How you write deco plan on your slate?

[Nick_Radov]

Diving on the fly is headless chicken diving, No plan and no discipline, and 100% will land you in trouble. Never do it shallow or deep. A plan demands discipline, if you like a DC or to write it down or both is up to the diver. Knowing the relationship between depth, time and decompression isn’t enough. I wouldn’t make a simple single tank dive without a plan.

You seem to be a bit confused about what divers are actually doing. Planning is an essential part of the pre-dive sequence.

The GUE Pre-dive Sequence

As you’d expect, Global Underwater Explorers (GUE) has a standardized approach to prepare your equipment for the dive, and its own pre-dive checklist: the GUE EDGE. Here explorer and filmmaker Dimitris Fifis preps you to take the plunge, GUE-style.

gue.com

Following a dive computer isn't really a "plan". Although it can serve as a useful cross check to ensure you don't do something crazy.
You can write down the plan plus various contingencies on your wet notes if you like. But for ocean tech diving things happen quickly; you need to be heads up watching your buddy, especially in an emergency, and may not have time to consult a written plan before acting. Knowing the relationship between depth, bottom time, and total deco time is enough to adjust the plan on the fly in response to an unexpected change in circumstances.

Let’s all go off and make it up as we go along, no one knows what’s happening including the surface supervisor.

Surface support is an essential part of the integrated team and obviously they are included in the planning process. For boat diving at a minimum that means agreeing on things like planned bottom time and run time, SMB deployment, and emergency procedures.

 

[Celt]

You seem to be a bit confused about what divers are actually doing. Planning is an essential part of the pre-dive sequence.

“Adjusting deco plans on the fly falls into that category.” Your words.

 

[Wibble]

Off topic, but I do hear this a lot.

I'm not an attorney, but everything I have heard in the last decade or so suggests that the old "dive boat captain is just a taxi driver" concept is no longer a viable legal defense. Yes, divers have the responsibility for planning the dives, but the topside crew had obligations as well..

Alas the ultimate response is to never go diving. Never drive. Always wear a helmet. Never fold paper without gloves... the infantilisation of the world. We go diving to get away from those ****ing ***kers.

Diving is the ultimate responsibility to oneself.

Thankfully the rest of the world doesn't have the plethora of ****ing **it-for-brains ambulance chasing lawyers that seem to infest the US of A. Had a hospital procedure: the last person to sign you off is a ****ing lawyer, then the accountant hands you the bill/check for 10x the cost of elsewhere on the planet.


Maybe this is why there's so few dive lifts on US dive boats!

 

[Nick_Radov]

“Adjusting deco plans on the fly falls into that category.” Your words.

What are you trying to say exactly?

You can't possibly write down an exact deco plan for every conceivable contingency. What you can do is get the entire dive team to agree on the intended dive plan, as well as a shared process for adjusting the deco plan on the fly should it become necessary. My words above were about the necessity of making this process a "memory item" that can be executed quickly without consulting written tables. This should have been covered in your training.

 

[Celt]

Surface support is an essential part of the integrated team and obviously they are included in the planning process

If the deco schedule has been adjusted “On the fly” how do the surface support and dive supervisor know? Telepathy.

 

[Wibble]

What are you trying to say exactly?

You can't possibly write down an exact deco plan for every conceivable contingency. What you can do is get the entire dive team to agree on the intended dive plan, as well as a shared process for adjusting the deco plan on the fly should it become necessary. My words above were about the necessity of making this process a "memory item" that can be executed quickly without consulting written tables. This should have been covered in your training.

"Dive team"?

Many people, myself included, work out the max dive time for a particular dive taking into account gases, volumes, SAC, etc. Then dive the dive until dive time + TTS is within 10 mins of the max dive time, or less if cold/whatever. It's not always a team thing even if you do meet other divers around the trapeze on a lazy shot.

Skippers are only interested in your planned dive time and that if you're coming up under an SMB that it's one per diver. Very occasionally it might be one SMB per team, but that means the skipper doesn't know when everyone's off the wreck and drifting.

 

[Celt]

What are you trying to say exactly?

You can't possibly write down an exact deco plan for every conceivable contingency. What you can do is get the entire dive team to agree on the intended dive plan, as well as a shared process for adjusting the deco plan on the fly should it become necessary. My words above were about the necessity of making this process a "memory item" that can be executed quickly without consulting written tables. This should have been covered in your training.

Of course you can write down the exact plan, that’s the objective of a plan. If the planned dive can’t be carried out for what ever reason the dive is aborted and the diver returns inside the planned run time, you don’t come up with a new plan “on the fly” and expect the surface support to know about it.

 

[Nick_Radov]

If the deco schedule has been adjusted “On the fly” how do the surface support and dive supervisor know? Telepathy.

The communication plan has to be adapted to the circumstances. For boat diving, the surface support would generally know by when the SMB appears; if that happens significantly earlier or later than the end of the planned bottom time then it's obvious that something has gone awry. The divemaster on the boat is supposed to write down each team's planned bottom time as well as their actual dive start time, and alert the captain in the event of a discrepancy.

Obviously the dive team shouldn't exceed their planned time unless some kind of serious emergency makes that unavoidable.

 

[Searcaigh]

The communication plan has to be adapted to the circumstances. For boat diving, the surface support would generally know by when the SMB appears; if that happens significantly earlier or later than the end of the planned bottom time then it's obvious that something has gone awry. The divemaster on the boat is supposed to write down each team's planned bottom time as well as their actual dive start time, and alert the captain in the event of a discrepancy.

Fat chance of that happening where I dive.

Back on topic, I use two Shearwaters and my backup plan is on wet notes in my pocket. I have a third computer on gauge mode attached to one of my camera strobe arms as a second redundant depth gauge.

 

[Nick_Radov]

I don't think anyone was suggesting using a written plan instead of a computer by choice. I think that the question was - is it worthwhile to write down your ascent plan in case your electronics fail. Now there are a lot of issues there, such as the fact that many tech divers have two decompression computers, and of course the issue of actually running stops with a total failure of your time/depth measuring devices. But unless you are running a known, square profile, I think that most people agree that the accuracy and decompression advantage of a DC are worthwhile..

I think a lot of divers are still confusing precision with accuracy. A dive computer, will output highly precise numbers, but is it truly more accurate than some other approach? There is no infallible source of truth to compare against so that is unknown, and unknowable.

And what does "accuracy" even mean in this context? This same discussion has been repeated over and over on various forums for decades and it is usually unproductive because the participants haven't clearly defined their terms and are focusing on different unstated priorities. Does accuracy mean a close match for the amount of inert gas in the diver's body? Or reducing the risk of DCS below some quantitative threshold? Or same for risk of acute oxygen toxicity? Or minimizing total deco time? Or keeping post-dive Doppler scores below some threshold? Or something else? If we can't agree on a clear definition of accuracy then discussions just go in circles and everyone gets angry without learning anything useful.

The important difference between precision and accuracy

Thought the two meant the same thing? Think again.

www.zmescience.com

To be clear, I have nothing against dive computers as a tool and use one myself. But I don't completely rely on it, or necessarily follow it's recommended deco profile. It's more like an additional electronic buddy who will hopefully tell me if I screw up the deco profile really badly.