How Quickly a Dive Can Go Wrong

The other night I joined up with a local boat here on Oahu to do a closed circuit rebreather training dive. The main goal was to work on skills and build hours for the next level of certification. We were heading to a site called Shallow LCU, it’s a wreck located off the leeward side of the island in about 60-80 fsw – right off the coast of Waianae.

The visibility was poor for out here, typically it’s around 60-90 feet. Today it was closer to 20 feet. It had been raining hard for the past few days so this wasn’t a big surprise. We spent the 40 minute transit chatting about life, preparing gear and conducting a pre-dive brief. By the time we reached the dive site it was dark and well on its way to pitch black.

The Captain used the plotted GPS position (we will come back to this later) to “find the wreck”. We drove back and forth over the wreck to locate the submerged ball that we use to tie the boat up directly to the wreck. Unfortunately, we were unable to find the ball. We decided to drop an anchor.

We took a heading on the plotted position of the wreck, hopped in the water and descended to about 20 fsw.

After conducting our S-Drills we started out on our predetermined heading to look for the wreck. We didn’t find it.

After running sectors for about an hour we eventually found the wreck and discovered a few things.

  1. There was no ball attached to the wreck.
  2. The plotted GPS position was inaccurate.
  3. Poor visibility severely hampers search efforts.

We spent about 20 mins on the wreck then started back towards the boat. As we swam along the bottom of the ocean, I noticed our depth increasing; we were swimming away from the boat. There is no way to be able to tell which way to swim to get back to the boat at this point. We could have swam shallower, but still not towards the boat. The Dive Supervisor signaled to ascend and begin our decompression obligations. I had accrued about 8 minutes at this point (we did about 90 minutes at an average of 70 fsw).

It was pitch black. We had no up-line. No idea where the boat was. Visibility was about 15 feet and we had to off-gas.

I had my DSMB (Delayed Surface Marker Buoy) and reel clipped to my backplate and confirmed with the Supervisor that I would be launching it as we didn’t brief that.

Hovering, mid water column, with no point of reference, on a rebreather when you’re task loaded with deploying a DSMB and owe a decompression obligation with a ceiling isn’t the easiest thing in the world. To be fair, that’s why I do this type of diving though. If it were easy; everyone would do it. I want to be challenged.

As I’m trying to hover at 40 fsw and deploy my DSMB all I could think about was not blowing my through my ceiling, risking DCI (Decompression Illness, aka “the Bends”).

I worked to remember my training and stayed calm as panicking, in any situation, is your own worst enemy. Once you start to panic, you stop thinking. Stop using your greatest tools; your wits, experience and your knowledge. The reality is that I was standing on the doorstep of a situation that could end up with me in the hospital, at a decompression chamber or worst case dead. But those are the risks we take. The real question is; how do we mitigate those risks?

I was able to get the DSMB deployed, we made our decompression obligations and we found the boat. All is well.

On the transit home I had time to reflect on how quickly things could have gone wrong and how quickly we strayed from the path of just a comfortable night dive. There were a few major factors that changed the profile of this dive and it could have ended up much worse.

First; visibility was poor. To be fair, I’ve been in much worse. But the team knew it and we were used to it. Out here, 15-20 feet is a bad day for visibility.

Second; the GPS position for the wreck was a second hand, unverified position that was handed down from someone else. The thing is, not all charts, chart plotters and chart systems translate directly to each other. Additionally, there is some error in GPS positions – they’re not accurate to +/- 0 feet. Add in conversions between coordinate systems and you can have an error on the scale of a few hundred feet. Easy to never find it on a low visibility dive.

Third; bad information with the ball. There was no submerged buoy to tie the boat too. We got dropped the dive Supervisor to look for something that didn’t exist; best case wasting time – worst case putting him at risk to achieve a task that couldn’t be done because the Captain’s information was incorrect (no fault on the Skipper).

Fourth; it boils down to skills practice. If you think knowing how to deploy a DSMB is a waste of time or compass skills aren’t for you; let me tell that you’ll be happy you practice those skills when the time comes that you need them.

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