Question 40 or 50 lb wing for doubles? And what about (future) stage tanks?

[Cheizz]

I am researching an expansion of my BC collection to accommodate for back-mounted doubles. They will be steel 12L doubles (232 bar) on a steel backplate that I already own. I am looking at the xDeep Hydros 40 or 50 as wing options. I will dive them in a drysuit (+ undergarments for cold water) in both fresh and salt water. I think the 40 lb wing would be enough lift capacity. According to the xDeep data sheet, they are suitable for 2x12 or 2x15 and in addition 2 stage tanks. (The 50 lb wing can support more stage tanks.)

BC System for technical diving HYDROS - specification

Technical parameters of HYDROS - BC system for technical diving in double tank configuration.

www.xdeep.eu

So, here are my three questions:
1. Can you guys confirm that 40 lb will be enough? Stage tanks may be in my future, but I can't imagine needing more than two in the foreseeable future...
2. In determining how much lift capacity you need, do you count stage tanks as ditchable weights? If they're still full and you encounter a catastrophic problem, you can just ditch them and ascend, right? So how do you take stage tanks into account? Or, do you have to calculate some lift capacity for them; you want to be able to float at the surface with full stage tanks, obviously...
3. Is there a source on in-water weight of different size and material tanks/tank configurations?

 

[barth]

I was using a 38 lbs wing. I did use 2x12 liter steel tanks (backgas ean32) and 3 aluminum stages, (2x 11 liter ean32 and 7 liter oxygen).

The 38 lbs wing was fully inflated and just enough to keep my head above the surface with 5 tanks.

At the end of the dive the tanks are neutral or even positive

(I was using a 55 lbs wing for 2 x 18 liter (trimix) tanks and 4 stages (trimix, ean32, ean50 and oxygen)…)

40 lbs lift is enough for 2 x 12liter steel.

 

[Cheizz]

Thanks. I guess 40 would be on the lower-but-not-impossible end when fully loaded (which won't happen that soon or often).

Found a nice 45 lbs wing as well. Nice colors too...

STREAM RING 20 col. ORANGE - BLACK | DTD

Circular style wing for diving with doubles

eshop.daretodive.eu

Maybe with some new heavier, stiffer fins to match...

Tecline Jetstream Fins Orange Scuba Tech Diving Buy and Sales in Gidive Store

Tecline Jetstream Fins Red with SS Spring Straps JET fins construction is characterized by high thrust and maneuverability, and the ability to fly to the rea...

www.gidivestore.com

 

[tbone1004]

1. 40lbs is probably enough but the profile on 50lbs is not much bigger. I personally dive a 60lb wing but that's because I sink like a brick and don't like to have a lot of gas in my drysuit.
2. stages are ditchable but they are also very minimal in terms of actual ballast, 2-3lbs each for nitrox/50%/O2, and usually floaty for trimix
3. for American tanks

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

huronscuba.com

You can also go to @DiveGearExpress and they have the currently manufactured tanks listed on there.

 

[Cheizz]

Here's some interesting maths to go with all of this:

 

[RyanT]

I dive a 60lb wing (for perspective, I don't dive dry, and typically dive LP85s). I hear people talk a lot about wing drag/streamlining, etc. In terms of drag, I can tell almost no difference between the 45lb wing (that pretty much sits on my shelf) & my 60 lb wing. What I do like about my 60lb wing, is the added lift on the surface. About a year ago I made a dive where conditions got ugly fast. When I surfaced, the seas were running about 8' with a few 10' rollers in the mix. Things with other divers had gone a little south, so I had to wait maybe 15 min for the pickup. Even with my 60lb wing fully inflated, I couldn't reach the top of the bigger waves and the wave crests would go over my head. I found that with a well-timed kick, I could keep my head above the surface with each wave. I had my regulator in and plenty of gas, so even if my head went under, it was more of an annoyance than anything. But, if I had only had my 45lb wing, things would have been a lot scarier.

Of course diving dry provides extra buoyancy, but with no noticeable increase in drag, I'll opt for 60lbs every time.

 

[Imla]

Yes. 40lbs is enough for D12 steels and 3 stages even with a full drysuit flood.
Tried and tested in cold baltic brackish water.

 

[inquis]

Air in a set of D12s weighs 7 kg. A full AL80 & reg is negative 2 kg. Total of 13 kg (with 3x 80s for deco or bottom stage) is easily supported by the 18 kg (40 lb) wing. Also supported by the drysuit if your wing fails. (13 liters of volume spread over your body is a pretty thin layer.)

You'd have to elaborate on your weighting to gauge the drysuit flood scenario, but it's likely not an issue. (Heavier layers or salt water probably require lead, but that can anso be ditched for a total suit flood.

FWIW, I use a 20 kg (44 lb) wing with 250 bar D13s.

 

[JoeTPhilly]

Good to know. As I am new to doubles and have only used Aluminum 80s. I have a 40lb Halcyon Evolve wing for the double aluminum 80s and wondered if it would be sufficient for double steel tanks (HP100s). Maybe you all could comment on my estimates. I use a SS plate which is -5 pounds. The steels would be Faber HP100 tanks which are about -16, manifold and bands -5ish, regulators -4, lights -3. That comes to about -33 before any lead. I guess any weight needed would probably have to go on a weight belt since a V weight would probably put the rig over 40lbs?

 

[inquis]

@JoeTPhilly fresh or salt? The spec buoyancy of -8.4 lb in seawater for a full HP100 should be adjusted by 2.4% of it's dry weight for fresh water use: -19.5 lb for the pair.

Are you sure on the bands/manifold? Mine are -11 lb, though will obviously vary some.

Drysuit or wetsuit? AL80s make a lot of sense for the latter. HP100s do not.

Yes, any additional lead on a weight belt is a good call and also gives options to handle a drysuit flood. Switching to an AL plate shifts ballast away from the rig to the belt if needed.