16kg lift enough for cold water dive?

[jonnythan]

Why? Proper weighting is a must. Realistically, you should not need to add air to your BC at the surface to remain there. You add the air to make you positive at the surface so you can rest and not over exert yourself, or to make up for compressed air spaces as you descend. Yes you need a certain amount of lift to keep your equipment afloat if you take it off in the water. If your equipment is 15 pounds neg, then you need 15 pounds of lift to keep it floating. (actually 16, 15 to be neutral + 1 to become positive)

Say you hit the water and go straight to 100 feet. At that point, you are negatively buoyant by the lost buoyancy of your suit (which can be significant when wearing a lot of neoprene) plus the weight of the gas in your tanks (which can be up to 8 or 9 pounds with a big steel tank).

Your wing needs to account for at least that much, which can be 20+ pounds on a deep dive with a thick neoprene suit and a large-ish tank. And this is with perfect weighting.. two "extra" pounds of weight add directly to this. So you're looking at a diver new to this rig potentially being up to maybe 30 pounds negative at the beginning of the dive at 90 or 100 feet or whatever.

That's the big problem with neoprene... every pound of lost buoyancy at depth is a pound you're overweighted at depth and need to make up for with air in the BC.

 

[jonnythan]

If your equipment is 15 pounds neg, then you need 15 pounds of lift to keep it floating. (actually 16, 15 to be neutral + 1 to become positive)

If I'm 15 lbs negative, I want a lot more than 16 pounds of buoyancy. I want much more than 1 lb of my head out of the water on the surface.

 

[doole]

If I'm 15 lbs negative, I want a lot more than 16 pounds of buoyancy. I want much more than 1 lb of my head out of the water on the surface.

Good point, given that a typical human head actually weighs about 15 lbs...

 

[scubamate]

If I'm 15 lbs negative, I want a lot more than 16 pounds of buoyancy. I want much more than 1 lb of my head out of the water on the surface.

That was an example, My point being....if you are perfectly neutral at the surface, it only takes an extra pound or two of lift to keep you afloat while breathing normaly. It's common sense that you want more than just your eyes out of the water, so yes, more lift is needed.

Under pressure air spaces are compressed and that volume is made up with the BCD and yes, (I mistated my meaning), is where you need "lift" to maintain neutrality.

Using a neutral buoyant tank helps with reducing the amout of extra weight you are required at the beginning of the dive also.

:1poke:

 

[MASS-Diver]

.

Using a neutral buoyant tank helps with reducing the amout of extra weight you are required at the beginning of the dive also.

:1poke:

It doesn't matter what type of tank you are using - no matter you start a dive overweighted by the weight of the gas. You balance the rig with it empty (or 500psi) but no matter what you can't start a dive neurtral because of the gas you carry.

 

[doole]

If I was only 1 lb positive on the surface I would have trouble keeping my head above water. 30 lbs lift on the surface will get your head and the top of your shoulders above water and is comfortable in most situations. I find, and this is a personal and therefore subjective mater...

Also true.

The real issue is - can you complete a safety stop at the end of the dive without struggling? If so, you have (at least) enough weight.