Wings seem to be too big or my maths is bad?

[Tom_Ivan]

I'm wondering why the lift capacity of wings are so high.

We know that if your buoyancy is correct, then the only lift you need is to counter the weight of air in a fully filled tank. Which is about 6lb.

Wouldn't that mean that the wing you need for a single tank be 6lb or 12lb for doubles? Maybe add a bit to take into account your wetsuit compressing, make it 8lb for singles and 16lb for doubles. Yet you can 60lb wings being advertised as suitable for doubles.

What am I missing?

 

[buddhasummer]

Kia Ora. Your wing needs to do two things, float your rig without you in it and compensate for the loss of buoyancy of suit at depth. Wing lift will need to accommodate which ever is greater. So as you can see a 6lb wing will not cut it by a long shot, ditto 12lbs with doubles.

This topic has been covered many times, Tobin from DSS is a master on the subject. I'll try to find one of his posts to link to.

A useful read:

The "Ultimate" wing lift calculator :)

For example, If you got into the water with a full tank, steel for example, regs etc would it float if you removed your rig even if your 6 or 8lb wing was fully inflated? If you were wearing a steel backplate? Weight Integrated BC?

 

[RayfromTX]

You also want to keep your head above water with a full tank of gas. That's a personal preference but I allow 10 lbs for the weight of my head. This is on top of all the calculations for being neutral at the surface at the beginning of the dive. I am open to have my understanding of this corrected.

 

[Lorenzoid]

Another way to state it is that the wing needs to compensate for anything that changes buoyancy during the dive. There are typically only two such things: (1) gas usage over the dive, and (2) wetsuit compression at depth. Thick wetsuits can lose 15 or more pounds due to compression.

And it also should be able to float your rig on the surface without you in it, as buddhasummer said.

 

[tbone1004]

read this thread. Tobin and I just went over helping someone with determining their weight requirements. Most of it for single tank diving comes from the exposure suit.
In terms of the size, 30lbs is really the sweet balance point for most people in most scenarios, but if you are diving an al80 in a bathing suit, a lot of people still dive without a wing
Universal wing to backplate fit?

 

[2airishuman]

I'm wondering why the lift capacity of wings are so high.

We know that if your buoyancy is correct, then the only lift you need is to counter the weight of air in a fully filled tank. Which is about 6lb.

Wouldn't that mean that the wing you need for a single tank be 6lb or 12lb for doubles? Maybe add a bit to take into account your wetsuit compressing, make it 8lb for singles and 16lb for doubles. Yet you can 60lb wings being advertised as suitable for doubles.

What am I missing?

I dive a two-piece 7mm with hood, boots, and gloves, and you can rest assured that the buoyancy swing is more than 8 pounds on all that. It's about 20 pounds from the surface at the beginning of the dive to 100 feet at the end, but I dive so that I'm neutral at the end of the dive at about 10', which knocks 5 pounds off my belt. I dive single 120s that have an 8 pound buoyancy swing to around 500 PSI reserve (8 *13 = 104 cf), so I'm dealing with a 23# total buoyancy swing with singles on a deep coldwater dive. I prefer to have some reserve buoyancy for various contingencies so a 30# singles wing is just right. (These contingencies include: wanting to be able to keep my head above water at the beginning of the dive before the dive starts, inherent variation in buoyancy from one supposedly identical cylinder to the next, dealing with small mistakes in weighting, and variations in body buoyancy depending on such factors as whether I had a proper English breakfast with baked beans in the morning)

With double 120s and a stage the total swing due to amount of gas carried increases by about 10# to, say, 33#, and my balanced rig is going to put me at neutral at 10' at zero gas rather than 500 PSI, which means I'm a few pounds heavier, call it a 36# swing. A 45# wing would probably be perfect as it would allow me to float with my head above water at the beginning of the dive. Mine are both 55# because that's what was readily available used. I don't find the slight excess capacity to be a problem.

 

[Tom_Ivan]

Cheers guys. Didn't realize that a wetsuits buoyancy swing was as high as that.

 

[Neilwood]

Cheers guys. Didn't realize that a wetsuits buoyancy swing was as high as that.

If you feel how thick a wetsuit is at 25-30m (80-100ft), you will know exactly why there is so much less buoyancy in it. It is a bit of an eye opener when that 7mm has become 2-3mm.

 

[ronscuba]

Wetsuit thickness, but don't forget size. A small or med size suit has less neoprene than a large or xl.

 

[Lorenzoid]

Cheers guys. Didn't realize that a wetsuits buoyancy swing was as high as that.

Maybe someone has mentioned this and I overlooked it, but as an experiment you could put your wetsuit in a mesh bag and see how much lead it takes to sink it in saltwater. At maximum dive depth it might lose nearly all of that buoyancy.