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Buoyancy Compensator Device Myths – Scuba Diving

April 2nd, 2011 | Add a Comment

So, you’ve decided to buy a new buoyancy compensator. You’re a smart shopper and an informed consumer, and you’ve done your homework. You’ve read everything you can find on the subject, and even called your instructor for a professional recommendation. You march into the dive store confident that you know all you need to know to make an intelligent purchase.

“I want a soft-pack BC that floats me face-up on the surface and I want the maximum lift I can get for my money,” you announce confidently. “And can I get that in lime green?”

Problem is, you’re probably armed with more buying power than accurate information. Much of what you’ve learned about BCs, the conventional wisdom and good advice, is more fiction than fact, more rumor than research.

The Making of the Great BC Myths

Although some notions about BCs and their use haven’t changed in the last 30 years, BCs have. First, they’ve become a mandatory and fundamental piece of dive equipment. The widespread use of the buoyancy compensator has made one of the most significant contributions to the safety, ease, efficiency and comfort of diving and opened diving to far more people. Second, their design and engineering has become very sophisticated – even more complex than regulators. This sophistication has led to specialized models. Today, some buoyancy compensators are made specifically for tropical diving, some are made for cold water, others have weights integrated into their designs and still others are made specifically for extended-range or technical diving.

But despite their complexity, the range of models now available and the impact they’ve had on the way we dive, surprisingly little testing and fundamental research has been conducted on BC design, selection and use. While manufacturers do test their own product designs, these tests are not comparative, and the information is not available to the public. No other piece of dive equipment has generated as much opinion and hearsay, based on so few facts and so little testing.

Part of the great mythology of BCs comes from the significant instructional lag in BC use and buoyancy control. We have had the modern BC for more than 30 years, yet only now are we beginning to see buoyancy skills taught effectively. Manufacturers supply us with technology, such as power inflators, while progressive instructors and divers provide us with techniques, such as safety stops. But the instructional associations are slow to change teaching materials and have no effective way to update instructors. And so the myths grow.

Myth 1: More Buoyant Lift Is Better

For years, manufacturers have boasted that BCs were better if they provided more lift. Just as cars got bigger and faster, so did BCs. But, as with cars, the realization has come that bigger is not always better. Unnecessary buoyancy costs you not only at the cash register, but in the water – with increased drag, reduced stability, poor fit and comfort, increased air trapping and poor ascent control. A BC with more buoyant lift than necessary is also more likely to contribute to an out-of-control ascent.

A BC that fits correctly and offers the correct amount of buoyant lift should:

Comfortably float you at the surface with your mouth out of the water
Offset the weight of any equipment used or items carried
Offset wetsuit compression
Provide a reserve of buoyancy for emergencies.

For most divers, particularly those in the tropics, these needs can be met with less buoyant lift than previously thought necessary. A range of 12 to 40 pounds of lift should be adequate for most divers, though professional dive leaders and extended-range and technical divers may require more.

Myth 2: Power Inflators Do Not Work in Out-of-Air Situations

This myth persists despite studies that have been out for years. Divers are often still advised to inflate their buoyancy compensators orally in an out-of-air situation. Remember, except in the extremely rare case of total regulator failure, there is no such thing as “out of air” – “low on air” is more accurate. Your power inflator will work even when tank pressure is so low that you can’t breathe adequately from your regulator. In order to work, your power inflator only needs to equalize pressure between your tank and your BC. Lower pressures only slow the process.

If you’re low on air, you can share air with your buddy and still have complete buoyancy control during your shared-air ascent.

Myth 3: Power Inflators Are the Primary Cause of Out-of-Control Ascents

At times, power inflators do leak, causing BCs to inflate, therefore increasing buoyancy and the likelihood of an out-of-control ascent. This, however, is uncommon. The primary cause of out-of-control ascents is human error, not mechanical failure. Most of these situations are caused by inattention to changes in depth and breathing, lack of buoyancy control skills and improper weighting. Even when a power inflator leaks into a BC, divers should have the skills to deal with the problem, rendering it an inconvenience, not an emergency. Divers should also have the skills to bring an out-of-control ascent under control quickly.

Myth 4: BCs Will Rocket You to the Surface Out of Control

Yes, there is a risk of a BC taking you to the surface very quickly, but the idea of a diver shooting out of the water like a Polaris missile is a myth.

In hundreds of out-of-control ascent tests, we were able to stop every ascent that started at a depth greater than 15 feet, with one exception (caused by a manufacturing defect in the BC). If control is lost in shallower water, there may not be ample time or distance to take the appropriate action to correct the problem. But if the BC has the appropriate amount of lift and fits correctly, the odds of losing control are less, and should control be lost, the ascent is slower and easier to bring back under control.

Putting the Pieces Together

BCs are constantly changing and, for the most part, improving. In some cases, however, improvement is a matter of perspective.

More padding has been added to buoyancy compensators, making them far more comfortable, even without a wetsuit. In the past this has also added to the problem of inherent buoyancy. This is the unwanted buoyancy built into a BC, and can cause it to be one to six pounds positively buoyant when empty. Inherent buoyancy requires you to add weight to offset this buoyancy. Fortunately, this is an area of BC construction where manufacturers have recently excelled. Most BCs now have less than one pound of inherent buoyancy, yet still have padding for comfort.

As BCs have evolved, air cells have moved from front buoyancy to wraparound to back buoyancy. Placing the bulk of buoyancy at the back, and less elsewhere, reduces the tendency of air to shift in the buoyancy compensator. It also helps you maintain a normal swimming position when under water and a stable position when swimming on your back at the surface. But it also tends to push you forward if you are vertical, or upright on the surface.

Integrated weights were first introduced more than two decades ago, and were heralded as making the weight belt obsolete. This did not come to pass, though BCs with integrated weights did develop a small, devoted following. Today, with better methods of ditching, the use of nonditchable trim weights, low-lift BCs that accommodate only a small amount of weight, and the use of standard weights, these systems are gaining in usefulness and popularity.

With the use of power inflators, oral inflation has been de-emphasized to the point that you may see oral inflators, at least as we know them, begin to disappear.

In an effort to improve fit within each size range, some manufacturers have gone to semi-permanent adjustments that are meant to be one-time or first-use adjustments. These do work, and do improve fit, but also vary from the easy to the complex.

One innovative design concept being employed by Dive Rite, Sherwood and U.S. Divers is interchangeable air cells with a selection of buoyant capacities. Regardless of your body size, you can select any one of several buoyant lift air cells, such as 20, 30 or 40 pounds. Since they are interchangeable, you could have one low-lift air cell for tropical diving, and switch to a larger air cell for technical diving in a matter of minutes. It is best to have your local dive store install these, or show you how it is done, since some can be a bit complex.