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Hollis Explorer Rebreather Training

With rebreathers becoming more and more common around the world I decided to do my first user course for the Hollis Explorer Rebreather.  The Explorer is a Semi-Closed Rebreather which only uses a small cylinder of Nitrox (32-40% O2) instead of two cylinders; one diluent and one pure O2.



Training started in the classroom with unit assembly and dis-assembly going through each part and its function in the rebreather.   I arrived fully prepared to take pages of notes and diagrams but it really wasn’t required; the Explorer is such a simple and user-friendly unit, paired with a great Instructor made it easy to understand.  When you first come face to face with a rebreather you can feel a bit apprehensive about making a mistake but the Explorer’s automated predive checks and PADI Checklists ensure that you complete each step in the correct order. In a nice relaxed environment we were taught how to correctly assemble the unit, pack the CO2 scrubber and go through the predive checks, with useful tips to look out for.  The Explorer does not require any tools to assemble and is very straight-forward with many parts being colour coded to aid assembly.  Once the scrubber was packed and the unit was assembled we were shown the predive safety checks. When you turn the Explorer on you must complete the predive checks to ensure correct function of the unit, all of this is explained by your Instructor and the unit itself.  The Explorer has a built in wrist computer which has a bright, colour coded screen that explains word for word what it is checking and any actions you need to take.  It will start by calibrating the three O2 and optional CO2 sensors as these require calibrating every now and again just like your O2 analyser.  After all of the checks the unit is ready to dive and will not allow you to progress unless each check is completed in the correct order.

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After we assembled our Explorers and Bailout Cylinders we had a dive briefing on the skills expected on the dive and off we went.  The Explorer feels different to Open Circuit SCUBA which I’ve been teaching for a few years now; in that there is no pressure behind the air that you breathe, the air that you breath is moved around the circuit by your breathing and one way valves.  One of the best features of the Explorer is the complete absence of noise and exhalation bubbles around your face which allowed us to get up-close and personal with a few Pike, Roach and Perch around the Nautilus. The main difference, other than the breathing, is the change in buoyancy; with Open Circuit the volume of air as you breathe changes which changes your buoyancy and makes you sink or float.  With rebreathers you have counterlungs which hold your breath either side of the scrubber so your gas volume only changes as you ascend and descend.  All you need to do is alter your weighting and buoyancy in your BCD or drysuit and once you have done this you can hover effortlessly without having to concentrate on your breathing.  You can hover motionless whilst breathing as heavy or as shallow as you like without ascending or descending which is perfect for performing tasks at a given depth. Skills required focused mainly on bailing out to Open Circuit but we also practiced no mask navigation and ascent, dSMB deployment, unresponsive diver underwater and others.  Many of the skills are required to be performed whilst neutrally buoyant which is quite straight-forward when you’ve got your head around your buoyancy.

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The Hollis Explorer Rebreather is a fantastic Semi-Closed Rebreather that is perfect for travel and UK diving.  It’s so easy to use and understand and after you’ve paid for the unit works out quite cheap per dive; a 5l 40% fill will cost you around £5 and scrubber will work out around £3, so less than £10 for a couple hours diving. I used both options; the BCD version and the Backplate / Wing version, the BCD option is very comfortable and feels a bit more than a single 12 but not as much as a twin set. The unit feels very secure with no wobble as it is bolted onto the BCD and moves with you.  The backplate and wing version is a one-size-fits-all harness (the Hollis Solo Harness) which makes sizing much simpler and reduces the amount of bulk around you for ease of movement. As far as sizing; I’m 5’10” and generally fit in Medium sized suits, I was wearing a Helly Hansen Warm Ice Crew Top with Fourth Element Arctic Bottoms with a Waterproof D10 Drysuit, the BCD version I used was a XXSmall-XSmall and it fit quite comfortably, which surprised me a little but I never struggled to get in or out of it.  The Backplate version can be fully adjusted with Hollis’ Solo Harness so there is little difference to an Open Circuit set-up. The Computer and Heads Up Display are incredibly clear and easy to use; with straight-forward traffic-light colour coding and simple user interface.  Your buoyancy control is easy but different to what you’re used to on Open Circuit; you have to be a bit more pro-active in adjusting your weighting and buoyancy control as depth changes affect you more on a rebreather.  We were advised to try to swim around things instead of over them, as the change in depth affects your buoyancy a lot. One thing I can strongly recommend, and I think the other students would too, is investing in the optional CO2 Sensor as it adds another level of safety, ensuring that you’ve packed the scrubber correctly, fitted all O-Rings correctly and best of all reduces your 5 minute prebreath to just 1 minute. To sum up; the Explorer is a fantastic rebreather and ticks all of the boxes for what it was designed for; it’s simple, easy to use and understand and it isn’t ridiculously expensive to run.  I can see more and more of these turning up at dive sites in the near future.  2014-10-15 08.59.39 


A big Thank You to my Instructor Matt Robinson from Midlands Rebreather Diving for looking after me and being so patient with the students and Bob & Joyce O’Brien at Willowmead Guest House for a great breakfast every morning and a nice room to do my homework.   Safe Diving,