amount of money for something that I use for MAYBE 2 dives a year? I think I've put 10 total dives on it, 6 of which were for rescue training where doubles were frowned upon. I dive singles so infrequently that it just doesn't make sense for me to switch to anything else. That set gets loaned out more than it gets used by me so I'm not going to put any more money into it. As of right now I sold the eclipse due to getting a free Dive Rite Travel wing which is nice because I can use it on my transpac that I use occasionally for doubles use and that wing has yet to get in the water. On the transpac though it is held even close to the plate than on a DSS style rig and it just limits the capacity of the wing so no advantage to it on there.

It's not the space available between the lower end of the tank and the divers butt that controls transfer through the lower arc of a donut wing, it's the tank wrap.

Picture a horizontally trimmed diver with a partially filled wing. The gas will in two bubbles, one running down the length of either side of the cylinder.

The lower Arc of the wing will have zero gas in it regards of whether a STA is used or not, simply because the center of the lower arc is held down by the cylinder.

To get this center of the lower arc to fill with gas it has to become the high point of the wing. Take a sharpie and make a dot on the center line of your cylinder just above the bottom on the diver's side of the cylinder. Now imagine what attitude the diver needs to be in for this point to be the high point of their wing.

The reality is minor buoyancy adjustments require venting a "bit" of gas, not the entire wing. Short of intentionally trying to shift 100% of the gas in your wing to the right side and then initiating a butt first ascent there is going to be some gas in the left side of the wing.

Folks diving single tanks even in fairly heavy exposure suits should never be very negative, no more so than about 1/2 the buoyancy of their suit. Typically 15 lbs or less, often way less.

The gas required to displace 15 lbs of water fills a "cube" about 7.5" on a side or about 420 cu inches. If a diver's BC is displacing 15 lbs or water at 15 ft (1.45 ata) and they rise to 10 ft (1.30 ata) the gas will expand by about 10% They need to vent 42 cu inches of gas, which fills a cube about 3.5 inches on a side, i.e. a mere burp.

In a 3mm suit these numbers get down to eye dropper size.

Of course if a run away corking has commenced and momentum is no longer your friend dumping greater volumes may be required.

That's why planning ahead is important.

Tobin

 

[tbone1004]

agreed, but whenever I dump out of habit from open water I lean pretty hard to the right to get most of the air up there, then roll back to level when I'm done. On ascent I'm usually coming up leaning most of the way to the right and change my attitude to control the flow. So the opv is cracked the whole time and as I ascent and the bubble grows it leaks out continuously. The travel wing I have is especially narrow and also has their weird stretchy stuff integrated around the whole bladder, it was free.... so that wing is a different animal.

If I were to grab a new wing now it would probably be your LCD30, but there's no point for me as what I have works just fine for the negligible use that it gets. Most single tank backmount for me is done in the tropics where I just don't bother taking a wing since I don't need it without a wetsuit on, the backplate with STA is just the right amount of ballast for me in the salty stuff with an AL80. My doubles wings are all horseshoes though and that is very nice for air packing to offset an imbalance in the rig, usually stage bottles.