BC Lift Question

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

gcarter

Contributor
Messages
8,428
Reaction score
9,069
Location
Ottawa, Canada
# of dives
500 - 999
This may sound basic to some, but I don't understand it - I'm a numbers guy, not a science geek.

In reading a number of posts, I see people talking about switching from a jacket to a BP/W to get more lift because they are going from wet to dry and need to add more weight, or changing the wing for one with greater lift.

If you are weighted to neutral +/- with an empty bladder, and if you can ditch your weight to make you positively bouyant, what difference would adding an additional 10 lbs of lift make? IOW, what are you actually acheiving? I am sure this will be a forehead slapper when I see the answwer, but there are some dots not connecting for me.

TIA
 
In reading a number of posts, I see people talking about switching from a jacket to a BP/W to get more lift because they are going from wet to dry and need to add more weight, or changing the wing for one with greater lift.
Those people probably aren't explaining themselves very well, since, in general, conventional jacket-style recreational BCDs are fitted with bladders that provide more than enough lift. However, it is true that, depending on the drysuit undergarment used, the material composition of the drysuit itself, and the thickness of the previous wetsuit, more lift may actually be required with the drysuit configuration. Bear in mind that lift requirements for the BC also depend on whether ballast is attached to the diver's body or the BCD/wing. More specifically, attaching all of the ballast to the BCD or BP/W will likely necessitate more lift. This is one of a couple of reasons why it makes sense to attach a certain proportion of the ballast to the diver himself (in the form of a weightbelt or weight harness).

Transitioning from wetsuit to drysuit, it is common for many divers to require more ballast to be properly weighted. Sometimes this additional ballast exceeds the room available in weight-integrated pockets and trim weight pockets on their current BCD. Divers are then faced with the problem of distributing that extra weight properly to promote horizontal trim. Stashing that extra weight in a BCD pocket might not be the best solution.

Conventional jacket-style BCDs will typically have some inherent padding which makes the BCD itself 2-3 lbs. positively buoyant even when there's no air in the bladder. Cold water divers might find a BP/W rig with a stainless steel (SS) BP attractive since the BP has 5-6 lbs. of weight built into it. All other gear remaining the same, it's not uncommon for divers transitioning from a jacket BCD to a SS BP/W to be able to shed 8-10 lbs. of lead weight.

Moreover, that extra weight built into the BP is positioned conveniently over the lungs when the diver is horizontal. This makes it easier to trim out the rig.

In my experience, a BP/W with a properly adjusted harness also makes the rig more comfortable for the diver to carry. I do a lot of shore diving here in SoCal and some sites feature quite a hike to the water's edge.


Hope that explains it for ya...
 
Part of it, thanks, but not all of it.

Why would someone need to switch between a 30 lb and a 40 lb wing?
 
The bladder makes alot of difference depending on what it is your attempting to do. For most recreational diving simple small bladders are more then enough for what you are attempting to achieve.

The larger lift bladders are more commonly a concern for tech divers where they resort to carrying a set of doubles and one or 2 deco bottles and any additional gear they carry (Im not a tech diver myself)

What you will find with this type of diving is with that much gear it is still influenced by gravity so there would be a strong downward pull. To counter the force pulling down you need more lift. Thats where the larger bladders come into play.

Now in some cases (though not all) Wearing drysuits may carry enough weight that people may want to have a larger lift but if you are properly weighted this should not be as much.

Now specialized diving may in some cases place enough gear on a diver that they may want a little more lift as well such as night diving where you carry more gear but this should in most cases be minimal too.

Drawbacks to oversized bladders is that the larger the lift rating the larger the bladder will be thus creating both more drag in the water and increase concerns with packing before a trip.
 
Part of it, thanks, but not all of it.

Why would someone need to switch between a 30 lb and a 40 lb wing?

because the increase in speacilized gear they are using for a dive increases downward gravity pull and you need more lift to counter the downward pull.
 
Part of it, thanks, but not all of it.

Why would someone need to switch between a 30 lb and a 40 lb wing?
...if their exposure protection, tank configuration, or the way they are attaching their lead weight (diver vs. BC) requires it.

To answer your question properly, you really need to understand what factors determine the minimal required lift for a BCD/wing.
The wing needs to have enough lift to do the greater of the following:
  • Float the rig at the surface without the diver attached to it.
  • Compensate for maximal loss of buoyancy of the diver's exposure protection at depth, i.e., in the event of a catastrophic drysuit flood.

Confused yet? :D
 
because the increase in speacilized gear they are using for a dive increases downward gravity pull and you need more lift to counter the downward pull.

I am trying hard to NOT be thick about this, really I am.

So if they need to take more gear down, why don't they just reduce their weights?
 
...if their exposure protection, tank configuration, or the way they are attaching their lead weight (diver vs. BC) requires it.

To answer your question properly, you really need to understand what factors determine the minimal required lift for a BCD/wing.

Can you point to a good link for that?
 
In reading a number of posts, I see people talking about switching from a jacket to a BP/W to get more lift because they are going from wet to dry and need to add more weight, or changing the wing for one with greater lift.

I wasn't aware of any threads in which people had advocated BP&W on the basis of providing increased lift capacity?!?

When people move to BP&W, they normally pay more attention to achieving the correct lift required. BP&Ws are modular, so the user can pick the bladder/wing size that best suits their requirements - which tends to be smaller than the unilateral amount provided with jacket-style BCDs. .
 
I am trying hard to NOT be thick about this, really I am.

So if they need to take more gear down, why don't they just reduce their weights?

Because if they are using a wet suit then remember that at the start of a dive your wet suit is not fully compressed. As you decend into depth the wetsuit begins to compress which in turn does 2 things. First it looses it begins to loose some of its warming abilities as its no longer as thick.

Second as it does compress it begins to loose buoyancy which in turn you need less weight at depth to keep you under then you would at the surface. So hypotheticly without doing math on it you may need say 16 pounds to get you to achieve your ideal weight at the surface where as when you are at say 100 feet you may only need 6 pounds. Again this is not an actual ratio just hypothetical.

With this theory im using in mind you now have all the weight of your gear plus over weighted by 10 pounds.
 
https://www.shearwater.com/products/peregrine/

Back
Top Bottom