Help with choosing BPW lift

[BlueTrin]

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[Filipe Marques da Costa]

The wing compensates for the weight of the gas you haven't breathed and wetsuit compression. A 12 L has about 5.5 lb non-reserve gas. An XL Bare Reactive 7mm (single layer) wetsuit has 16 lb of buoyancy. When properly weighted, the most the wing would need to lift is 22ish lb, usually will be less, so the 28 lb would be plenty in that case. If you have a double-layer 7mm, the 38 lb would be a better choice.

Thanks for the input. Yeah, this is what I'm trying to estimate. I'm using an Aqualung Iceland 7.0 "semidry" size M. I imagine it'd be a little less buoyant than the XL Bare Reactive (that has graphene right? btw does that make it more positive?). Between compression, the SS plate, the gas and tank, and the normal stuff we need to carry around (SMB, torch...) I'm a bit concerned at depth. But at the same time I've never seen anyone ever come close to inflate their wings with that amount of air anyway hence my question. I'd like the smallest wing possible for my needs to optimize streamlining but I get the feeling I may be exaggerating.

 

[Filipe Marques da Costa]

If I said I'd just be diving dry suit would that definitely tip the answer towards the 28lbs/13kg? I'd have redundancy but on the other hand would be more vulnerable in case of dry suit flooding no?

 

[Cheizz]

I'm a bit bigger than you are (1.82, 90 kg) But I also dive in a 7mm wetsuit. I have opted for the Zeos 38. That size was recommended by xDeep. And I had the chance to see and feel the 28 and 38 lb wing side by side... They don't differ that much in terms of profile. I have been diving with it, also with a steel 12 L tank, and there is no flapping or tacoing going on. Asked my buddy to check and film me, which confirmed my own experience.
Even if you were to pick the 38, I don't think your streamlining will suffer by much.

 

[Filipe Marques da Costa]

I'm a bit bigger than you are (1.82, 90 kg) But I also dive in a 7mm wetsuit. I have opted for the Zeos 38. That size was recommended by xDeep. And I had the chance to see and feel the 28 and 38 lb wing side by side... They don't differ that much in terms of profile. I have been diving with it, also with a steel 12 L tank, and there is no flapping or tacoing going on. Asked my buddy to check and film me, which confirmed my own experience.
Even if you were to pick the 38, I don't think your streamlining will suffer by much.

Thank you Cheizz, that input helped me a lot.

 

[inquis]

If I said I'd just be diving dry suit would that definitely tip the answer towards the 28lbs/13kg?

Perhaps. My drysuit with undergarments for low 60s *F has 16 lbs of buoyancy (conveniently the same as the Bare 7mm), so a 28 lb wing would easily work for single tank in those conditions, even with a total suit flood.

For colder water, my undergarments push the buoyancy to 24ish lbs (mandating another 8 lbs of lead). If totally flooded, dropping that 8 lbs of lead puts me back in the same situation as the flooded temperate scenario (16 to 22 lbs negative depending on air in the tank) where the 28 lb wing was fine.

Therefore, for colder waters (thicker layers), the 28 lb wing seems borderline. If you practice/simulate such a condition (by dumping your wing rather than actually flooding your suit), it's doable IF you keep your wits about you. However, it's certainly easier to mash an inflator on a 38 lb wing than remembering to drop lead. Borderline cases are where personal calls have to be made.

 

[happy-diver]

By the time you squeeze your 28 between your tank and plate it won't be 28 anymore
and when you surface in a sea your head won't be comfortably out of the ocean either

 

[Pearlman]

I've read a bit and even played with a fantastic excel spreadsheet I found on these forums that helps calculate necessary wing lift. But I'd like to hear your experience on this.

I have a brand new Xdeep Zen with ALU BP waiting for the opportunity for pool session trials for trim and weight adjustments post the lockdown period currently in my city. I got Zen for its double enclosed bladder ( protect from puncture) and possibly move to tech/doubles (same BP doubles wing) in the next 3 years so I can dive some exotic sites in my bucket list.

The old SB thread from 2006 with XL calculator has web links that have gone rogue with adware. Can you share the XL sheet you have? I need to run some calculations myself.

 

[Filipe Marques da Costa]

Perhaps. My drysuit with undergarments for low 60s *F has 16 lbs of buoyancy (conveniently the same as the Bare 7mm), so a 28 lb wing would easily work for single tank in those conditions, even with a total suit flood.

For colder water, my undergarments push the buoyancy to 24ish lbs (mandating another 8 lbs of lead). If totally flooded, dropping that 8 lbs of lead puts me back in the same situation as the flooded temperate scenario (16 to 22 lbs negative depending on air in the tank) where the 28 lb wing was fine.

Therefore, for colder waters (thicker layers), the 28 lb wing seems borderline. If you practice/simulate such a condition (by dumping your wing rather than actually flooding your suit), it's doable IF you keep your wits about you. However, it's certainly easier to mash an inflator on a 38 lb wing than remembering to drop lead. Borderline cases are where personal calls have to be made.

Great input, thank you. I think I'll go with the 38 considering everything what was advised.

 

[Filipe Marques da Costa]

I have a brand new Xdeep Zen with ALU BP waiting for the opportunity for pool session trials for trim and weight adjustments post the lockdown period currently in my city. I got Zen for its double enclosed bladder ( protect from puncture) and possibly move to tech/doubles (same BP doubles wing) in the next 3 years so I can dive some exotic sites in my bucket list.

The old SB thread from 2006 with XL calculator has web links that have gone rogue with adware. Can you share the XL sheet you have? I need to run some calculations myself.

I found this thread from 2019 (let's see if I can link it):

Info - Optimal Buoyancy Computer

The Optimal Buoyancy Computer A tool to help nail buoyancy and improve safety, before you splash 1) How much lead should I carry with my new wetsuit? 2) How big a wing should I buy? 3) Will my BCD support my lead, both at the surface and when my wetsuit is compressed at depth? 4) Will my BCD...

scubaboard.com

I had a great time figuring it out, reading the manual and playing with it, learned a lot about buoyancy.