Buoyancy is key to a lot of things. It helps make the dive easier in a lot of ways. When using a closed circuit rig (CCR) it keeps you from rocketing to the surface, it prevents you from dropping to the bottom when you stop to fix your gear or “Dräger” talk/ yelling at your dive buddy.
There are two keys to buoyancy: balance and breathing
The two significant factors in achieving neutral buoyancy.
• 1st Wear the right amount of weight for the dive. This will differ depending on the thickness of your wetsuit/ dry suit and gear you are wearing.
• 2nd Breathing slowly and evenly and not having too much air in your breathing bag. If diving a CCR
What is the best way to maintain proper buoyancy?
Pre-dive preparation. Buoyancy control begins, with the pre-dive preparation. As you pick what to wear for a dive. Double-check to make sure nothing has changed that could affect buoyancy. A new wetsuit is more buoyant than an older one and will need more weight. A new suit has more inherent buoyancy at first because diving, especially deep diving simply bursts its bubbles. New gear; compare the old version to the new. Gear is always being updated with new buckles or martial so when you switch from old to new make sure you know what the buoyancy is of the new stuff. So when you go to the new magazine pouch make sure you know how it is in the water. Check the weights on a scale; often there is variation between claimed and actual weight. If diving open circuit, are you using a new cylinder? Some cylinders are negatively buoyant when full and simply less negative when empty; others sink first and float later.
Do a buoyancy check. Here is the best way to do a proper buoyancy check. With your lungs half-full, you should float at eye level with no air in your BC. If you are diving open circuit, remember the average cylinder loses about 5 pounds as it empties. So you might have to add about 5 pounds to your weight if you have done your buoyancy check with a full one.
Keep a log
Keeping a log of what gear you have wore, what the temperature was and the type of water (salt/fresh /brackish). What equipment you used, how much lead you carried, how much your body weighs and whether you seemed too heavy or light. Knowing the weight of the gear that you used on the dive will help. Make sure you understand that if you are going to remove something during the dive you need to account for that on the return trip home. If you plan ahead by recording in training what you used it will help when you have to do it the next time.
Saltwater VS Freshwater.
If most of your diving is done in the ocean, then ballast calculations should be done in the ocean. Jumping in the pool to check your balance will get you close, but it won’t be 100% correct. If you switch back and forth, you’ll need to adjust your ballast. Be prepared to add anywhere from 4 to 7 pounds going from fresh to saltwater.
Buoyancy, Trim, Position, and Breathing
The secret is buoyancy control, begins with fine-tuning your weighting. How much lead you put into your pouches or have on your weight belt. If you are carrying just the right amount of weight, you will only have to put a little air in your BC. That means less drag and more efficient finning. Less BC inflation also means less buoyancy shift with depth, so you’ll have to make fewer adjustments. There are many tricks, but buoyancy control is the fundamental skill. Precise control of your buoyancy is what enables you to hover motionless and fin through the water, at any depth, without using your hands at all or stirring up mud or silt from the bottom. In addition to using the right amount of weight, make sure you are correctly balanced to optimize your position under water. Keeping a more horizontal position makes you more hydrodynamic. Distribute the weight as uniformly as possible from side to side; you should never notice that you put on more weight on one side while diving. You must also consider the weight of your dive gear and any other additional gear you might be wearing. I.E gun belt or special gear. Make sure it is balanced on your body and it doesn’t shift when you are diving. The lowering you wear your dive rig can cause a tendency to push the diver forward (upside down) in the water, so the placement of weight towards the back can help reverse this position, especially on the surface. While carrying weight in the pockets on the back of the vest or taped to you rebreather can help with the adjustment. Lastly, any dive weight you put on should be easy to remove in an emergency.
The factors that affect your buoyancy besides ballast weight are BC inflation, your trim, exposure suit, depth and breathing control. Your ballast weight and your trim are the only two factors that, once you’ve selected them, stay put. Ballast is the amount of weight it takes to keep you neutral in the water. Trim is about the position of your body weight relative to the position of your weight. Sometime when diving a rebreather you can tape lead washers on it to help with your trip.
There is one more thing to understand that will help with your buoyancy. It is controlling your breathing. Make sure you maintain proper breathing. Take long, relaxed breaths this will allow you to maintain control over your buoyancy.
To determine the amount of weight you need, you take your body weight, the diving suit you are going to use, the weight of your equipment and the environment you are diving in salt or fresh water. You can use about 10 percent of your body weight, is a good starting point for a full 5 mm or more and for a 3 mm suit, use 5 percent of your body weight.
Dry suits and thick neoprene suits require more ballast to counteract the increased buoyancy of those suits in comparison with the thinnest. Body composition (the muscular density, for example) will also influence the necessary weight.
Remember to calculate for everything you are going to do and wear on your dive. If you are doing a long dive and plan to leave or remove something half way thru your dive. Say doing a ship attack, and you are taking limpets off. Plan for the whole dive. To check your buoyancy get into water deep enough to stay in an upright position, without treading and releasing all air from the vest. Inhale, in a normally, the surface of the water must be at the level of your eyes. When you exhale, you should sink until water covers your head and inhale again, you should emerge once again until the level of the eyes. Adjust your weight in small increments about 1 pound at a time.
Once you get your ballast weight and trim dialed in, you will be ahead of about 75% of all divers toward perfect buoyancy control. Now you can fine-tune your BC inflation to compensate for the very predictable changes due to breathing down your tank and changing depth and use only breath control to drop gently down to that cleaner shrimp, hover inches above it as long as you want and lift away from it harmlessly.
Lastly, there are advanced classes that you can take that focus on advanced skills like this. This may seem like a lot of work, but it will help make diving a lot better and make you more efficient at it.