Buoyancy Compensator, The Diver’s Exoskeleton: BC Basics Part One
By Fred Stratton
Instructor & Repair Technician
fred@bubblesornot.com
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| Image: Pixabay |
An exoskeleton - from the Greek exo (outer) and skeletos (skeleton) - is an external structure that supports and protects an animal's body. As a diver you know about marine creatures having exoskeletons like crabs, lobsters (crustaceans), chitons, nautilus, clams and snails (molluscs).
While not a perfect metaphor, the BC is like a diver's exoskeleton in that it supports and integrates the cylinders and regulators we use to breathe underwater into one unit. It enables us to maintain neutral buoyancy and exemplary trim as we gracefully glide through the water like mantas. The BC also supports an array of general and dive-specific tools such as whistles, lights, weight and trim pockets, and cutting devices. (We'll explore these aspects next month in BC Basics Part II.)
The BC is a relatively new invention. Divers in the 1940's and 1950's used nylon webbing woven through hard plastic mounts to strap single steel scuba cylinders to their backs. There were no bladders with low pressure inflators to maintain buoyancy. Divers simply used fin power and breath control to ascend and descend. Jettisoning one's weights to ascend in a low-on-air situation was a common practice. This was also in the days before submersible pressure gauges (SPG) became ubiquitous.
Fenzy Frenzy
While not a perfect metaphor, the BC is like a diver's exoskeleton in that it supports and integrates the cylinders and regulators we use to breathe underwater into one unit. It enables us to maintain neutral buoyancy and exemplary trim as we gracefully glide through the water like mantas. The BC also supports an array of general and dive-specific tools such as whistles, lights, weight and trim pockets, and cutting devices. (We'll explore these aspects next month in BC Basics Part II.)
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| Image: Pixabay |
Archimedes in Action
Cave divers in the 1950's and 1960's experimented with buoyancy control by exhaling into plastic jugs. They proved something fundamentally important in their crude yet effective application of the Archimedes Principle: displacing water to achieve neutral buoyancy reduced physical effort, increased bottom time and made diving easier.Fenzy Frenzy
The Frenchman Maurice Fenzy gave us the first true BC in 1961. Originally called an Adjustable Buoyancy Life Jacket or ABLJ, the more user-friendly term buoyancy compensator was adopted. The diver orally inflated the Fenzy at the surface or underwater. It had a tendency to ride up on the diver's neck, even when using a crotch strap. Nonetheless, the Fenzy improved diving safety and attracted other equipment manufacturers into the BC market.
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| Image: Scubapro BC Innovation Accelerates |
Watergill unveiled its At-Pac wing-style BC in 1972. Revolutionary at the time, the At-Pac was the first unit to integrate a backpack, regulator, BC and weights into one unit and came standard with a low-pressure inflator (LPI) hose that tapped into a LP port on the first stage.
Scubapro introduced its Stabilizing Jacket in 1977. It featured a chest strap, cummerbund and waist strap which increased fit and comfort. It also incorporated a quick-dump valve activated via a lanyard secured to the right shoulder. Integrated pockets allowed for storage of diving accessories. The current Scubapro Classic BC is a modern version of the "Stab Jacket" which advanced diving safety, function and comfort by leaps and bounds.
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Image: Dive Rite
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Dive Rite introduced its wing-style BC the following year. Mating the wing to a backplate is an efficient means of providing weight and buoyancy control to single or double cylinders, sidemount rigs and rebreathers.
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Image: Dive Rite
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You can also use a set of wings mated to a harness and two cylinder straps to dive this configuration on a single cylinder for recreational diving. This combination is relatively light, a benefit when trying to limit your carry-on bag to 50 pounds en route your dream dive destination.
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| Image: Dive Rite |
Fast forward to 1995 when Dive Rite debuted their TransPac harness. It is infinitely adjustable to all body shapes and sizes. Quick releases make donning and doffing one's kit easy. A crotch strap, waist belt and chest strap secure the unit in place, and lumbar padding increases comfort. Heavy denier nylon and beefy fitting make the current version, the TransPac XT, nearly indestructible. (The author has a 20-year old TransPac and set of RecWings that are in perfect working order.)
Bubbles or Not proudly carries Dive Rite, Scubapro and TUSA BCs. These lines offer the best value and quality for a range of diving abilities and aspirations, from newly-certified Open Water divers to more experienced Advanced, Rescue and Master Scuba Divers, including those considering certification in sidemount, technical and rebreather diving.
BC Buying Considerations
Talk to a BoN dive professional before you invest in a BC. Talk about the diving you like to do and the diving goals you may have. You will make a wiser buying choice once armed with accurate information that is relevant to your diving needs. Do you find your diving Zen on single-tank dives to colorful shallow reefs? Your BC choice will be different than someone keen to pursue a Tec Trimix 65 certification to visit the hangar bay in the USS Oriskany at 175 feet!
Jacket Style versus Back Inflation
As stewards of our undersea world we all aspire to be good AWARE divers. Lakes, reefs, walls, wrecks and caves all have unique environmental considerations. Back inflation BCs by design put divers in a near-perfect horizontal position, particularly when a backplate or trim pockets are used for weighting the diver. Jacket style BCs require the diver to overcome a somewhat diagonal body position due to the concentration of lead on the hips and the BC's air bladder wrapping around the diver's torso. You well know that horizontal is the optimum swimming position.
Myth: It’s difficult for new divers to learn in a back inflation BC.
Fact: Starting one’s diving adventure in a back inflation BC is no harder than using a jacket. Doing skills on one’s knees in a back inflation BC requires a slightly different body position than in a jacket, but it isn’t harder. Besides, good divers are only on their knees while practicing and mastering skills. Otherwise, we are horizontally trim throughout the dive. Back inflation BCs actually help new divers master trim and buoyancy faster!
Q: What about BCs for sidemounting?
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| Image: Scubapro |
A: Some mature divers prefer sidemounting because they can walk individual cylinders to the water’s edge, an easier task than carrying banded double cylinders. Sidemount rigs have a lower profile than back-mounted cylinders, an advantage where access to some caves and wrecks may be tricky. Sidemount harnesses are distinctly different, although wing-type BC can serve various diving applications, making them a smart investment.
Q: What if I'm interested in tech diving but I'm not ready to commit?
A: In addition to the TransPac XT and wings, the Scubapro X Tek and TUSA's X Wing BCs are terrific choices for divers who may want a great BC now that also could be used for initial technical diving courses. Both have back inflation, multiple stainless steel D-rings and impressive lift capacity.
* Special thanks to Odessa Stratton for editing and improving this article.
Coming in March
Maintenance and equipment configuration in BC Basics Part II.
Maintenance and equipment configuration in BC Basics Part II.
Very informative BC article, with so many options out there it can be overwhelming. This article highlights the need to know what type of diving you want to do in order to properly choose the best BC for you!
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