313 meters - Now that's deep! Part 2
Posted By Mark Ellyatt on 13 August 2004
I dived in Phuket, Thailand - 35 miles offshore. The dive site was on the edge of the continental shelf at 450m+ depth. The drop line was weighted and marked every 1m. The tides were right the day of the dive, as was the weather. . The dive boat and rescue boat were courtesy of ScubaCat.com (where I’ve been working). The support divers were great, just as they were in February when they held me on the line during the 3 hours of convulsions and vomiting due to counter diffusion induced DCI. Medical support is great in Phuket with plenty of state run,good, inexpensive chambers. Phuket treats its divers seriously and you need never be more than a 1 hour journet from a chamber (our rescue boat had 900 petrol horsepower bolted to the back!).
The regulators were chosen for there heavyweight, all-metal construction helping to maximise internal temperatures. The DFC system is great at managing high gas flows with its smooth operation as opposed to venturi flow support. Finally, no environmental seal means less Intermediate pressure amplification with the ensuing high pressure seat instability etc. The water temp was 3-4 degrees celcius at depth, the gas flows were enormous but regulators provided zero free-flow or stutter.
The descent went very smoothly, the unusual currents would go down then up then get weaker then stronger, but mainly because of the slack tide window and neaps dive time, the tides didn’t have a detrimental effect. Once 180m depth came, it brought with it the darkness. Underwater lighting has come along way in the last year and its now possible to virtually guarantee operation to 300m (with the right lights of course!)
My head mounted lights shone onto the down line and every once in a while I would check my depth on the taped measurements against my depth gauges.
By 250m I still felt in charge, my lowish helium content added the sort of (couple of pints) confidence that would help avoid helium tremors and other HPNS symptoms. The water temperature was chilling, but my dry suit kept the icy water out, I noticed the shakes in my body and hands, but couldn’t really say whether it was the cold externally or internally or helium induced tremors. By 280m I started to grip the line tighter to slow down, I checked my back gas contents gauge and was not impressed by the figure! I had reached my gas turn around pressure by 300m. I didn’t seem overly concerned and this concerned me! I dropped to 310m and looked again at the gauge, 20 bar behind schedule and planned drop time exceeded by one minute. At this time I looked down and saw a ghost like image of some kind of large hydroid, I scanned my eyes from left to right to check for any visual abnormalities and to check the distance more exactly of my jelly like visitor. The little checks I do told me that my concentration was sometimes stalling into a complacent mind lock and this set the narcosis alarm bells ringing. This hydroid looked on coarse to hit my descent line and looked over 2 metres in length!
I checked the depth on the line, it was deep enough for today. I grabbed the line marker at 313m and headed for 249m the first deep stop. I shut my eyes and ascended hand over hand, not wanting to see the contents gauge. When using twin 20 litre tanks, you have a virtual inexhaustible supply, even when they equalise with the surrounding water pressure at 26 bar, you simply head up 5m and because of the huge volume, you can breath again and again.
The deeper stops came and went without drama, which was not surprising due to the slow ascent rate. The first gas switch was my only concern the rest would be easy. Because of the minimal time at depth, the risk was acceptable. The journey to the first support diver was uneventful (ish), I met Sveinung at 90m and he handed me a 15l of Trimix 14/56. Phil gave me a similar tank at 75m, as did Khun Gai at 60m.
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