Ten Foot/3 Metre Stops in Heavy Swells?

[cfenton]

A couple of weeks ago we did a dive on the wreck of the Vanlene in Barkley Sound which is pretty much exposed to the open Pacific. We did 110' avg for 40 min and brought O2 for deco.

At a 110' when we came around the stern of the wreck to the exposed side a strange current picked up that wasn't constant. When we got to our 30' stop the swells were pushing us back and forth a good ten feet. By the time we made the gas switch it was getting ridiculous. We were getting tossed around and our gauge was reading back and forth from 25' to 17'. When we finally got back to the boat and asked the captain about the bottom current he told us it was the ground swells. I had never experienced them at this depth before.

So my question to those of you who are experienced in this type of conditions; what is the best way to deal with the deco? Should we have moved shallower to avoid the 25' on O2 which of course means we would have been getting tossed around even worse? On a longer dive would you just do more air breaks?

Thanks,

 

[rjack321]

A couple of weeks ago we did a dive on the wreck of the Vanlene in Barkley Sound which is pretty much exposed to the open Pacific. We did 110' avg for 40 min and brought O2 for deco.

At a 110' when we came around the stern of the wreck to the exposed side a strange current picked up that wasn't constant. When we got to our 30' stop the swells were pushing us back and forth a good ten feet. By the time we made the gas switch it was getting ridiculous. We were getting tossed around and our gauge was reading back and forth from 25' to 17'. When we finally got back to the boat and asked the captain about the bottom current he told us it was the ground swells. I had never experienced them at this depth before.

So my question to those of you who are experienced in this type of conditions; what is the best way to deal with the deco? Should we have moved shallower to avoid the 25' on O2 which of course means we would have been getting tossed around even worse? On a longer dive would you just do more air breaks?

Thanks,

If you were along a shoreline or shallow, the groundswell will push you around. In more open water not so much. E.g. Limeyx and I have swum away from Ship Rock to avoid the surge-y water close to shore. In the open ocean even very large swells are essentially imperceptible. On something like the Vanlene, the question becomes can you get into deep enough water to minimize their effects.

Swells usually don't just start all of a sudden, so you should have experienced them on descent. Although I admit descending midwater and coming back up a shoreline its easy to get duped and potentially smacked around.

 

[rjack321]

While it may have originated in the caves I can assure you that there are hundreds of people diving DIR in open ocean enivronments.

Scooters make better Jon lines everytime.

 

[cfenton]

If you were along a shoreline or shallow, the groundswell will push you around. In more open water not so much. E.g. Limeyx and I have swum away from Ship Rock to avoid the surge-y water close to shore. In the open ocean even very large swells are essentially imperceptible. On something like the Vanlene, the question becomes can you get into deep enough water to minimize their effects.

Swells usually don't just start all of a sudden, so you should have experienced them on descent. Although I admit descending midwater and coming back up a shoreline its easy to get duped and potentially smacked around.

Your absolutely right; we were well aware that we would be doing the 20' deco in heavy swells. The Vanlene lies from 140' to 20' of water. The person leading deco brought us right up the slope to 20'. After getting our asses kicked for a few minutes we did move into somewhat deeper water where it got a little better. On the dive debrief we decided to ascend directly from the deeper part of the wreck next time.

Even when doing deco at 20' with a lot of water below your depth will still be fluctuating in heavy swells. I'm wondering how critical this is when on O2? The OP was talking about 10' and one solution was to do the stops deeper. Obviously with O2 this isn't an option.

 

[DeepSeaExplorer]

AFAIK jon line is not DIR.

Actualy, when I took Tech 1 our GUE Instructor demonstrated how to use your spool as a John Line. That was some years ago now, but it was taught at one time.

 

[rjack321]

Even when doing deco at 20' with a lot of water below your depth will still be fluctuating in heavy swells. I'm wondering how critical this is when on O2? The OP was talking about 10' and one solution was to do the stops deeper. Obviously with O2 this isn't an option.

Depends on the wave period (time between swells). If its long enough you just ride it up and then down and your gauge moves very little. The rule of thumb is you don't want swells to be shorter (time) than they are high (ft). The steep ones tend to throw you up and down more - although I think its really your inertia holding you semi still as the swell goes though. Not enough time for your body to rise and fall within the moving water. In shallower water (not deep ocean) along a shoreline (even if you move away from it) with wind waves on top of swell all the little rules sorta break down tho.

One option if its bad but not too bad is to just shorten the BT and do little or no O2 deco. That's what I'd do if I was looking at a 15 to 25ft bouncy O2 deco. Or pick a backup site. This time of year I'm always keeping alternatives open.

 

[leeblackman]

Hey I'm new, can someone tell me exactly what a Jon line is?

 

[battles2a5]

If there is a current running then you will have to consider it's speed and look to either floating deco, kick against the current...

Sorry, I'm not DIR and I'm not trying to start an argument but I've seen this in practice before and it shocked me. Doing deco, comfortably resting at 20ft on O2 (current and swell) watching two guys kick feverishly into the current because they refused to deploy a jon line or hang on the line. Maybe it's me, but working hard at 1.6 PO2 is not high on my list of things to do. On an anchored wreck dive, is this really the recommended approach?

 

[battles2a5]

Hey I'm new, can someone tell me exactly what a Jon line is?

A jon line is a line that you attach to the anchor line and either hang onto or attach to your harness so you can a) sit in the current without have to hold the line or get knocked around my the anchor line in swells or b) makes more room on the line when multiple people are decoing (or both). There are different designs, but they are usually about 6-8ft long.

http://www.diveriteexpress.com/tools/cutting.shtml (scroll down to jon line)

 

[rjack321]

On an anchored wreck dive, is this really the recommended approach?

You started down the path of errors when you anchored on the wreck. If the anchor is out (and sometimes it is, although its way overused) I scooter the deco. If you can't scooter the deco due to current you DEFINATELY should not have anchored.