Emergency Descent During Deco

[dumpsterDiver]

Recently a friend of mine was doing a drifting deco dive a few miles offshore in SE Florida. The current was running about 4 kts (according to the GPS). He had about 20 minutes of deco remaining, when he heard a ship coming while on his 20 ft deco stop.

Even though he was pulling a 6 ft tall smb, a large ship would probably not see it, but there was a the dive boat that was following the float. As the ship approached very quickly, the diver quickly realized he was in danger of being run over by a large ship. So he dove down, I think his depth was around 35 feet or something.

We later found out that was probably not deep enough to avoid the ship or the props, but the ship passed close by without incident. He was using a computer to plan and manage his dive, so he just followed the computer for guidance as what effect the excursion during the deco may have caused.

If this were to happen in the future, he would probably abort the deco stop and descent to 75 feet or maybe 100 to be safer from the prop wash.

What would the tech divers do in this situation if they didn't have a computer? Certainly a quick descent to 100 feet is not something they plan on?

 

[peterbj7]

I've been in a similar situation in the English Channel. The really big ships not only have very deep draft, but will suck you into them. So I would dive down, very deep probably (100ft?), and if I had any idea where the boat was passing I'd swim sideways to get away from it. From that point on it's luck.

I can't imagine a tech diver not having a computer.....

 

[tphelps]

Holy smokes, talk about your string of bad luck! I would hold position as long as possible and only descend if danger was absolutely inevitable (since you cannot ascend). Usually you carry a second lift bag, if possible have a team mate deploy the second.

If you dont have two computers on you, you should NOT be tec diving! We carry our stops and dive profile on a wrist slate to follow. This just goes to show the importance of a Liquidvision, Shearwater or other computer that can adapt to a change in dive plan.

 

[Ste Wart]

I can't imagine a tech diver not having a computer.....

If you dont have two computers on you, you should NOT be tec diving! We carry our stops and dive profile on a wrist slate to follow. This just goes to show the importance of a Liquidvision, Shearwater or other computer that can adapt to a change in dive plan.

I don't have a computer, neither do the guys I dive with. Why would you need one? It's like saying all Cave divers need a computer, Cave profiles are not always so linear yet they figure out the deco on the fly.

If I was doing drift deco I would expect the boat I'm diving off to be covering me, warding off approaching traffic.

Failing that I would drop to 21m and pad the deco as per an omitted deco schedule

 

[ajduplessis]

Interesting topic. I personally stay clear of shipping lanes and is fortunate enough to dive in MPA's or caves. I would think that environments like these dictate that DC's are compulsory along with additional buoy and reel. I am not sure what you would do during final couple of min during last stop and you need to drop back down to 100ft

 

[Tortuga68]

I can't imagine a tech diver not having a computer.....

If you dont have two computers on you, you should NOT be tec diving! We carry our stops and dive profile on a wrist slate to follow. This just goes to show the importance of a Liquidvision, Shearwater or other computer that can adapt to a change in dive plan.

Like Stewart said, there are plenty of technical divers that never us a computer, just a BT (and backup BT/watch), running cut profiles. I did all of my tech dives that way, down to 100m, until I got an X1 earlier this year. Depending on the nature of teh dive (square profile or not) I usually still cut a run time (on Decoplanner) and will often follow that with the X1 as a 'backup' incase the dive turns out not to be square or the dive plan changes to something I don't have/know a run time for.


Back to the OP, it would depend on the run time/depth of the dive but since he still had 20 mins remaining I assume it was either deep or long, or both. Anyway, in the absence of an 'on-the-fly' computer, I would probably restart the planned deco stops from the depth I descended to (to avoid the boat) and maybe add some extra time at 6m (gas allowing). This should be relatively conservative given that you would only be back at depth for a short amount of time until the boat hazard passed by.

Another (better?) method would be to use ratio deco to recalculate based on your average depth/time (after completing your 'boat hazard deep stop'), if gas was an issue I would probably do that although since I would normally plan the dive to surface with half of all my gas remaining (back & deco) I would hope that wouldn't be the case.

In any case if I ran out of deco gas/ses I would switch back to the next richest mix and adjust the stop times accordingly (e.g. if using 50% instead of O2, double the stop time/s).

In my view 'omitted/missed deco' protocols are not applicable to this scenario, although they may work in practice.

 

[dumpsterDiver]

I don't have a computer, neither do the guys I dive with. Why would you need one? It's like saying all Cave divers need a computer, Cave profiles are not always so linear yet they figure out the deco on the fly.

If I was doing drift deco I would expect the boat I'm diving off to be covering me, warding off approaching traffic.

Failing that I would drop to 21m and pad the deco as per an omitted deco schedule

I HOPE the boat would protect me, but a 25 ft boat versus a 450 ft ship moving 30 mph is not something I can "expect" to protect me.

What does a second lift bag do in this scenario?

 

[chrpai]

Is this situation avoidable in the first place?

Can you look at the charts, location of the reef and shipping lanes, current direction and speed and say "maybe we shouldn't do this dive today?"

 

[HowardE]

Recently a friend of mine was doing a drifting deco dive a few miles offshore in SE Florida. The current was running about 4 kts (according to the GPS). He had about 20 minutes of deco remaining, when he heard a ship coming while on his 20 ft deco stop.

Even though he was pulling a 6 ft tall smb, a large ship would probably not see it, but there was a the dive boat that was following the float. As the ship approached very quickly, the diver quickly realized he was in danger of being run over by a large ship. So he dove down, I think his depth was around 35 feet or something.

We later found out that was probably not deep enough to avoid the ship or the props, but the ship passed close by without incident. He was using a computer to plan and manage his dive, so he just followed the computer for guidance as what effect the excursion during the deco may have caused.

If this were to happen in the future, he would probably abort the deco stop and descent to 75 feet or maybe 100 to be safer from the prop wash.

What would the tech divers do in this situation if they didn't have a computer? Certainly a quick descent to 100 feet is not something they plan on?

A quick descent to 35 feet is relatively benign compared to a quick descent to 100' (4 ATA) which is an ongassing situation. The drop to 35 FSW (approx 2 ATA) would have little effect on the decompression profile since it's not really an ongassing situation at that depth. Also, upon making a quick descent, am I changing back to my back gas? Am I still using my deco gas? What is my deco gas? Does this throw me into a high PO2 situation?

Dropping to 100' would certainly throw off your decompression schedule, and most likely depending on the time at depth, the answer would be a variable depending on the profile of the dive. Just by a guess, 20 minutes of deco remaining would imply that he probably had somewhere in the neighborhood of 5-8 minutes at 20 feet and 10-15 minutes at 10 feet?? If it was me, and I had to wing it, I suppose I'd make 1 minute at 50' 1 @ 40. 3@30 and then start my 20' stop over +2 minutes, and add a few minutes to the 10' stop to be safe. Hanging at 10' for a few extra minutes wouldn't hurt anything - given I had enough gas.

I also wouldn't dive without a computer... but that's another argument to argue, and not necessarily relevant.

 

[danvolker]

Recently a friend of mine was doing a drifting deco dive a few miles offshore in SE Florida. The current was running about 4 kts (according to the GPS). He had about 20 minutes of deco remaining, when he heard a ship coming while on his 20 ft deco stop.

Even though he was pulling a 6 ft tall smb, a large ship would probably not see it, but there was a the dive boat that was following the float. As the ship approached very quickly, the diver quickly realized he was in danger of being run over by a large ship. So he dove down, I think his depth was around 35 feet or something.

We later found out that was probably not deep enough to avoid the ship or the props, but the ship passed close by without incident. He was using a computer to plan and manage his dive, so he just followed the computer for guidance as what effect the excursion during the deco may have caused.

If this were to happen in the future, he would probably abort the deco stop and descent to 75 feet or maybe 100 to be safer from the prop wash.

What would the tech divers do in this situation if they didn't have a computer? Certainly a quick descent to 100 feet is not something they plan on?

I would just drop down to about 70 feet --if this was a cruise ship or huge tanker, then in less than a minute it would be gone and you would hear the doppler shift....then I would just do a 30 foot per minute ascent to the stop I had been at before....and maybe add a minute or two from where I had left off. I don't see this as causing much of an issue from a tech dive to 200 or more, since even at 70 feet you are still off-gassing the excess nitrogen from 200 feet. The insignificant amount of in-gassing involved in the return to 70 is not in question( irrelevant), only bubble dynamics from 20 to 70 and then back to 20.....

If it was a real tech dive, you should have pure O2 for the 20 foot stop, so any bubbline would be resolved anyway.
If it was just a little 160 foot deep air profile for some shooting, and it required deco ( knowing your interests, this could be the deal here), bubbling would still be best dealt with by a 20 or 30 cu ft bottle of pure O2, whether you need to do a short blast to 70 feet or not

I have dropped down from a 20 to around 50 feet, on a deep tech deco, to assist others in the past...and it never caused any issues even remotely discernable.