Mark Powell reviews the Poseidon Discovery CCR

When I was asked to try out the Poseidon Discovery MkV1 I expected to hate it, because almost everything about it seemed to be counter to standard practice on every other rebreather. The fact that it only used two oxygen cells instead of the more-common three, the fact that it made all the decisions for you, and the fact that there was no way for the user to control what was in the breathing loop were all things that went completely against conventional rebreather logic. Now sticking to conventional logic is not always a good idea, but most of the conventions that have grown up around rebreather design have arisen for very good reasons.

The day started with Simon from Poseidon giving me an overview of the unit. This was my chance to ask him all the difficult questions about the design decisions they had made. What quickly became clear is that the Discovery has adopted a very-different approach because Poseidon wanted to build a very-different rebreather. They did not want to build a rebreather that would appeal to technical divers, but instead wanted to build one that appealed to recreational divers. The most-common answer to my questions was “but this is a recreational rebreather”. It took me most of the day to get my head around this concept. To begin with I wasn’t even sure what a recreational rebreather was, or whether there was even a market for a recreational rebreather.

I was sitting in on a course and talking to the guys that had bought the unit and were undertaking their training gave me an insight into why they had gone down this route. Two of them were single-cylinder divers who did not want to go down the twinset route but wanted to extend their diving by giving themselves a new challenge, the other was a twinset diver who had resisted the idea of a rebreather. One was interested in photography and saw a rebreather as a benefit in this area. In each case the existing models of rebreather had not appealed to them and seemed overly difficult, it was only the Discovery that had seemed practical for their style of diving. Gradually, in talking to these divers, I began to see why for them a rebreather such as the Discovery would offer some benefits.

Once we got round to diving the unit it was no surprise to find that it is very easy to set up and use. Putting the unit together is very straightforward, although to be fair, no easier or faster than some of the better-thought-out technical rebreathers. The use of the Extend Air cartridges, rather than having to pack the scrubber yourself, saves time and effort, but works out slightly more expensive than packing it yourself.

The Discovery runs through over 50 self-checks when you turn it on which tests everything from buzzers and electronics through to checking for leaks in the breathing loop. It also prompts the user whenever they need to do anything. This is designed to ensure that the unit is set up correctly and is working fully without depending on the user to remember to do the pre-dive checks. If any of the tests fail then the unit will not go into dive mode and so prevents the user diving when there is a problem.

Diving the unit is very easy. As the diver does not have to worry about manually controlling the unit it reduces the initial task loading. However, there are many other fully electronic rebreathers which will do the same and so this is not unique.

The Discovery does have some very clever features. For example, the controller regularly validates each of the oxygen sensors during the dive to detect any problems. Air is flushed over the sensors at regular intervals to check that the reading is as expected. Existing rebreather dives refer to this as a diluent flush, where the whole breathing loop is flushed with the diluent gas so that the diver can check that their cells are reading correctly. Doing this manually has a number of disadvantages. It uses up valuable diluent gas, it takes time, it can affect buoyancy and finally it depends on the diver being able to calculate the readings they expect to see at whatever depth they are at. However, the Discovery does this automatically every few seconds using only a tiny amount of gas. This allows the unit to constantly monitor the behaviour of the cells. All of this is invisible to the diver and they are only alerted if the unit thinks there is a problem with the cells. It is this constant validation of the cells that allows the Discovery to use two cells - a primary and a back-up - rather than the traditional three or more cells.

After two days of diving the unit I certainly didn’t hate it as I expected. I wouldn’t say I loved it, but I certainly respect the thought and attention to detail that has gone into the design. I’m not sure how big the recreational rebreather market is going to be, but whatever the size, the Discovery is well placed to satisfy that market.