Henry’s Ridge…

“There is no cure for life and death save to enjoy the interval” – George Santayana

There are probably two dives at Dorothea that one could say were ‘famous’. Famous in that almost everyone interested in the more ‘technical’ side of diving knows about them.

The first is the ‘57 metre tunnel’. At the absolute limits of diving with air as a breathing gas due to the narcotic effects of the nitrogen, it’s not a dive to be undertaken lightly or without the right equipment and training. The second is even more challenging; it is known as “Henry’s Ridge”.

Henry’s Ridge is a narrow ridge of rock that runs through the quarry at a depth that ranges from 12 metres to 70 metres. You might be wondering why there would be a ridge running through the middle of a massive slate quarry? The answer is that originally Dorothea was not one, but many smaller quarries. Over time as the works expanded, the smaller sites were eventually ‘swallowed up’ and amalgamated. As the two main parts of the quarry continued to grow deeper and wider, a cliff like almost vertical ridge was left separating them.

I have to admit I’ve spent a lot of time diving at Dorothea. I love the scale of the place, the remoteness and the challenging nature of the diving. In the early days I was amazed how my buddies/instructors could effortlessly navigate this murky underwater landscape.

As my diving progressed I was able to dive deeper and longer, and I myself started to learn more about the layout of the quarry. Every trip became one of exploration and learning, and we were able to push ourselves that little bit further with each dive. We learnt the main areas like the back of our hands – ‘The Pinnacles’, ‘The Forty Metre Shelf’, ‘The Flooded Forest’ and ‘The Crane Jib’.

Then our training introduced us to ‘Advanced Decompression Procedures’ and we had access to gases with much higher percentages of oxygen to speed up our decompression times – meaning we could stay underwater longer, and reduce the risk of decompression illness. This opened up new dives – ‘The 50m Narcosis Test’ was first, and we were able to drop deeper down ‘The Pinnacles’.

It was around this time we became more interested in the layout of the quarry. We already had some knowledgeable members in our club at the time. Richard Bufton was one of the first divers to produce a fairly accurate map of the quarry, and we were introduced to Dr Gwynfor Jones who had many old photographs of the quarry, and had given talks in the local pub on the history of Dorothea.

The research led us to the Dorothea Facebook page, and a huge amount of information was opened up to us. The group contained vast amounts of knowledge and information, from those that had dived every corner of the quarry to those who had been employed there during its working days. Photographs spanning decades gave us an idea of how the quarry had developed, and how it looked now. It was here that I first saw the images of Henry’s Ridge.

Photograph taken by Clive Midgley in 1961 showing Henry's Ridge - Before the quarry flooded

Photograph taken by Clive Midgley in 1961 showing Henry’s Ridge – Before the quarry flooded

It was while looking at these pictures we actually realised we’d dived part of the ridge already. It starts at the forty metre shelf, drops down to around 70 metres at its maximum point, and then ascends to just below the surface as ‘The Pinnacles’. Every dive we did from this point forward involved Henry’s Ridge. From the forty metre shelf we’d locate the start of the ridge and then swim out along it as far as we’d dare – or as far as we could see it from our maximum operating depth. We’d do the same on the pinnacles – but the limitations of the gases we were breathing meant we couldn’t even consider traversing the entire ridge.

Then came ‘Trimix’. The problem with diving with air, is that it contains lots of Nitrogen. Breathing Nitrogen under pressure produces a narcotic effect not dissimilar to that produced by alcohol. It affects all divers slightly differently, and can be unpredictable. By replacing some of the nitrogen in our breathing gas with helium, you could reduce this narcotic effect and safely dive deeper.

The plan to dive the whole of Henry’s Ridge was formed with my buddy Martin. We would go in from the Pinnacle side of the ridge, make our way across and finish on the forty metre ledge side. From here we would take our usual route to the surface and exit at the concrete platform.

It was a complete disaster! To reduce in-water time I told my buddy I’d take us down the buoy marking the pinnacles. Little did I know the buoy had been moved – or in my excitement I simply became disorientated and sent us in the wrong direction (I prefer to think it’d been moved!). We ended up on a dive known as the ‘Car Stack’ – and completely disorientated I had no choice but to thumb the dive and take us back up the wall and the surface. I was totally gutted and extremely angry with myself.

We made out way round to the normal entry point and discussed what to do next. We ran the numbers for a second dive, but Martin had used most of his deco gas – we couldn’t attempt it again. “You need some gas?” came a voice. A friend of our’s called Steve was carrying out some repairs on some of the buoys. Steve was still underwater at the time, but his friend offered to decant some gas for Martin. I think it may’ve been Steve’s gas!?

We accepted and ran the numbers again. We could complete the dive from this side of the quarry, where it’s much easier to navigate.

We kitted up, checked equipment and headed down to the forty metre shelf. We located the start of Henry’s Ridge and slowly made our way across. I remember it being a curious mix of fear and excitement – we were finally doing the dive we’d been talking about for years. The ridge starts off extremely narrow, before widening slightly in to a section with distinctive peaks and troughs. The deepest trough is in around 70m of icy cold water. It was also dark – but the water was crystal clear and our torches could light up ten to fifteen metres in front of us – it was an awesome sight.

It didn’t take us too long to reach the pinnacles. Looking up you could see them extend to just below the surface – it looked such a long way to go! We started our ascent – quite grateful we had the visual reference of the pinnacles to assist us. Our first deco stops were around 32m where Martin made his first gas switch. More stops at 24m, then 21m, 12m and 9m – where Martin switched to his second decompression gas. We finished with around 20 minutes hanging at 6m – just in front of the ‘beach’ area at the opposite side of the quarry from where we’d entered 90 minutes earlier.

It was a fantastic dive and we were both really pleased that we’d completed it as planned.

We packed up the kit, and spent the drive home talking all about all the different parts of the dive, and when we’d be able to return and do it again.

Henry's Ridge

This memorial plaque was placed on the ridge by the friends of Henry Le Coz. Picture courtesy of Nick Turton.


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