This has been a bad year to start diving and gaining skill. Right after I got my OW I ruptured my ear drum. Just as I get clearance to dive again my appendix decide it was time to come out. This all has meant not being in the water a lot. I took the time to learn/read as much as I could on scuba. My biggest problem has been buoyancy, must noticeable is being over weighted. I weight 245 pounds and wear a 7mm suite, boots, hood and gloves and needed 32 pounds to get down in fresh water. The last month I have worked hard at reducing that weight as much as possible. Today I found my weight and felt great in the water. Today, I dove with only 22 pounds and held a 3min. safety stop at 15 with 500 psi in an 80AL. I just hovered there. I feel like I could drop a few more pounds but dont want to get to confident and get in trouble because of one good day. I would like to get to a point where I dont need to use air in my BCD unless at the surface is this even possible?
With a 7mm the compression at depth is more than you can deal with using lung volume but with thinner or no wet suits it is not only possible but exactly how you should be diving. What most divers forget or more likely never actually understand it is a BC- buoyancy COMPENSATOR. It's purpose is to
compensate for buoyancy
changes that happen during the dive, not to hold up lots of extra pounds of unneeded weight. Assuming for a moment that you are not wearing a wet suit, what is going to change buoyancy during a dive ? Answer-only your tank and nothing else. The swing in an 80 CF tank is around 4 lbs (yes I know it has closer to 5 lbs of air in it but that hopefully the diver will not empty it). So at most you will only need 4 lbs of added buoyancy to make up for the 4 you will lose during the dive if you intend to dead on neutral at the end. Obviously this will have to be adjusted up or down depending on your tank size but the idea is the same. So can you dive without adding air to your BC? The average total bouyancy swing from empty to full lungs in an adult male is somewhere in the 10 lb range, +/- some depending on body size. If we look at what we have to work with, we have a 4 lbs swing in the tank and somewhere in the 4 to 5+/- lb swing in our lungs to use. With some practive this is doable but honestly it's not fun. If however you properly weight for "no air in the BC" diving it's an easy amount to deal with. Instead of weighting to be dead on neutral with a full tank, weight to be dead on neutral with a 1/2 full tank. With an 80 this means being about 2 lbs overweighted at the beginning of the dive. 2 lbs is an easy amount to keep afloat with lung volume alone, much less with a little finning. As the dive progresses you go from slightly over weighted to neutral to slightly under weighted by about 2 lbs, again a very easy amount to deal with using lung volume alone. Now, if you have a BC why not just go ahead and start 4 lbs over weighted using the BC to COMPENSATE for that amount and vent a little along as the dive progresses, ending up the dive dead neutral? Perfect way to do it. If you add in a wet suit then you have to take it's
buoyancy change into consideration as well. How much that is depends on the thickness of the suit, how large it is (takes more rubber to cover a big boy
) and the type of material it is made out of. For most divers using modern wetsuits this is more of a swing than they can comfortably manage with lung volume alone, you have to use the BC. An experienced "no air in the BC" diver can handle a 5mm or less wetwsuit made of old school material (Rubatex) fairly easily and 3mm or less of modern materials is not difficult with some practice.
One of my favorite ways to dive is old school, the way it was done in the early days of diving, with no BC and a simple harness. Diving that way demands you be properly weighted and understand buoyancy changes unlike most divers today that simply weight themselves until they sink like a rock then add a huge bubble of air to keep them "neutral".
