Probably stupid question

[emoreira]

My thinking is that you will need more buoyancy depending of the suit you are using. Suppose for a moment that you are diving dry and your zipper suffers a catastrophic fault and your suit gets flooded. In that case you will need a huge buoyancy force to go back to the surface. That's why BCDs in general need to have more buoyancy for cold water diving than in tropical diving.

 

[Curious_George]

Mostly good answers, but this is probably the best one: optimal buoyancy calculator. Thanks to @rsingler and the others who built it.

 

[Rechno]

If you are properly weighted the lead you carry is to compensate for the buoyancy of you/ your gear (with nearly empty tanks at the end of the dive) etc. so
so at the start of the dive you would be overweighted by the weight of the gas in your tanks, which needs to be be compensated by the BCD/Wing.

As others have stated if there is a loss of buoyancy in your suit, you would also need to compensate for this.

So these sums are basically the amount of lift you absolutely need.
All extra buoyancy is then depending on your contingency planning and preference.

 

[kablooey]

Another factor in determining wing size:
You need a wing with enough positive buoyancy when inflated to keep your system afloat.

• with you not in it.
• with a full cylinder.
• without ditchable weights.

For some reason you need to remove your system in the water?
This could be to return to a boat without a swim step, or assist another diver in an emergency.

Not enough buoyancy to float independently means your system will sink without you in it.

.

 

[Edward3c]

Another factor in determining wing size:
You need a wing with enough positive buoyancy when inflated to keep your system afloat.

• with you not in it.
• with a full cylinder.
• without ditchable weights.

For some reason you need to remove your system in the water?
This could be to return to a boat without a swim step, or assist another diver in an emergency.

Not enough buoyancy to float independently means your system will sink without you in it.

.

Years ago I demonstrated this with a warm water diver who wanted to dive in the UK with the same kit.

I fully inflated the BCD placed their weightbelt on it and we watched the whole lot sink. They bought a new BCD with larger lift capacity for UK diving.

 

[CT-Rich]

Generally, most divers only want one BCD. When you choose it, you are generally thinking about have maximum flexibility for for all foreseeable situations. At 100 fsw all the buoyancy will have been wrung out of a 7mm wetsuit which could easily leave you 25-30 lbs negative on the bottom with a full tank.

On the surface, I have never heard someone complain about having too much buoyancy. I had a BCD failure on a shore dive and handed off my ditchable weight to my buddy for the swim to shore. He had plenty of lift to spare. If you live where you only ever use a 2 mm shorty, a small lift capacity would be fine.

I would suggest buying a BCD based on the most extreme conditions you are going to encounter with any regularity.

 

[EireDiver606]

It’s not a stupid questions. There are no stupid questions when you’re trying to learn.

You’re right, it shouldn’t change unless the tanks or exposure protection changes.
The wing needs to hold your main tanks on your back and to keep you above the waterline at the surface comfortably. Extra bottles like stages shouldn’t be steel (unless in special circumstances) as they do not contribute to a balanced rig and then you will be overweighted

If you have a balanced rig, you don’t have a huge wing flapping all over the place and have the least amount to descend while exhaling while still being able to hold your shallowest stops with an empty wing and low gas.

 

[EireDiver606]

Years ago I demonstrated this with a warm water diver who wanted to dive in the UK with the same kit.

I fully inflated the BCD placed their weightbelt on it and we watched the whole lot sink. They bought a new BCD with larger lift capacity for UK diving.

The weight belt is ditchable ballast apart of the diver not the diving system on the back.
In reality, you don’t need your wing to hold the weight belt as it’s being held up with the positive buoyancy of your exposure protection as that’s where you’re wearing it - around your waist.

 

[AfterDark]

My reason for the weight wing I use is double tanks, 7MM farmer John wet suits, heavy lead to offset, and diving with other divers geared up the same way. If I need to get myself with doubles and another diver with doubles that has a BCD issue to the surface, I'm going to need some help.

 

[EireDiver606]

My reason for the weight wing I use is double tanks, 7MM farmer John wet suits, heavy lead to offset, and diving with other divers geared up the same way. If I need to get myself with doubles and another diver with doubles that has a BCD issue to the surface, I'm going to need some help.

Just move some weight from your rig to a ditchable weight system. Hold onto your team? Problem solved.