Narked at 90Ltd TM
Of course, most people involved in the diving industry 
know of the well established major international companies that provide rebreather equipment to the military and other organizations. There are however, a number of smaller companies that are building excellent reputations for developing new products that are proving to be valuable & reliable advances in diving safety and what’s more, are being marketed at costs well within comfort zones. One of the main advantages of such small companies is their ability to work closely with customers to provide tailor made solutions to bespoke problems that larger companies are just not able to respond to.
One such company is ‘Narked at 90’ of Kettering, Northants, United Kingdom. Here’s a team where ideas certainly become reality. They are fast becoming known as ‘rebreather component specialists’. John Routley and Brent Hudson are a partnership which has grown their company from strength to strength.
Before Narked at 90 was formed, John and Brent were rebreather home builders, designing and building their own rebreathers (CCUBA). John being the man he is, always tried to perfect his designs and Narked at 90 was born. They now produce over 50 products that are sold worldwide, and were the winners of the most prestigious (DEMA) Gordon Smith award for innovation in 2007. The award was given for their work in rebreather safety, specifically a device called THE CELL CHECKER (TM) this device has now been taken up by the military and civilian alike, with customers such as National Oceanographic Atmospheric Administration, Diving Diseases Research Centre and the NATO Research dive team.
Under the leadership of John Routley, Narked at 90 has listened to the community and gone from strength to strength concentrating its efforts on products that add to diver safety.
John Routley is Managing Director and founder of Narked at 90 ltd. John started diving nearly 20 years ago and has an extensive back ground in engineering and fault finding culminating in an electrical engineering degree. John has worked in many industries over the years from electronic diagnostics and fault finding to machining and heavy engineering. So with John's back ground in engineering and design it was no surprise when he and Brent Hudson met some 5 years ago, and that there would be great things ahead.
Brent Hudson is the Technical Director of Narked at 90 Ltd. His involvement in complex control systems, safety and marine applications is long and prestigious with achievements that include being co-author of the Health and Safety Executive’s published guidance on Safety Related Control Systems, senior safety related controls systems expert for two (BERR (DTI) appointed Notified Bodies and a CENELEC appointed expert in electrical control standards and European Directives.
Cell Linearity and Current Limiting Checker. 
CCUBA (rebreathers) use Oxygen cells to monitor the gas content that the diver breathes. This process is critical to the primary function of the life support system, and is also the weakest link in that control system. Oxygen cells behave in a similar way to electrical batteries in that they have a finite lifespan which is dependent upon use. The reaction of oxygen on the cell creates an electrical output that has a predicted voltage which is dependent on the materials used. In theory they should give that voltage from the day they are made until they are exhausted, but this is often not the case.
Failures in cells can be life threatening for technical divers and in particular, rebreather divers. The failure modes common to these cells are: failing with a higher than expected output due to electrolyte leaks, current limitation due to exhausted cell life and non linear output across its range.
Preventing accidents in rebreathers from cell failures is possible in most cases by accurately testing the cells before use. The only way to accurately test a cell is with a calibrated test chamber which can hold a static pressure without deviation and the ability to log the results and graph them.
Current limitations and none linearity of galvanic oxygen cells has been a problem for rebreathers from the start and has caused a number of fatalities. This fact pushed the Narked at 90 team to try and minimise the problems encountered on dives with current limited cells.
So they came up with the CELL CHECKER. It has passed all the CE requirements and is now in production. So now you can check your cells for current limiting ‘before’ you get in the water.
I asked John Routley who founded the company to elaborate on this unique little product.
“Calibration on the surface can only produce an output from the cells for 1 bar PPO2. Diving at a set point greater that 1.0 will put you at risk of Hyperoxia unless you can verify the cells integrity,” he explained.
He went on to say, “Usually this involves an Oxygen flush at 6m depth and watching the cells are linear and not current limited. Doing this after a dive or whilst doing deco is too late and can be tricky at the beginning of a dive if the current is flowing or you're pressured into a fast descent. You end up in a situation of inaccurate readings that will not tell you if your cells are capable of maintaining their output over a period of time without dropping off.”
“The original concept was drafted a few years ago, and a lot of hard work has gone into producing the CELL CHECKER in its current form. We firmly believe it will save lives or at the very least ensure that the rebreather will be fitted with components that won’t fail mid-mission.”
The Cell Checker shows you true milli-volt readings from the cells, so does not need to be calibrated as a PPO2 readout will need to be, making the unit very easy to use.
There is a Quick start guide and lookup table in the lid of the unit and very comprehensive lookup tables in the manual that covers supply gas percentages from 91% up to 100%.
The product also features a cell output plotting graph for you to input your readings to, so you can see a graphic of the cells output. This is very helpful in determining a limiting curve.
The Cell Checker will accept most of the diving cells available with no more than a change in heads (3 types available) 
John and his team have also been working on a version that is PC linkable via a USB port and is compatible with Windows 98, 2000, XP and VISTA and a miniature and economical version that can be used by individuals.
This unit has all the features of the standard unit above plus the PC link and software that gives a real time graphical display and then saves your data
This unit is aimed more towards the dive shops that rent rebreathers to the public or instructors that teach rebreathers to the public as it gives a clear record of cell health before a course or rental takes place, However, such a unique little product should soon be motivating interest with those in the military and security services that suffer all the same problems faced by leisure divers using rebreathers.
Electronics for divers
The Shearwater Pursuit is another product from Narked at 90 that confirms many improvements have been made to improve safety for rebreather divers, such as the simple bail out procedure. Narked at 90 has worked closely with Shearwater Research in Canada over the last few years to ensure that their customers get the very best that is available. The Shearwater electronics suite has been recently redesigned and is proving to be the most intuitive and reliable electronics available for today's technical diver. One of the unique abilities of Narked at 90 is to produce bespoke software for customers in their dive computers and rebreather controllers. Brent Hudson explains “We can write bespoke and custom software for customers that allow the user as much or as little features as is required. The Sport and Technical diving customer requires as much information and control over their equipment as possible as they are self reliant and do not benefit from the backup that military divers have. Conversely the combat diver uses the CCUBA to obtain mission objectives and the rebreathers advanced functions are superfluous and secondary in importance.” Brent also explained that their reputation for excellence and technical ability has promted Shearwater Research to appoint them as their only authorised service and repair facility in Europe. “This important development means that we can support our customers better than any other in the market outside of the manufacturer themselves.”
The availability of a simple reliable ‘bailout’ procedure can make the difference between life and death. With the ‘Pursuit’, the diver simply presses the menu button and selects "OC" and presses select. This simple action hides a multitude of changes, which are automatically taken care of by the Pursuit computer. Firstly the computer switches the entire gas lists from those that were programmed in as closed, to open circuit. There is no need to switch gases on or off. Then the computer decides on the most appropriate of the open circuit gases that have been programmed by the user for that depth, and also changes the decompression algorithm to take into account the new gases. Time to surface and all decompression stops are recalculated in a blink of an eye. Simplicity when you need it most.
Speaking of decompression algorithms, most technical divers and rebreather divers carry more than one set of electronics. This may be your rebreathers' controller or any other electronics. Matching decompression profiles can be impossible with fixed tables or schedules; this is why the Pursuit used "Gradient Factors" where the user can choose almost any decompression profile that they like. In real terms, this means you have total control over the deep and shallow stop times you want to engage in. You can make the Pursuit as conservative or aggressive as you choose. The choice is yours. In addition, those deep stops are "actually" calculated from tissue saturation compartments and not compulsory and arbitrary deep stops which are not calculated like some other third party rebreather computers.
Viewing your dive computer underwater has always been a matter of compromise, whether you set your backlight on all the time and waste battery, or timed to a push button which takes user action. The Pursuit was made to overcome this obstacle with automatic back lighting that adapts to ambient light. When its dark, the backlight is on, when it is bright, it is off. Simple? I think so, but I also think it is additional safety when you consider that you will always be able to see that critical PO2 at a glance.
The Pursuit has a communications port that allows the user to remote update his computer at any time, this means Narked at 90 can send updates to customers without depriving them of their diving equipment when they improve or add functionality to the system.
The Shearwater Pursuit is available in five configurations to suit your diving or your pocket. Each configuration is fully upgradeable to any other via PIN access that you can get from Narked at 90.
The other features for the Shearwater Pursuit are illustrated below:
# Buhlmann algorithm decompression.
# Automatic switch-on by depth and/or pressure
# Configurable automatic or manual setpoint changeover
# Handset crush depth exceeds 185 meters.
# Battery life of up to 360 hours
# Millivolt display for all cells ‘on demand’
# Flip Screen for left or right hand use
# Open circuit Nitrox, Trimix and Heliox gases
# Semi closed circuit mode w here the decompression algorithm will use the current PPO2 as a FiO2 and will properly predict TTS and time at stop. When in SC mode, air calibration is enabled.
The Deep Pursuit Rebreather controller.
The Deep Pursuit was designed and built to exceed the requirements of the most demanding rebreather diver.
Producing a setpoint controller wasn't enough for Narked at 90, they demanded a stable power supply system, fault tolerance and redundancy as well as a full feature set.
The 'Deep Pursuit' comes in few forms, the standard Deep Pursuit, The Deep Pursuit Expedition and the 'Altus'. The Deep Pursuit has setpoint controller, full trimix on-line decompression, and a HUD.
The Deep Pursuit Expedition has setpoint controller, full trimix on-line decompression, and a HUD and is also fitted with a second isolated handset with or without Decompression.
The 'Altus Pursuit' is their top-flight system which has an increased depth limit and a tertiary redundant system with a second handset with or without full decompression. Altus systems are expected to be used only by the top 0.1% of rebreather divers and are available by special order only.
Narked at 90 has invested more than half of its revenue back into R&D. Their state of the art in-house design and manufacturing ensures that every component is personally selected to exceed the standards their customers have come to expect from the technical diving industry. Brent illustrated that “3D modelling and flow dynamics are a cornerstone to our design. There is no room for guesswork. Narked at 90 believe customers are pioneers, not beta testers.” 
The centre piece to their controller system is the head which is machined from a single billet of Delrin. Dimensional accuracy is guaranteed by CNC manufacture and a rigorous inspection regime.
Inside the head are three cavities populated by the cells and solenoid, Electronics network and HUD. The handset being in its own 1ATM housing provides the failure tolerance you demand in critical equipment.
Even a full flood of the system will only result in wet oxygen cells and wiring. The cell wiring loom consists of three cables terminated at each end by an SMB connector, all connectors are 24k gold plated to resist corrosion. These cables are user replaceable in seconds which means that even a full flood will only result in the cells and three cables to be replaced to have your system as good as new. Considering the remote places that technical divers travel, the Deep Pursuit can keep you in the water. Can any other system make such a boast?
Replacing the cells is simplicity itself; building on the design of the hugely successful 'Beanie holder', the same system was employed allowing the cells to be easily removed by pulling out the entire cell holder.
The Head Up Display on the Deep and Altus Pursuit is primarily an independent PO2 monitor. When we say independent, we really mean it. Power supplies, physical compartment and calibration are all separate from the controller or any handset. This means that a single handset and HUD gives you complete redundancy.
Brent Hudson explained to me that "there are "bad" alarms and "good" alarms. For example a fire bell is a bad alarm. It is bad because the absence of a ringing bell doesn't mean there is no fire. It just means the alarm isn't ringing. The fire bell may not be ringing because the battery is dead or the smoke detector isn't in the right place ........
It doesn't mean that everything is ok.
A good alarm is one where there is an obvious difference between the lack of function and the lack of an alarm. A solid green light doesn't do that so we didn't use one."
In order to be a PO2 monitor, you must be able to read actual PO2 from the device. LED's have been used before to display PO2 by flashing to correspond to the sensor output. Using one LED means you have to wait and remember a sequence that must happen three times before you can make a judgement. The three LED's on the Pursuit indicate the PO2 simultaneously and in time with each other. This gives all divers a clear indication of both the PO2 and any deviation without having to do much thinking.
The LED's are tricolour and indicate one green flash for each point above a PO2 of 1.0 and one red flash for each point below 1.0
The LED's are tricolour and indicate one green flash for each point above a PO2 of 1.0 and one red flash for each point below 1.0
When selecting components to be incorporated into the "Deep or Altus Pursuit," Narked at 90 wouldn't settle for 'off the shelf' components from the cheapest supplier, they insisted on the right components for the job regardless of cost. Their solenoid is designed for use with pure oxygen in a pure oxygen environment. The only one of its kind that I am aware of that is certified for this purpose and supported by the manufacturer specifically for use in a technical rebreather. The failure mode of this valve is in the closed position, reducing the risk of an oxygen toxicity hit at depth. User serviceable without tools using inexpensive parts.
Every conductive part used in the head enclosures have been plated in 24k gold. All cables and connectors are gold plated and user replaceable. This reduces any possibility of a premature failure from oxidization, a common fault in other units and an ongoing cost in respect to a yearly service. All electronic components are protected from corrosion
John Routley said, "Selecting components that exceed the performance of any other is not enough, we need to be doubly or triple sure that you have the necessary tools to be safe regardless of the circumstances that you encounter. That is why you get double redundant PO2 monitoring with true independence as standard, apart from the oxygen cells, no independent system shares resources with any other."
The "Altus Pursuit" benefits from triple redundancy as the two handsets and the HUD are truly independent. The primary handset runs setpoint control and gives 'real time' decompression, the HUD gives real time PO2 and the second handset mirrors the primary in all aspects except solenoid control.
The saying goes that we are more than the sum of our parts, and this can also be said for the "Deep Pursuit". All critical systems are encased in their own hermetic compartments. Accidental and catastrophic ingress of seawater cannot migrate from one compartment to another. Independence should be a philosophy, true and defined and not limited to just wiring or logic. The same philosophy has been applied to the most critical of any ECCR, the Power supplies;
All systems (Controller, HUD and solenoid) have their own independent power supplies. No loss of any single power supply will lead to the diver not knowing his PO2. And just to make sure that we have all the bases covered, and to give you a choice, every Pursuit system is fitted with a fourth cell holder as standard.
Last Updated: February 05, 2009