Wing Lift Capacity

[eelnoraa]

26(on belt) +15(for head)= 41 pounds.

Not sure why he needs that 26 pounds, but then I've never worn a 5mm suit. I wore a 7mm once and don't think I used that much weight. How much buoyancy is lost with depth with a wet suit? Using Boyle's law, @33 ft you've lost 50%, At 66ft, you've lost %66, @ 99ft, you've lost %75 and so on. With a dry suit, you have to worry about a total loss of buoyancy. This isn't like weight. I want a little buffer with my lift, 'just in case'. There is no real benefit to having "just enough" lift to get by. In reality, you will probably limit the dives you can accomplish with this false economy.

It doesn't sound so crazy when you start crunching the numbers. Does that explain my rationale?

I don't think that number should be added. When a diver is properly weighted, he/she is only negative by the weight of the gas he/she is carrying. So at the beginning of the dive, with full kit, full tank (AL80), he/she is 6lb negative. He/she is never 26lb negative. If so, he/she has a much bigger problem. Now +15lb for head. He needs 21lb of lift in that situation.

Since he/she is with AL80 with 26lb. AL80 is +4lb empty, he is suit can't have more +22lb buoyancy (which is on the high side), so it can't lose more than 22lb. So he/she needs 22lb for this situation. With a wetsuit, you never had a case where you lose all suit's buoyancy and need head above water. So in this case, I will say get a 30lb wing.

I also agree the "no benefit to just have enough lift" part if the additional lift doesn't cause a drawback. IMHO, single wings at 30-35lb are still very streamline. Most 40lb start to get flappy and taco-ee unless it is Oxycheq MkV. So there is a cost going too big too

 

[Patoux01]

26(on belt) +15(for head)= 41 pounds.

Objection sir Chairman!

Summing a pear and a potato does not make two apples, nor do a pine and an apple make a pineapple.

It's either "he needs 26(weight) + 6 (gas) pounds" if he is wrongly weighted aka everything on the rig (remember those folks claiming they can remove their rig midwater? Yeah that reason exactly) and wants to float the rig, or "he needs 15 (for head) + 6 (gas)" because he's in the rig, but then he and his suit would make up for 20-ish pounds of weight he's carrying.

If one were to try to float a rig with all the weight on it plus a head for some reason, then he'd probably have some other issues before calculating buoyancy

 

[The Chairman]

I don't think that number should be added.

No one's going to force you to dive in any particular way. This is how I choose my gear and how I dive.

When a diver is properly weighted,

Most people with 26 pounds are diving a dry suit, n'est pas? What do you do if/when that dry suit floods? Lose a $100 of lead or be able to float yourself easily? Everyone seems to want to plan for the perfect dive and not the perfect storm. Again, at 100 feet, you've lost 3/4 of your dry suit's buoyancy. -20 - 6 =-26 pounds of negative lift for a full tank at depth and there's absolutely no buffer in there. As a rule of safety, I want a bladder that holds all of my weight plus 15.

Most 40lb start to get flappy and taco-ee unless it is Oxycheq MkV.

None of my sidemount rigs taco. Neither my Zeagle Express Tech nor my Dive Rite Hunter Pac taco at all. Not even a little bit. The only time I would worry much about being streamlined were if I were racing scooters. Then hell, I'll even wax my wing to reduce that drag! BTW, the ET basic sells for about $280 or so. Pretty damn cheap.

I want 'just enough' weight when I dive, but I don't want 'just enough' air or 'just enough' lift. I want plenty of both and there's simply no downside to it.

those folks claiming they can remove their rig midwater?

Dude, removing your rig underwater has nothing to do with how overweighted you might be. I can teach any student, dry suited, wet suited or even naked to do that easily. The secret? Keep the heavier item on top and instead of moving the gear, move the diver. It's simple ying and yang. I am fat and unusually buoyant. With an aluminum tank and no exposure protection, it takes 14 or so pounds to get me neutral. When I take off my weight integrated BC, I get perfectly horzontal, remove all of my straps and then I spin out of my BC with me now looking up and my BC sitting on my stomach. I can cut any entanglements easily, tighten the tank, whatever I need to do and then I spin back into my BC. It's far cleaner than the monkey humping a football imitation that I see in most OW classes. If I'm wearing a weight belt, I do the opposite since I am the sinky thing and my BC is now the floaty thing. In both cases, it's the diver that moves: not the gear. It's hard to get your mind around that at first, but it's simple and fun and a bit of training should make it easy.

 

[Patoux01]

Dude, removing your rig underwater has nothing to do with how overweighted you might be.

But it has everything to do with the repartition of your weight. Unless, of course, you like bear-hugging a rig in order to not float to the surface while having it sink to the bottom. If that's what you mean, knock yourself out, but it's really much easier to have everything "close to neutral".

 

[The Chairman]

Unless, of course, you like bear-hugging a rig in order to not float to the surface while having it sink to the bottom.

No need to bear hug: always keep the floaty part under the sinky part. Let physics work for you and not against you. This is sooooooooo easy that all of my OW students can do this and usually on the first try. Here's one of my Trim, buoyancy and propulsion students on her second try. She got better, but note that this is in the shallows. She's only in about 6 foot of water, in a jacket BC and with danglies. The deeper you get, the easier it gets. She's floaty, so also note how she stays under the sinky BCD. I hope this helps.

​

 

[eelnoraa]

No one's going to force you to dive in any particular way. This is how I choose my gear and how I dive.

Sure, I respect how you dive. There are more than one way to dive, but there are still the right logic and wrong logic when accessing a situation. In OP's case, there is absolutely no case where he/she will lose any suit buoyancy and need head above water because of the wetsuit. So 22lb (26-4lb for AL80) + 15lb case will never happen. Even if you count that, it is still 37lb.

Most people with 26 pounds are diving a dry suit, n'est pas? What do you do if/when that dry suit floods? Lose a $100 of lead or be able to float yourself easily? Everyone seems to want to plan for the perfect dive and not the perfect storm. Again, at 100 feet, you've lost 3/4 of your dry suit's buoyancy. -20 - 6 =-26 pounds of negative lift for a full tank at depth and there's absolutely no buffer in there. As a rule of safety, I want a bladder that holds all of my weight plus 15.

A drysuit won't lose any buoyance due to depth, zero. And again, at 100ft, you head is not above water by any stretch, so that 15lb for head shouldn't be counted in this case. A drysuit will only lose buoyance if it is flooded. But again,I respect your gear choice, but I don't agree with the reason.

None of my sidemount rigs taco. Neither my Zeagle Express Tech nor my Dive Rite Hunter Pac taco at all. Not even a little bit. The only time I would worry much about being streamlined were if I were racing scooters. Then hell, I'll even wax my wing to reduce that drag! BTW, the ET basic sells for about $280 or so. Pretty damn cheap.

We are not talking about side mount here, right? I am definitely no expert in side mount, so can't comment on wing size. But for back mount Hunter Pac does NOT have a 40lb wing, so I can see why it isn't taco-ing.. Bad design single wing, even at 38lb, will look flappy and taco-ee. I don't want to name that wing here

 

[The Chairman]

A drysuit won't lose any buoyance due to depth,

But a 5 mil will. On the 'perfect dive', a drysuit can be filled as you descend. You can even control your buoyancy with just your dry suit. But what happens when you get a full flood? You lose all of that buoyancy. It's happened to me. I was in Bonterre mines, just outside of St Louis when that happened to me. 56 (?) degree water too. Holy schneike, was it cold and I was diving two steel LP 120s with no additional weight. Talk about heavy metal! Hoooooooooooooweeeeeeeeeeee, it was chilly, but I was being taken on a special dive, just Mike and me through his favorite parts. I flooded on initial descent (neoprene neck seal poofed out) and I did the whole dive chittering and a chattering. At the end, Mike was surprised that I had flooded, as it didn't affect my diving. "You should have told me! I would have called the dive!" And that was precisely why I didn't tell him. What a fun dive. I've experienced a full flood three times now and I don't dive dry suits that often.

Even if you count that, it is still 37lb.

And 44 is only 7 pounds more than that. Not a big deal.

We are not talking about side mount here, right?

I'm talking about the full range here. There's just no compelling reason for me to sacrifice safety to look cool and sexy. All the cool kids want to trim down their BCD lift like it's going to help them. I'm definitely old school and want my BC to have a sufficient capacity for cuando la mierda golpea el ventilador.

Everybody wants to plan for everything going well. I plan for everything going badly.

 

[INQuarryDiver]

Great info. I am still at the very novice stage. The instructor weighted me with 26 lbs using 5/3 mm (?) wet suit in very shallow salt water (10-15 ft). I later used about 20 lbs in similar suit down to 75 ft.

I appreciate everyone sharing the knowledge with me! Thank you.

 

[MaxBottomtime]

If you're diving in a wetsuit the suit itself will be buoyant at the surface. You should be able to dive with the weight you need to get down and enough buoyancy to remain at the surface, even with a 15 pound head.
Here's a look at divers who must be freaks of nature.
Gallery of California Backpack Divers : 1999-2001

 

[cool_hardware52]

Hello All,

I am looking to buying a BPW or Zeagle Express Tech. I am unsure how much lift I'll need from the wing. I'll only be diving relatively warm waters 60 F and above. At most, I've used about 26 lbs of weight in salt water w/ a 5mm wetsuit, and AL80 tank.

I checked the search function couldn't quite find what I was looking for. Is there a formula to determine how much lift is needed?

Any advice is appreciated.

Any BC needs to offer enough lift capacity to meet two criteria:

Float your rig at the surface with a full cylinder

&

Be able to compensate for the maximum possible change in buoyancy of your exposure suit.

The two are not addiitive, which ever is larger dictates the minimum required lift capacity.

With a BP&W your "rig" will be the back plate, harness, regulator, full cylinder and any ballast you choose to add to your rig.

For example with a typical Stainless Steel Plate and aluminum 80 you rig will be about -10 lbs with a full tank; 6 lbs for the plate and harness, 2 for your reg, and 2 for a full al 80. This rig will provide about 4 lbs of ballast when the ~6 lbs or so of gas in the al 80 is removed.

With a HP 100 steel tank your rig will be about -18 lbs. A full HP 100 will be about -10 vs the -2 for the al 80. and will provide about 10 lbs of ballast when the ~8 lbs of gas is removed from the HP 100.

The choice of plate material, i.e. stainless vs aluminum or Kydex and tank type, i.e. needs to made by considering the buoyancy of your exposure suit. A SS plate and negative steel tank would be a poor choice with a 3mm suit that may be only +3-5 buoyant.

Remember what a buoyancy compensator does. It compensates for the change in buoyancy of your exposure suit.

Exposure suits can only lose the buoyancy they start with, no more.

If you start the dive in a 3mm wetsuit that is +4 lbs the most you can lose is 4 lbs.

Your suit is the only thing that can lose buoyancy. Your personal buoyancy does not change WRT to depth, as long as you are breathing compressed gas. Your tank is getting less negative as you breath it down.

Smaller wings offer advantages in terms of stability, ease of venting and a bit less drag. As long as you understand proper weightingany BC that meets the two criteria listed above are not a risk to safety, and wings larger than required offer no increase in safety.

As others have noted the early days of scuba routinely saw divers using no BC's. Careful weighting and modest sized cylinders made this easily possible.

Over weighted divers are a genuine risk, and huge BC's unfortunately often mask this risk, until the day a BC fails or panic leads divers no using their BC.

I'd be happy to walk you through how I size wings, and how I define minimum ballast. Best to give me a call. 626-799-5078.

Tobin