Tuesday, September 24, 2013

Buoyancy Control

 Buoyancy control

  I wrote briefly about this in my post on the backplate and wing configuration, but the subject warrants deeper discussion.  Poor buoyancy control is bad for all parties involved.  Divers damage their surroundings, be that a 100 year old coral reef, or a 10,000 year old cave formation.  Divers ruin visibility from kicking up silt.  Divers hurt their gas consumption by working needlessly to stay in trim or neutral, skip breathing, and constantly adding or dumping gas to their BC, limiting bottom time.  Divers risk injury when they are unable to maintain depth.

 None of this is necessarily their fault.  Often, their training agencies did them a disservice teaching them this style of diving is acceptable, and not equipping them with a tool set to achieve the goal of consistent neutral buoyancy.  This is unfortunate, but this is fixable.

 Whether your goal is conservation of our underwater environment, taking better photos, or simply enjoying a more comfortable, safe dive, proper buoyancy control is key.  This post won't solve everyone's buoyancy issues, but hopefully can set some divers on the right path.

Lack of neutral buoyancy The first step to being consistently neutral is to get weighted correctly.  In open water class, new divers are taught to load up enough weight to sink like a stone, add a little gas to their BCD, then use their lungs to float neutral.  From the outset this sets a diver up for failure, skating a thin line between plummeting to the bottom or rocketing to the surface.  

This excessive amount of weight is used as a training tool, helping new divers sink easily, but rarely are they taught how to shed this crutch and dive properly.  The correct amount of weight will be different for every diver, but the rules are the same:

- Your kit should be light enough to swim to the surface with a complete failure of your BC
- Your kit should be heavy enough to permit you to hold a safety stop at 10' with 500 psi.

This concept is known as a "balanced rig".  

Once a diver is using the appropriate amount of weight, they need to rethink how they breath underwater.  Instructors tell their students to "breathe normally" under water, but don't give them the means to do so.  This is because, simultaneously, they instruct them to use their lungs as a primary source of buoyancy.  To breathe in to float, exhale to sink.  This leads to skip breathing behaviour in order to remain neutral, causing CO2 build up in the lungs, and means that a significant exhale or inhale will cause a loss of neutrality.

Neutrality should be achieved with a BCD, not with a diver's lungs.  This is based on 50% of your lung capacity.  So, take a natural breath, and exhale approximately 1/2 of it.  This will estimate the average volume of gas in your lungs during a dive.  Use this baseline and add gas to your BC until neutral.  If done correctly, this allows a dive to breathe normally (at the same cadence they do on the surface) without significantly impacting neutrality.  They key is to use the BCD as your source of buoyancy, adding or dumping small amounts of gas as depth dictates, but do not change your breathing pattern.

The last piece to the puzzle is holding a horizontal position.  When in the horizontal "swimming (or "trim") position, a diver glides through the water down the path of least resistance (in this case, forward).  The arrows represent hydrostatic pressure, and in the trim position, a majority of it is working in the diver's favor, holding him at depth, not preventing forward motion.

This principle also holds true when vertical underwater, except in this case, the diver glides toward the surface with less resistance,  while the majority of pressure is halting his forward progress. This is what we are trying to avoid.  Maintaining a flat diving position uses this pressure to our advantage.


Now, the right equipment certainly helps with this style of diving, but proper and consistent neutral buoyancy can be achieved in any gear configuration.  My advice would be to devote a dive (or several dives) to testing your weight, establishing and holding neutral buoyancy, and getting comfortable with a normal breathing cadence, and being more still in the water.

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