Help with wing lift calculation

[49north]

I’m sure that if one maintains and inspects their equipment regularly, this would go a long way to avoiding a complete wing failure. So this begs the question, are the advantages of having a smaller, more streamlined wing worth the risk of perhaps needing extra lift one day to assist a buddy?

 

[rsingler]

Tearing a wing on sharp coral or with a reef hook may be independent of good maintenance. But unless your buddy has both a torn wing AND is out of air, you have time to approach this incrementally.
Can he/she swim up 5#?
Can you jettison a little weight from his/her trim pocket?
Can he/she jettison just ONE weight pocket while you stay "heavy" until you dial in your ascent?

Not wanting to jettison weights is a mindset which has killed a lot of divers. I understand not wanting a runaway ascent. But lighten the load a little, link up, and add buoyancy until you two are neutral. As you ascend, expanding gas will take over, and you'll need to vent. If your wing is maxed out, you may need to swim up a little until suit compression lessens, and you both become more buoyant.
Decide in advance, that if one diver tears a wing, the rescuer has control. It's not a time for misunderstandings about buoyancy. All the victim has to do is breathe and follow instructions (e.g., "swim up a little harder").
Understand that it may be possible to trap a pocket of air by keeping the tear lowest.
But when you get to the surface in a measured fashion, there is NO reason, ZERO!, to be reluctant to jettison all of both of your ditchable weight.
Look at each of your "torn wing with jettisoned weights at end dive" buoyancy requirements (at the surface) on the spreadsheet (cell B30). If you want to always be able to float your buddy, pick a wing with a sum of your two buoyancy numbers in that cell. But that added buoyancy requirement is actually often minimal or zero, after ditching weights. So the question is really, how much effort will you need to make, or how much incremental weight will you need to shed, to ascend until suit compression lessens?

How many failures to plan for is one of our tougher challenges.

 

[49north]

Tearing a wing on sharp coral or with a reef hook may be independent of good maintenance. But unless your buddy has both a torn wing AND is out of air, you have time to approach this incrementally.
Can he/she swim up 5#?
Can you jettison a little weight from his/her trim pocket?
Can he/she jettison just ONE weight pocket while you stay "heavy" until you dial in your ascent?

Not wanting to jettison weights is a mindset which has killed a lot of divers. I understand not wanting a runaway ascent. But lighten the load a little, link up, and add buoyancy until you two are neutral. As you ascend, expanding gas will take over, and you'll need to vent. If your wing is maxed out, you may need to swim up a little until suit compression lessens, and you both become more buoyant.
Decide in advance, that if one diver tears a wing, the rescuer has control. It's not a time for misunderstandings about buoyancy. All the victim has to do is breathe and follow instructions (e.g., "swim up a little harder").
Understand that it may be possible to trap a pocket of air by keeping the tear lowest.
But when you get to the surface in a measured fashion, there is NO reason, ZERO!, to be reluctant to jettison all of both of your ditchable weight.
Look at each of your "torn wing with jettisoned weights at end dive" buoyancy requirements (at the surface) on the spreadsheet (cell B30). If you want to always be able to float your buddy, pick a wing with a sum of your two buoyancy numbers in that cell.

How many failures to plan for is one of our tougher challenges.

This makes good sense.

I tried the spreadsheet and it works well, nice job you did on it! I do have one question. For cubic feet of air, I entered 77.4 for an AL80 and a tank buoyancy at 0 psi of +4. I got these values from a table. Would this be correct?

 

[rsingler]

This makes good sense.

I tried the spreadsheet and it works well, nice job you did on it! I do have one question. For cubic feet of air, I entered 77.4 for an AL80 and a tank buoyancy at 0 psi of +4. I got these values from a table. Would this be correct?

Yes, those numbers are correct. What is less clear from those tables is whether or not the buoyancy is with or without the valve. It's supposed to be buoyancy with the valve, but not all manufacturer's tables follow this custom.
Now add a pound of negative buoyancy back for 500 psi.

 

[49north]

The table I used specified with valve.

Thanks for all of your input on this, it has been very helpful.

The only wings we have used is our 40lbs. In all honesty, they seem to work fine in warm water, so we are still on the fence about whether or not the smaller wing will be worthwhile.

 

[NAM001]

I’m sure that if one maintains and inspects their equipment regularly, this would go a long way to avoiding a complete wing failure. So this begs the question, are the advantages of having a smaller, more streamlined wing worth the risk of perhaps needing extra lift one day to assist a buddy?

I dont see an issue with streamlineing as regards to size. the wing with 3 liters of gas in it is the same volumn whether it is a 10# wing or a 40 # wing. The problem , as i have experienced is that the larger the wing the more ability of a bubble running from the hips to the shoulders making trim hard to maintain. The smaller the more the bubble remains stationary. A full wing has no bubble movement a 1/4 filled wing has the potential for a lot and a half stays reasonablely in place with little shift as you take minor up and down angles. major stability difference between 1/4 full and 3/4 full.

 

[seeker242]

I wear a very similar single tank setup with a 25lb wing, although with an aluminum plate. With a 5mm, 10 lbs of lead, a 25lb wing is more than enough. It can float me on the surface when only about 1/2 full. I can't imagine a single tank setup in the tropics where a 23 or 25 lb would not be good enough. You would probably have to wear a 7mm farmer john or something. But nobody wears that much neoprene!

 

[rsingler]

I wear a very similar single tank setup with a 25lb wing, although with an aluminum plate. With a 5mm, 10 lbs of lead, a 25lb wing is more than enough. It can float me on the surface when only about 1/2 full. I can't imagine a single tank setup in the tropics where a 23 or 25 lb would not be good enough. You would probably have to wear a 7mm farmer john or something. But nobody wears that much neoprene!

Exactly!
And the spreadsheet proves he's right theoretically. The setup @seeker242 describes requires only 10# air buoyancy at the beginning of the dive, and requires NO wing buoyancy with weights dropped at the end of a dive. The only time the wing is closer to full is at depth (with wetsuit compressed) at the beginning of a dive with a full tank. But with half of your weight dropped, you'd have no difficulty swimming up a similar buddy with a torn wing. Then at the surface, with his weights dropped, he needs no wing at all.

Like I said, I'm perfectly happy with my 18# VDH, and carrying a sausage for redundancy. @KWS had it right - the smaller the wing, the better the air distribution for trim.

 

[rsingler]

Spreadsheet from Post #16 tweaked for minor issues.
Retained air weight at 500 psi revised slightly
Instructional marginal notes added
Buoyancy calculator page locked (unlock with PW: scuba)

EDIT: error noted by @seeker242 corrected. Thanks!

 

[49north]

Spreadsheet from Post #16 tweaked for minor issues.
Retained air weight at 500 psi revised slightly
Instructional marginal notes added
Buoyancy calculator page locked (unlock with PW: scuba)

Wouldn’t you want to include the reg weight regardless of whether or not the tank buoyancy includes the valve?

BTW, the suit buoyancy calculations came out to within a couple of pounds of actual measured buoyancy, so good job on that!