Best Way to Conduct Deco Stops at 20' When Waves and Currents are Present?

[ScubaInChicago]

There are a few things going on there that should be addressed. It's always safest to let someone on the surface know what happened and continue your deco from 10' below your missed deco obligation. There is also very little benefit from doing deco at 10' and can all be done at 20'. It should also be mentioned that there's a risk of getting oxygen bent from a quick ascent on O2 from 20'. I prefer a 6 min ascent from 20' to avoid any issues.

 

[Jax]

When I completed the stops and got back in the boat, I tried to understand what happened with other divers. Someone said:"the line lost tension", that I had, probably, more air than necessary in my wing, "that is why I don't grab the lines, etc."

"OK" the line, don't grab it. The boat lifted, probably dragging you 5' up, and into the 'oh ****' zone.

Good for you for keeping your head and going back down. Shame on you for lack of awareness.

 

[dumpsterDiver]

Why in the world are you doing deco when you apparently have no experience on how to hang on a line in small waves or a current? Seriously, isn't that the issue here?

 

[ldeleon68]

Not exactly; I do safety stops all the time at 20' in caves and open water. However, I made some mistakes and want to be sure I learn from them.

Thanks for taking the time to reply.

 

[dumpsterDiver]

Learn how to ascend on an anchor line, BEFORE you try deco on it.. 2-3 ft waves are not a big deal. It sounds like you "climbed" up the anchor line and failed to vent gas. Easy to do if it is rough and you are strong, when moving up and down an anchor line - up is more important.. relax a little and check if you are close to neutral.. don't let your self get out of wack on an ascent... It is much easier to tell when wearing a normal BC, because it squeezes you and back inflate gives much less warning.. Not sure what other advice I can give.. maybe a hang line - jon line they call them.. I never had need for one.

 

[Akimbo]

I have done a fair bit of in-water decompression in heavy weather. If the swell is up but the current is low then a small cherry buoy loosely tethered to the anchored boat’s stern, preferably amidship, with 30+ Lbs of lead isn’t bad. The cherry buoy isolates you from the rolling of the boat and you raise and lower with the swell. I like downlines with a hand loop at each stop and one for each diver so you aren’t constantly banging into each other.

The only practical option I have found in high currents and high swells is to drift, preferably secured to a chase boat in the same manor above. You have the chase boat tie-off to the downline, typically to a wreck or other worksite, and have them cut loose as soon as all divers are on their lines. I have been in seas where you would wave in the current like a flag in a stiff breeze, even though it felt like a gale.

An option when there is no downline is to pop and SMB on a reel and wait for the chase boat to gather you up with suspended heavily weighted lines. It is hard to do for more than two teams per chase boat though. It is labor intensive but works. There main limitation of an SMB in high seas is there isn’t much weight to keep you down since you are usually pretty neutral at that point.

Edit: It was not unusual to also have the chase boat with a couple of "K" bottles of Oxygen in the bilge feeding hoses that reached the 20' stop... but we were doing Sur-D-O2 (Surface Decompression using Oxygen) in a decompression chamber after completing abbreviated water stops.

 

[Bennno]

I had planned to grab the line from the wreck to the vessel in the surface. When I reached the 20' mark, I thought I had adjusted my buoyancy when I started switching to the last deco bottle (100% O2)%, then I realized my computer was flashing (red numbers); I was going to the surface!

In the rush of finding the air deflator, I started blowing out all the air in my lungs; but, it was too late, I had my head above the water!

If you can't control your buoyancy you really shouldn't be doing deco dives! You need to be able to control your ascent without a line and you need to be aware of your depth at all times.

Hate to say it, but to me, this is clearly a skill/training/experience issue! Before you try another dive like this you need more training and/or experience! Even short deco dives are not to be taken lightly.

IMHO there is no point in trying to "fix" this issue with gear. Forget the jon line, the 80% and all that stuff.

Edit: dumpsterDiver hit the nail right on the head.

 

[decompression]

Although I'll not comment on the OPs abilities, our local dives (Canadian west Coast) it's not uncommon to be controlled by the water, so being moved by serious current, upwellings and large tidal exchanges is part of the experience. A few years ago a diver got caught in a down welling on the slope of an island, when the body was recovered the computer read 250'....
We use our training to minimize the risk under these conditions.


Sent from my iPhone using Tapatalk

 

[Diver0001]

I want to share my story with you so you can give me some recommendations:

This last weekend I conducted a dive to 166' deep that required a 14 minutes deco stop at 20' (last stop) using 99% O2 (Buhlmann GF 30/80). The waves were around 2-3 feet and a strong current was present.

I had planned to grab the line from the wreck to the vessel in the surface. When I reached the 20' mark, I thought I had adjusted my buoyancy when I started switching to the last deco bottle (100% O2)%, then I realized my computer was flashing (red numbers); I was going to the surface!

In the rush of finding the air deflator, I started blowing out all the air in my lungs; but, it was too late, I had my head above the water!

I never entered in panic; but, I thought I might pass out at any moment. I did not feel any symptom in the 1 second it took me to decide to go down again and restart the deco process at 40'.

When I completed the stops and got back in the boat, I tried to understand what happened with other divers. Someone said:"the line lost tension", that I had, probably, more air than necessary in my wing, "that is why I don't grab the lines, etc."

As of today (+48 hours later), I have no signs of bends; what bothers me is, what should be the best way to complete deco stops at 20' when waves and currents are present (deploying the safety sausage to stabilize, swing around all the time? What about doing the last deco stop at 25'-30'? I am not used to do decompression stops in open water but in caves, again, your advises are welcome.

You know, I've seen quite a few divers over the years -- some of whom were very experienced -- who have surprising trouble operating in mid-water. I would advise you to do some mid-water dives in a lake before you engage in another ocean dive of this nature with all of the complications it presents. I think you got off easy and your story makes me think you could do with additional practice.

Your solution to the problem was ok. I think in Mark Powell's book it mentions doubling the duration of missed stops in a "skipped deco" event but I'd have to look it up. Given that you are doing such dives, if you haven't read his book you should. "Deco for divers" by Mark Powell. Get it. Read it.

As for doing deco on an unstable up-line. What I've always done in the past is to use a John Line and to just float in the current and do the deco essentially free-floating. The John Line will stop you from losing contact with the up-line without getting pulled up and down on it. I also use 50% to deco in ocean conditions because you can switch early and it's pretty much "botch proof" when you're shallow. Finally, if you don't use one, then get a multi-gas computer and use it. In my humble opinion, a computer is vastly superior to using tables in less than ideal conditions.

R..

See under: Graphic of a John Line.

 

[ldeleon68]

Thank so much for this advise