How much "taco" is allowed?

[Ed Palma]

So, we've all read the threads talking about using doubles wings for singles and vice versa. All the discussions about drag etc...

In the threads I've read, a wing is supposed to:
1. Float the gear on the surface
2. compensate for the loss of exposure protection buoyancy at the heaviest point (full tanks with all gear)

I've never really come across anyone seriously saying that you might need reserve lift to aid in a buddy's buoyancy loss.

So, with tall this in mind, my question stems from an actual situation I'm in. I've started the transition to doubles, and initially, since I was starting out with a small set (steel 72 dubs - 10lbs neg at most when full). I did the math: -10 for the tanks, plus manifold and regs and bands, maybe -16 lbs. Wetsuit buoyancy, maybe -6 lbs, for a total of 22 lbs buoyancy needed.I tried out using my original singles wing - a 32lb EXD wing. (shown beside my dedicated singles wing -also rated at 30lbs).

I noted a wide center panel so I though to myself to give it a try. Surprisingly, I was able to support myself, the rig, and a al40 with no problem on the surface in fresh water. (of course, this is underwater...)

There's minimal wrap or "taco" around the sides of the tank.

Just to be sure, I bought a new 50lb doubles wing. It'll have about 2 inches of excess wing on either side of the twins.

My question is: Is the 32lb wing enough for these tanks, or would you be more comfortable with a larger wing? Why?

I'm not trying to cheap out here (i did get the doubles wing...) I just want to see if there's any additional benefit to having just that bit more "excess" wing of the 50 with this set-up, as opposed to the 30lb wing.

 

[spectrum]

I can't say for sure but it is possible to impinge on a wing and not realize the stated lift. Unrestrained it will fully inflate. If pinched between cylinders, plate or other gear it will displace less.

Pete

 

[Ed Palma]

I can't say for sure but it is possible to impinge on a wing and not realize the stated lift. Unrestrained it will fully inflate. If pinched between cylinders, plate or other gear it will displace less.

Pete

That was my initial concern. I'm sure I'm getting a lot less than 32lbs of lift - but in spite of that, I can still stay on the surface. Some threads advocate using the minimum lift needed in order to avoid excess wing which will increase drag. I was just wondering what the board thought of using this small wing for dubs seeing as it actually works.

At any rate, I'll be trying my new 50 wing soon. The one advantage I can think of is that with just a little bit more "taco," I'll be able to isolate a bit more gas off to one side or the other to offset the effect of the stage.

 

[RJP]

The one advantage I can think of is that with just a little bit more "taco," I'll be able to isolate a bit more gas off to one side or the other to offset the effect of the stage.

"Taco" as a technical term typically refers to using an overly large or doubles wing on a single tank, such that it wraps around the tank itself trapping air. Have never heard the term used - or even seen the issue - where a doubles wing was too large and thus wrapped around a set of doubles, other than getting a completely over-board amount of buoyancy on smallish doubles.

Some of the wing protruding slightly past the edge of the doubles does not a taco make...

 

[cool_hardware52]

So, we've all read the threads talking about using doubles wings for singles and vice versa. All the discussions about drag etc...

In the threads I've read, a wing is supposed to:
1. Float the gear on the surface
2. compensate for the loss of exposure protection buoyancy at the heaviest point (full tanks with all gear)

I've never really come across anyone seriously saying that you might need reserve lift to aid in a buddy's buoyancy loss.

How many failures are you planning for?

If *your* wing is sized so you can:

Float your rig at the surface with full tanks if you ditch it
&
Compensate for the maximum possible change in buoyancy of your exposure suit

How does your teammates wing failure require *you* to have more lift?


My question is: Is the 32lb wing enough for these tanks, or would you be more comfortable with a larger wing? Why?

In a drysuit with doubles in normal operation the wing only compensates for the weight of your back gas. Suit for comfort, wing for gas.

With 2 x 72's you have about 11 lbs of gas. Why not use an 11 lbs wing? What happens in the event of a total drysuit failure? Unlikely to be sure, but if you jump in the water with the zipper open, or blow out a neck seal, or tear the suit there is the potential to loose all the buoyancy the suit provides. If you can't replace this lost buoyancy with your wing you going to have real problems.

There's a reason why minimum wing lift for doubles = weight of back gas + minimum drysuit buoyancy + 2-3 lbs.

Plan for this contingency and you will have plenty of lift to assist a teammate if needed.

One final point, never a good idea to CLAMP your wing bladder between your cylinders and your back plate. This is exactly what you will be doing if you use a wing with a center panel that's narrower than the manifold spacing of your dubs.

I'm not trying to cheap out here (i did get the doubles wing...) I just want to see if there's any additional benefit to having just that bit more "excess" wing of the 50 with this set-up, as opposed to the 30lb wing.

Doubles wings have to inflate outboard of where the cylinders contact the plate, no other way to do it. Excessively large, high capacity doubles wings will wrap up or "taco". Think 94 lbs lift on a pair of 72's.

This presents exactly the same issues as taco on a singles tank, the diver has to break trim to move gas or vent. Understanding the real lift requirements and matching the wing lift to the application is the best way to avoid too much tank wrap.

Tobin

 

[Cave Diver]

Man I hope Idoc doesn't see this thread.

 

[Ed Palma]

My question is: Is the 32lb wing enough for these tanks, or would you be more comfortable with a larger wing? Why?

Tobin, I was hoping you'd chime in on this thread. Thanks. To answer that question, I guess I would feel more comfy with a larger wing, hence the purchase of the 50. As to the "why" that's the part I'm i bit unsure of. I guess its because I can float myself up without having to fully inflate the whole wing. Maybe because I'll be a bit higher up out of the water when saddled with full gear. Or maybe simply because I'll be using a wing meant for doubles.

One final point, never a good idea to CLAMP your wing bladder between your cylinders and your back plate. This is exactly what you will be doing if you use a wing with a center panel that's narrower than the manifold spacing of your dubs.

Granted, there is a degree of clamping of the wing between the plate and tanks. I guess this is the best argument against using the 32lb wing,

 

[cool_hardware52]

Tobin, I was hoping you'd chime in on this thread. Thanks. To answer that question, I guess I would feel more comfy with a larger wing, hence the purchase of the 50. As to the "why" that's the part I'm i bit unsure of. I guess its because I can float myself up without having to fully inflate the whole wing. Maybe because I'll be a bit higher up out of the water when saddled with full gear. Or maybe simply because I'll be using a wing meant for doubles.

Humm, I provided the *why* already. Said another way: You need to start the dive negative by the weight of your back gas +2-3 lbs. This allows you to hold a shallow stop and breath your back gas tanks all the way down and put a little extra gas in your suit for warmth.

If you start the dive negative by the weight of your back gas + 2-3 lbs you will by definition need to inflate your wing the same amount just to stay at the surface.

Now what happens if you suffer a total failure of your suit? You need to have that amount in reserve.

Weight of your back gas + Minimum buoyancy of your suit + 2-3 lbs.

If you follow this method you will have plenty of lift for comfort at the surface assuming your drysuit is intact. With full bottles and a working drysuit you have reserve capacity at least equal to the buoyancy of your suit. That's typically 20-30 lbs. Why would you need more?

Granted, there is a degree of clamping of the wing between the plate and tanks. I guess this is the best argument against using the 32lb wing,

No, not really. IMO it's way down the list.

#1 Not designed for the task

#2 Potentially not enough lift even if fully inflated

#3 Lift reduced even further by plate and cylinders restricting full inflation.

#4 Good way to damage wing.

I'm frequently surprised how complicated folks want to make wing calcs, speadsheets, 100 post threads etc.

It's very simple:

Float your rig at the surface with full bottles.

Compensate for the max possible change in buoyancy of the exposure suit.

Tobin

 

[flots am]

How does your teammates wing failure require *you* to have more lift?

You may not have the convenience of needing to rescue your perfectly weighted team mate.

A rescue is much more likely to be required for some overweighted random diver who jumped in without a pre-dive check and discovered that he's OOA or has a failed BC or wing and is now panicking on his way to the bottom.

I've seen your other posts and know that you have a laser-like focus on "just enough" lift, but in the real world, it's nice to have a little extra for when the brown stuff inconveniently hits the fan.

Also, the entire "drag" concept is overblown. If the additional drag caused by a larger wing is causing problems, you're trying to move to fast.

flots.

 

[cool_hardware52]

You may not have the convenience of needing to rescue your perfectly weighted team mate.

A rescue is much more likely to be required for some overweighted random diver who jumped in without a pre-dive check and discovered that he's OOA or has a failed BC or wing and is now panicking on his way to the bottom.

Humm, I'll posit that you have either not read my posts or my point has failed to register.

If you have enough lift to compensate for the maximum change in buoyancy of your exposure suit *IN RESERVE* as you would if you follow my recommendations, you have enough to help even a grossly over weighted random diver.

Perhaps examples will help.

Drysuit with Steel doubles

Drysuit min buoyancy = 24 lbs

2 x HP 100, weight of air or nitrox = ~16 lbs

Extra 3 lbs for suit inflation = 3 lbs

Gas + suit + 3 lbs = 43 lbs. Use a 49 lbs wing

Now if this diver is weighted so they are negative by their back gas + 3 lbs they will be 19 lbs negative at the surface at the beginning of the dive. To stay at the surface requires no less than 19 lbs in their wing. 49 - 19 leaves 30 lbs in reserve.

30 lbs should be more than enough to assist another diver.

7mm Wetsuit + single HP 100

Wetsuit is +20 lbs
Wing should be larger than bouyancy of their wetsuit, I'd suggest a 26 lbs lift.

If this diver is weighted so they are eyelevel at the surface with no gas in their wing and a full cylinder they have may be 20 lbs of wing available to assist another diver.

One can of course create tortured scenarios involving multiple failures, overweighted divers, and aliens landing, but a with a little understanding of the actual requirements it easy to see how huge wings are seldom warranted.

Tobin