Why do the big OMS wings have 2 inflators?

[Randy43068]

Tell us how you REALLY feel!!!

That pretty much sums it up.

 

[Reg Braithwaite]

If the diver is negative only by the weight of their backgas it's pretty hard to see a scenario where a drysuit cannot offset the loss of a wing. Even 2 x 130's will only hold ~20 lbs of gas.

Sorry for the overly n00bish question about basic weighting, but... Is it really possible to balance yourself and the rig such that you are only negative by the weight of the gas? Or are you almost always negative by more than the weight of the gas when logging around a pair of heavy steel tanks and/or multiple deco bottles, can lights, reels, and so forth?

 

[Randy43068]

Sorry for the overly n00bish question about basic weighting, but... Is it really possible to balance yourself and the rig such that you are only negative by the weight of the gas? Or are you almost always negative by more than the weight of the gas when logging around a pair of heavy steel tanks and/or multiple deco bottles, can lights, reels, and so forth?

A real issue is that your weight is dynamic. As you change depth your suit and anything crushable will crush making that less buoyant. The opposite happens as you ascend the water columb. Also, as you breath off your air, or gas then you don't have that weight either. Your tanks get lighter.

Buoyancy is a balancing act throughout the dive. Not unmanageable by any notion, however, as long as you understand that buoyancy is dynamic you'll be able to manage it throughout the dive.

 

[cool_hardware52]

Sorry for the overly n00bish question about basic weighting, but... Is it really possible to balance yourself and the rig such that you are only negative by the weight of the gas? Or are you almost always negative by more than the weight of the gas when logging around a pair of heavy steel tanks and/or multiple deco bottles, can lights, reels, and so forth?

Start with the *Minimum Buoyancy* of your dry suit.

What is the minimum buoyancy of your suit? It is the amount of ballast you need to get neutral if you were wearing only your undergarment and drysuit, in neck deep water with an open exhaust valve.

Let's say you test your suit and find that it takes 24 lbs to get neutral with only your undergarment and drysuit on.

What is the goal for your total weighting? To have your total ballast equal to the minimum buoyancy of your suit (+ 1-2 lbs) with empty tanks.

Why? If you need to hold a shallow stop while you breathe down your backgas to zero you need enough ballast to offset the buoyancy of your suit. Pretty simple.

If your "rig" i.e. back plate +harness + empty tanks + bands and manifold + regs + can light provides more than ~26 lbs. (24 +2) then you need to change components, lighter plates, lighter tanks etc. until it does.

If your rig provides less than 26 lbs you need to add ballast, or you will not be able to hold a shallow stop with empty tanks. Different plates, and or adding ballast to the rig or using a belt.

Now if your rig provides ballast equal to the minimum buoyancy of your suit +2 lbs with empty tanks how negative will you be when you have full tanks?

The weight of your back gas + 2 lbs.

Do you ever **need** to more negative? No. If not why select components that increase the problems a diver will face if they suffer a buoyancy failure?

Carrying more ballast than is required to hold a shallow stop with empty bottles offers no advantage, and increases the risks for the diver.

Over weighted + a larger wing is simply ignorance in action.

Tobin

 

[Lucy's Diver]

A lot of theory here....

I know that my vulcanized rubber drysuit will not effectively float the full set of steel 120s I dive for my recreational dives. Either bladder in my redundant wing will. Need I say more? Probably....

I also carry a lift bag and pretty large SMB that can be a lift bag. I know I could do various things with that (shoot it and reel up, fill it and vent on the way up), but orally filling the second bladder is faster and is an easier skill. I've done all these things. Management of the wing is just an easier, cleaner skill.

I operate lift bags for work all the time. I operate jackhammers and brocos and manage four or five lines at once in zero viz. Trust me when I say operating a lift bag as a wing is really difficult. Why do it when you have a wing that works (your redundant bladder)?

I'm not changing components. Its what I'm issued and paid to dive in. Not everyone can swap out different styles of backplates, tanks, and lead for different exposure suits. And guess what - at 300 PSI in 15 FSW I can barely hold depth with this configuration, so I am not over weighted.

What exactly is the problem? Its not like the redundant bladder will reach out and choke you if you choose to utilize a different lift device. It takes up no real space and requires no real equipment alterations. Don't hook up an LP to it and you have exactly zero risk of a runaway inflation. It requires little, if any training, as the skill is the mirror image of what you do every dive, and what you were trained to do in a pool with an AL80. I don't get the emotional reaction.

 

[cool_hardware52]

A lot of theory here....

I know that my vulcanized rubber drysuit will not effectively float the full set of steel 120s I dive for my recreational dives. Either bladder in my redundant wing will. Need I say more? Probably....

Using a drysuit for buoyancy is not a "theory". While I do not advocate the practice some recreational agencies teach using the drysuit as primary buoyancy control.

I've never tried it with my 120's, but I have with 2 x 100's. No problem. I find it hard to believe that the ~3 additional lbs of gas in a pair of 120's is the "straw that breaks the camel's back"

If anybody doubts that your drysuit can provide sufficient buoyancy to overcome the negative buoyancy of a pair of full doubles just leave your exhaust valve closed at the surface and blow up your suit a bit at the start of your next dive. Now dump your wing and try to descend........


Tobin

 

[Reg Braithwaite]

Start with the *Minimum Buoyancy* of your dry suit.

What is the minimum buoyancy of your suit? It is the amount of ballast you need to get neutral if you were wearing only your undergarment and drysuit, in neck deep water with an open exhaust valve.

Let's say you test your suit and find that it takes 24 lbs to get neutral with only your undergarment and drysuit on.

What is the goal for your total weighting? To have your total ballast equal to the minimum buoyancy of your suit (+ 1-2 lbs) with empty tanks.

Why? If you need to hold a shallow stop while you breathe down your backgas to zero you need enough ballast to offset the buoyancy of your suit. Pretty simple.

If your "rig" i.e. back plate +harness + empty tanks + bands and manifold + regs + can light provides more than ~26 lbs. (24 +2) then you need to change components, lighter plates, lighter tanks etc. until it does.... More ballast than is required to hold a shallow stop with empty bottles offers no advantage, and increases the risks for the diver.

That sounds wonderful. But what baffles me about this explanation is what happens if my minimum buoyancy is quite small and simultaneously I wish to dive something that requires larger and therefore heavier tanks or double tanks or both.

It seem to me that something has to give. Either I don't ever do those dives because the tanks would be too heavy, or I dive overweighted. I anticipate having this problem: Compared to most of the divers I know up here in Ontario I am very lean and I don't wear heavy undergarments.

 

[cool_hardware52]

That sounds wonderful. But what baffles me about this explanation is what happens if my minimum buoyancy is quite small and simultaneously I wish to dive something that requires larger and therefore heavier tanks or double tanks or both.

It would be pretty uncommon for a single rig to be more negative than almost any cold water exposure suit.

For example: E8-130 + SS Backplate and Harness + Reg + can light is still only about -21 lbs with a full tank, and -11 with an empty tank.

Is your cold water exposure protection less than 11 lbs positive? I doubt it.

One thing most divers transitioning to doubles discover is they need more insulation. More gas = longer / deeper / colder. More insulation = more buoyancy.

The fact remains that careful selection of tanks, plates etc. can result in a rig that is not more negative than your suit is positive.

Example 2 x al 80's + Kydex Plate and Harness + Dual regs, Bands and Manifold + Can light is only about -16 lbs with full tanks and - 4 with empty tanks.

Even 2 x E8-130 + SS plate & Harness + regs, bands and Manifold + Can light will only be about -38 lbs with full tanks and -18 with empty tanks.

Few drysuits with even modestly warm undergarments will be less than 18 lbs positive.

Is it possible to configure a rig that's more than -38 with full tanks? Sure. Start with a couple Faber HP120's These tanks are about -7 lbs EACH empty. Use these with a SS plate & Harness + Regs + bands and Manifold + Can light and you can have a rig that's -50 with full tanks and -30 with empty tanks. The question is if your suit say +22 lbs., WHY use Faber HP120's and a SS plate?

Tobin

 

[Tassie_Rohan]

Tobin - I agree that drysuits are the way to go for redundant buoyancy with doubles in cold and tepid water but, I know you will find this hard to believe: there are divers out there who dive water so warm that wearing a drysuit, especially during shallow deco stops, is actually uncomfortable!

Up in the tropics my 3 mm needs only 5 lb of lead. My total kit therefore can only be 6-7 lb negative with no weights. If I want to use anything other than double Al 80's or tiny steels then I'm going to have to resign myself to being overweighted.

Like it or not many divers do dive big steel doubles in warm water. In this case you have to either use a lift bag for redundant bouyancy (which comes with its own set of hazards at a time when you need things to work and be simple), or just go with a redundant wing.


Cheers,
Rohan.

 

[cool_hardware52]

Tobin - I agree that drysuits are the way to go for redundant buoyancy with doubles in cold and tepid water

Why do you find a drysuit is superior to a redundant wing for cold water?

Tobin