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.).

Stability, trim, body position and finning technique...
Stability is critical in determining a divers comfort level and performance in the water. The consequence of instability includes increased stress and effort (to compensate for

Factors that affect stability include: the distribution of weight and buoyancy on the diver, equipment choices, and how a piece of equipment is used. Once the diver has his/her equipment squared away it's much easier to concentrate on developing a good posture in the water and utilising efficient and versatile finning strokes.

The right finning strokes allow divers to effectively control their position in the water without physical aids or damage to the marine environment.

Weighting and stability

In general all weight should be located low down on the body (when the diver is horizontal of course) and the buoyancy higher up. To put this another way; to maintain horizontal stability the centre of buoyancy should be above the centre of gravity. A consequence of this is that lighter aluminium tanks are preferable for single tank diving. Heavier steel tanks or tank keel weights cause a keeling effect which make the diver inherently unstable (another reason steel tanks are undesirable for single tank diving). Twin tanks are more stable so heavier tanks can be used if needed and if the diver has a drysuit.

Since a diver being unconscious on the surface without assistance is a very unlikely scenario, weighting the diver for inherent instability most of the time (by using a keel weight or heavy tank) to allow for this eventuality doesn't really make sense. This is also a reason wing style BC's are preferable as CORRECTLY designed wings make the diver much more stable in the lateral position (some wings have bungie cords that trap air in folds or an odd shape that traps air in some parts of the wing leading to instability). Jacket style BC's allow buoyancy to migrate to the chest, which can make the diver inherently unstable (with a tendency to roll onto his/her back or side).

Weight should be evenly distributed between the 'north and south pole' either side of the longitudinal centre of gravity. (The legs can compensate for a shift in weight to some degree and there are other ways to 'cheat', but this results in flow on effects such as increased drag and inefficient finning technique).

For example, small steel tanks are undesirable as they shift a lot of the weight onto the 'north pole' making the diver top heavy with a tendency to roll head down. In a similar way putting all of the divers weight on a weight belt and all of the buoyancy high up on the body, (a typical open water diver) makes the diver very unstable in this plane and leads to the legs down/head up posture adopted by most open water divers.

Using a wing style BC and the correct tank in combination with a metal back plate, lighter weight belt and perhaps canister light allows optimal distribution of weight and buoyancy.

Inappropriate equipment choice or poor weight distribution can result in either pole requiring additional weight or lift to balance the diver. (Heavier weight belt to compensate for short heavy tanks, extra air in drysuit to lift legs, ankle weights on dry suits, etc). These measures increase the complexity of the divers kit, introduce new problems to deal with and result in increased drag and other problems affecting the dive. For a good description of stability issues in configuring your equipment see...
http://www.baue.org/faq/dynamic_instability.html

Body position

Correct body posture in the water is critical if a diver is to correctly perform all of the skills taught in a DIR Fundamentals course and, in my view, to be most comfortable in the water. Incorrect posture results in inefficient propulsion, increased drag and poor trim. Getting the right body position significantly improves the efficiency of swimming strokes, in much the same way that body position affects swimming and body surfing. To develop a good posture in the water the following points should be considered:

      � Maintain a prone (horizontal) position at all times, including during ascent and
         descent. (This helps prevent a rapid ascent or descent and makes it much
         easier to swim to a buddy if there is a problem).
      � Arch the back.
      � Hold the head up and knees up (do not allow the knees to drop while swimming
         as this promotes an inefficient swimming stroke and creates drag).
      � Hold the feet flat, sole facing up; and
      � The groin should be the lowest part of the body.

Swimming strokes

Most openwater divers are generally only taught the flutter kick in basic training and encouraged to swim with a straight leg motion. While the flutter kick can be an effective stroke in some circumstances, it has many limitations.

The flutter kick can only be used to drive the diver forward with a continuous swimming action, there is no finesse or directional control. The flutter kick generates a lot of turbulance and the down stroke often results in the fins hitting the bottom, kicking up silt and damaging fragile marine life. Particularly when the diver gets close to the bottom to look at something. The down stroke results in drag, (much like the flaps employed to slow an aircraft on landing) reducing the efficiency of the stroke and preventing the diver from conserving energy in a drift phase.

DIR divers employ a number of finning techniques, principally; the modified flutter kick (basically a flutter kick employing only the lower leg), the frog kick, the reverse kick (basically the frog kick backwards) and the helicopter turn (back kick with one leg and frog kick with the other, allowing the diver to pivot on the spot much like the way caterpillar tracks on tanks and earth moving equipment work).

Learning to perform these strokes correctly gives the diver a lot more options and a lot more control of their position in the water, reduces divers impact on the dive environment and improves efficiency and air consumption.

Cave and wreck divers will be familiar with the frog kick and modified flutter kick as important tools in reducing silting in silty environments like the inside of caves and wrecks. The reverse kick and helicopter turn (which allow the diver to back up, hold position or swivel round on the spot) in particular have changed my diving completely. It was worth the trip to Sydney and the cost of the Fundamentals course to learn these strokes alone. It's hard to appreciate the difference until you experience it for yourself. Most divers (including myself prior to doing the course) have very little real control of their position in the water, employing a number of crutches (like dragging the fins on the bottom or putting a finger or hand out to stop themselves.) It's not until you dive with someone who has mastered these skills that deficiencies in your own technique become apparent.

Here are a few points that apply to all finning strokes:
   �   Maintain a prone position in the water and arch the back.
   �   Don't bend the knees or waist while performing any of these strokes. Avoid
       hunching in the middle, keep the back arched and don't drop the knees.
   � The body shouldn't porpoise while performing any of these strokes. To do so
       indicates poor technique.
   � You should be able to drift between strokes, shouldn't be rushed or a continuous
       effort. A relaxed style with a drift phase is best.
   �   Most strokes are driven by the ankles not the upper leg (as taught in basic
       SCUBA training).

I won't attempt to describe the different finning techniques here. To learn these strokes properly you really need to do a course. There are video's showing the different finning techniques at the following web sites: http://www.fifthd.com/ or http://www.gue.com

Accessories

I try to avoid carrying too much (this hasn't always been the case). Often the rationale for carrying many of the accessories people attach to themselves doesn't stand up to close examination, (proper dive planning, buddy skills and other fundamental diving skills make them redundant).

The items I consider essential include; a knife (sometimes I also carry scissors in my pocket as these are easier to use on marine critters that are snagged by fishing line), torch (Scout backup light for day dives, primary and backup for night), Wetnotes and a pencil, a whistle and for most open water dives an open circuit lift bag or safety sausage and safety spool.

Sometimes I take a strobe, which is more effective as a surface marker at night than a static light. This is obviously in addition to basic items like a depth gauge/
timer (computer) and compass.

I carry an Extreme Exposure safety spool with 150 feet of cave line. A spool is important for overhead diving but also useful in openwater (as a buddy line between divers in low vis, for use in searches (as a snag line or to setup a search pattern), to maintain contact with an anchor line in low vis, as an ascent line to deploy a surface marker after drifting away from a mooring line and a host of other applications I can't think of right now!)

Spools are preferable to a reel for deploying a surface marker as a reel can jam resulting in the surface support getting away from the diver and a separation between the divers and surface support (as the boat follows the buoy). The correct deployment of a surface marker at depth is an important skill for DIR divers to master.

I carry scissors (Sea Snips, but I buy the same thing from a chemist or surgical supply shop for a fraction of the cost) at the moment, clipped in a pocket. These serve as a backup cutting device but scissors are more effective than a knife for freeing marine life from fishing line or other entanglements.

Wet Notes or Aquanotes are a more effective and versatile communication medium than a slate. Messages can be left for other divers by tearing out sheets or sent up with a buoy to alert surface support of a potential problem.

You also have a virtually endless supply of writing space. For research work I print proforma survey sheets on waterproof paper and insert them into my Wetnotes. This is much more efficient than carrying a large slate.

I recently ordered a new surface float to use for drift and research diving, or in other circumstances where a surface marker is desirable. On advice from George Irvine (Director WKPP) I am buying a Riffe spearfishing torpedo float and attaching/
deploying it with a reel and cave line. (I currently use a foam torpedo float with GPS attached for survey work). The combination of a lightweight streamlined float and thin cave line significantly reduces drag (common to other float designs). This style of float could also be carried and deployed from depth.

Lights

Lights are a useful tool in most diving environments (and a standard piece of kit for a DIR diver).

My backup light is a Halcyon Scout, I attache it to the left shoulder D-ring. I bought the Scout light to replace another brand of light that was prone to flooding. (I've had at least two lights from one manufacturer that flooded).

Scout lights are very simple and reliable and incredibly easy to fix if there is a problem. I find that most lights sold by dive shops are of poor quality and unnecessarily complex. The Scout light is compact, has a good beam, lasts for ages on a set of batteries and is virtually indestructible. It costs more than most lights available in dive shops but for such an important piece of safety equipment it's worth the extra expense.

My primary light is worn DIR style on the waist belt. I now own an Extreme Exposure (Halcyon) Pro 6 10 watt HID primary light. This is the older style (larger) HID light head with lead acid battery pack. The light output from this light is stunning. The first time that I used the light it just blew me away. There was no comparison with the lights that I'd used before, including my old 50 watt halogen canister light. The beam cuts through the mirk like a light saber.

HID lights are more efficient (I can get 5 hours burn time out of the same battery configuration my old Halogen would have drained in 40 minutes) and have a much higher output for a given wattage than halogen lights.

Unfortunately they are also a lot more expensive. The newer design lights have a significantly smaller battery pack (employing the latest battery technology) and more compact and rugged light head. Like the Scout light the battery pack and light head is Delrin which is extremely strong and light.

Importantly the light head is fitted with a goodman handle that holds the light head on the back of the hand making it hands free. This allows the diver to operate other equipment while using the light. This is far better than placing lights on the mask or some sort of helmet.

Having the light on the head prevents the diver from using the light to signal effectively, usually ends up blinding the buddy when you look at them and also sends false "distress" signals. Head mounted lights should never be used.

DIR divers use a fairly simple system of light signals. Circling the beam on the bottom in front of someone means "OK" and requires a response. A slow backward and forward motion or up and down means attention. A rapid up and down or side-to-side means "emergency" or "I need urgent attention".

This makes much more sense than the approach taught by some other agencies where divers must remember if up and down or side to side means distress or attention respectively. It follows that torch movements must be slow and deliberate and that divers must be able to see other team members (buddies) lights. Divers need to adopt a good group formation to facilitate this.

Tips from DIR fundamentals: The backup light must be turned on prior to deploying it. That way if you drop the light you can easily locate and recover it.

Knives

A knife is a standard piece of kit for a diver, they are not a weapon for protecting divers from marauding sharks but a practical safety tool. The principal function of a knife is to cut lines and entanglements however knives may be used as prising tools or for a whole host of other purposes.

A large knife isn't necessary but a good cutting edge is essential. As with all equipment choices the divers knife and scabbard should be simple and uncomplicated in design. The knife should be in a position where it is immediately accessible; when you need a knife you need a knife!

Knives are a good case in point to illustrate the unnecessary level of complexity in basic SCUBA equipment sold by dive manufacturers. Most knives in dive shops are elaborate in design and above all expensive.

In DIR the knife is small simple and functional. The knife is housed in a small pouch on the waist strap next to where the waist strap passes through the crotch strap (on the left, just off centre). Here it can be quickly and easily accessed with either hand. In this position the knife can also be employed to keep the loose end of the divers waist strap out of the way and when diving without a canister light the long hose can be passed under the knife to keep it in check. There should be no complicated mechanism that might jam or fail to hold the knife in place. A simple pouch is all that is required, if correctly made the knife will stay in place without any retaining device. The knife can then be easily pulled out and replaced.

Knives are one of the most common items divers lose and many divers go to considerable effort to prevent their loss. Unfortunately these efforts either make the knives more difficult to access when they're really needed or add unnecessary complexity to your rig (with lanyards, long strings to mess with and other potential entanglements).

A better solution is to have a knife that is cheap enough to replace so that its loss becomes a non-issue. It's easy and cheap to make yourself a knife if you want to save a few dollars. All that is needed is a small length of weight belt webbing for the pouch and a low cost stainless steel steak knife (with the end of the blade ground off for safety and to allow the knife to be used as a screw driver if needed).

A box of these knives can be purchased for a fraction of the cost of a traditional dive knife (you might even get a set for free if you use tele-marketing). It's important that the knife blade passes right through the handle of the knife, however. Some cheaper steak knives don't and these can break easily.

Find out more �

In the conclusion to this series, (in the March/April issue of Nekton) Simon talks about cylinders, 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

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/