What makes equipment DIR?
To answer this question, we must first ask another question - what is DIR? DIR, aka Doing-It-Right diving is based upon safety. The DIR diving system is based around maximising safety in the water. A DIR diver is trained in many protocols and drills that add to this foundation of DIR equipment.
The traditional BCD jacket that most divers learn in their open water course is not DIR. Why? Firstly, the nature of the device is restrictive. Movement is limited and even breathing can be made more difficult.
So what is a DIR BCD?
The answer is the harness and wing. The wing provides the buoyancy you need unobtrusively. The wing is mounted between the harness and the cylinders, as a result the lift is provided against the weight of the cylinders exactly where you need it. This helps keep the diver in a perfectly flat position in the water. Also, using this method, the wing will wrap around the cylinder. This means that the drag caused by the wing is minimal. It is a substantial difference in drag between using a wing and jacket.
So the harness, why? Well the harness is infinitely adjustable - unlike the jackets that come in a few select sizes with a bit of adjustability in each size. A harness can be made to fit the smallest person in the world, right up to the largest and be a perfect fit. The DIR harness is simple - a few d-rings to attach equipment such as lights, regulators and SPG's is all that is required. Pockets on the wetsuit or drysuit for any auxiliary equipment is all that is needed.
Most of the time, you will see a DIR diver in a twinset, but this isn't always the case. Cylinder capacity is chosen primarily on a concept called minimum gas (MG). MG is the gas it will take to get yourself, plus a panicked buddy sharing air all the way to the surface from your deepest point completing all safety stops on the way. For a 30m dive this is approximately 1200 litres. In a single cylinder this means reserving 100bar, so only 130bar for the dive itself. Whereas in twin-12's, reserving this gas is only 50bar, meaning 180bar for the dive.
Also, a diver may choose to use a twinset out of convience, why take two cylinders and switch them out, when you can take a twinset and dive all day without changing your equipment? From this, you should be able to derive that a DIR diver will choose to use a single cylinder on shallow dives where the MG is not a significant part of the total capacity.
Other benefits to a twinset - you need less weight. A twinset weighs a lot - I'm a big lover of having as much weight in my equipment as possible - so I'll dive my twinset over a single cylinder plus weight belt.
Finally, in-water stability is much greater, with a twinset you are much more stable. The weight is spread over a wide area of your back, so when you just roll a little bit to see what your buddy is up to, you don't go completely over as the cylinder pulls you over.
Aluminium or steel?
Aluminium for warm water when you are wearing a wetsuit.
Steel for when you are wearing a drysuit.
Why is this the case? Breifly it is to do with the buoyancy of the cylinders in water. Steels are very heavy and if you have a BCD failure you won't be able to swim up without ditching weight, however, if you ditch the weight, once you become shallow your wetsuit will be more buoyant and you won't be able to hold a stop. Conversely aluminium cylinders are much lighter and the previous situation is manageable in a wetsuit. If you dive with steel cylinders, you must dive a drysuit so that you have an alternative form of buoyancy to assist with the ascent so you don't have to ditch weight and be unable to hold stops.
There is a debate about piston or diaphram regulators. I think its got about as much merit as the yellow face plate on an octopus. The argument is that piston regulators are more reliable if they get flooded, which is a possibility when using stages. I however, use diaphram regulators on everything. My twinsets all have diaphram regs, so does my argon bottle and so does both stages. So far I've not died... :-)
The Apeks DS4 first stage is ideal - well engineering and the ports are in a good position. The Apeks DST is useful for the right post when using a twinset as it allows the long hose to swivel which makes deployment easier, its also perfect for stage bottles.
I use the XTX40/50 and the ATX40 and frankly there is no peformance difference between any of them. The ATX range is much lighter on the mouth than the XTX range so that makes them arguably better. Hence why I sell them.
The Scubapro Jetfins or the Turtle Fins are really the two choices you have. Why? They are made from extremely heavy rubber which is good for keeping your feet weighted when using a drysuit, but also it meets that you can put the power through your legs into the water. Plastic fins will just bend and you end up with no power.
Again two options - 3mm neoprene wetsuit or a membrane drysuit. Why? If you're single tank diving in warm water you will use your wetsuit, which also implies the use of aluminium cylinders. If you are diving steels you are in a drysuit. But why a membrane? Well neoprene suffers from compressability. By the time you've dropped to 30m that neoprene drysuit has lost alot of its buoyancy and now you are massively overweighted. Membrane drysuits offer constant buoyancy (as long as you keep equalising the suit during the descent!). Your drysuit also wants to be a front entry/zipper suit so that it gives you flexibility to reach your valves - back entry suits restrict mobility.
When diving as a DIR team - we are all trained identically. All of the procedures and drills are identical. Our equipment is rigged completely identically. Why? Standardisation improves safety as familiarity improves comfort. I can dive with any DIR diver around the world, we might not even speak the same language but we can still dive together and I know that if my regs fail and I go to him asking for a reg, I know which one he will give me. If my buddy's primary regulator free-flows I know which post to shut down for him. Standardisation builds team work and improves safety ... but most of all, it makes the dives more fun!
I hope this article helps, please leave me some comments and I will know how to improve it.
Thanks for reading.