Required buoyancy in wings

[kidsdream]

I keep reading various threads where experts continuously use the buoyancy of a a persons wetsuit as a key factor in wing selection.

I really don't agree. As a diver who gets out in all kinds of conditions and frequently dives from both private boats and pangas (like the Naia and the Galapagos Aggressor) that require you to get out of your rig in the water, your rig's buoyancy needs to be sufficient to float your rig with full tanks even if you are not in it.

Based on that, if you are diving larger steel tanks with "cave fills" your tanks negative buoyancy alone can exceed 14lbs (my Faber mid pressure 100's are over 15lbs negative with 3700psi). So add in a SS plate, regs, lights and a pony and my single rig is the in the 27lb negative range (without a cannister light or camera). The good part is I don't need any weight even in my thick 7/6 Bare wetsuit (my Florida winter wear). I do of course have tanks that are less negative, and I even have an ALU plate (I owned a beautiful Kydex plate but just never used it) but I my std warm water,single tank rig is fitted with a 30lb wing and I certainly would not go with less buoyancy.

Similarly, I don't exactly support determining buoyancy based on just keeping my head out of the water. I like to be able to be able to be at least 3 or 4 inches higher than that in the case I have to be topside drifting, waiting for a boat pick-up for awhile.

The very small wings may be OK for tropical dives with ALU tanks in calm conditions, but if you dive in all kinds of weather, I personally recommend more than some would suggest. And it is not because I am trying to make one wing fit all (I own 3 wings, down from 4). I do like wings that are "narrow" but that is a separate matter.

.... just another viewpoint.

 

[redacted]

All the threads I recall said there are 2 considerations for selecting the buoyancy of a wing. 1) It must be ably to establish neutral buoyancy at depth (where wetsuit compression is a key variable). 2) It must be able to float your rig on the surface.

Where did you find threats that did not cover both points?

 

[RAWalker]

I couldn't agree more on the 30# minimum for a singles wing.
I also like to be streamline in the water and use a Oxycheq Mach V Signature.
Beside that I also own a OMS 45# bungie wing which does a fair job for singles but I'm holding on to as a light doubles wing.

 

[kidsdream]

http://www.scubaboard.com/forums/gear-equipment-classifieds/270126-fs-deep-sea-supply-single-tank-wing.html

In this thread there was actually somebody selling what I would believe to be a great vacation rig. It was suggested that this was an odd combination and that wings to be used in warm water could easily be in the sub 20lbs range. I just created my post for people to consider alternative viewpoints based on what admittedly may be a more adventurous diving style - nothing more nothing less. If I was going to have a dedicated rig for ALU 80's & calm water then a 20lb wing might be an option - aka the Bonaire rig. But even for places like South Florida where big steel tanks are the norm, a bit more buoyancy is in my mind the way to go.

All the threads I recall said there are 2 considerations for selecting the buoyancy of a wing. 1) It must be ably to establish neutral buoyancy at depth (where wetsuit compression is a key variable). 2) It must be able to float your rig on the surface.

Where did you find threats that did not cover both points?

 

[redacted]

My tropical rig has an 18# wing and it is perfectly adequate with Al tanks and little or no neoprene. And the whole rig is under 2 pounds so it packs and travels quite nicely. My heavier rig (6 lb plate and 30# wing) does not get to travel by air any more with the newest baggage restrictions. That 30# wing might not be enough for really thick wetsuits like a large 7mm 2-piece which may have about 30 lb of buoyancy loss at depths in the 4 to 5 atm range.


Added response: Post #14 in the above referenced thread by Tobin (an expert) addresses the two considerations. BTW, I did get that 18# wing with an UL plate for Bonaire and other tropical destinations. But I will probably also use that wing at the FGB in the summer time which can also present more adventuresome seas.

 

[rstofer]

That 30# wing might not be enough for really thick wetsuits like a large 7mm 2-piece which may have about 30 lb of buoyancy loss at depths in the 4 to 5 atm range.

I have been quite concerned about the idea of a 30# wing, a 7mm Farmer John, a HP 100 (-10.5# at the start of the dive) and a depth in the 4 atm range.

I just don't see a loss of 30# buoyancy in the wetsuit. This exact configuration worked just fine at 100' at Monterey a couple of weeks ago. No problem establishing neutral buoyancy even with 26# of lead.

In my view, the lead is excessive but, as yet, I have been unable to find time to prove it.

26# lead + 6# for backplate + 9# for tank (some air was used on the way down) + 2# for regulator = 43#. On the other side, 30# lift from wing + 13# lift from wetsuit (I assume). Whatever the wetsuit contributed, it was enough to provide neutral buoyancy.

I guess it could be that the wetsuit originally required 43# of ballast and subsequently provided 13# of lift thus indicating a 30# change in buoyancy. But that just seems high. My guess is that the lead is at least 6# heavy. If so, there would be even more buoyancy available at 100'. That would be a good thing.

One reason I have been thinking about this is whether or not to use HP 100s while wearing a thick wetsuit. Part of the question is what to do about total wing failure at the start of the dive and the other part is to decide how much lift is required.

At the moment, I don't have the answers. I do have some guesses.

Richard

 

[redacted]

I have been quite concerned about the idea of a 30# wing, a 7mm Farmer John, a HP 100 (-10.5# at the start of the dive) and a depth in the 4 atm range.

I just don't see a loss of 30# buoyancy in the wetsuit. This exact configuration worked just fine at 100' at Monterey a couple of weeks ago. No problem establishing neutral buoyancy even with 26# of lead.

In my view, the lead is excessive but, as yet, I have been unable to find time to prove it.

26# lead + 6# for backplate + 9# for tank (some air was used on the way down) + 2# for regulator = 43#. On the other side, 30# lift from wing + 13# lift from wetsuit (I assume). Whatever the wetsuit contributed, it was enough to provide neutral buoyancy.

I guess it could be that the wetsuit originally required 43# of ballast and subsequently provided 13# of lift thus indicating a 30# change in buoyancy. But that just seems high. My guess is that the lead is at least 6# heavy. If so, there would be even more buoyancy available at 100'. That would be a good thing.

One reason I have been thinking about this is whether or not to use HP 100s while wearing a thick wetsuit. Part of the question is what to do about total wing failure at the start of the dive and the other part is to decide how much lift is required.

At the moment, I don't have the answers. I do have some guesses.

Richard

I don't think your total "weight" of 43# is the right number to consider assuming that was the weight (minus some air) you need to hold depth at a shallow stop at the end of a dive. A friend of mine has a large 7mm 2-piece that I measured as 32 # buoyant. At 5 atm (130 ft) that should be reduced to about 6# of buoyancy by compression leaving him 26# negative due to suit compression. Add to that the weight of the gas in the tank of approximately 5# and he could be 31# negative at depth. Also, you need to add any excess weight you might be carrying. So, in that case, he would have to be swimming up a bit to get "neutral" with only a 30# wing. It would only be a few pounds so probably doable but not a good idea. Stopping at 4atm where the suit still has 8# of buoyancy and it is still close. I think I would go for a larger wing when it starts to get close.

My understanding is that many wings have a bit more buoyancy than rated so that may help some. But I believe my 30# Diverite travel wing is actually a bit less than rated because my plate and tank limit its expansion somewhat. My 18# Oxycheck wing is on a soft plate and is longer so it appears to be capable of full expansion.

 

[ianr33]

I couldn't agree more on the 30# minimum for a singles wing.

Guess I'm going to die then.

My singles wing has 27 pounds lift. It works just fine with a thin wetsuit,an Al tank and another Al 80 slung on front.

I would not use it with a cave filled 104 and a 7mm farmer John wetsuit. I dont use my iPod to hammer nails either.

 

[rstofer]

I don't think your total "weight" of 43# is the right number to consider assuming that was the weight (minus some air) you need to hold depth at a shallow stop at the end of a dive. A friend of mine has a large 7mm 2-piece that I measured as 32 # buoyant. At 5 atm (130 ft) that should be reduced to about 6# of buoyancy by compression leaving him 26# negative due to suit compression. Add to that the weight of the gas in the tank of approximately 5# and he could be 31# negative at depth. Also, you need to add any excess weight you might be carrying. So, in that case, he would have to be swimming up a bit to get "neutral" with only a 30# wing. It would only be a few pounds so probably doable but not a good idea. Stopping at 4atm where the suit still has 8# of buoyancy and it is still close. I think I would go for a larger wing when it starts to get close.

Plugging your wetsuit numbers into the handy-dandy 'wing lift calculator', I get a lead requirement of 24# (assuming a 6# backplate) and a lift requirement of 34#. Pretty consistent with what you came up with.

If the wetsuit is only 25# buoyant at the surface, the lead requirement drops to 17# and the lift to 27#.

Either way, the lift seems marginal. The good news is that deep dives are not planned any time soon.

Richard

 

[DA Aquamaster]

26# lead + 6# for backplate + 9# for tank (some air was used on the way down) + 2# for regulator = 43#. On the other side, 30# lift from wing + 13# lift from wetsuit (I assume). Whatever the wetsuit contributed, it was enough to provide neutral buoyancy.

The issue I see here is that if the 26 lbs of lead is in some way attached to the plate/tank wing, the 43 lbs will sink it on the surface if you take it off - even if the tank were empty.

A friend of mine has a large 7mm 2-piece that I measured as 32 # buoyant. At 5 atm (130 ft) that should be reduced to about 6# of buoyancy by compression leaving him 26# negative due to suit compression. Add to that the weight of the gas in the tank of approximately 5# and he could be 31# negative at depth. Also, you need to add any excess weight you might be carrying. So, in that case, he would have to be swimming up a bit to get "neutral" with only a 30# wing.

The issue her I think is that you are estimating wet suit compresssion as a linear equation where at 5 atm you would have 1/5 the buoyancy present at the surface. I don't think that is the case as the rubber surrounding the bubbles in the neoprene adds some structure, especially as it compresses more and more, and the rubber itself does not change in buoyancy and is more or less constant so it will not behave like an unconfined/unsupported bubble.

You'd have to take the suit down in a mesh bag and then measure the buoyancy with something like a fish scale both at the surface (just under) and at 1 atm intervals to perhaps 4 or 5 atm to see if the rate of buoyancy loss is indeed linear.

-----

That said, I agree that some divers get carried away with trying to go small with a wing. It is true that a larger wing may add more drag, but you have to go to extremes of lift over kill in a given application for this to be an issue. What does count in my opinion is that you can indeed get your head above water on the surface and achieve neutral buoyancy with your configuration at depth.

Most people do not factor in the weight of your head - about 15 lbs. So at the surface your wing needs to be able to float the rest of your rig if you take it off. And, the combination of your wet suit and your wing has to generate 15 lbs more buyancy than is needed to keep you neutral at the beginning of the dive to enable you to keep your head above water.

Consequently with an HP 100 that is between -8.5 (PST) and -10 (worthington) pounds nbouyant when full, a -2 lb AL plate and -2 lbs of regulators you have potentially -14 lbs buoyancy already leaving you only 16 lbs of reserve buoyancy with a 30 pound wing. Just enough to get your head above water if you have no exposure suit or a flooded drysuit that will not contribute to your over all buoyancy. That supports the idea that a wing smaller than about 30 pounds is not sufficient with a steel tank.

More importantly it also means you can't put more than about 15 pounds of integrated weights on the plate or harness and expect it to still float on the surface if you take it off.

With an AL80, the tank is only 1.4 lbs negative when full, so you would have only -5.4 lbs of bouyancy and a 20 pound wing may be sufficient if you are not wearing an exposure suit, but again would only allow 15 pounds of integreated weight if you did wear a wet suit.

At depth, the wing has to support any buoyancy loss that occurs as you decend and the wet suit compresses. In the case of the steel tank and 30 pound wing above, you have the same 16 pounds of reserve buoyancy. Ideally you will be weighted so that the suit it neutral at the surface, and if so a 30 pound wing will provide for the loss of only 16 pounds of suit buoyancy due to compression. That will probably work with a 3mm one piece, a 3mm one piece and hooded vest, a 3mm farmer john or a dry suit as they will most likely not lose that much buoyancy.

It gets iffy with a 5mm one piece or farmer john and is inadequate with a 7mm one piece or 7mm farmer john as those suits potentially lose more than 16 pounds of buoyancy due to compression at depth.

Again with an AL 80 you can tolerate a thicker wet suit with a 30 pound wing as in that configuration it would provide about 25 pounds of reserve buoyancy.

Howver in both cases, you can't more lead to an integrated configuration than the wing can support with a full tank.

So in short, you have to look at the whole configuation at various phases of the dive and ensure you will have at least some reserve buoyancy at all times when you look at it that way you quickly find that a wing smaller than 30 pounds becomes much more limited in terms of the tanks and exposure suits it will be compatible with.