Anatomy Of A Deep Trimix Dive
This post is quite a bit longer than I'd intended so bear with me.
Preparation
Preparation on morning of the dive starts by analyzing the oxygen and helium content in the tanks I'll be carrying. As I analyze each tank I mark it with the mix, the MOD (maximum operating depth) for that mix, and my name.
Once I know the final mixes it's time to sit down with Will (my Advanced Trimix instructor and guide/buddy for this dive) and "cut" tables that will show our decompression schedule. We work out a reasonable profile on ProPlanner that gives us 5 minutes at 100 meters, another 5 at 80, and a total dive time of 105 minutes.
We copy the schedule to our wrist slates along with contingency schedules to be used in the event I lose travel or deco gasses. Although we'll be following our computers on the way up we carry the decompression schedules we created as a backup in case they fail.
I enter my mixes into my computer and do a final visual check of my gear. When everything is ready we help the boat crew load our gear. I finish my second bottle of water for the morning and buy another one for the boat then we set out for Don Yang wall. Shortly after we start moving Will and I go over our pre-dive START check and afterwords I zip up my wetsuit, attach my wrist slate and backup bottom timer to my left arm and my primary dive computer to my right. Then we take a few minutes of quite time to relax during which I visualize the dive, walking through each of the important steps and checkpoints.
With 10 minutes to go to the dive site the boat slows down so we can finish gearing up. I lift my twinset to the side of the boat, open both tank valves and confirm the manifold is open. I don't like wearing a wetsuit hood so it's the last thing I put on before I climb into the harness. I put on my fins, clip my spare mask to the chest strap, hang the spare regulator around my neck, and route the long hose over my chest and around the back of my neck so my primary reg hangs over my right shoulder. Since the 12/63 bottom mix (12% oxygen, 63% helium) doesn't have enough oxygen to use on the surface I make sure to test both regulators using the purge valve instead of by breathing from them.
With help from the boat boys I attach my remaining tanks. The 24/33 travel gas clips to my harness on my left side. The 81% (i.e. nitrox containing 81% oxygen) deco tank clips on my right side with the smaller bottle of 51% clipped to it. I verify the long hose wasn't trapped by the deco tanks then presurise the regulator on each of the extra tanks, leaving the valve on the travel tank open since that's what I'll be breathing at the start. The last piece of equipment I attach is my reel which I clip to a D-ring on my belt where it is out of the way but easy to reach. Finally I spit in my mask, hand it to a boat boy to dip, pour the water he brings up in it over my face, and slip it on.
As the boat nears the GPS coordinates for the dropoff I turn on my computer and verify one last time that the travel gas is selected. Timing to hit the wall is pretty tight so I'll be doing a "negative entry" with my wings fully deflated and meet Will under the boat. With a few seconds to go the driver starts a countdown and at 0 meters I slap the travel regulator into my mouth and roll backwards off the boat half a second after Will.
Bottom Time
As usual the pre-pinnacle-dive jitters vanish the moment I hit the water. I immediately kick down to clear the boat before turning to find Will who's just leaving the surface. At 7 meters Will does a bubble check for me, looking for leaks from the valves, manifold, and other plumbing behind my head. Normally I would do the same for my buddy but Will likes to do his own using his dive computer as a mirror. I pressurize my deco tanks again to look for leaks. We signal each other that everything is OK and drop. I grab the regulator on my long hose to make sure it will be available for the upcoming gas switch.
Visibility isn't great but at around 30 meters we can see the top of the wall appear 20 meters below us and we angle across the slight current towards the edge. At 45 meters I switch my computer to the 12/63 bottom mix, spit out the travel regulator and start breathing from the long hose attached to the twinset on my back. A quick exchange of OKs and it's over the top of the wall and passing through 55 meters as I close the valve on the travel tank and tuck the reg away. At 65 meters and around 3 minutes my computer beeps and throws up an 11 minute ascent time as I exceed my no decompression limit.
A minute later we hit a strong thermocline just below 80 meters and it gets cold as the temperature drops suddenly by 7 degrees C. At the same time the visibility opens up to more than 30 meters. I start adding occasional spurts of gas to my wings to control the descent. At 90 meters (the depth of my previous deepest dive) I start holding the inflator button open. By 95 meters I've slowed my descent to a crawl and level off at 97. It's now 4 1/2 minutes into the dive and we're about 1 1/2 minutes ahead of schedule. Will turns and shakes my hand than we turn right along the wall and drift down a bit more. I just kiss the 100 meter mark then float up a meter to give myself a buffer. There's no actual harm going a meter or two below the planned depth for a few seconds but it's sloppy and I try to avoid it.
In contrast to the shallows, the water is crystal clear at 100. Hugging the wall I spend the time looking in a constant circle from the pressure gauge hanging off my left shoulder, to the computer on my right wrist, to the wall, and out into to the blue. I'm tearing through back gas at this depth and I can tell early on that I'm going to hit my turnaround pressure before the 11 minute mark. I concentrate on my breathing pattern and we move at a nice relaxed pace with gentle kicks. Vigorous exercise is a killer at this depth. Literally.
I spend some time amusing myself by looking up at the wall looming over us until it vanishes somewhere above. At some point I notice my computer is showing a 40 minute ascent time and spend some time watching that number climb. At 9 minutes into the dive the SPG on my twins reads 130 bar so I signal Will that I've hit my turnaround pressure. We start the 2 minute ascent to our multilevel stop at 80 meters with my computer showing a total ascent time of a bit over an hour as we leave the bottom. At 80 meters we pass back through the thermocline and can see a clear black shadow separating the layers in the water. As we come through to the warmer water we encounter the other team starting their ascent from their 85 meter dive and swim with them for a minute until they continue on up to their next stop.
Our plan gives us 5 minutes at 80 meters so we level off and start swimming along the wall again. We signal our respective ceilings to each other to prepare for the first leg of our ascent. Five minutes later, with my computer showing just under 90 minutes ascent time, we start the long trip back to the surface.
Ascent
Will hits his first deepstop at 66 meters. I pause for few seconds then continue up to my ceiling 2 meters above that for my first 90 second deepstop.
Sometime during the ascent up over the top of the wall we hit a colony of something or other and my ankles start itching like crazy from the bites. When I hit 60 meters I start I prepare my travel gas for the upcoming switch. As I pass through 50 meters I signal my gas switch, exchange regs, switch my computer back to the 24/33 travel mix, and continue ascending to the next deepstop at 47 meters.
At the 35 meter deepstop we deploy our DSMBs (Delayed Surface Marker Buoys). This gives us something to hang from during the rest of the ascent and also allows the boat crew to find us. Will sends his up first and I follow with mine. Deploying from this depth is fairly easy as you only need to fill the bag 1/4 full but it's still a skill I need practice on. I lose a bit of buoyancy and drift below the deepstop zone for a few seconds during the deployment. I correct quickly and return to the ceiling to finish the stop then it's up to the next one. At around 30 meters I catch myself ascending too fast and dump air from my wings. I'm too late to avoid tripping the ascent rate alarm on my computer and it adds an extra minute or two of deco time to compensate.
Coming out of the last deepstop my computer gives me my first hard ceiling at 20 meters. From here on up the stops are real decompression stops rather than the semi-optional deepstops we've had below this depth. As I resume my ascent I prepare my 51% deco tank. As soon as I pass through the 21 meter MOD for that mix I confirm I have the correct reg in my hand because I really don't want to kill myself by breathing 81% oxygen at 20 meters. I perform the switch and stop my ascent just below my ceiling. I wait out the first deco stop hanging in the narrow gap between my 20 meter ceiling and the 21 meter MOD below which it is unsafe to breath the 51% mix.
As my ceiling moves up I follow it, normally keeping myself about 1 meter below. Each stop is a little longer than the one before it but soon I'm approaching 9 meters. I start preparing my 81% tank so I can switch to it asap when I pass above its 9.5 meter MOD. By this time the boat crew has dropped a tank containing an extra suppply of 80% deco gas down my line for contingencies and it's hanging at 9 meters. I need to keep an eye on that as I'm ascending head first directly up my line underneath it and surface swells are bouncing it around like crazy.
Meanwhile, the current has been pushing us over a ridge so I've been watching the bottom slowly creep towards us. With my ceiling at 8.7 meters we're quickly running out of bottom. Normally I would wait until my ceiling creeps a bit higher before proceeding to 9 meters and switching gas however I'm running out of room. I hug the ceiling and switch gasses while dodging small coral heads. While I'm doing this Will takes the drop tank from me to lighten my task load, hauls it up a meter, and ties it off. Then we kick across the current to slightly deeper water to give ourselves a bit of extra breathing room.
Hang
At the final gas switch my computer is showing 51 minutes of ascent time remaining. From here on there is nothing much to do except follow the ceiling as it slowly moves up and tops out at 3 meters. Ultimately I'll spend a full 3'rd of the dive just hanging between 4 and 5 meters. About the time I reach 6 meters we drift off the ridge and the rest of the dive will be spent in the blue. Occasionally I haul the drop tank up, tie a new knot in it's line, and clip it off at our current depth. At some point Will points out a tiny fish swimming in the eddy created by the drop tank. That's good for a minute or two of entertainment.
Will's computer clears with mine still showing about 15 minutes but he sticks around. On deep trimix dives it's especially important to watch your buddy towards the end of the dive. The long time on high oxygen deco mixes means this is the most likely time for a convulsion due to CNS oxygen toxicity. The convulsion itself isn't harmful but chances are you're going to lose your reg and drown if it happens. Of course our dive has been planned well within the safe oxygen exposure limits so this is extremely unlikely to happen.
Four minutes before I'm done Will surfaces to signal the boat while still keeping an eye on me. Eventually my computer clears and I slowly ascend, taking a full minute to cover the final 4 meters to the surface.
109 minutes after hitting the water I break the surface and the dive is over.
Preparation
Preparation on morning of the dive starts by analyzing the oxygen and helium content in the tanks I'll be carrying. As I analyze each tank I mark it with the mix, the MOD (maximum operating depth) for that mix, and my name.
Once I know the final mixes it's time to sit down with Will (my Advanced Trimix instructor and guide/buddy for this dive) and "cut" tables that will show our decompression schedule. We work out a reasonable profile on ProPlanner that gives us 5 minutes at 100 meters, another 5 at 80, and a total dive time of 105 minutes.
We copy the schedule to our wrist slates along with contingency schedules to be used in the event I lose travel or deco gasses. Although we'll be following our computers on the way up we carry the decompression schedules we created as a backup in case they fail.
I enter my mixes into my computer and do a final visual check of my gear. When everything is ready we help the boat crew load our gear. I finish my second bottle of water for the morning and buy another one for the boat then we set out for Don Yang wall. Shortly after we start moving Will and I go over our pre-dive START check and afterwords I zip up my wetsuit, attach my wrist slate and backup bottom timer to my left arm and my primary dive computer to my right. Then we take a few minutes of quite time to relax during which I visualize the dive, walking through each of the important steps and checkpoints.
With 10 minutes to go to the dive site the boat slows down so we can finish gearing up. I lift my twinset to the side of the boat, open both tank valves and confirm the manifold is open. I don't like wearing a wetsuit hood so it's the last thing I put on before I climb into the harness. I put on my fins, clip my spare mask to the chest strap, hang the spare regulator around my neck, and route the long hose over my chest and around the back of my neck so my primary reg hangs over my right shoulder. Since the 12/63 bottom mix (12% oxygen, 63% helium) doesn't have enough oxygen to use on the surface I make sure to test both regulators using the purge valve instead of by breathing from them.
With help from the boat boys I attach my remaining tanks. The 24/33 travel gas clips to my harness on my left side. The 81% (i.e. nitrox containing 81% oxygen) deco tank clips on my right side with the smaller bottle of 51% clipped to it. I verify the long hose wasn't trapped by the deco tanks then presurise the regulator on each of the extra tanks, leaving the valve on the travel tank open since that's what I'll be breathing at the start. The last piece of equipment I attach is my reel which I clip to a D-ring on my belt where it is out of the way but easy to reach. Finally I spit in my mask, hand it to a boat boy to dip, pour the water he brings up in it over my face, and slip it on.
As the boat nears the GPS coordinates for the dropoff I turn on my computer and verify one last time that the travel gas is selected. Timing to hit the wall is pretty tight so I'll be doing a "negative entry" with my wings fully deflated and meet Will under the boat. With a few seconds to go the driver starts a countdown and at 0 meters I slap the travel regulator into my mouth and roll backwards off the boat half a second after Will.
Bottom Time
As usual the pre-pinnacle-dive jitters vanish the moment I hit the water. I immediately kick down to clear the boat before turning to find Will who's just leaving the surface. At 7 meters Will does a bubble check for me, looking for leaks from the valves, manifold, and other plumbing behind my head. Normally I would do the same for my buddy but Will likes to do his own using his dive computer as a mirror. I pressurize my deco tanks again to look for leaks. We signal each other that everything is OK and drop. I grab the regulator on my long hose to make sure it will be available for the upcoming gas switch.
Visibility isn't great but at around 30 meters we can see the top of the wall appear 20 meters below us and we angle across the slight current towards the edge. At 45 meters I switch my computer to the 12/63 bottom mix, spit out the travel regulator and start breathing from the long hose attached to the twinset on my back. A quick exchange of OKs and it's over the top of the wall and passing through 55 meters as I close the valve on the travel tank and tuck the reg away. At 65 meters and around 3 minutes my computer beeps and throws up an 11 minute ascent time as I exceed my no decompression limit.
A minute later we hit a strong thermocline just below 80 meters and it gets cold as the temperature drops suddenly by 7 degrees C. At the same time the visibility opens up to more than 30 meters. I start adding occasional spurts of gas to my wings to control the descent. At 90 meters (the depth of my previous deepest dive) I start holding the inflator button open. By 95 meters I've slowed my descent to a crawl and level off at 97. It's now 4 1/2 minutes into the dive and we're about 1 1/2 minutes ahead of schedule. Will turns and shakes my hand than we turn right along the wall and drift down a bit more. I just kiss the 100 meter mark then float up a meter to give myself a buffer. There's no actual harm going a meter or two below the planned depth for a few seconds but it's sloppy and I try to avoid it.
In contrast to the shallows, the water is crystal clear at 100. Hugging the wall I spend the time looking in a constant circle from the pressure gauge hanging off my left shoulder, to the computer on my right wrist, to the wall, and out into to the blue. I'm tearing through back gas at this depth and I can tell early on that I'm going to hit my turnaround pressure before the 11 minute mark. I concentrate on my breathing pattern and we move at a nice relaxed pace with gentle kicks. Vigorous exercise is a killer at this depth. Literally.
I spend some time amusing myself by looking up at the wall looming over us until it vanishes somewhere above. At some point I notice my computer is showing a 40 minute ascent time and spend some time watching that number climb. At 9 minutes into the dive the SPG on my twins reads 130 bar so I signal Will that I've hit my turnaround pressure. We start the 2 minute ascent to our multilevel stop at 80 meters with my computer showing a total ascent time of a bit over an hour as we leave the bottom. At 80 meters we pass back through the thermocline and can see a clear black shadow separating the layers in the water. As we come through to the warmer water we encounter the other team starting their ascent from their 85 meter dive and swim with them for a minute until they continue on up to their next stop.
Our plan gives us 5 minutes at 80 meters so we level off and start swimming along the wall again. We signal our respective ceilings to each other to prepare for the first leg of our ascent. Five minutes later, with my computer showing just under 90 minutes ascent time, we start the long trip back to the surface.
Ascent
Will hits his first deepstop at 66 meters. I pause for few seconds then continue up to my ceiling 2 meters above that for my first 90 second deepstop.
Sometime during the ascent up over the top of the wall we hit a colony of something or other and my ankles start itching like crazy from the bites. When I hit 60 meters I start I prepare my travel gas for the upcoming switch. As I pass through 50 meters I signal my gas switch, exchange regs, switch my computer back to the 24/33 travel mix, and continue ascending to the next deepstop at 47 meters.
At the 35 meter deepstop we deploy our DSMBs (Delayed Surface Marker Buoys). This gives us something to hang from during the rest of the ascent and also allows the boat crew to find us. Will sends his up first and I follow with mine. Deploying from this depth is fairly easy as you only need to fill the bag 1/4 full but it's still a skill I need practice on. I lose a bit of buoyancy and drift below the deepstop zone for a few seconds during the deployment. I correct quickly and return to the ceiling to finish the stop then it's up to the next one. At around 30 meters I catch myself ascending too fast and dump air from my wings. I'm too late to avoid tripping the ascent rate alarm on my computer and it adds an extra minute or two of deco time to compensate.
Coming out of the last deepstop my computer gives me my first hard ceiling at 20 meters. From here on up the stops are real decompression stops rather than the semi-optional deepstops we've had below this depth. As I resume my ascent I prepare my 51% deco tank. As soon as I pass through the 21 meter MOD for that mix I confirm I have the correct reg in my hand because I really don't want to kill myself by breathing 81% oxygen at 20 meters. I perform the switch and stop my ascent just below my ceiling. I wait out the first deco stop hanging in the narrow gap between my 20 meter ceiling and the 21 meter MOD below which it is unsafe to breath the 51% mix.
As my ceiling moves up I follow it, normally keeping myself about 1 meter below. Each stop is a little longer than the one before it but soon I'm approaching 9 meters. I start preparing my 81% tank so I can switch to it asap when I pass above its 9.5 meter MOD. By this time the boat crew has dropped a tank containing an extra suppply of 80% deco gas down my line for contingencies and it's hanging at 9 meters. I need to keep an eye on that as I'm ascending head first directly up my line underneath it and surface swells are bouncing it around like crazy.
Meanwhile, the current has been pushing us over a ridge so I've been watching the bottom slowly creep towards us. With my ceiling at 8.7 meters we're quickly running out of bottom. Normally I would wait until my ceiling creeps a bit higher before proceeding to 9 meters and switching gas however I'm running out of room. I hug the ceiling and switch gasses while dodging small coral heads. While I'm doing this Will takes the drop tank from me to lighten my task load, hauls it up a meter, and ties it off. Then we kick across the current to slightly deeper water to give ourselves a bit of extra breathing room.
Hang
At the final gas switch my computer is showing 51 minutes of ascent time remaining. From here on there is nothing much to do except follow the ceiling as it slowly moves up and tops out at 3 meters. Ultimately I'll spend a full 3'rd of the dive just hanging between 4 and 5 meters. About the time I reach 6 meters we drift off the ridge and the rest of the dive will be spent in the blue. Occasionally I haul the drop tank up, tie a new knot in it's line, and clip it off at our current depth. At some point Will points out a tiny fish swimming in the eddy created by the drop tank. That's good for a minute or two of entertainment.
Will's computer clears with mine still showing about 15 minutes but he sticks around. On deep trimix dives it's especially important to watch your buddy towards the end of the dive. The long time on high oxygen deco mixes means this is the most likely time for a convulsion due to CNS oxygen toxicity. The convulsion itself isn't harmful but chances are you're going to lose your reg and drown if it happens. Of course our dive has been planned well within the safe oxygen exposure limits so this is extremely unlikely to happen.
Four minutes before I'm done Will surfaces to signal the boat while still keeping an eye on me. Eventually my computer clears and I slowly ascend, taking a full minute to cover the final 4 meters to the surface.
109 minutes after hitting the water I break the surface and the dive is over.
3 Comments:
Dude that is awesome... I have questions and look forward to talking with you about it :)... By the way, I flew a Nighthawk for the first time yesterday and already killed a loot thief with it :)...
Impressive! What an experience!
I know Joey! I really like that Nighthawk.....
Oh, you mean the deep dive :)....
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