Wing size/lift calculation questions.

[TSandM]

Well, I think you can make a conscious choice for a setup that won't float your gear, if you want. But I do some diving off RIBs or off our own boat, where you take your gear off in the water before reboarding, and I would really rather not see my dive gear headed for Davy Jones' locker because I missed the clipoff . . . It seems to me, as well, that someone on this board had his gear fall OFF a boat, and it would far easier to retrieve it if it floated (and easier for the recovery diver, if there was one, to lift it if it could lift itself).

And in answer to the person who asked what happens if the inflator hose comes off the BC . . . you had either better have adequate backup buoyancy (and a dry suit should be able to do it, so long as one is not severely overweighted) or have ditchable weight.

 

[Akimbo]

I can see several issues at play that might lead to the recommendation to have a BC with enough capacity to float the rig. Unfortunately this guideline, like so many others, has evolved into a decree by God.

It is certainly a convenience for diving off a kayak or inflatable. It is also a good idea in limited shore diving situations where the best option may be to use you rig as a surf mat to avoid getting beat to crap in the rinse cycle. Most of all, it can be desirable in a rescue scenario. There are times you can get a panicky diver out of their rig and make them use it like a lifeguard’s float, rather them risk using you as a step ladder to get higher out of the water. Letting the rig sink is an option for the unconscious diver rescue, but less desirable.

It gets more complex with drysuit flooding. The early drysuit undergarments were woolies that took-on a lot of water to the point that, over time, it was assumed that suit buoyancy could drop to near zero — far less of a concern with modern high loft synthetics.

I have never been a fan of fully integrated weights in cold water anyway so wing size even on large doubles were never out of line with meeting this goal. I think the bigger problem with overstated BC capacity is caused by lazy instructors who teach students to be grossly over-weighted and the two controls at the end of the inflator hose are elevator buttons.

 

[Eric Sedletzky]

The reason I brought up the topic of an overweighted diver as a side note in this discussion was illustrate the danger of overweighting plus the humongous wings used these days that covers for overweighted divers at the surface.

There was a diver who died 50 feet from shore in San Diego several years back because he was overweighted and his inflator came undone at the wing which allowed all his air to vent and he dropped like a rock. Two divers were coming back in after a shore dive and there was a little beach break happening. Diver A (the one who made it) and diver B (the one who died) were just outside the break zone setting up to get through the break and get to shore.
Many times during those types of exits it becomes every man for himself because of the intensity which can be very high and all your energy gets used just trying to get yourself in and keep things under control. Both divers said OK see you at the beach and they started in. Somewhere along the line diver B's inflator broke off and all his air vented and he went straight down. Apparently he did not have his reg in his mouth or lost it and could not find one to breath off in the chaos. He must have panicked and was unable to ditch his weights or his rig. The result was that he drowned 50 feet from shore in 10 feet of water. They found later that the diver was grossly overweighted and if he had been properly weighted he would been able to stay on the surface even with no air in his BC and would not have sunk like a rock to his demise. I blame the huge wings that can lift a bus for helping to mask the problems of overweighting.
In my understanding of what I have learned over the last 13 years is that a diver should be able to float on the surface with a full tank with no air in the air cell. I have found that with this system a diver may need to descend head first and kick down for the first few feet but then after a certain amount of suit compression there will be a neutral zone then upon further descent a little air can be introduced into the air cell to achieve neutral buoyancy.
The system of loading up a diver with tons of weight then relying on the wing to elevator dive to me is not only nuts, it's cumbersome, annoying, and unsafe.

Drysuit only divers that like to load up your rigs with all kinds of non ditchable weight, I have a question.
What if you were to have a catastrophic failure of your drysuit (total flood) and your inflator came undone so you have no redundant buoyancy whatsoever. Do you have enough of your weight on your belt to lighten up enough to swim you and your rig up?

Don't poo poo wetsuit divers too much we're smarter than you think.
A wetsuit IS a form of redundant buoyancy. It doesn't flood and fail even if ripped wide open or if a zipper comes completely undone. You might get cold but the suit material is still there and will still provide floatation. It might work a little differently than a drysuit but it's reliable every time.

 

[Akimbo]

…
Don't poo poo wetsuit divers too much we're smarter than you think.
A wetsuit IS a form of redundant buoyancy….

I go one step further. A wetsuit is the most reliable form of buoyancy. BCs are a distant second. SMBs work, but are bordering on silly for that purpose.

I agree to the point that I don’t like to make pure solo dives in a drysuit — beach or kayak dives when nobody is around. I am confident I get to the surface, but a long swim in a flooded drysuit is another story. Solo diving off a charter dive boat does not have the same risks.

 

[Nixdax]

In regards to the OP's comment about lift rating on wings

"I have used a 4 pound backplate with an HP steel tank wearing a thick 7mm suit, 20 pound weightbelt and an 18 pound wing and had plenty of depth compensation diving as deep as I need to go. The wing was responsible for covering the compression of my suit which was probably around 10 to 12 pounds of loss. An 18 Lb wing worked fine with room to spare. However the rig would not float well on the surface with a fully inflated wing and it would slowly make it's way down. Maybe those Oxycheq wings are not rated right because a steel 120 with a 4 pound plate should be less than 18 pounds in water but who knows "

The lift rating of the wing is determined without anything attached to it other than a rope and weight usually. Therefore, if any part of the plate, harness, tank, diver, etc... restricts the wing from FULLY inflating it will not acheive the rated lift. This is why many wings do not acheive their rated lift in real life situations.

As for whether or not your rig should float on its own, that is a personal choice. There are no scuba police to enforce that one either way ;o)

 

[Eric Sedletzky]

As for whether or not your rig should float on its own, that is a personal choice. There are no scuba police to enforce that one either way ;o)

That is the whole point of this thread, to open a discussion about that because some declare that a wing must be able to float a rig on the surface.
My point is that no they don't. Some of us dive with no wing at all, and when we do dive with a wing we only use it at depth to offset minimal heaviness. With this mindset we can keep the wing very small and unobtrusive and see the rig as part of the diver not some huge behemoth that we just happen to be underneath guiding around.
I'm merely trying to shed light for newer divers that there is another way besides the retoric oozed by todays industry.

 

[cool_hardware52]

OK, so there's a lot of philosophies out there about what the size an air cell should be for different applications.
It is mentioned that a wing or air cell has to do two things, compensate for the added weight when a suit compresses at depth and it has to be able to float a rig on the surface.

My question is when did these rules come into play and who says?

Simple physics and common sense.

For cold water diving, if one does not hang 100% of their ballast on their rig, the buoyancy of the exposure suit will virtually always dictate the minimum required wing capacity.

For cold water diving with "normal" sized single tanks I like to see ballast roughly equal to the weight of the gas carried on the divers person, i.e. weight belt or weight harness. For most that means ~8 lbs in a belt.

Tobin

 

[Akimbo]

Nixdax

A Worthington X7-120 is rated for -11 Lbs full. That would be –15 Lbs with your back plate. Have you included your cam bands and regulator? Two investment cast stainless cam bands are a little under 1½ Lbs. Your regulators and miscellaneous could push it over 18. Most manufacturers’ ratings are based on a bare single bottle with valve.

To your primary point, I wouldn’t be very concerned about slowly sinking when full either. Most rescues are when cylinders are low. Same with removing tanks when boarding an inflatable. Sinking bottles can be an inconvenience at times, but far from a crime against humanity.

 

[elmer fudd]

And in answer to the person who asked what happens if the inflator hose comes off the BC . . . you had either better have adequate backup buoyancy (and a dry suit should be able to do it, so long as one is not severely overweighted) or have ditchable weight.

Actually, you can just manually inflate your BC. It takes a little practice to get used to, but it's not hard.

edit: disregard. I thought you were referring to the LP hose coming off the power inflator, not the hose coming off the BC itself. My mistake.

 

[cool_hardware52]

Actually, you can just manually inflate your BC. It takes a little practice to get used to, but it's not hard.

Ah, not not really. If the corrugated hose separates from the bladder your kinda done using the BC for buoyancy.

Tobin