Typical tdi deco procedures advanced nitrox course length.

[Marie13]

@Marie13, if there isn't a strong current running, you can get neutral and keep a loose grip on the line. When the line jerks up and down, let it slide through your hand. This method isn't perfect and won't hold you perfectly still. But with a little practice learning to anticipate the pulls, you'll find that it really alleviates a lot of the jerking. You can also do your deco stops deeper than required. You lose some off-gassing efficiency and add to your overall deco time, but its sometimes worth the improvement in comfort.

I’ve never heard of divers having to deal with really strong current, but perhaps it’s because I’ve never specifically asked the question.

 

[RyanT]

I'm an ocean diver, so I wouldn't know anything about currents in the great lakes. I wasn't going to make the assumption that it's not a thing.

 

[rddvet]

You know.. I make my students spend a lot of time at Hudson Grotto for this very reason, it's really a good place to practice shooting bags and doing OW ascents. I spent last Sunday there with two guys working on normoxic trimix. We're supposed to be down in Pompano today diving the Lowrance but something came up this weekend that kind of changed our plans.

They are cave divers, they only want to do cave diving, but I made them spend a day at Blue Grotto, a day at Hudson and I'm making them do their final two days in the ocean.

You should be ashamed for making people swim in satan's butthole.

 

[PT4476]

I'm glad I did my normoxic trimix training in S. Florida, we did hot drops and drift deco on all but the first two dives. I think blue water (or grey-green water skills in the great lakes) are essential for decompression boat dives. There can be significant current in the great lakes but generally most captains are do not want divers doing planned drift deco, sh*t happens though and sometimes a diver has to shoot a bag and deco off the line. Has not happened to me (yet) but I'm glad I've got some drift deco experience—coming up on a bag in the cold, low vis water of the lakes is most likely not much fun but if it happens at least I have some prior experience in a more drift deco friendly environment…

 

[ChuckP]

Doing deco in a cave is so easy compared to while hanging onto an anchor line in current or drifting in blue water. It's really like comparing apples and french fries (not even two types of fruit).

What makes cave deco so different? I've seen videos of people doing long deco sitting on a ledge or something but is it just the no current thing?? If you are in a hard overhead and can't shoot a bag, I'd hate having to pay attention for 30-45 minutes maintaining whatever depth LOL.

I learned in OW and mostly do OW - anchor lines are a PITA for me due to the crowd but jon line helps. I'd much rather hang on a bag drifting along, there's virtually no effort mental or physical at all in it.

 

[kensuf]

In a cave you don't need to maintain buoyancy during your deco, you can simply lay on a log if you're not that good.

In a cave you can drop off your deco bottles at the start of the dive and pick them up on the way out. No need to carry them throughout the dive.

In a cave you generally don't have wildlife concerns (note, this isn't universally true, but for the majority of recreational cave divers it is).

In a cave you don't even need a depth gauge for your deco stops if you have even the most basic familiarity with the location. Let's take Ginnie for instance, the 50' stop is where the gold line used to begin/end, the 40' stop is at the top of the slope, the 30' stop is right by the stop sign, the 20' stop is right at the entrance.

In a cave you don't have bros on jetskis turning your SMB into their personal slalom course.

Let me know if you need more examples, I can keep going.

 

[Caveeagle]

Kudos for that. I wish that was more common in cave country. I took the typical 4 or 5 day AN/DP in cave country years ago. It was a decent enough class (nothing outstanding in retrospect) but was more focused on deco as it's related to cave diving. Now that I have the rebreather I'm really interested in doing some more serious boat diving, but lack of experience with OW deco procedures is one of the things that's stopped me. And it's not like you can show up on a boat and buddy up with a random instabuddy for a deco dive. In retrospect I wish we'd done OW skills in more depth and done a boat dive or two. I figure at this point I'll get the experience when I take CCR Trimix

I am in a very similar spot. I also crave some deeper ocean wrecks and have only done some very limited anchor line and drift deco. I have been on a few recent drift dives that were hot drops and essentially solo ascents. I am pretty calm and don’t get freaked real easy, but it was obvious to me that my training had been a little light on this type of thing.

They are cave divers, they only want to do cave diving, but I made them spend a day at Blue Grotto, a day at Hudson and I'm making them do their final two days in the ocean.

Jeeze Ken... I have been looking for a good excuse to sign on to a class with you, but wasn’t aware of this sadistic side of you.

In a cave you generally don't have wildlife concerns (note, this isn't universally true, but for the majority of recreational cave divers it is).

..just way different types of wildlife. Gators, mermaids and giant unicorns

 

[Jim Lapenta]

I’m really interested in learning how the locals do deco on Great Lakes wrecks with fixed mooring lines when the line is really jerking due to wave action at the surface. Jon line or do they shoot a lift bag to deco next to the line? Dang near had my arm pulled out of my shoulder doing a safety stop on the line with 3-4ft waves topside last weekend.

Never try to do deco hanging on the mooring line if there's any chop. That's asking to get hurt. Use a jon line hooked to the mooring if you have to in any real current that's difficult to swim against. Otherwise, just use the line as a VISUAL reference and maintain your buoyancy while hanging in midwater a foot or two away. Occasionally you can reach out with a finger to touch it. Shooting a bag is just as bad. If not worse because now you have a line bouncing up and down and the bag may get taken by the wind.

A diver should not have to hang onto the line to maintain depth. If they do, they shouldn't be doing deco dives yet. For TDI in order to pass the deco class, you have to maintain a stop without hanging on to anything to maintain depth within a foot. Can't pass the class until you can do that repeatedly. Current is one thing. That may require holding onto a line. Wave actions on the top may require you to adjust for a little deeper final stop, learn to use a jon line, or get better at judging when the risk is too great.

On the Osprey that we were on yesterday with Captain John, he made sure we knew that 3 - 4 ft waves turn the swim platform and ladder into things that will not hurt you. They will just flat out kill you and you either do exactly what he says for boarding, or you don't do the dive. That's another thing that needs to be taken into account with chop on the Lakes. Deco is easy, getting back on the deck may be much more of an issue.

Also in the Great Lakes, allowing a mooring line to slide with hour hand around it is a good way to get fish hooks embedded in your hand, get your glove sliced by Zebra mussels, get your hand under the glove sliced by them, resulting in a nasty infection starting before you can even get back to the dock. For some reason, the Zebras, at least in Lake Erie, have something that leads to rapid infection.

The simple answer is before you try to do deco on Great Lakes dives, make sure you can maintain depth in chop without hanging on to something. Otherwise, don't do the dives unless conditions are better.

 

[RyanT]

In a cave you don't have bros on jetskis turning your SMB into their personal slalom course.

Or bros on jet skis that literally snatch the bag out of your hand and drive off with it.

 

[electric_diver]

I’m really interested in learning how the locals do deco on Great Lakes wrecks with fixed mooring lines when the line is really jerking due to wave action at the surface. Jon line or do they shoot a lift bag to deco next to the line? .

Basically what Jim said. Don't touch the line but maintain visual reference to it. If I'm bored I'll swim circles around the line and all the divers on it. If wave chop is bad the 10 foot stop becomes 15.