Wing Size/Doubles Weighting Math

[JHumbert15]

Hi All,

I'm sorry, but yet another post about doubles wing size and weighting.

I'm looking into a wing for 2x LP85s, and I'm struggling with the math a little bit to determine wing size. I know people have said 40 vs 60 based off of tank diameter, but I'd rather understand the "why" behind it.

I'm looking at a Halcyon evolve (40 or 60).

Here we go:

As I understand the wing has to do 2 things:

1. float the rig at the surface *without me in it*
2. compensate for the loss in buoyancy of exposure protection (I'm in a dry suit so I'm not worried about this as much because I'm not necessarily losing anything due to compression, and while maybe I technically am, I'm sure it's not near 40 pounds)

My weighting:
Regs: -4

Bands: -2

Manifold: -4

SS Plate w Harness and webbing: -6

Total: -16

If I really pump the 85s with gas, let's call them 12 pounds.

Right now I'm at -28. If I add 2 AL40 deco tanks, I get to -2.5 x 2 = roughly -5

This brings me to -32. If I have to add a v-weight at 5-7 pounds, I come in at -37 to -39.

I'm afraid adding flashlights and a can light could push me over the 40 pounds.

When I'm in the rig at the surface, I'm not necessarily concerned because the drysuit should be balanced by the ballast of the regs, plate, bands, and manifold plus a small v-weight, so when I'm wearing the rig I'm looking at the wing only needing to compensate for the gas in the back tanks, plus stages, plus my head to be comfortable. However, if I need to float the rig without me in it, this looks like it could be marginal.

Is my math and thinking correct here or have I misunderstood something somewhere? How are people comfortable in a 40lb wing, 85s, and a couple deco bottles?

I also understand the answer could be move weight on a belt, or change the whole setup to deal with 2 deco tanks, but I like the way the 85s are so if I could keep this config I'd rather do that and understand the thinking behind this math and process.

Thanks!

 

[rx7diver]

You're from NE Ohio, so I'm guessing that you're interested in diving fresh water (e.g., the Great Lakes). If this is correct, I think that the negative buoyancy of your full isolation-manifolded LP 85's and full Luxfer Al 40's, with tank bands and stage rigging and attached regulators, should be a bit more than you've indicated.

rx7diver

 

[Kendall Raine]

Hi All,

I'm sorry, but yet another post about doubles wing size and weighting.

I'm looking into a wing for 2x LP85s, and I'm struggling with the math a little bit to determine wing size. I know people have said 40 vs 60 based off of tank diameter, but I'd rather understand the "why" behind it.

I'm looking at a Halcyon evolve (40 or 60).

Here we go:

As I understand the wing has to do 2 things:

1. float the rig at the surface *without me in it*
2. compensate for the loss in buoyancy of exposure protection (I'm in a dry suit so I'm not worried about this as much because I'm not necessarily losing anything due to compression, and while maybe I technically am, I'm sure it's not near 40 pounds)

My weighting:
Regs: -4

Bands: -2

Manifold: -4

SS Plate w Harness and webbing: -6

Total: -16

If I really pump the 85s with gas, let's call them 12 pounds.

Right now I'm at -28. If I add 2 AL40 deco tanks, I get to -2.5 x 2 = roughly -5

This brings me to -32. If I have to add a v-weight at 5-7 pounds, I come in at -37 to -39.

I'm afraid adding flashlights and a can light could push me over the 40 pounds.

When I'm in the rig at the surface, I'm not necessarily concerned because the drysuit should be balanced by the ballast of the regs, plate, bands, and manifold plus a small v-weight, so when I'm wearing the rig I'm looking at the wing only needing to compensate for the gas in the back tanks, plus stages, plus my head to be comfortable. However, if I need to float the rig without me in it, this looks like it could be marginal.

Is my math and thinking correct here or have I misunderstood something somewhere? How are people comfortable in a 40lb wing, 85s, and a couple deco bottles?

I also understand the answer could be move weight on a belt, or change the whole setup to deal with 2 deco tanks, but I like the way the 85s are so if I could keep this config I'd rather do that and understand the thinking behind this math and process.

Thanks!

Make it easy on yourself. Go with the 60. Even a 55 would be fine. It will give you the ability to move up in cylinder size/add deco gas at very little incremental cost in terms of drag. In addition, you may decide at some point to add a bit more weight to the rig in order to use more loft on the hang (stay warmer).

 

[JoeTPhilly]

Maybe this article will be of help:

Halcyon Dive Systems

Halcyon began as a group of divers who knew exactly what they wanted, but could not find it in any dive store. Our passion for diving led us to designing wings and lights to satisfy ourselves.

halcyon.net

 

[SpeedyJ]

Great lakes diver who is happily diving a 40-lb with LP85s. The size and shape of the wing dictates how and where the gas ends up sitting during the dive, and how easily you can dump gas from the wing.

Some of what you're adding is ditchable weight: deco tanks and can light. And remember your tanks get lighter throughout the dive. So if you're at >40lbs at the start and have an issue resulting in total loss of drysuit provided buoyancy you can ditch the deco tanks and can light and you've ditched 7-10lbs. It's not an issue later in the dive when you actually need the deco tanks, because you've shed back gas weight.

Even diving off a rib, you're not going to take your rig off with the AL40s still attached. You'll pass them up or clip them off on a line before pulling the gear off.

 

[JHumbert15]

Maybe this article will be of help:

Halcyon Dive Systems

Halcyon began as a group of divers who knew exactly what they wanted, but could not find it in any dive store. Our passion for diving led us to designing wings and lights to satisfy ourselves.

halcyon.net

Thanks, I actually read that a couple days ago when it came out. I (think I) understand the principle I just wanted to make sure my math checks out.

Even diving off a rib, you're not going to take your rig off with the AL40s still attached. You'll pass them up or clip them off on a line before pulling the gear off.

This is a good point I'm not sure how I overlooked. Thanks for the input.

A brief question though, does my thought process seem correct in the numbers above? If so given the point you made that actually makes me feel more confident in going with a 40. A 60 would taco too much with the 85s I'm afraid.

 

[crofrog]

I’d not overthink it. Diving a 60lb wing with 7.25” tanks sorta sucks to manage the bubble and you’ll have more drag in the water from the extra wing size.

 

[rx7diver]

I’d not overthink it. Diving a 60lb wing with 7.25” tanks sorta sucks to manage the bubble and you’ll have more drag in the water from the extra wing size.

A Faber LP85 cylinder has a nominal outer diameter of 7.0" (rather than 7.25"). This difference seems small, but it is noticeable (to me, at least).

rx7diver

 

[SpeedyJ]

A brief question though, does my thought process seem correct in the numbers above? If so given the point you made that actually makes me feel more confident in going with a 40. A 60 would taco too much with the 85s I'm afraid.

Overall the thought process is solid, it’s just a matter of knowing when and how the numbers line up. Some folks disagree with me, but even a catastrophically flooded drysuit can probably hold air somewhere, and the thick undergarments we wear on the Great Lakes have some inherent buoyancy even when wet. You’ll be fine with a 40lb wing.

Personally the thing I’d question more is the use of 2 AL40s (50% and 100%?) vs. an AL80 of 50% on a typical Great Lakes dive where LP85s are are your choice of tanks for backgas. Multiple gasses make sense on deep stuff, but OC you’re going to also be on bigger tanks at that point for back gas. To me getting out of the water a couple min quicker doesn’t outweigh the safety of more gas available deeper, having only a single gas switch with no opportunity to grab the wrong reg, and the economic saving of only needing to refill one deco bottle each dive. Outside of the very earliest part of the season thermal exposure on deco isn’t a huge issue as the thermocline is below the longer shallow stops.

 

[happy-diver]

This is interesting, I am also about to build too, but two plates at 5kg each
and my main consideration when you take a bite of the big gear sandwich
is the size of the centre panel, the breadth of the tanks and also your back
and how much of these wings will protrude from the sandwich, to give lift