BC Lift Question

[DevonDiver]

Can you point to a good link for that?

Take a look at: Scuba Resources

There is a wing lift calculator there, amongst other tools.

 

[gcarter]

Thanks all, appreciate the patience, aparently I have more reading to do.

When I went on vacation last fall, I didn't think I was sending myself back to school LOL.

 

[Bubbletrubble]

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?

Remember that "proper weighting" means that the diver is weighted so that he can comfortably hold a safety stop (or shallower depth) with near empty tank(s) and empty BCD/wing at the end of the dive.
Strictly speaking, proper weighting is a separate issue from determining minimal required lift for a BCD/wing.

Thanks all, appreciate the patience, aparently I have more reading to do.

When I went on vacation last fall, I didn't think I was sending myself back to school LOL.

It's probably not your fault. Basic OW scuba courses tend to not teach this well...or at all.

Any thoughtful, conscientious diver would be asking the same questions.

 

[k ellis]

Thanks all, appreciate the patience, aparently I have more reading to do.

When I went on vacation last fall, I didn't think I was sending myself back to school LOL.

Hey patience is not a big deal. We were all new once!

 

[Hatul]

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.

Hope that explains it for ya...

Can you explain the reasoning here? It would seem to me that weight is weight regardless of where it it.

Adam

 

[Hatul]

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

Weighting to be neutral near the surface at the end of the dive with empty wing is a way to set the amount of weight to take. Choosing the wing lift is a different issue.

The wing is used to compensate for buoyancy changes in your suit and use of air. So the size of wing depends on that, plus the scuba unit needs to be able to float and have a few pounds in reserve as margin of error.

I don't dive with a drysuit so someone can correct me here, but I believe with drysuit you can actually get away with a slightly smaller wing, because inflating the suit at depth provides some of the suit compensation, and the drysuit can provide some of the reserve lift of the wing, as long as the suit does not flood.

Adam

 

[DevonDiver]

Can you explain the reasoning here? It would seem to me that weight is weight regardless of where it it.

It's really about starting to view your configuration from a 'Balanced Rig' perspective. Not only dealing with what weight you need, but also calculating your distribution of ditchable and non-ditchable weight, on the basis that you may need to swim the rig up in an emergency (i.e. wing failure/burst bladder).

Whilst this isn't directly connected to the wing lift necessary, it is all part of a cohesive and intergrated approach to configuring an optimum set-up. Calculating required wing lift, must be based on precise and effective weighting...and must also consider the contingency of wing failure.

Bear in mind that weighting may be in the form of lead, but may also be in the form of equipment that is carried by the diver; such as torches, pony cylinders etc. All of this has to be factored into the overall 'balanced rig', when determining lift capacity and the ability to surface if the wing lost buoyancy.

 

[k ellis]

the drysuit can provide some of the reserve lift of the wing, as long as the suit does not flood.

Adam

You kind of hit the nail on the head with that statement. Drysuits take considerable more weight because their is air inside the suit as opposed to a wet suit filling with water. Should that suit flood your going to have a very large amount of weight being pulled down by gravity with very little air to counter the flood except what your bcd can hold.

Ideally one would be able to get to the surface without ditching their weights as we all know ditching can be a bad choice if other options are available. (No Im not down talking dropping ones weights if its the last resort). If you can get to the surface without ditching weights you potentially avoid a run away ascent. For this reason a larger bladder may come in very handy should one ever find their self in a flooded drysuit.

I do like Devons response though in reguards to proper weighting in reguards to wing failure. Thank you for bringing that up as well

 

[turnerjd]

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

Yes it is a forehead slapper, and I'll try and keep the answer simple.

People going to dry suit diving are doing so for two reasons.

1. the water is very cold, either because it is in a cold region, or because they are starting to go deeper, where the H2O is colder.
or
2. the water is a bit cold, but they are going down for much longer (e.g. with mandatory decompression)

The major problem is what to do if you flood the drysuit. Drysuits have air in them, providing a lot of buoyancy, flooding the suit loses the buoyancy of the suit.

Now, in neither of the above cases is dropping the weighbelt an enviable option of regaining the lost buoyancy, as it can cause major problems. OK not getting to the surface at all is perhaps the problem to end all problems, but a rocket propelled buoyant ascent from the deep missing mandatory stops will cause a goat to explode.

So, all they do is have "redundant buoyancy" in that they have a bladder big enough to get back the lost buoyancy if they flood the suit and get to the surface in a controlled, safe, and unbent manner.

Now, the going from BCD to BP/W is a red herring, it is the change of diving style, and the start of thinking about such problems as flooded suits that is the underlying factor. Again, changing the size of the wing is to just maintain the necessary redundant buoyancy as the rest of the equipment changes.

OK?

Jon

 

[DevonDiver]

I've never completely flooded a drysuit, but where does this extra 'weight' come from?

I understand that it would be pretty difficult to climb back up the boat ladder in a flooded suit, or even to maintain postive buoyancy at the surface, but whilst submerged a flooded drysuit won't add 'weight' to the diver. It would just remove buoyancy. But that wouldn't be a problem, as they have their BCD anyway for that purpose...so there is no question of having a need to ditch weights.

As there is no extra 'weight' added by a flooded drysuit, then there is no need to increase the wing capacity beyond what was already calculated.