BC free diving

[ajtoady]

I am still new to the diving world, especially compared to some of the divers I see on this site. My question, however foolish it may seem, is this: How do the divers that don't use a BC function properly? The point being without a compensator at the beginning of a dive would you not either be too heavy with a full tank of gas to say at 60' crash into the bottom? Or at the end of the dive be too light to stay at your safety stop with the added buoyancy of a lighter tank and the wetsuit expanding again? I know I am probably missing something here but, am always willing to learn. I have also noticed that on the bottom I use it (BC) to hover without effort and make my air last longer because of the lack of exertion thereof. On another note : I did not ask this to start a fight over BC's versus BP/W.

 

[Wetsuit 4 life]

I believe that before the invention of the BCD, buoyancy was controlled more by lung volume and by body placement in the water. And maybe less weight to sink, which would explain the heads down dive to get below the surface at the start of a dive.

Hope that helps

 

[gypsyjim]

Wetsuit4life is correct. BCD's were still unheard of when I certified in '70. We dived in pretty heavy wetsuits, and most of us with steel tanks. You had to experiment to get the right weight for the particular conditions and depth you intended to dive.

It was not unusual for me to grab a rock or two to add to compensate, and shed as needed. Not sure who else adopted this technique, as I did not have a lot of communication with other divers back then. Lung volume was our only adjustable buoyancy control. Many of us did wear the old yellow or orange May West vests, for surface buoyancy, although I do remember one fellow claiming he would orally add a bit of air to his at depth, which at the time struck me as weird.

In my picture here on SB there are images both of a few of us diving w/o BCD's in '70, and one of SB member Herman diving on Bonaire recently, with no BCD. BCD's are a lot less needed if one is not having to compensate for thick compressible wetsuits, that is for sure!!

 

[herman]

Now Jim, would I actually dive without one of those things?
It's all about proper weighting and technique. First off, remember that BC stands for buoyancy compensator, so what exactly are you compensating for?? There are only 2 things that must be compensated for in normal diving, gas use and wetsuit compression. With thick wetsuits and/or large tanks it is a little difficult to do....not worth the trouble IMO but with lighter wetsuits and 80's or less tanks it is very easy to do and my much preferred way to dive. I have described how it's done on other threads on the subject but basically, I weight such that I am dead on neutral at 1/2 tank pressure. The usable shift in an 80 is around 4 lbs so I weight for dead on neutral at 1500psi. This leaves me a shift of +/- 2 lbs to deal with assuming little or no wetsuit. The average total available buoyancy shift of a male is in the 10 lb range or +/- about 5 lbs. At the limits it is a pain to control but in the 2 to 3 lb range it is actually very easy to do once you get the hang of it.
Honestly, if you are adding or removing more than a tiny amount of air from your BC with a thin wetsuit you are over weighted. You also have to understand there is a wide variation in the compression of wetsuits. The modern softer ones compress more than the Rubatex ones of old , which by the way can still be gotten but not from the more common brands. When diving with a wetsuit I usually revert to an old one made of Rubatex which only adds another couple of pounds of shift to my buoyancy. I compensate for it by weighting slightly on the light side, then swim down the first few feet where compression of the suit takes over and compensates for the slight underweighting. While this does make safety stops a little more difficult they are still possible. 3 minutes is not that long and honestly, most of the diving I do san's BC is warm shallow diving where a safety stop is not needed much less required. Like any other form of diving, there are dives it's a good choice and others that is not.

 

[Akimbo]

Changes in displacement were much less of an issue when wetsuits were made of higher density, less compressible and much less stretchy materials. Rubatex G-231 dominated the market before the BC. To a lesser extent, cylinders were also a little smaller (72 Ft³ versus 80-100 ft³) so there was correspondingly less weight change between full and empty.

In a classic chicken and egg scenario, the BC came first; which made more compressible wetsuits more acceptable. To be fair, modern suits are warmer and more comfortable than Rubatex… until 30-60’ anyway. Diving without a BC is still easy in warmer water and a 3mm suit.

 

[smellzlikefish]

Akimbo's got it. I dive sans BC, wetsuit, and weightbelt in the summer because it significantly decreases the amount of gear I have to drag to a dive site. When properly weighted, you really get a sense of renewed freedom, like a mix of freediving and scuba. It has a few downsides, but the upsides more than make up for it.

 

[gypsyjim]

Diving w/o a BCD, alternate air source, SPG, etc, was much more streamlined than what is now condidered streamlined. IJS

 

[Teamcasa]

Changes in displacement were much less of an issue when wetsuits were made of higher density, less compressible and much less stretchy materials. Rubatex G-231 dominated the market before the BC. To a lesser extent, cylinders were also a little smaller (72 Ft³ versus 80-100 ft³) so there was correspondingly less weight change between full and empty.

In a classic chicken and egg scenario, the BC came first; which made more compressible wetsuits more acceptable. To be fair, modern suits are warmer and more comfortable than Rubatex… until 30-60’ anyway. Diving without a BC is still easy in warmer water and a 3mm suit.

Beside using wetsuits that did not compress much, the tanks were simply strapped on, sometime with a plastic plate, not the 3-5lbs positive Jackets in use today. We also picked up rocks as nearing the end of the dive.

 

[Akimbo]

Beside using wetsuits that did not compress much, the tanks were simply strapped on, sometime with a plastic plate, not the 3-5lbs positive Jackets in use today. We also picked up rocks as nearing the end of the dive.

So true. I can appreciate the OP’s question if all you have experienced are modern 5-7mm blended Neoprene full wetsuits... there’s a lot of buoyancy change even in 15’.

I am sure some form of BC would have been on the market near the beginning of sport Scuba if the same suit buoyancy characteristics were prevalent then. It is interesting to see how the evolution of one piece of gear influences or even creates the market for others. For example, I don’t think we have even begun to see the impact of decompression computers on this industry. Interesting times

 

[ajtoady]

Well from what I see here I'll stick with my BC. Grabbing for rocks and working to maintain depth on a safety stop does not sound like fun. I can see no BC at shallow depths but not at 50-60 ft. or in cold water. Thanks for the input and taking time to respond.