BCD Lift Capacity

[Colliam7]

I mostly dive in warm or temperate water with a exposure suit of 5mm max. I don't bring much extra equipment except for a camera. Would the 24lbs lift be enough? I don't think I will do any cold water dive in the near future.

Yes. At least with an aluminum cylinder. If you were to dive with a thinner wetsuit (1mm, maybe even 3mm), AND use a large, negatively buoyant steel cylinder, you might find that you were close to the edge of adequate buoyancy. But, even then, a 24lb BCD is actually quite functional for the diving you describe.

 

[Calvin Shia]

thanks for all the tips guys, very reassuring indeed, seems the Scout is the perfect choice for me!

 

[blueskies_up_ahead]

I'm picking up this old thread. I was looking for info on lift as I'm shopping for my first BCD. Someone commented that big lift isn't necessarily a good thing. Is that because a big bladder creates drag?

I'm 1,81m, currently 82kg. I dive in a shorty, 7mm at home and may well look into dry suit diving in the future. So I'd like something rather versatile. I've been looking at the Apeks Exotec. It has huge lift and I wonder if that's a good or a bad thing and how much lift I need given the various equipment options. I'm a rather new diver so the weight I need will go down. But as reference, in Egypt in a shorty I used 9kg (12l aluminum tank). I've only used my brand new 7mm on 3 dives in sweet water, but those started out with 8kg, then 7kg and feel like I can bring that down to 6kg or maybe even less. That was with a 10l steel tank.
Any advice appreciated.

 

[bradlw]

I'm in the camp that bigger lift isn't better. yes, more drag...but more than that it tends to trap air pockets that roll around inside and throw off your trim/balance...and it's just extra fabric in the way.

 

[Cheizz]

I've been looking at the Apeks Exotec. It has huge lift and I wonder if that's a good or a bad thing and how much lift I need given the various equipment options.

How much lift does the Exotec have? I can't find it anywhere...

EDIT: found it - 45 to 49 lbs depending on the size. That is a huge amount. Unless you're diving doubles with it, I don't see the need for that amount of lift. And I don't think the Exotec is made for doubles.

On the other hand - if it isn't in the way of anything....

 

[blueskies_up_ahead]

I'm in the camp that bigger lift isn't better. yes, more drag...but more than that it tends to trap air pockets that roll around inside and throw off your trim/balance...and it's just extra fabric in the way.

thanks, that's very useful!

How much lift does the Exotec have? I can't find it anywhere...

EDIT: found it - 45 to 49 lbs depending on the size. That is a huge amount. Unless you're diving doubles with it, I don't see the need for that amount of lift. And I don't think the Exotec is made for doubles.

On the other hand - if it isn't in the way of anything....

yep, 23kg in metric. The Exotec is for single tanks only.

So, how much lift do I need? I remember reading somewhere that 17kg is about what you should have but that seemed a general rule of thumb that does't take into account any of the parameters such as body weight, lead, wetsuit etc. But then again, a lot of those parameters change.

 

[Cheizz]

thanks, that's very useful!

yep, 23kg in metric. The Exotec is for single tanks only.

So, how much lift do I need? I remember reading somewhere that 17kg is about what you should have but that seemed a general rule of thumb that does't take into account any of the parameters such as body weight, lead, wetsuit etc. But then again, a lot of those parameters change.

Not sure where the 17 kg comes from. That's still on the higher end of the single-cylinder range I think.
When using Backplate + Wing, I would say anything between 12 and 15 kg would be more than enough. 17 kg is the biggest single-tank wing size I have come across (maybe there are bigger ones).

In a jacket-style BCD there's a little more potentially buoyant stuff you would need to offset with some extra lead weight. But I wouldn't imagine that is more than 0.5 kg.

Still, 23 kg seems excessive. But I imagine there are other features of the Exotec that you really like. There's more to it than just lift capacity, I suppose.

 

[rsingler]

Here are some rules of thumb for wetsuit diving.
1) Though weight belts are passé these days, if you put all your ditchable weight in the integrated pockets, your wing needs to float your gear with a full tank of gas, without the added benefit of your wetsuit.
2) At the surface, your wing only needs to support a) your personal buoyancy, b) the in-water weight of your gear, c) your tank's buoyancy (+ or -), the weight of a 12l air fill, your carried lead, and the surface buoyancy of your wetsuit. At worst, based on what you've told us, that could be -2kg, -3kg, -3kg, -9kg, +4kg, or a 28lb wing unless you carry less weight.
3) At depth, you lose 75% or more of your wetsuit buoyancy due to compression, so add another 7lb to your requirement, or 35lb lift.

But this is estimated worst case. I think 25lb would be plenty if you don't have all of
a) a "sinker's" body composition
b) a steel tank that's negative when empty
c) lots of carried lead
and d) an old wetsuit that's lost much of its buoyancy.

Seems to me the Exotek is wasted buoyancy with added fabric and drag. My 2 cents. I just dove a week with a fluffy full 3mm suit with vest and hood with an 11l alum tank with 6kg lead and an 18# wing, putting 2kg on a weight belt. No problem floating my gear to hand it off to the guys on the panga before climbing into the boat. YMMV

 

[blueskies_up_ahead]

Not sure where the 17 kg comes from. That's still on the higher end of the single-cylinder range I think.
When using Backplate + Wing, I would say anything between 12 and 15 kg would be more than enough. 17 kg is the biggest single-tank wing size I have come across (maybe there are bigger ones).

In a jacket-style BCD there's a little more potentially buoyant stuff you would need to offset with some extra lead weight. But I wouldn't imagine that is more than 0.5 kg.

Still, 23 kg seems excessive. But I imagine there are other features of the Exotec that you really like. There's more to it than just lift capacity, I suppose.

Yes, of course. I like the design, it has pockets that are not too big and dump valves in all corners. But lift / trim / moving air are more important aspects. Main function first, then accessories, then looks.

Here are some rules of thumb for wetsuit diving.
1) Though weight belts are passé these days, if you put all your ditchable weight in the integrated pockets, your wing needs to float your gear with a full tank of gas, without the added benefit of your wetsuit.
2) At the surface, your wing only needs to support a) your personal buoyancy, b) the in-water weight of your gear, c) your tank's buoyancy (+ or -), the weight of a 12l air fill, your carried lead, and the surface buoyancy of your wetsuit. At worst, based on what you've told us, that could be -2kg, -3kg, -3kg, -9kg, +4kg, or a 28lb wing unless you carry less weight.
3) At depth, you lose 75% or more of your wetsuit buoyancy due to compression, so add another 7lb to your requirement, or 35lb lift.

But this is estimated worst case. I think 25lb would be plenty if you don't have all of
a) a "sinker's" body composition
b) a steel tank that's negative when empty
c) lots of carried lead
and d) an old wetsuit that's lost much of its buoyancy.

Seems to me the Exotek is wasted buoyancy with added fabric and drag. My 2 cents. I just dove a week with a fluffy full 3mm suit with vest and hood with an 11l alum tank with 6kg lead and an 18# wing, putting 2kg on a weight belt. No problem floating my gear to hand it off to the guys on the panga before climbing into the boat. YMMV

Thanks for the detailed answer! I appreciate the time you took! Not sure I understand it all though

I checked the buoyancy of steel and aluminum tanks. What I found is about -7kg for steel and less than -2kg for aluminum (full). If I dive with 6kg lead with a steel tank and 9kg with an aluminim tank, that brings the weight to 16kg and 11kg respectively. Is that what you meant? My wetsuit is positively buoyant but I don't know by how much (also changes depending on the type of wetsuit, so let's go with a shorty). You said at worst -9kg. I cannot imagine a shorty + me having buoyancy of +7kg. Do I miss anything? From your explanation of loss of buoyancy of the wetsuit I deduct the wetsuit at surface has a buoyancy of 4,3kg. Not sure if that is a 7mm full body wetsuit or a shorty though.

Body composition: I don't know tbh. Steel tank, can happen. Lead, see above.

What I wonder about as well is: shouldn't I be able to lift another diver's weight (incl gear) in case of an emergency? I'm not there yet in my certification / learning, but I will be eventually.

Finally: any other recommendations? I was also looking at the Scubapro Seahawk 2 (lift of 17-19kg depending on the size), Hydros Pro (16 kg), Aqualung Dimension (21kg) or Rogue (17kg). I'm kind of considering a back plate and wing as well but it makes me feel kind of uncomfortable / overwhelmed. Not really common over here either for beginner divers. I'll have a chance to try a Finnsub though. So who knows.

 

[rsingler]

Not sure I understand it all though

It's a complex subject, but pretty straightforward. Just take it piece by piece.

I checked the buoyancy of steel and aluminum tanks. What I found is about -7kg for steel and less than -2kg for aluminum (full).

You're correct, but typically we think in terms of empty weight, so that we can compare beginning and end dive (which removes 5# weight in a typical AL80 going to 500psi). So start with -2kg for average steel and +2kg for common aluminum. Plan on beginning of dive (-3kg carried air), and end of dive (-0.5kg carried air).

Personal buoyancy can be -2kg for a heavy-boned muscular male who can't float in a fresh water swimming pool, to +4kg for a "fluffy" diver in salt water.

Most bc's are 0 to -1 kg after buckles and D-rings, and after any open-cell foam gets saturated. Backplate and wing can be negative if there's a steel or aluminum plate. So you just carry less lead.

shouldn't I be able to lift another diver's weight (incl gear) in case of an emergency?

No. Don't plan on multiple failures. If he's unconscious, don't presume he's also got a failed bcd. Add enough air to his bcd to make him neutral and take him up. Then dump his weights on the surface.
If he's conscious but can't swim up against his failed bcd, have him dump part of his weight until you two can ascend. Once wetsuit expansion makes him a tad light, you just hold him back with less air in your bcd.

I cannot imagine a shorty + me having buoyancy of +7kg.

Easily possible. New 7mm stretchy neoprene shorty could be +4kg. Add body fat and it's conceivable. 75% of the wetsuit buoyancy is lost at 100ft.

Then do the math for needing to start up from the bottom at 100'.
Me: +2kg in salt water (70kg/173cm/avg build)
bcd: -1kg
Steel tank: -2kg
All carried air at dive start: -3kg
Wetsuit: +1kg after compression at depth
Carried lead for 7mm shorty at surface: -6kg
Total: -9kg
I really only need a 15lb wing, and can easily swim up against the remaining -2kg with a deep breath and a little finning... then my wetsuit starts to expand and it's zero added effort to ascend from 70' on up.
A 35# wing is really overkill.

And if you go to drysuit and carry 13kg lead for some reason? That's still only -16kg.
A 25# wing will work fine since you have redundant buoyancy in your drysuit. And with a hypothetical drysuit flood, just drop a few kg (not all!), inflate and go.

Finally: any other recommendations? I was also looking at the Scubapro Seahawk 2 (lift of 17-19kg depending on the size), Hydros Pro (16 kg), Aqualung Dimension (21kg) or Rogue (17kg).

Ask ten people and you'll get 15 recommendations. Of your list, I'd only consider the Rogue, except that I HATE the Sure-Lock weight system. Maybe the Seahawk.
But here's a thought...send a DM to @Tracy and order a Hydro-Lite from Dive-Rite through him. It's a soft backpad and medium wing that will cover you for all that you've listed. Incredibly comfortable and light, it travels well and trims perfectly. It won't break the bank like the Hydros Pro. It lets you try out backplate and wing without the rigging complexity.

HydroLite BC – Dive Rite | Equipment for Serious Divers

www.diverite.com

ScubaBoard is very wing-centric, but for a reason - it works.