Escaping Down Drafts

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Here's a harrowing encounter with open water downcurrents, for a group of tech divers on doubles with what would seem to be plenty of breathing gas margin, and less dense "easy breathing" 18/45 trimix with a deep MOD (67m @ PO2 1.4) margin to fight or ride out a strong downdraft:

I thought I would share a recent experience that really drove home a few lessons and made me very happy about the training me and my team mates had received. Some background. The site was in Bunaken island (Sulawesi, Indonesia), known for its incredible wall dives. The plan was for a technical dive with a maximum depth of 50 meters (164ft), average 45m (148ft), with a bottom time of 25 minutes and 30 minutes deco (deco is padded, but that is a different story). We were a group of 5, all of us with double alu 80s containing trimix 18/45 for bottom gas, 3 of the group were carrying an additional alu 80 for bottom gas with the same mix (with the intention of not touching their back gas). All of us had an alu 80 with nitrox 50 for our deco gas. We had all been to this particular site before at recreational depths, and we have each 10s of dives in the Bunaken area, so we felt reasonably confident about our plan.

The dive started very relaxed. The visibility was very good and we quickly descended to our target depth along the wall. The bottom flattened out somewhat and we started to drift with a light current along a sandy slope. As the dive progressed, the current started to pick up, still carrying us along the wall/slope. Twenty minutes into the dive at a depth of around 45-43 m (148-141ft), we went over a small ridge and suddenly were in a raging downwards current. We had expected a little of it given the topology of the site, but the strength caught us off gard. In a few seconds we had descended 10m and only because we managed to hold on to the reef. Although I am normally a prety efficient swimmer, I had to fight extremely hard to reach the wall, and as I held on to a giant sponge with all my strength and watched my bubbles rocket downwards into the blue, I had a moment to asses the situation. My depth was around 53m (174ft) and my gas was 90 bar (a full fill is 200bar or 3000psi). One diver was slightly above me and another slightly below, both holding on to the reef. My other 2 team mates where well below (I later learned one of them hit 64m, 210ft) and were trying to reach the reef. As luck would have it, it was the people who got sweept down the furthest that had the extra gas (they were practising their recently acquired tech1+ cert that allows them an extra bottle). Myself and the diver just above me only had our back gas and we were huffing and puffing just to hold on to that wall. It immediately became apparent that we needed to head for the gas switch as quickly as possible as we were going through our reserves fast. I took a few seconds to bring my breathing under reasonable control and focussed on climbing up that reef. It took significant focus to go up with a reasonably efficiency both in breathing and speed. As we reached around 24m (gas switch is at 21m), the downcurrent changed to a sideways current, we let go of the reef and proceeded to perform the switch while drifting away from the wall. The gas switch proceeded without apparent incident and we did our deco as we floated away from the island rapidly. As we ascended after 30 min we realized we had drifted far away from the island and we were in the middle of a channel and could not see the boat any more (although we knew where it should be). We had launched an SMB during deco, but we were too far away for them to see it, and they were expecting us along the wall, rather than a few miles away in an orthogonal direction. The strongest swimmer in our group then decided to swim towards the entry point and try to get the boat's attention. After swimming for 2 hours, he reached the boat and 20 minutes later the boat reached us.

Some more information. At the end of the dive I had 60 bar (870psi) of backgas left. My other team mate with only backgas had actually run out exactly at the switch and had nothing left in his tanks. My teammates that were breathing bottom gas from a stage sucked it dry and consumed a significant fraction of their backgas. We all consumed more than usual on deco.

Lessons learnt:

-Strong down currents are more dangerous and scarier than I thought. In this particular dive it was exacerbated because we were towards the end of the dive and near our maximum depth.
-Never, ever be tempted to go beyond minimum gas, it is there for a very good reason.
-Taking time to take control and assess a situation is worth it, even if it seems like you have no time to spare.
-Good team mates trained in the same set of procedures are an incredible resource. It got hairy, but nobody lost their composture and we took the time to check on each other as soon as we could, helping to calm everybody down.
-In ocean dives, carry a BIG SMB. We were all carrying SMBs, but they were the tiny versions and I had to confess I had a large one sitting in my dive bag in the hotel ... I was not the only one :shakehead:. Ultimately we were lucky to be close enough to be able to reach land by swimming, but a few boats passed reasonably close and did not see us with our punny little orange smbs, so we could have been stranded for quite a while longer.
-It is not a stupid idea to take a cap or cloth to protect you from the sun if there is a possibility of being lost. Needless to say none of us had one and we got burnt to different degrees under the blazing Indonesian sun.

Thinking about the dive, I feel it was kept under control, but I also realize that we were at the edge of what we could handle. Had one more thing gone wrong, I am not sure things would have turned out fine. Definitively gave me some things to ponder about.

Minimum gas, underwater climbing and drifting away ...
It turned out to be very treacherous encounter indeed --even as a planned technical dive prepared for & expecting currents as they did. . .
 
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Covered in depth here: current

Here's the original post, but there's more in the thread that's also worth reading, including other accounts from other divers on the same dive:

After years of reading (and occasionally feeling anxious) about down currents in Cozumel, I got to experience a real live Cozumel down current today. Here's what happened:

Our first five was a nice nearly current-free run Tormentos. I( was diving sans my wife buddy for the day) At the end, when we were on the surface and getting on the boat, we got a very significant upwelling that smoothed out the chop like glass and slowly spun the boat like a top. Nothing too weird about that, right?

For our second dive we headed north to check out Eagle Ray wall. Our DM checked the current and at the top it was heading North so we dropped in. It turned out we were a decent distance off the wall, as the water underneath us was dark blue and I couldn't see any bottom.

I dropped somewhat slowly because I've been needing more time for my ears to adjust, while others dropped fairly quickly. At about 20 or 30 feet I noticed a distinct shift and I felt like I was heading down faster than I ought to be. Two of the divers in our group looked like they were rocketing down straight under me with at least 50 feet of depth on me and they weren't slowing down. We were on EAN 36 and I became worried about depth. At least one person looked to be shooting past 100 feet while I was watching him and I didn't see him check his depth. (He later told me he hit 121 feet.)

At 60 feet and still deep blue underneath I was kicking hard for the wall and found that it was slow going - the current I was in was both down and out from the wall. I kept feathering my BCD and tried to use the current to plane into the wall. Rather than scrub the dive I figured if we could get to our agreed upon destination - the top of the wall - then the current might be alright and we'd have an okay dive of it. At the least we'd be where we had agreed we were supposed to go.

I eventually made it to the wall at about 80 feet and lost another 10 (my comp says I hit 94 feet max) before i was able to stop. The DM had passed me a minute earlier after telling us to stick together going about 10 knots (okay, maybe less) on her way back out to help others.

Two of us had made it to the wall so 4 were still somewhere else. The two of us (talk about insta buddies! My official buddy was helping the DM with other people) decided to go up the incline to the top of the wall. From there I figured we'd have a better view and could decide if the dive was a total scrub or if everyone else showed up.

Stuck to the wall at 94 feet I never felt desperate - I have an absolutely massive amount of lift in my BC and I'm a decent swimmer so I figured between those two things plus my SMB and 4 pounds of weights I could ditch I could always get up. Once we were on the wall I was also much less worried about going past the EAN 36 depth limit but I didn't want to get dragged to Playa Del Carmen either, so up the wall seemed like a better bet than out into the blue.

The other diver and I made it to the top of the wall and I wrote him this note:

View attachment 203863

Yes, "fem" minutes are "few". Stress typo maybe?

So, we waited. And waited. Aaaaaaand waited. Nothing. Not even a bubble. (The current wasn't too bad at the edge of the wall so at least it was a fairly easy wait.) We decided to do our safety stop and surface.

This meant I got to play with my sausage (ha ha ha!) which I always love doing. I filled it up generously, figuring we might be blown all to hell all over the coast and I wanted the boat viz, and I dumped my BC to empty, not sure of what would happen between the wall and our stop. The currents were doing pretty much everything they could to be amusing.

I locked the line at 18 feet and noticed that we were back in a significant down current. I could tell because I kept bobbing down on the end of the line and had to hold on quite tight and some of our bubbles were going down, not up, which is fairly unusual. Bubbles aren't supposed to do that. Additionally a lot of the sargassum that should have been floating above us, on the top of the water, was going down past us to the bottom.

At one point when I checked on my dive mate I saw a funnel about 50 feet behind him. It went from the surface all the way to the bottom and was pulling sargassum and bubbles all the way down to the sand. It was freaky cool and scary looking. He moved much closer to me, and I felt extra good about having the SMB out.

After a proper safety stop we surfaced. I manually inflated my BC to max and topped off the SMB so it was sticking straight up. We spotted the boat about 400 yards north of us picking up somebody. As they were doing that I saw another SMB go up about 800 yards north and a couple hundred yards west of us, so in pretty short order we had been blown all over the place. Our boat captain pinged the nearest boat to us and after a few mins that dive boat came over to us and we told him we were fine and he radioed back to our boat. Our boat then picked up the further out group and then came back for us.

Dive time was 16 mins, float time maybe 20-30, max depth was 94 feet for me and I burned about 1200 PSI.Nobody was hurt, the DM did an extremely good job securing everyone and we dove shallows next and saw an octopus, so I got that going for me.
 
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Wow. Scary.

My experience was in Maldives. We weren't on the wall, it was a bad drop. Trying to fight our way forward in the oncoming current is when I realized what was happening. I felt fortunate that while it was a down current, it wasn't shoving us deep, though we were exceeding MOD. Those above us didn't seem to be affected. It took a few minutes to get sorted, especially getting my buddy's attention, all the while wondering if we'd get an oxtox hit.

I've no advice. We were in an open patch and we swam diagonally up and forward. No idea where we'd have ended up otherwise.

The currents in Maldives are ridiculous. I think I'm over that place. :)
 
Scary stuff, especially if you're not on a wall. I don't believe it has been mentioned and I failed to include it in my original post, but if you can't seem to halt the descent I think it's probably wise to dumb weights as well. I realize there's a high risk of injury from a rapid ascent, but I'd rather be rescued on the surface rather than recovered on the bottom or never recovered at all.
 
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Although I have never encountered a down current I have a personal rule that I won't dive any Nitrox mix on a dive where the hard bottom exceeds the MOD unless I have two independent buoyancy systems. Don't flame me, it is a personal decision, but on wetsuit dives along a wall where a loss of lift can potentially send me below the MOD of my back gas and ruin my day I dive air only. If I am dealing with a loss of buoyancy or a down current I don't need to add an O2 tox to my growing list of concerns.
 
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Dhboner, No reason for any flaming here. Though I rarely dive nitrox, this is exactly how I think.
 
How do you guys manage to dive walls that have a hard bottom below recreational depths? Some of the walls in places like Bunaken, Maldives, T&C, and even Cozumel extend well below ranges that would be safe on any breathing gas ...

... Bob (Grateful Diver)
 
Although I have never encountered a down current I have a personal rule that I won't dive any Nitrox mix on a dive where the hard bottom exceeds the MOD unless I have two independent buoyancy systems. Don't flame me, it is a personal decision, but on wetsuit dives along a wall where a loss of lift can potentially send me below the MOD of my back gas and ruin my day I dive air only. If I am dealing with a loss of buoyancy or a down current I don't need to add an O2 tox to my growing list of concerns.

Thanks for that. It seems like a good guideline/rule to adopt.
 
Although I have never encountered a down current I have a personal rule that I won't dive any Nitrox mix on a dive where the hard bottom exceeds the MOD unless I have two independent buoyancy systems. Don't flame me, it is a personal decision, but on wetsuit dives along a wall where a loss of lift can potentially send me below the MOD of my back gas and ruin my day I dive air only. If I am dealing with a loss of buoyancy or a down current I don't need to add an O2 tox to my growing list of concerns.
someone posted they take a pony with air to switch if they exceed MOD but i think its probably better to either avoid the area or stay on air not EAN- swapping bottles on a down draft is over taxing
 
Those of you limiting yourself to hard bottoms and air, may need to get out more and expand your diving horizons.
 
https://www.shearwater.com/products/perdix-ai/

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