82 replies to this topic

[BubbleBoy]

As I start to gravitate towards a new rig for diving here in the Northeast, I have been thinking a lot lately about buoyancy issues with diving gear. So, I’m going to take a big chance here and comment on something that I (presently a lay recreational diver) know very little about.

Reading the comments about tech divers who put 50+ pounds of lift in a BC wing, I see a similar kind of risk as a diver who puts 30+ pounds of weight on a belt they plan to dump in an emergency. Either way you are exposing yourself to the dangerous possibility of a sudden and rapid buoyancy change. As even some techies have pointed out, it may not be so easy as it seems in the panic of the moment to quickly correct for a 50lb BC blowout with lift bags, dry suit lift adjustments, etc. If you are diving on a wall you could drop 60ft. before working out a solution.

I have always viewed BC gas as something primarily for making relatively small buoyancy adjustments while diving. My goal in setting up my diving rig is to use a maximum of 15lbs of variable lift in my BC and 10lbs of dumpable weight on my belt. If I’m neutral within those ranges, I can probably use or loose either of those systems and still swim out of the situation. If I need more than 15lbs. of lift in my BC to stay neutral, I would probably rather add some fixed lift to my rig, like extra neoprene, lighter tanks, Styrofoam, whatever. That way I would never be exposed to a sudden buoyancy drop if my BC fails.

If this all sounds like total ignorance to you techies, go ahead and blast me. I am curious though, under what diving circumstances do you require BC lift to vary from zero to 50lbs?

[Moderator note: posts split from Dual Bladders thread to create new thread regarding BC/Wing lift capacity, i.e. new topic]

[PerroneFord]

PM coming.

[Dive_Girl]

PM coming.

If it's in regards to BubbleBoy's post - it would be great if you shared it in a post. I am in interested in hearing what other think about lift. I personally do not chose a wing with what I considered excessive/unecessary lift capacity for my style of diving. My singles wing is a 50lb wing and my doubles is a 59lb wing because I liked the way it positioned me in my doubles best.

[PerroneFord]

I am in interested in hearing what other think about lift. I personally do not chose a wing with what I considered excessive/unecessary lift capacity for my style of diving. My singles wing is a 50lb wing and my doubles is a 59lb wing because I liked the way it positioned me in my doubles best.

Lift:

My singles wing is a 27# unit

I have a 45# doubles wing and a 59# doubles wing.

Both are overkill and will be even moreso when I decide to dive dry.

Edited by PerroneFord, 26 July 2006 - 07:54 PM.

[drbill]

Likewise I carry 28# of lift in my wing and 36# on my belt (to stabilize on the bottom for filming). I have wings up to 100# lift (which sits high and dry in my dive locker).

My lift has been sufficient at all depths I've dived down to 180 ft (assuming no catastrophic failure). One thing I am in the process of doing is creating weighting with 20# on the belt and 16# easily ditchable.

[Dive_Girl]

I am in interested in hearing what other think about lift. I personally do not chose a wing with what I considered excessive/unecessary lift capacity for my style of diving. My singles wing is a 50lb wing and my doubles is a 59lb wing because I liked the way it positioned me in my doubles best.

Lift:

My singles wing is a 27# unit

I have a 45# doubles wing and a 59# doubles wing.

Both are overkill and will be even moreso when I decide to dive dry.

Thank you for sharing what you dive. I have often thought my singles wing is excessive, but my thought was that is is small enough in design for a singles set up, but could double as a backup to my doubles wing so I don't need to buy a third wing.

I couldn't go as low as 27 lbs for my singles set-up though where I dive. As a reminder I dive in cold salt water (Pacific Ocean), with a drysuit and fluffy undergarment which relies on air layer for warmth (it's not fleece). So when I dive with that set-up and diving a bit heavy for students, I have on a 5lb backplate, 2lb tank adapter, 5-7lb negative steel single tank, and a 16lb weight belt. Add that up and it exceeds a 27lb wing. Unless I am misunderstanding the purpose and math of wing lift capacity.

[Dive_Girl]

Likewise I carry 28# of lift in my wing and 36# on my belt (to stabilize on the bottom for filming). I have wings up to 100# lift (which sits high and dry in my dive locker).

My lift has been sufficient at all depths I've dived down to 180 ft (assuming no catastrophic failure). One thing I am in the process of doing is creating weighting with 20# on the belt and 16# easily ditchable.

you have 28lbs of lift and wear 36lbs of weight? Maybe I have this all wrong - which isn't unheard of. You'd be surprised how often we as divers walk around with info we swear by that was just misinformation handed down from diver to diver as fact. You often don't have reason or need to question it. That's the beauty of dive forums to me - to gain info without feeling to terribly foolish.

But well, this issue could...

I just know I had a BC that was rated only for 30lbs of lift and I tested its hold of me at the surface with 38lbs - I thought I was going to drown. I had to kick to maintain my head above water. What an uncomfortable feeling. Bill do you dive with aluminum tanks that become positively buoyant at the end of the dive?

[PerroneFord]

Unless I am misunderstanding the purpose and math of wing lift capacity.

I don't know. Lets look:


BP = 5#
STA = 2#
Tank = 7#

That's 14 pounds before you add the belt. How buoyant are your drysuit undies? Assume they are 25 pounds buoyant. Difference between your drysuit buoyancy and your gear is 11 pounds. If you put 11 pounds on a belt, you'd be neutral in the water. With 16 pounds you are 5 pounds negative. As long as the world is ok, you need 5# of lift. If your drysuit floods, you remove the belt. You are now offsetting 11#. The question is between your wing and your drysuit if you can put gas in it, can you get up?

If your wing were to fail, you'd be 5# negative. Assuming the drysuit stayed intact, you should need 5# of gas in the drysuit to remain neutral.


So... do you need a 50# wing?

[drbill]

you have 28lbs of lift and wear 36lbs of weight? Maybe I have this all wrong - which isn't unheard of. You'd be surprised how often we as divers walk around with info we swear by that was just misinformation handed down from diver to diver as fact. You often don't have reason or need to question it. That's the beauty of dive forums to me - to gain info without feeling to terribly foolish.

But well, this issue could...

I just know I had a BC that was rated only for 30lbs of lift and I tested its hold of me at the surface with 38lbs - I thought I was going to drown. I had to kick to maintain my head above water. What an uncomfortable feeling. Bill do you dive with aluminum tanks that become positively buoyant at the end of the dive?

I dive with a steel HP120 and a 19 cu ft Al pony on my soft harness and wing. My 7mm wetsuit and 7mm hooded vest give me more lift than most who just wear the 7mm wetsuit. I wear both (so far even in this HOT summer) because even now it can be 50 F at depth and I often lie motionless for long periods while filming.

I occasionally have to kick down to submerge.

[PerroneFord]

I just know I had a BC that was rated only for 30lbs of lift and I tested its hold of me at the surface with 38lbs - I thought I was going to drown.

So you had a variance of 8# between the wing lift and the weight? Ever drop an 8# weight in the pool? Sinks pretty fast. If you'd have had a 40# lift wing, you wouldn't have gone anywhere. But it would have been FULL.

Generally, things restrict wings so they cannot be used to rated capacity. Good to have a little margin

[PerroneFord]

I occasionally have to kick down to submerge.

How do you hold your stops if you have to kick down to submerge?

[Dive_Girl]

BP = 5#
STA = 2#
Tank = 7#

That's 14 pounds before you add the belt. How buoyant are your drysuit undies? Assume they are 25 pounds buoyant. Difference between your drysuit buoyancy and your gear is 11 pounds. If you put 11 pounds on a belt, you'd be neutral in the water. With 16 pounds you are 5 pounds negative. As long as the world is ok, you need 5# of lift. If your drysuit floods, you remove the belt. You are now offsetting 11#. The question is between your wing and your drysuit if you can put gas in it, can you get up?

If your wing were to fail, you'd be 5# negative. Assuming the drysuit stayed intact, you should need 5# of gas in the drysuit to remain neutral.

So... do you need a 50# wing?

Lift capacity ratings delve in the amount of weight a BC/Wing can keep afloat, right? According to one source (you might recognize this one too ):

"Buoyancy Compensator: Adjusted based upon needed lift whether one is diving single or double tanks. Buoyancy should be sufficient to float equipment by itself while at the surface."

And

“However, if a diver does need more than 65 pounds of lift for diving doubles, or more than 30 pounds for diving singles, then they do not have a balanced rig. The diver should be able to drop unnecessary weight and swim up without a functioning BC. As with all diving, the key component to proper buoyancy is diving with a properly balanced rig.”

My double wing isn’t more than 65lbs and my single, as I said was purchased to double as a back-up. I recognize it’s excessive for simple recreational singles diving.

I am learning a lot here. And I did have some misconceptions regarding the whys to lift.

[PerroneFord]

I have seen divers do 20k ft penetrations at 300ft with twin 130s, 3 stage bottles, 3 scooters, and 8-10 pound lights with a 55# lift wing.

[Dive_Girl]

I have seen divers do 20k ft penetrations at 300ft with twin 130s, 3 stage bottles, 3 scooters, and 8-10 pound lights with a 55# lift wing.

Well see that's what I'm diving...and what were you doing at 300' PF?

I think, I'll grab some shop wings and run some tests when I am in the pool next. I'll post what I find.

[PerroneFord]

Yep, flood your drysuit and see how much lift you need to get off the bottom. Then start doing your calculations from there.