Too heavy after a certain depth ?

[fjpatrum]

That's part of it. A BC also needs to be able to float itself without the diver in it should it need to be removed for any reason (tangled up in something or kayak diving as examples) It would be a shame to remove it and watch it sink to the bottom if you let go of it.

No, a BC does not lose "lift power". A BC that displaces 30 lbs of water on the surface when full will displace 30 lbs of water at 100 feet when full as well. It just takes 4 times the amount air to fill it.

That last part is true if, and only if, the diver doesn't accidentally let water into the BC while dumping. If you're using the wrong dump valve (not the highest in the water column) then you can let water in the BC, thus removing some of its lift capacity.

Other than that, CTSean is right.

 

[socc]

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:sunny:

Ohh yeah ! Good point. I used to do that by mistake in my first dive.

Thanks for reminding me !

Socc

Sent from my GT-I9505 using Tapatalk

 

[NAM001]

You understand correctly.

Hello KWS,

First of all many thanks for your very detailed and explanatory reply !

I think I get it. Something that many beginners forget (at least thats what I think), is that air actually has weight ! Also, in my OW course no one really told me about all this kind of stuff and I think that is probably for most people. They just tell you, that you put weights to compensate the positive buoyancy from the suit which looses lift at depth, etc. but nothing in detail to understand what is really going one and how important might this be. Probably this is because it the first certificate you get and it might not be that important, but I actually find it important and I am trying to improve my knowledge in diving using this forum. Some people that do not do that though, they might have troubles (hopefully not, but...) !!!

So the method I mentioned above is quite reliable but not perfect, right ?

Also, from what I understood, with almost empty tank you should have neutral buoyancy with zero lift from the BCD (i.e. empty BCD) at safety stop depth. In addition, the BCD should be able to compensate the weight of a full tank at safety stop depth to start with.
Then, as the suit looses buoyancy by going deeper, the BCD should be able to compensate the full tank and lost lift from the suit.
Finally, as you breath air the tank becomes lighter so after some point you get quite a lot of lift back and your BCD needs lift to compensate. To end with, as you start to ascend, air in the BCD expands giving you more lift and the suit starts giving you more lift as well.
Did I understood right ?
So at the end of the day you have to make sure that your BCD can compensate mainly the weight of a full tank and the lost lift from a neoprene suits depending on the planned max depth ?

Another question I have is: Does the BCD loose lift "power" (sorry I did not know how to state it otherwise) as you go deeper ? If so why ? Or its lift "power" is the same whatever the depth ?

Many thanks,

Socc

---------- Post added February 12th, 2014 at 03:46 PM ----------

socc
somthing hit on by others that i did not mention in my post was in sizing the bcd or wing the size has 2 goals.
1. enough lift to hold the rig on the surface without the diver in it.
2. hold the diver and the rig and the misc gear on the surface with the divers head out of the water.

With a thick wet suit #2 may not come into play as the lift is from the suit and not the bcd to keep the head out.
#1 is there ike others has mentioned. dont want to take the rig off and watch it sink.
This aspect is important when you are exiting the water and you cant get out with the rig weight on. (small boat)

Another comment on the OP and that is when ou are weighting and find that you think your scenerio could come into play it is time to go to a dry suit. The dry suit depending on type eliminates the compression problem so it is no longer a factor. you still have to manually inflate it as you go deep. It suto vents as you ascend. It has its price and not just initial cost. However DS bouyancy is another topic for when the time comes.

 

[socc]

You understand correctly.



---------- Post added February 12th, 2014 at 03:46 PM ----------

socc
somthing hit on by others that i did not mention in my post was in sizing the bcd or wing the size has 2 goals.
1. enough lift to hold the rig on the surface without the diver in it.
2. hold the diver and the rig and the misc gear on the surface with the divers head out of the water.

With a thick wet suit #2 may not come into play as the lift is from the suit and not the bcd to keep the head out.
#1 is there ike others has mentioned. dont want to take the rig off and watch it sink.
This aspect is important when you are exiting the water and you cant get out with the rig weight on. (small boat)

Another comment on the OP and that is when ou are weighting and find that you think your scenerio could come into play it is time to go to a dry suit. The dry suit depending on type eliminates the compression problem so it is no longer a factor. you still have to manually inflate it as you go deep. It suto vents as you ascend. It has its price and not just initial cost. However DS bouyancy is another topic for when the time comes.

KSW, thank you very much for your reply !
I think I have learnt a lot of stuff from this thread and I am sure that I will learn a lot more generally in this forum !!!

Thanks to everyone else who also contributed in this thread !

Many thanks,

Socc