trapped in net trying to ascend

[beester]

A couple of days ago during a wreckdive on a North Sea wreck both me and my buddy got entangled, this has for obvious reasons shaken me a bit and I would like to share.

The context is as follows: I'm a intermediate diver with about 180 dives (all kinds of circumstances, cold, low vis, deep, current, etc). An experienced wreck diver asked me along with his group to do wreckdives stating that I would love it. (which I do).

The incident happened on my 6th wreck dive.

This was a wreck with a max depth of 110 feet. We were diving nitrox 32 on dual (Y) valved 119 HP tanks. Plan was to call the dive when hitting 60 bar or getting within 2 min of NDL. (if we plan on deco dive we obviously would plan more conservative). Make a free ascend to 45 feet, blow SMB and make our way up to 15 feet for a 5 min safety stop before finaly ascending.

What happend was the following. We descended along the buoy line to a depth of 110 feet on the wreck... vis was not bad (around 20 feet). We started enjoying the wreck occationally looking into holes for bugs or cod (but without entering any overhead environments). When we were about to call the dive after 30+ minutes on the wreck my buddy got caught in monofillament netting. I turned to him to aid him and was caught too.

At first we tried to swim loose slowly which was a mistake and made the situation worse... we stopped and we started to clean eachother off... cutting as many lines as possible (very hard to see). In the end we had to cut off the fins from my buddy in order to release us. When we finaly started ascending we had about 25 bar left (about 4 min worth of gas at that depth depending on anxiety it could have been 2). We came up to 40 feet (him without fins) shot our SMB and lined up to 15 feet and did our 5 min of safety stop. We came up with 10 bar of pressure.

Obviously we cut this too short. I'm still a bit shaken and have not yet analysed the shortcomings but anyway things I'll be looking at will be:

Pro:
- We didn't panick. If we had panicked bad **** could have happened.
- We worked quite well together under water... if we had been separated we would have had more issues.
- we managed to keep our composure and even with complications (my buddy without fins) we managed to ascend safely, deploy smb and do a safety stop after we got out of the netting.

Con:
- Gas management: We cut it too short. Of course the incident happened at the worst possible moment (close to return pressure) but still.

Anyway... have a go at me

 

[hudson]

What cutting devices were you using? Run-of-the-mill dive knives may not have been optimal perhaps?

Ignoring the idea of reserving additional gas to deal with significant risk of entanglement on a wreck... it sounds like you have reserved about 30cuft of gas in your plan and were able to ascend with about 7cuft from 110ft...you had a long safety stop but the ascent speed otherwise sounds like it was about 60fpm? You would also have had to blow the safety stop if one of you were stressed out. A bit more reserve gas would allow for that and a slower ascent, perhaps with a deep stop as well. With 60bar reserve you only have enough gas for this kind of ascent if one of you has an OOA emergency at the end of the dive.

 

[Web Monkey]

This was a wreck with a max depth of 110 feet. We were diving nitrox 32 on dual (Y) valved 119 HP tanks. Plan was to call the dive when hitting 60 bar or getting within 2 min of NDL. (if we plan on deco dive we obviously would plan more conservative). Make a free ascend to 45 feet, blow SMB and make our way up to 15 feet for a 5 min safety stop before finaly ascending.

FWIW, being within 2 minutes of the NDL isn't a good place to plan to turn a dive. First (as you discovered), you might have problems that prevent immediately returning to the surface, which then puts you into unplanned deco without the necessary gas reserves to handle it. If for example, you landed in a big wad of mono from a popular fishing site or in part of a discarded net, and it took you ten minutes find and untangle/cut everything, you didn't have gas to handle the 10 minutes of extra bottom time (at a much higher SAC rate) or the deco stop.

Second, the NDL isn't a precise, hard, fixed limit that applies equally to each individual. Being 2 minutes under the NDL could in reality be over the NDL for any specific person, depending on all sorts of hard-to-identify factors (hydration level, previous dives, personal physiology, etc). In fact, it varies considerably between tables and computers from different sources.

Gas management: We cut it too short. Of course the incident happened at the worst possible moment (close to return pressure)

That's when they all happen. If an emergency happened at a convenient time when you had plenty of gas, it wouldn't be an emergency. For example, if you got tangled in mono in 10' of water at the beginning of the dive, it would hardly rate a mention. Just cut it and move on. However it becomes much more dangerous when you're low on gas. The trick is to plan things so the emergencies become annoyances.

As was mentioned (and as you discovered) 60 Bar isn't enough of a reserve. Especially when diving single tanks on a deep dive, thirds would be more appropriate (1/3 in, 1/3 out, 1/3 for when the poop hits the fan), and at the depth and conditions you were in, doubles would be even better.

You might also want to consider diving with

A line cutter

Which is great for tangles of mono-filament,

and EMT Shears, which work great on stainless steel leader.

As well as a regular knife for everything else. Unfortunately, cutting mono-filament with a knife is difficult and usually requires two free hands, and cutting stainless steel leader with a knife is only good if you enjoy frustration and have lots of extra gas. OTOH, both of these tools are useless with big stuff, which is why you still need a knife.

The line cutter is very nice, since you don't have to actually be able to see the line; you only have to get it into the hook and make sure it isn't anything important like a hose or your part of buddy.

Anyway, congratulations on your "learning experience", and we're all very happy that this thread doesn't also have a friend in the "condolences" forum.

Terry

 

[needforspeed751]

good job with not panicking and i'm glad you two made it out safely!

 

[beester]

Thanks for the replies...

Some remarks... after uploading my computer stats:

- We called the dive at 60 bar. still 5 min within NDL
- We were free from netting and started ascending after 3 min.
- We did 5 min of (safety) stop at 15 feet.

You are correct regarding gas management. Doubles might be in order... however strict rules of 3rds are not necessary imo on a square profile with no or only slight ceiling. (never penetrating wrecks). Keeping a full 3rd as backup gas is advicable... but using 1 3rd for ascending is over the top IMO. What do you think?

I was carrying 2 knives on different locations. I'll look into replacing one of the knives with a linecutter.

CHeers

 

[TSandM]

I don't think you need to dive thirds in open water, unless you are in a high current situation where you absolutely MUST make it back to the anchor line and up to your boat. You do need to reserve enough gas to get you and your buddy up to the surface from any point in the dive, but once you have set that aside, you can decide how to allocate the rest of your gas. If you can ascend at any place and any time, it's an "all available air" dive, and you can begin your ascent when you have reached your reserve gas. If you'd like to get back to your starting point, but it isn't critical, then you divide the usable gas in half. Only if you MUST return do you need to dive thirds.

That said, some people use a thirds approach to avoid having to set aside the safety reserve.

 

[b1gcountry]

On a lot of square profile dives like these, I will plan on thirds one way, then get back to the line with a third of my usable gas left. I use that to check things out in another direction. I see as much, my dive is just as long, but it's a little safer, and I have a lot more gas to find the anchor line if I miss it.

As far as what you did wrong, not too much, but I would probably have kept a bigger reserve. I would also say that you should pay a little more attention to your surroundings to try to avoid things like monofilament, etc that could snag you. At that depth, and that visibility, things get pretty dark, and it may help things if you are diving with a strong light.

Also, with monofilament, pulling on it, or trying to swim out of it seems to make things worse, but you probably know that more than anyone at this point, right?

Personally, I consider anything below 100' a deco dive. I use doubles, and make a full dive plan. I'm not zealous about it, but it works for me, and it gives me peace of mind.

Tom

 

[mbwilliamn]

I'm a big fan of the shears....anyone ever try and cut mono one handed? Or as Terry noted, steel leader? I'll leave my knife on board before my shears!

 

[mbwilliamn]

I started diving with a 19 CF pony about 2 years ago and won't go below 30 ft deep or 15 ft of viz without it! It's much more convienent than doubles, and provides a reasonable bailout if needed. I plan my dives as if its not there, but when "Murphy" shows up, I'm still OK.

I love this quick draw bracket.
Quick Draw Pony Bracket, Ultimate Products