Tech Diving Equipment

Double cylinders (Twinset)

A twinset is comprised of two cylinders of the same size, that are joined with two bands and connected at the top by a manifold. They may be steel or aluminium and are available in numerous sizes- 7L, 8.5L, 10L, 11L, 12L, 15L and even 19L (the size of each cylinder in metric, sorry America). The manifold has an isolation valve that allows the gas to flow from both cylinders. It can be closed in an emergency to isolate each cylinder.

Redundancy

In the unlikely event of a catastrophic failure, the gas in one cylinder is saved. Such failures include a burst disk or neck o-ring failure. Moreover, the cylinder valves only turn off the regulator for the cylinder they are connected to. So, if there is a problem with a regulator, the valve can be closed and the diver can leave the isolation manifold open and breathe the gas from both cylinders with the other good regulator.

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. Twinsets are considered to be standard tech diving equipment.

Benefits of a twinset

Extended Dive Times- Two cylinders means increased gas capacity, which means deeper and/or longer dives are possible.

Redundancy and Safety- Two cylinders provides redundancy in case of a gas supply failure or emergency, which increases safety. Both cylinders are still usable in the event of a regulator failure.

Even Buoyancy- Twinsets distribute the weight evenly across a diver’s body, which helps to maintain balance and trim.

Wing and Backplate

Wings and backplates form the foundation of a technical diver’s buoyancy control system. offering enhanced stability and excellent streamlining.

Wing

A wing is a technical diver’s BC, designed to provide lift and allow a horizontal diving 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 or doughnut shaped. 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 can be reached with the left hand to allow gas to be vented 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

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 tech diving equipment.

Left-post

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 can be between 1.9 to 2.1m in length (6.2 to 7ft). It runs down the right side of your body, and then diagonally up your torso and around your neck. That may sound 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-post

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 streamlined, with no kinks or tight bends in the hose and reduced risk of entanglement. It is also easy to deploy.

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

Tech Diving Equipment for Sidemount

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 (UTD have ther own Z-system to connect them). 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 sidemount systems come as a complete set. The same features that you find on a backmount harness are also present on a sidemount harness to maintain a standard in tech diving equipment- 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 6′ low pressure hose can be attached to each regulator, which is used for the wing and drysuit. Sidemount regulators 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. Check out this article I wrote for TDI about reaching the valves on a 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 the material makes them very stiff, which limits your ability to move. They usually have a rear entry zip across the shoulder, which also limits movement.

None of these bode well for allowing you to reach those valves. The advantages of using neoprene relate to the thermal protection offered. If the drysuit floods it will keep you warmer than a membrane suit.

Membrane drysuits

Membrane suits usually come in several “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 the undersuit you wear. Unless you put on numerous thick layers under the drysuit,  they will provide more freedom of movement than a neoprene suit.

Height adjustment

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 somewhat, though not entirely lacking in neoprene drysuits- some are available with zips at the front. Membrane suits tend to be the preferred 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.

Rigid versus flexible fins

Tech diving equipment is heavy. For this reason, fins need to be rigid so that when you kick you don’t lose the kinetic energy. Flexible fins will not propel you as efficiently as rigid fins. If you don’t believe me, go for a deco dive in a twinset and deco cylinder in a current whilst wearing split fins.

Split fins may be comfortable to wear, but they are pretty useless at propelling you through the water. There is a slight trade off however, extremely rigid fins will be hard to move through the water, which may sap energy greater than it improves propulsion. Tech fins do bend after all.

Weight of Fins

Another component of tech fins that some divers look for is the weight- the fins need to be heavier than standard fins (mostly for cold water diving). 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. Conversely, some divers have very heavy legs, and would benefit from some of the lighter tech fins that are now available. It’s all dependent on the individual. The important thing is that ankle weights are made extinct.

Delayed surface markers buoys (DSMBs)

There is an almost endless choice of tech diving equipment on the market, so obviously there is also an endless choice of DSMBs to choose from. 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.

Disadvantages of open DSMBs

Using a 2nd stage also increases the chances of entanglement and finding yourself going up to the surface quickly with the DSMB. Free flows are also common in cold water.

The other main disadvantage of open DSMBs is that if they have a tendency to fall over on the surface, which allows the gas to escape and 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.

Advantages of closed DSMBs

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. They are designed so that a LPI hose can be pushed onto the opening to add gas without being able to attach securely as they do to a LPI. This system 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 go wrong with a proper cave reel (e.g. the Tecline explorer reel or Halcyon Pathfinder). I own a Dare to Dive cave reel and it’s had a lot of use for 10 years and is still going strong. 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. The amount of terrible tech diving equipment available warrants a seperate webpage.

Modern Designs for spools

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 underwater you have slightly more of a chance of grabbing it before it sinks your ego. The aluminium ones are more negatively buoyant.

Dive Computers for Tech Diving

Technology has come on in leaps and bounds over the last 10 years. This is especially true of dive computers. They are one of the most crucial pieces of tech diving equipment, and thankfully are generally very well built, reliable, highly functional, and have good battery life.

Tech diving computers 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-L16C with gradient factors is more common. Changing the low and high gradient factors allows the percentage towards tissue supersaturation to be adjusted. These settings change the depth of the first deco stop, along with the length of the shallow stop.

There are two main dive computer brands that lead the way; Shearwater Research and Heinrichs Weikamp with their range of OSTC computers. They make well built, highly functional dive computers, and provide fantastic customer service. The Garmin Descent 3 also fares well with functionality, and is also a smartwatch with a heartrate monitor and GPS.

Primary light

The standard set up of primary lights consist of a battery pack connected to a light head by an electrical cord. The light head has a handle that you put your hand through. Primary lights originated from cave diving, the field lab for tech diving equipment. They needed to be bright and have a long burn time, so they came with large battery packs.

As technology has improved, battery packs have become smaller. There are some models available to buy that contain the light and battery in one, so there’s no need for a battery pack attached to the waist or a cord connection to the handle.

Beam Width and Burn Time

If you’re considering buying a primary light it’s worth factoring in that in the future you may want to do wreck penetrations or cave diving. As such, you need to consider the burn time that you want. It needs to provide power for the entire dive.

Also factor in the beam width. You do not want to become the least popular person underwater by blinding everyone just because your light is vaguely facing in their direction. Modern primary lights can be adjusted so they have a wide or narrow beam as required.

Back-up lights

As with primary lights, back-up lights originated in cave diving. Any cave dive requires 3 light sources- one primary and two back-up. Each back-up light needs to have enough burn time to will get you out of the furthest/deepest part of a cave.

They also need to be relatively small so they can be stowed away easily in a streamline position- usually clipped to the shoulder D-rings with the bottom secured in place with rubber. This makes them easier to deploy than if stowed in the drysuit pockets.

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. Technical divers 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- Essential Tech Diving Equipment!

Wetnotes are very useful pieces of tech diving equipment. I use them as an alternative to having a dive slate on my arm. My dive plan is in my head, but is also written in the notess 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 can be invaluable for prompting students.

Paying for Brand Names

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.

I’ve compiled a list of popular technical diving brands, listed by equipment type. You can view it on the technical diving websites page.