Equipment for Technical Diving

Twinset

A twinset is comprised of two cylinders of the same size, connected together by a manifold. They may be steel or aluminium and are available in numerous sizes- 11L, 12L, 15L and even 19L. The manifold has an isolation valve that, when open, allows the gas to flow into both cylinders. It can be closed in an emergency to separate the cylinders or isolate a regulator that may be leaking. The cylinder valves are known as modular valves.

Twinsets require two regulators- one for each cylinder. The hoses that are attached to each first stage are slightly different. More on that below. Twinset diving is also called backmount, or diving with doubles.

Benefits of a twinset

Extended Dive Times- Twinsets offer increased gas capacity, allowing divers to stay submerged for longer periods in order to undertake deeper and/or longer dives.

Redundancy and Safety- The use of two cylinders provides redundancy in case of a gas supply failure or emergency, thus increasing diver safety. The isolation manifold may allow both cylinders to still be used if you have a problem with one of the regulators.

Balanced Buoyancy- Twinsets distribute the weight evenly across the diver’s body, maintaining better buoyancy control and balance.

Backmount wing

Wings and backplates form the foundation of a technical diver’s buoyancy control system, offering enhanced stability and excellent streamlining. A wing is a technical diver’s BC, designed to provide lift and allow you to stay comfortably in a horizontal position- also known as the prone position (think of a skydiver).

Wings come in different sizes and shapes, but most commonly they consist of an air bladder, sandwiched between an outer shell and an inner bladder. They are either horseshoe shaped, or doughnut shaped- gas is allowed to travel the whole way around. Because of an increased likelihood of coming into contact with a cave wall or the insides of a wreck, wings are typically made of robust materials like nylon or cordura.

Wings have the same features as standard BCs- an inflator and deflator, the ability to orally inflate, and a dump valve. The dump valve is situated so you can reach behind with your left hand and easily dump gas whilst remaining in the horizontal position.

Benefits

Improved Streamlining: Wings provide a streamlined profile, reducing drag and enhancing diver hydrodynamics.

Enhanced Stability- The horizontal position of the wing promotes a more balanced and stable diving platform to keep the body flat.

Different lift Capacities- Wings come in various lift capacities to accommodate different equipment configurations and diving environments.

Backplate

Backplates provide a sturdy and simple harness system. They are typically made of stainless steel or aluminium, offering durability and corrosion resistance. Backplates attach to the bands on the twinset, or to a rebreather. The wing is situated in between.

A webbed harness allows you to wear the backplate, and features D-ring attachment points on the shoulder straps and crotch strap. An adjustable buckle tightens around the waist to provide a secure fit. Decompression cylinders and lights are clipped to the D-rings. The crotch strap D-ring can be used to attach reels and spools, or a leash that holds additional decompression cylinders.

Benefits

Stability and Weight Distribution: Backplates distribute the weight of diving equipment evenly across the diver’s back, enhancing stability and comfort.

Customisable Configuration- The position of D-rings can be easily changed, and the harness can be adjusted for when diving in a wetsuit or drysuit.

Regulators for a twinset

Technical diving regulators are designed to withstand demanding conditions such as diving in cold water and deep diving. They are built to maintain ease of breathing with high gas densities. Whether diving on a twinset or in sidemount, two regulators are required- one for each cylinder valve.

Choosing the right regulators is one of the most important considerations whenit comes to equipment for technical diving.

Left-side

On the left side as you view the twinset with the valve openings facing you, the first stage has two hoses. One is the Low Pressure Inflator (LPI)- 45cm or 18″ hose length. The other is the primary second stage, known as the longhose. The longhose is 2.1m in length (7ft). It runs down the right side of your body, and then diagonally up your torso and around your neck. That may sound incredibly confusing, but the video on the right should help to make sense of it (skip to 5.45). The longhose allows you to donate gas to an out-of-gas diver in single file if in a confined space.

Right-side

The regulator on the right is the short hose. This consists of the first stage, a drysuit hose (hose length depends on the location of the cylinder and width of your chest), an SPG (60cm or 24″ hose length), and a 2nd stage regulator on a short hose (60cm or 24″ hose). This is connected to a bungee that loops around your neck. This is your backup regulator, and if you needed to donate your longhose to an out-of-gas diver, your short hose is easily found under your chin.

Benefits

Hose routing from the 1st stage is smooth and streamlined, with no kinks or tight bends in the hose and reduced risk of entanglement.

The selection of which hose runs from which 1st stage allows for redundancy. If the left regulator needs to be shut down, you will still have buoyancy for your drysuit from the right hose.

Sidemount equipment

Sidemount diving requires a different configuration to backmount diving. This is because the cylinders are attached to the harness at the sides of the diver, rather than on the back. The other main noticeable difference is the absense of any kind of manifold to join the cylinders together. Other than that, the regulator differences are minimal and the overall philosophy of keeping everything simple and streamlined still applies.

Sidemount wing and harness

Sidemount wings have the advantage of not having to be sandwiched between your body and your cylinders. Because of this, the shape is more streamlined and aligned to your body. They are balanced so that most of the lift provided is lower down the body. This makes it easier to maintain a horizontal position when the cylinders sit at your side.

The harness can be separate to the wing, but most of the products you can buy come together as a complete set. The same features that you find on a backmount harness are also present on a sidemount harness- harness straps with D-rings, a waist buckle, and a crotch strap. One key difference is that they are made of tough webbing rather than steel or aluminium, and usually have an in-built system for holding weights- usually in pockets running down the spine.

Benefits

They are lighter and therefore easier to travel with than twinset wing and backplates. The whole system feels comfier than having a twinset on your back.

D-rings can be adjusted to add decompression cylinders and other accessories.

Regulators for sidemount

Sidemount regulators have a slightly different configuration compared with regulators set up for twinset diving. The biggest difference lies in the first stage. Sidemount regs have a 5th port, which means an additional hose can be screwed in. They also have swivel turrets. Regs for twinsets may or may not have turrets. Other differences are outlined below.

Right cylinder

The first stage has a longhose connected, tucked into bungee or rubber hose so that it’s streamlined and ready to be deployed when required. The SPG is 6″ long, and runs downwards towards the base of the cylinder. The 5th port previously mentioned is used for a 6″ low-pressure inflator hose, which is used for the drysuit.

Left cylinder

The 1st stage also has a 6″ SPG running down the cylinder. The 5th port is used for the wing inflator hose, and is 6″ in length. A short hose is connected to the swivel turret. The 2nd stage of the short hose has a length of bungee, that goes around your neck.

Drysuits for technical diving

There is a distinction to be made about drysuits as they relate to technical diving. Of course, you can use any drysuit you like when diving. However, for technical diving there is one crucial element that a drysuit needs to have. It must provide you with as much movement as possible, especially when it comes to reaching your arms behind your head to manipulate the valves on your twinset.

There are two main types of drysuit, discussed below.

Neoprene drysuits

Neoprene drysuits are usually made of crushed neoprene. They are thick and offer the most thermal protection you can get in a drysuit. So if you’re diving in cold water, why wouldn’t you use one? Two reasons. The extra thickness of material makes them very stiff, which limits your ability to move. They usually have a rear entry zip going across the shoulder, which also serves to limit movement. None of these bode well for allowing you to reach those valves.

Membrane drysuits

Membrane suits usually come in a number of “flavours”, they may be trilaminate or even quadlaminate. This is the amount of layers that make up the suit. The main difference compared with neoprene suits is that they are much thinner. Due to this, all thermal protection depends on the type and thickness of undersuit you wear. Unless you put on numerous thick layers under the drysuit,  they will provide more freedom of movement than a neoprene suit.

Membrane suits are often “telescopic”. They have extra material at the waist to allow greater movement. The zip is also at the front rather than across the back, which serves to allow greater movement due to how the armpits are stitched. Whilst this extra material helps to allow greater range of motion, a balance must also be found between thermal comfort and freedom of movement. This balance is lacking in neoprene drysuits. This is why membrane suits are the preferred type of drysuit for most technical divers.

Tech fins

Not so long ago, the only requirement for a fin to be a tech fin, was that it was black. Thankfully, times have changed somewhat; it makes more sense to have orange or yellow fins in order to be more visible to your dive team. Styling aside, there are practical reasons why a fin is called a tech fin or not.

Tech divers carry a lot of heavy equipment for technical diving. For this reason, fins need to be rigid so that when you kick you don’t lose any energy of your kicks by the give of the material against the water. If you don’t believe me, go for a deco dive in a current wearing split fins. Split fins may be comfortable to wear, but they are pretty useless at propelling you through the water, especially when tech diving.

Another component of tech fins that some divers look for is the weight- the fins need to be heavier. Surely that doesn’t make any sense, why add even more weight when carrying all that equipment? The simple answer is that some divers have floaty legs when wearing a drysuit. Heavier fins can provide just enough weight to compensate for this- a balanced rig as we say, is important for tech diving.

Delayed surface markers buoys (DSMBs)

There is an almost endless choice of DSMBs on the market, but they all fall into two main types- open and closed. Open DSMBs allow gas to be added either by inserting the 2nd stage regulator or by using your exhalation breaths. However, there are problems with these methods. Trying to fill it with your exhaled bubbles may be slow and frustrating, and having a thing attached to a loop so close to your face before it’s about to shoot to the surface is maybe not the best idea.

Using our 2nd stage also increases your chance of entanglement and finding yourself going up with the DSMB. The other main disadvantage of open DSMBs is that if they fall over on the surface, the gas you put in can escape, which potentially eliminates it’s purpose as a surface marker, which was kind of the whole point in deploying it. At least you’ll still have a visual reference for your ascent.

The preferred option for technical divers is the closed DSMB. They don’t leak gas, and they have a valve that allows you to either blow into them, or add air via your inflator hose. This is very useful for rebreather divers that don’t really want to have to take the loop out of their mouth. DSMBs are ususally deployed deeper on technical dives than recreational dives, so they take advantage of Boyle’s law. You don’t need to put a lot of air in them, as the air will expand as it ascends.

Primary reels and spools

Without going into a lot of detail about which particular reel or spool you should buy, there are a few general principles that determine what you should go for. For primary reels, you can’t really (excuse the pun) go wrong with a proper cave reel (e.g. the Tecline explorer reel or Halcyon Pathfinder). They are designed to make it very easy to lay out or pay in line, and they won’t jam up- as long as you keep tension on them.

Primary reels with brakes, handles and god only knows what other features are usually not well made (with the exception of Kent Tooling products) and will jam up at the first available opportunity.

It sounds a little strange, but something as simple as a spool has seen a bit of a resurgence in design in the last few years. You can now buy all kinds of colours and metals, and multicoloured line. I prefer to buy the cheap ones with the plastic barrel. They have just the same functionality as the fancy new ones, they are also cheap to replace. Moreover, if you accidentally dropped one you have slightly more of a chance of grabbing it. The aluminium ones are more negatively buoyant.

Dive computers

Technology has come on in leaps and bounds over the last 10 years. This is especially true of dive computers. They are generally very well built, reliable, highly functional, and have good battery life. When it comes to equipment for technical diving, what more do you need?

Well, tech divers do need a few more things. They need an algorithm that is in tune with current thinking on decompression theory, they need to be able to adjust the conservatism settings to suit their own diving, and they need to be able to use multiple gases.

Deep stops used to be all the rage, so it was very common to use VPM or RGBM algorithms on dive computers. Nowadays, ZH-L16 with gradient factors is more common. Gradient factors allow the depth of the first deco stop to be adjusted, along with the length of the shallower stops.

There are two main dive computer brands that lead the way; Shearwater Research and Heinrich Weikamp. Although, the Garmin Descent II also ticks all of the above boxes, and is also a smartwatch with a heartrate monitor and GPS.

Knifes and cutting devices

Some divers love to have a knife strapped to their leg that’s almost as big as them. Who am I to trample on their dreams. For technical divers, we select equipment that will be functional, suitable for the job at hand, and crucially, accessible. Cave and wreck divers use line to help them navigate in overhead environments and confined spaces, so a purpose-built line cutter is the perfect tool to carry.

There is also a degree of expect the unexpected in diving. Divers do come across fishing nets, mooring buoy lines, and even large fish pots from time to time- in bad visibility. No-one needs an entanglement to ruin their day, so it’s very useful to carry a knife capable of cutting large ropes. I personally carry a line cutter like in the video, attached to the bungee of my dive computer. I also have a knife similar to the first one reviewed, kept in a sheath on the waist strap.

Wetnotes

Wetnotes are very useful pieces of equipment for technical diving. I use them as an alternative to having a dive slate on my arm. My dive plan and any contingencies are written in case I need to reference them at any point during a dive. They are also very useful for writing quick notes back and forth. For an instructor, they are invaluable for prompting students.

There are many brands that sell wet notes, and they are largely the same no matter which you get, you’re just paying for branding. The replaceable book and pencil are universal and cheap to replace.