Dates: November 2008,
Author: Luke

Last Summer, on our trip to Cornwall, a few of us visited the AP Valves factory in Helston to look at rebreathers and subsequently decided that they were the way forward for deeper diving, and that we should all get them!  After a failed attempt to get a cheaper second hand unit, I ordered a Sentinel rebreather and a training course from Richie Stevenson.  I chose this particular rebreather after looking around at what was available and decided that while relatively new to the market, it had a lot of features that set it apart from the competition (including computer checks to remind you of the important pre-dive sequences).  Rebreather diving, while arguably safer for deeper diving, introduces more little things that can go wrong and so a system to minimise these is a definite benefit!  The only downside (other than the cost) was the wait – there was a significant backlog in orders meaning the normal time to delivery.  Fortunately, the instructor had two units pre-ordered for delivery in November, so I only had a two month wait (though it seemed MUCH longer). Finally, last Wednesday, I headed down to Vobster Quay to start my course.

Day 1

The first day was spent doing theory lessons and learning how to assemble the rebreather.  This went without too much hassle – the theory was relatively straightforward but there was a lot to remember with the assembly.  The main principle behind a closed circuit rebreather is that exhaled gas is passed through a scrubber that removes the carbon dioxide while oxygen sensors detect a fall in oxygen as you metabolise it, replacing it from a cylinder of O2.  As a result, gas consumption is massively reduced and decompression obligations are also cut, as you’re reducing the levels of inert gas over the length of the dive.

Day two

We hit the water.  After assembly, calibration and pre-dive checks, we entered the lovely warm water of Vobster Quay for our first dive, which was about 90 minutes long.  After a relatively short interval, we went in for a second dive, doing lots of skills and drills (just like being a novice again!).  I initially found my buoyancy to be dreadful – exhaled gas doesn’t leave, as it does on open circuit diving, so you can’t descend by breathing out and ascend by inhaling.  If you move up or down in the water, the large amount of gas in the breathing loop expands or contracts a lot, either giving you too much air or reducing the amount available, giving you the impression of suffocating (even though you’re not!).  Once I was used to that, and breathing out of my nose to vent excess gas, I found it pretty easy going.

Day 3

More drills, still in Vobster.  We practiced what to do if the electronics failed and potential errors that could occur.  I was beginning to get somewhat annoyed with the leak in my drysuit leg which gave me a constantly wet left foot and at the surface, it was bitterly cold, even in a drysuit and undersuit.

Day 4

We’re at the sea at last!  We’d headed down to Plymouth for this and were lodging on the Loyal Watcher, a nice hardboat with a lovely welcoming crew.  Diving was from Fort Bovisand, which will be familiar to everyone who came to ET this year…  This time around, the shop was open and there were hot food and drinks available.  They also had an incredible dive platform – a 10m RIB with a good sized cabin, loads of room to kit up and that was much faster than a hardboat.  We dived the Persier in the morning and the Scylla in the afternoon.  On these dives, I realised the other advantage of a rebreather.  With no noisy exhaust bubbles, fish and other sea life are no longer scared of you and will let you get much closer.  If I had a bag with me, I could easily have had a couple of wrasse that were sitting on the wreck (though not sure how good they are to eat – any ideas for recipes?).  Breathing gas is also a lot warmer than open circuit meaning that you emerge toasty warm and happy from even long dives.

Day 5

Day five, and the inevitable cock-ups started occurring.  On the first dive, the viz was bad and the group kept separating and so we decided to ascend.  On the ascent, the other student on the course had buoyancy issues and lost control of his reel, meaning he initially tried to tie me up in string and then ascended directly into me, forcing me up and pushing me into an unstoppable ascent from 6m.  Fortunately we had no decompression to do and there seemed to be no adverse effects.  The next and final dive went much better with a textbook ascent and lots to see on the dive.  Then, after dekitting, washdown of the kit and repacking, it was time to head home (which took five hours… I need to move closer to the coast!).

All in all, a great course, with a great instructor and what I think is a great unit (though I have little to compare it with).

Conclusions on Rebreather Diving

My personal opinions on rebreather diving following the course:

Pros – greater no-stop times, more flexibility, some increased safety measures and warmer breathing gas, when compared to open circuit diving.  Trimix diving gets cheaper per dive (ignoring the initial costs of buying a rebreather).  It also looks cool and is the ultimate diving gadget!

Cons – cost (of the unit and consumables) and pre-dive preparation (there are mandatory checks to be completed prior to each dive that can take from about 90 seconds to ten minutes). Buoyancy is harder than on open circuit and you have to treat the unit with some care (you are trusting your life to it!).

I’m looking to do a lot of practice dives to get better at diving with this unit, so if anyone wants to go to a quarry / to the sea at some point, let me know!  I’d be more than happy to show you how it all works and let you try it on…  If anyone wants to ask any questions as to the benefits and problems with rebreathers, I’d be happy to provide my thoughts – just drop me an email.