Wing Size/Doubles Weighting Math

[crofrog]

SCUBA Cylinder Specifications – Huron Scuba, Snorkel & Adventure Travel Inc. PADI 5 star IDC in Ann Arbor, MI

huronscuba.com

Full to empty is around a 6lb swing with air/nitrox
Deco 50% or 100% is a little less
A lot less when you start adding helium

Yeah but it really don’t matter that much. You’re not likely to have all of your stages, clipped off and need the wing to float all of them without you in it. And most people don’t take into account the full empty weight of the the deco stages for weighting

 

[happy-diver]

Perspective

The rig has a 32 OMS wing I use with twin 55s

 

[jeffmg]

Yeah but it really don’t matter that much. You’re not likely to have all of your stages, clipped off and need the wing to float all of them without you in it. And most people don’t take into account the full empty weight of the the deco stages for weighting

I don’t really understand what you’re saying

Assume you start a dive with double hp130s with nitrox and a 100% o2 deco cylinder
Min gas for that dive is 1000psi so you are using 70% of the nitrox in those tanks
Also assume you have a perfectly balanced rig that is neutral at the end of the dive with no air in your wing and as much air out of drysuit as possible
You will be 16lbs more negative at the beginning of the dive vs the end of the dive

A 40lb wing in this case is more than enough when your weighting is correct

If you add a bottom stage of 32% that you intend to breathe all of you add another 2-4lbs

More stages than that you’re really into 55-60lb wing territory

 

[JHumbert15]

I don’t really understand what you’re saying

I think he may've been commenting on your post where you said a 40lbs wing is good for doubles and 1 stage, and doubles and 2 stages is 60lb wing territory. I think you guys were kinda applying different scenarios.

I see what you're saying and yes the math adds up, but I would still argue (again as I think Crofrog was) that the wing can also have to deal with the size of the cylinder. It seems most would agree 60lbs is too much for LP85s, so even with full LP85s, and 2 stages, you're still in 40lb territory because full LP85s at -10/12 if they're really filled up, plus 2 bottles at even -5 each, so -10 total, brings us to -20/-22. The 40lb can more than compensate for that at depth.

Again what I think he was saying, and also what I'd agree with, is that at the surface, even in 2x LP85s and 2 deco bottles, floating the rig without your person in it is still doable because in this case you likely don't have the stages clipped floating there as well, so again, a 40lb wing is fine for back gas + ballast on the rig (backplate, v-weight, bands, regs, etc). Once you clip the deco bottles off it wont matter because the drysuit is about offset by the ballast of the rig (in my case an attached v-weight, others may have a weight belt etc), so the wing is only floating you at the surface compensating for the back gas plus the stage bottles plus a little more since you'll be overweighed at the beginning of the dive to be able to hold that stop at the end. I know that you know this I'm just explaining what I think the thought process is.

Obviously with different tanks this changes. I'm applying all this to my situation with 2x LP85s. Once you get to larger diameter tanks, I'd go with a 60 just for that reason because I don't even think a taco or trapped gas situation would really arise.

 

[crofrog]

I don’t really understand what you’re saying

Assume you start a dive with double hp130s with nitrox and a 100% o2 deco cylinder
Min gas for that dive is 1000psi so you are using 70% of the nitrox in those tanks
Also assume you have a perfectly balanced rig that is neutral at the end of the dive with no air in your wing and as much air out of drysuit as possible
You will be 16lbs more negative at the beginning of the dive vs the end of the dive

These are actual measurements I made in water, minus the "empty" tank weights which are from published empty buoyancy weights.

As you'll see with cave filled LP85s it just floats the rig with all of the non-ditch able weight, with AL80s it's not an issue at all with everything on the rig. With LP108s / 133s the empty tank weight varies by about 5lbs with fibers being 3lb positive and the older 108s and PSTs being about 2 negative.

If you're really worried about a v-weight floating the rig without you in it, then put some of that v-weight onto a weight belt.

A 40lb wing in this case is more than enough when your weighting is correct

If you add a bottom stage of 32% that you intend to breathe all of you add another 2-4lbs

More stages than that you’re really into 55-60lb wing territory

When you start adding stages you're not planning on the wing floating all of the stages on the surface without you in the rig when everything is full. Once you're in the rig it's only offsetting the gas weight if you're weighted correctly so floating the stages isn't a big deal.

Based on weighing the stages they're about -6lbs full.

With a 40lb wing you've can float about 3 AL80 stages when you're using stuffed LP85s before the wing is not going to be able to float it. You don't take the weight of the stages into account when you're figuring out your weighting, and if you are coming out with nothing but empty stages most of them will be just ever so slightly negative when empty but even if they're slightly positive the weight of your min gas / gas you reserved for the stages is more than enough to offset the slightly positive stages.

I think he may've been commenting on your post where you said a 40lbs wing is good for doubles and 1 stage, and doubles and 2 stages is 60lb wing territory. I think you guys were kinda applying different scenarios.

I see what you're saying and yes the math adds up, but I would still argue (again as I think Crofrog was) that the wing can also have to deal with the size of the cylinder. It seems most would agree 60lbs is too much for LP85s, so even with full LP85s, and 2 stages, you're still in 40lb territory because full LP85s at -10/12 if they're really filled up, plus 2 bottles at even -5 each, so -10 total, brings us to -20/-22. The 40lb can more than compensate for that at depth.

Again what I think he was saying, and also what I'd agree with, is that at the surface, even in 2x LP85s and 2 deco bottles, floating the rig without your person in it is still doable because in this case you likely don't have the stages clipped floating there as well, so again, a 40lb wing is fine for back gas + ballast on the rig (backplate, v-weight, bands, regs, etc). Once you clip the deco bottles off it wont matter because the drysuit is about offset by the ballast of the rig (in my case an attached v-weight, others may have a weight belt etc), so the wing is only floating you at the surface compensating for the back gas plus the stage bottles plus a little more since you'll be overweighed at the beginning of the dive to be able to hold that stop at the end. I know that you know this I'm just explaining what I think the thought process is.

Obviously with different tanks this changes. I'm applying all this to my situation with 2x LP85s. Once you get to larger diameter tanks, I'd go with a 60 just for that reason because I don't even think a taco or trapped gas situation would really arise.

Yes...

 

[divezonescuba]

I normally dive AL80 twinsets with a 45 pound Diverite REC with up to 3 stage / deco / travel gas tanks. In salt water, I use 14-16 pounds in a 5mm. When I boought a set of LP85s, I discovered that my head was too low in the water with the 45 pound wing to be comfortable. I did not have any other tanks when that happened. I do not use any weight with LP85s. I purchased a Diverite 60 pound classic rig and am much more comfortable with that particularly with stage / deco / travel gas tanks.

When people do bouyancy / lift calculations they forget that their heads weigh 10-11 pounds. So, if you want your head out of the water you need at least that much additional lift. I prefer to have more than just my head out of the water. So, I like more like 15 pounds reserve.