Ascending without BC's deflation / inflation

[Rich Keller]

PS: I left off a few benefits. If you use this technique you will greatly reduce, if not eliminate the risk of an out of control assent. You can also use a smaller, less cumbersome and usually cheaper BC if you have not purchased one already. This also reduces your dependency on the technology and leaves the full lift capacity of the BC available for use when you do need it. The same technique can be applied to using dry suits but there are more variables involved.

 

[Rich Keller]

dumpsterDiver, Yes suit compression will leave you slightly negative at the bottom but usually not enough that you should need to add air to compensate. By the end of the dive most tanks that were negative at the start will be neutral or slightly positive at that point compensating in part for the suit compression. I did post a link earlier that will show you the bouncy for tanks when they are full and empty for most common tanks in use today that should help in planing your dive using this technique. The reason for the generalizations is do to the variables involved like the type of tank, the type of suit and the depth as I stated earlier. So each diver will have to tailor their use of this technique depending on what equipment they are using and how deep they are going. Last I never claimed to be an expert or used the word "always" in any statement I have made on this subject.

 

[TSandM]

Yes suit compression will leave you slightly negative at the bottom but usually not enough that you should need to add air to compensate. By the end of the dive most tanks that were negative at the start will be neutral or slightly positive at that point compensating in part for the suit compression.

First off, some friends of mine took a 7 mil full suit to 100 fsw, and they measured a loss of over 20 lbs of buoyancy. No one can compensate for being 20 lbs negative with their breath! Even if you use Tobin's weighting system, which weights the diver neutral at the surface at the BEGINNING of the dive (with full tanks), the diver is still going to be in the range of 15 lbs negative at depth. Statements like yours are quite applicable to warm water and thin exposure protection, but are not universally true.

Second, many of us who dive in very cold water, where thick exposure protection is required and therefore very heavy ballast, will dive with tanks that are mildly to extremely negative. (There are some Faber steels that are 7 lbs negative when empty!)

Although I do not like negative, swimming ascents for a number of reasons, they are probably not a completely unreasonable idea when diving a 3 mil wetsuit and an aluminum tank. In Puget Sound, in a dry suit with a steel tank, if I blew all the gas out of my BC AND my dry suit, I'd probably have to ditch weight to have any hope of making it to the surface. A fully negative ascent here is not only a bad strategy, it could well be dangerous.

 

[Rich Keller]

TSandM, Yes one of the variables is the depth. While this technique will work for most applications it is by no means a cure all for every dive or every diver. Also I would be interested in knowing how they measured the 20lb loss. That could be very useful information to use in refining this technique further.

 

[Thalassamania]

Lynne, keep in mind that all rubbers are not equally compressible, you lose much more buoyancy with the squishy stretchy rubbers.

 

[dumpsterDiver]

PS: I left off a few benefits. If you use this technique you will greatly reduce, if not eliminate the risk of an out of control assent. You can also use a smaller, less cumbersome and usually cheaper BC if you have not purchased one already. This also reduces your dependency on the technology and leaves the full lift capacity of the BC available for use when you do need it. The same technique can be applied to using dry suits but there are more variables involved.

Most all of this is ridiculous...

A diver adds or vents air in their BC to compensate for a variety of factors, but the important thing is to keep your bouyancy close to nuetral on ascent ( I advocate newer divers staying on the negative side). To tell people to not add air in the BC because it might make them ascend too fast is very poor advice. Divers need to learn to manage the air in their BC (and/or dry suit) not be afrais of it and avoid using the gear as it is intended.

 

[Garth]

As a rule you should always empty your BC completely before you start you ascent. And during your ascent you should continue to try to release air to account for expanding air inside your bladder during ascent. Failure to do so could result in an uncontrolled and buoyant ascent. The only time you should be adding air to your BC is for minor buoyancy adjustments and when on the surface (such as starting and ending a dive).

this is what I'm talking about.

 

[Rich Keller]

Most all of this is ridiculous...

A diver adds or vents air in their BC to compensate for a variety of factors, but the important thing is to keep your bouyancy close to nuetral on ascent ( I advocate newer divers staying on the negative side). To tell people to not add air in the BC because it might make them ascend too fast is very poor advice. Divers need to learn to manage the air in their BC (and/or dry suit) not be afrais of it and avoid using the gear as it is intended.

I would have to disagree with weighting yourself negative if for no other reason than if you have an equipment failure you will have to swim up carrying extra weight and have to support that weight at the surface until you get back on the boat. Newer divers are the ones more prone to have an out of control ascent, this just reduces that risk. This is not a hard or dangerous concept but it will take a little more prep to get yourself weighted properly. You will have to adjust your weights until you get to the point that you are floating with a full breath of air but start to slowly sink when you completely exhale. Try it without any equipment first as this also serves as a survival swimming technique. Full breath you float, exhale you sink but if you go from full breath then exhale 1/2 to 3/4s of your air and breath in again your face should remain just above the surface without you ever having to use you arms or legs to stay afloat. When I started diving this is what everyone had to do as BCs had not yet been invented. This technique reduces air consumption, reduces risk, reduces your dependency on the equipment and leaves the diver with one less system to monitor and manage on ascent.