Nekton

Because I am asked a lot of questions about my equipment this series of discussions is, hopefully, intended to go some way towards answering them. Remember though, I'm still only learning about this stuff myself. (I've only taken the most basic level GUE course to date). Don't take my opinions as gospel, seek information from a range of sources and use your own common sense - or save yourself the angst, contact GUE and do a course! (In some sections, I have also included links to web resources that I have found useful.).

Backplate and harness
A tape harness is simple, cheap and reliable and is the optimal solution for any type of diving with no need to change the set-up when deciding to pursue more challenging diving activities like deep, tech, cave, scientific, etc. It provides a low profile, comfortable and

Unfortunately divers have a distorted image of what a BC should look like, (jacket style BC's are more a fashion accessory or status symbol than a truly functional piece of kit). New divers are taught that they "need" a whole lot of "features" that, in truth, just complicate the set-up, promote poor technique and introduce a whole host of new failure points. A good piece of kit performs the basic function it is designed for and doesn't complicate its functionality by pandering to marketing whims.

A BC harness is not a backpacking harness and you don't need a whole lot of padding and adjustments, (these just make your set-up more complicated and add unnecessary drag). In the weightless environment of the ocean the function of a harness is to secure the tank and BC t the diver. A tape harness does this best. You don't need a whole bunch of D-rings or other attachment points. Three to five D-rings, correctly placed, are all that is needed even for the most advanced forms of technical and cave diving. Quick release clips are completely unnecessary. Once the shoulder loops, waist strap and crotch strap are set right you can forget about it. The harness slips on and off easily without any need for quick release clips and never needs adjusting.

A number of major manufacturers (including Halcyon, Dive Rite, Scubapro, OMS and Zeagle) now make backplates for double or single tank diving. The plate pictured here is an OMS aluminium plate that I modified to fit my newer design Halcyon wing (with built in single tank adapter). Plates from most manufacturers appear similar (although some lack slots in the correct location to suit the newer Halcyon wings, they can be fitted with single tank adapters). There are some privately made plates that differ in design, making them impossible to fit to some wing designs. Some privately made plates I've seen are also too heavy for open-water use. I'd be reluctant to recommend anything but the Halcyon plate.

A metal back-plate allows a seamless transition from single
tank to double tank diving. By allowing the diver to use a
tape harness, a back-plate facilitates a much cleaner and
more streamlined rig, which makes sense at all levels of
diving but is particularly beneficial to new divers who don't
need to fight with cumbersome or complicated BC designs.
Another advantage is that metal back-plates neatly redist-
ribute some of the weight from around the hips without the
drag caused by special weight pockets or weight integrated
BC's. These are, in my opinion, a bad idea.

Everyone knows how to use a weight belt and should be
able to ditch one in an emergency. All weight integrated systems are different - and some don't even look like weight systems. It is suggested that familiarisation with a buddy's should be part of the pre dive checks. But what if it isn't your buddy performing the rescue? There is also the issue of whether the buddy will have the presence of mind to deal with a less familiar weight system when under stress and/or affected by narcosis?

Integrated systems also prevent divers ditching and donning their gear safely underwater and create extra bulk and drag. Bringing some weight up further on the body with a metal back-plate promotes horizontal trim and the associate benefits (less energy required to swim, less damage to the bottom, less silting, etc) and puts less strain on the lower back. It should be stressed, however, that this is not the weighting system and some weight should be retained on the weight belt.

Several manufacturers are now selling back-plates with tape harnesses. The Halcyon harness is the only one that's correctly rigged, but some others are close. Unfortunately other manufacturers often insist on adding quick release clips, extra D-rings or some other modification. These are totally unnecessary and should be avoided at all costs. My own harness I made myself from a continuous length of weight belt webbing (there is an excellent diagram showing the layout of a DIR harness at http://www.gue.com/equipment/backplate6.html). All the stainless steel D-rings and bolt snaps were bought from a local chandlery (boating supply store). Wings and back plates (or even full kits including the tape harness if your not a do-it-yourself-er) are available from Halcyon. In my experience (having bought all the bits and built up my gear from scratch) it's cheaper in the long term to just buy a complete Halcyon package from one of the regional retailers. This saves a lot of time and unnecessary expense and angst.

Cave and technical divers have a front D-ring on their crotch straps to act as a tow point for a scooter. (There must be no quick releases on the crotch strap, in this application a failure would result in the waist strap being pulled up around the diaphragm, significantly increasing air consumption and discomfort). I don't use a front or rear D-ring on my crotch strap. The front D-ring isn't really necessary, since I don't own or use a scooter.

I used to use a rear D-ring, but was concerned that storing items here might be an entanglement risk if I needed to dump a weight belt in an emergency. For the same reason I don't have tank boots on my tanks. I've had belts get hung up between the boot and my waist during rescue training drills so they pose a real danger. For safety, tanks and dive kit should be laid flat when out of the water, making the tank boot redundant most of the time anyway.

For a discussion of how to correctly size a harness and back-plate see...
http://www.baue.org/faq/backplate_sizing_inline_images.html

My webbing is a little short. Normally the buckle on the waist strap would come round further, closer to the back-plate on the right side (to hold the canister light in place). Unfortunately, since breaking my wrist - and having a plate inserted - I don't have the flexibility or strength to do up a buckle this far back and have to settle for holding my canister light in place with a second buckle. (This also allows me to don and doff gear in open water without losing the canister, so it's not a bad idea anyway!)

Some people feel they need quick release clips on a BC or harness. These are totally unnecessary; introduce additional failure points and more complexity and potential entang-
lements to the set-up. They can loosen off during a dive, making the tank move around on your back underwater, or cause the BC to float up around your neck when on the surface. They also interfere with the correct placement of backup lights and the bungie cord used to contain the inflator hose and prevent it catching or dragging on the bottom.(Something that's given at least one manufacturer the dubious excuse to remove the inflator hose altogether! Again, the wrong solution caused by the wrong equipment choice in the first place.)

The harness can be easily removed above or

below the surface using the "flip over" method. Once the waist strap is undone the harness comes off very easily using this or other methods. Divers can also be extracted from the harness easily during a rescue by pushing the arms back through the shoulder loops. Another option is to simply cut the webbing with a knife or shears. Importantly though the harness can only come off when it is intentionally taken off (there's nothing to work loose or fail). At all other times it provides a secure and comfortable fit and the tank can't move around underwater on the divers back as is often the case with sloppily fitting jacket style BC's.

Wing

I use a Halcyon Pioneer 27 pound single tank wing. I have yet to find an acceptable alternative made by any other manufacturer. Dive Rite produce a travel wing with minimal lift that some use, and Zeagle apparently has a 30 pound lift capacity wing that I've yet to see. However, I cannot recommend too highly the Halcyon wing. I've owned two, both still in service. They are a great example of simple, solid, functional design.

Most manufacturers of back inflation BCD's insist on making them with far too much lift, (50 pounds and upward). This makes little sense, especially if the diver employs proper weighting and a "balanced rig". The principle function of the wing is to compensate for the change in buoyancy of the divers exposure suit, (if diving wet) and any extra weight carried to offset the buoyancy change of the tank/s. More lift than required just equals more drag. Also, wings in particular, as well as BC's with a lot of lift, tend to trap air or be difficult to dump effectively. I feel that this problem, together with poor technique, has contributed to a number of uncontrolled ascents I've witnessed.

Large wings wrap around tanks and are sloppy and unstable, both on the surface and underwater. Some manufacturers try to make wings that will work on both single and double tanks; some use bungie cord to resize the wings for single tanks. Bungie wings are dangerous as they trap air in folds, increase drag, are unstable, (air trapped in folds results in an uneven distribution of buoyancy), dump air too quickly and make manually inflating a wing - or using the inflator as a third backup regulator - potentially difficult or impossible. A failed dump valve or other leak may also result in the wing deflating. Why choose a complicated solution to a simple problem. The best approach is to buy a wing designed specifically for single tank diving, (and buy a double tank wing later should the need arise). The Halcyon wing is a simple and uncomplicated design that works.

I'm of the view that most divers over estimate the amount of lift they require in a BC. By considering the buoyancy characteristics of all of your gear, (tank/s, exposure suit, lights, etc) and determining the change in buoyancy experienced during a dive, it is possible to determine the minimum lift required. Some equipment will be negatively buoyant, some equipment will be positive. This should be considered before adding additional weight.

During a dive only the buoyancy characteristics of tanks and wetsuits change (and perhaps drysuits if you add excess air for warmth, generally dry suits should be worn "shrink wrapped" with a little air added only after 6-8 metres when squeeze is more significant). An alumium tank will be slightly negative at the start of a dive and slightly positive at the end. Steel tanks are generally undesirable for single tank diving, because often they are so heavy no weight is carried in a ditchable form, making the diver overly reliant on lift from the wing to make an ascent should a failure occur at depth. (When the wetsuit is compressed, the diver may be very negatively buoyant and unable to ascend). A wetsuit is positively buoyant but compresses and becomes less buoyant with depth (and age/use).

Once you're aware of the change in buoyancy in both the tanks and the suit, it is possible to work out how much extra weight will be required to remain neutrally buoyant when near the surface at the end of a dive with no air in your wing and when your suit and tank are most buoyant. (A consideration for drysuits might be how much extra air needs to be added to be comfortably warm on deco?)

This can be tested in the pool or ocean, with appropriate adjustments made to go from fresh to salt water if necessary. If you are neutrally buoyant at the end of the dive - when the buoyancy of your suit and tank is balanced by the weight of your back-plate, canister light (if you have one), weight belt and any other gear - then it stands to reason that you will be negatively buoyant at depth at the start of the dive when the tank is heavy and your suit is compressed.

Knowing how negative you are will give an indication of roughly how much lift is required in a wing, (plus a small margin for error) to allow for a more buoyant exposure suit, or perhaps to float your gear independently on the surface.

Remember, you should never use your wing/BC as a lift bag. Allowing extra lift to retrieve weight belts or anchors or other finds is to encourage poor technique. Either take the appropriate training and use a lift bag, or just leave it behind).

In open-water diving, in my view, it is important that you be able to ditch sufficient weight to ascend and remain on the surface without assistance in the event of a BC failure. This means that a good proportion of the weight should, generally, always be retained in a ditchable form such as a weight belt and/or canister light.

What is wrong with most BC's/wings?

Here are some of the features that I, personally, believe are poorly conceived and that should be avoided on most commercial BC's and wings...

Too much lift - I discuss this above. However, I did miss one important point. BC's with excess lift are extremely dangerous if/when an inflator sticks open. A stuck inflator in combination with a larger BC/wing providing far more lift than the diver needs can result in a rapid and uncontrolled ascent to the surface.

All round air cell - Wing style BC's are a lot more stable than BC's with all round lift. Having air cells on the front also creates a much larger profile for drag, particularly when there are pockets on the front of the BC. Anything on the front of a diver will create drag by effectively increasing the girth. Adding pockets or folds to act as sea anchors would logically increase effort and air consumption. Inflating this style of BC can cause restriction to breathing, resulting in a CO2 build-up and increased narcosis. (Divers typically go to the greatest depth early in a dive, when they are most negative and add the most air to their BC's).

In my experience, front inflation BC's
do not reliably float an unconscious
diver face up on the surface. In my
opinion, the only way to promote a
face up position on the surface is to
use a tank keel   weight. I'm   not
aware of any stringent testing in this
area, though, and tank weights are
not recommended by strong advo-
cates of DIR diving because of the
entanglement risk; the potential for
over-weighting on the surface, (in
the event of a BC failure at the start
of a dive); and the static instability
caused by having the centre of grav-
ity above the centre of bouyancy.
Finding   yourself   on   the   surface,
positively buoyant, unconscious and
unaided would seem to me to be a very unlikely scenario. A keel weight causes ongoing problems during every dive and these would appear to outweigh any potential benefit.

Quick release straps - Unnecessary because once a harness is set to fit a diver   it   never needs   adjusting, (unless they change   their   exposure suit substantially, in which case a small adjustment can be easily made prior to diving); and because a diver can doff or don a properly fitted harness easily without them - or be extracted from one easily in the event of an emergency.

They are a failure point and can loosen or break during a dive, creating stress or discomfort. They are an entanglement risk. They compromise the placement of key safety equipment, (like backup lights or the effective positioning of the inflator hose - which is held in place by bungie on a DIR setup to prevent entanglement and providing immediate access to add or dump air).

Too many dump valves - The primary function of a BC is to compensate for shifts in buoyancy during a dive and to provide support on the surface, (although if properly weighted and equipped this is less of an issue). A buoyancy bladder needs to be able to hold air and allow air to be added and removed during a dive. This function can be achieved with a simple wing type bladder and a combined power inflator/dump on the inflator hose. Every extra hole made in the bladder, (every extra dump valve added, every extra seam) potentially compromises the integrity of the air cell and its ability to hold air.

Dump valves can and do stick open, leak or fail. Usually because of grit catching in the valve; the ball attached to the string getting caught under something; poor maintenance, or threads working loose with use and falling off. More dump valves means more chance of failure.

If the BC has only one dump valve (in addition to the inflate/dump), positioned on the bottom corner of the wing, a failure of this valve can be compensated for by maintaining a position that holds the air bubble

within the bladder. Pull dump valves on the inflator hose are particularly ill conceived. Not only are they unnecessary if you employ good technique, but they also put a lot of strain on the inflator hose, potentially dislodging it. A simple elbow joint is all that is required on the inflator hose.

Regardless of how many dump valves you have, it's a good idea to remove the small balls, or similar devices that manufacturers place on pull dumps. These can become trapped under weight belts or other gear and prevent the dump valve from closing - and therefore preventing the BC from holding air. A string alone is sufficient to allow you to operate the dump valve.

Integrated weight systems and other accessories - See earlier discussion!

No crotch strap - People seem to be shocked that I like using a crotch strap. The crotch strap prevents the BC from floating up and stabilises the tank and harness. Manufacturers appear to have forgotten that SCUBA equipment is used in the water rather than on land. In the water, gravity is less pronounced and because divers generally orientate themselves in a horizontal position there is a tendency for buoyancy and water movements to pull the SCUBA gear in different directions - often up toward your head.

Most manufacturers seem to model their BC's on hiking harnesses that are designed to carry heavy loads on land where gravity pulls in the one direction, down. As hiking long distances with SCUBA gear is a bad idea, it seems to me to be a better idea to design a harness that properly secures the SCUBA unit in the water where it's used. A tape harness and crotch strap does this best. Many of the add-ons like chest clips and cumber-bands on conventional BC's are to compensate for the fact they don't have a crotch strap.

Conventional BC's necessarily ride higher on the body and have a tendency to float up round the head on the surface. Bringing the buoyancy further down the body promotes horizontal trim. I also find the crotch strap handy for keeping my gear together between dives and retrieving it when diving from Zodiacs.

No room for growth - Most BC systems on the market are tailored toward a particular "type" of diving, such as travel, recreational or technical diving. As the diver's need changes - when new equipment is added, (drysuits, lighting systems, twin tanks, etc) or their interests develop into, say, technical or cave diving, or other challenges within the scope of open-water diving) - they are obliged to invest money in new equipment and to re-learn established skills.

Often this new bit of kit is a badge of honour that is intended to set a diver apart, ("I am a tech diver because I have a BC with lots of D-rings on it"). Targeting equipment to these perceived niche markets is beneficial to manufactures and shops because divers have to buy more expensive gear as their interests develop.
Although different diving environments offer new challenges there is an underlying commonality that exists. A DIR style harness and wing can be employed across the broad spectrum of diving pursuits. New equipment and challenges can be added without substantially changing the fundamental framework. (Adding a drysuit is a seamless transition - many conventional BC's will not allow easy attachment of the inflator hose; adding doubles requires only a dedicated double tank wing, tank bands and manifold - much cheaper than a so called "tech" BC.)

Find out more �

In Part 3, of this series, (in the November/December issue of Nekton) Simon talks about hose configurations, accessories, and trim and stability techniques, but to find out more about DIR diving and its underlying philosophy, he recommends the following web pages as a good starting point:

What is Doing It Right Diving? by Jarrod Jablonski
Beyond Hogarthian...Doing it Right by Dan Volker
Doing It Right Gear Configuration by George Irvine
Halcyon FAQ page
Transcript of George Irvine's lecture to BAUE
Online video streaming of DIR 1 and 3 video's by George Irvine (note you may need to install Windows Media Player on your computer and use Internet Explorer (DIR 3 is aimed at recreational divers))
NEW DIR books (Fundamentals of Better Diving, Tech 1 and Cave 1 manuals) by Jarrod Jablonski (available for online purchase)

Simon Hartley is an Associate Lecturer in the School of Environmental Science and Management; teaching computing, statistics, geographic information systems (GIS) and remote sensing and undertaking undergraduate and postgraduate supervision. He is currently undertaking a Masters by research examining the marine benthic communities of Julian Rocks (Byron Bay). His research interests include marine science and GIS. Simon is an experienced scientific diver with over 13 years diving experience. He has been involved as a research diver or team leader on many staff, undergraduate and postgraduate projects in the School including; several coral community studies from the Solitary Islands to the southern Barrier

Reef, work on shallow water Rhodoliths in Moreton Bay, underwater heritage studies in Byron Bay, work as a team leader for a Marine Archaeology field school in South Australia, turtle tagging and monitoring studies, surveys of wobbegong and grey nurse sharks off Byron Bay and ongoing work on the effects of trawling in Moreton Bay. Simon has a diverse range of diving skills and interests including; underwater photography (still and video), general marine survey techniques, use of light tools and lift devices and maritime archaeology. As the President of the North Coast Chapter of the Australian Marine Sciences Association, Simon is involved with promoting postgraduate and undergraduate marine research on the North Coast of New South Wales. Simon has worked part time in the recreational dive industry for six or seven years and has also been active in a number university and private dive clubs over the years, including being on the executive of the Southern Cross University dive club for five or six years. He has taken part in a number of community based projects, including population studies of the grey nurse shark and the development of the code of conduct for recreational diving with sharks, and fosters links between the dive industry and university. He can be contacted at: shartley@scu.edu.au or visit his website at: http://www.scu.edu.au/schools/esm/staff/pages/shartley/projects/gear/