Dive planning and "terrain" diving

[TSandM]

I'm a fairly anal and compulsive person, and I absolutely buy the arguments that blindly diving a computer algorithm is not the most responsible way to dive. And I should be able to come up with a satisfactory answer to the question I am about to pose, but I haven't.

I think everybody would pretty much agree that standard dive tables were designed for square profile dives -- go down to the wreck, poke around, come back up. Given that there are various tables created using various algorithms, they are still the best tool we have for planning such dives.

The PADI wheel is an attempt to create a tool that will give divers a little more realistic planning for multi-level dives. This works if you are, for example, diving ledges, and go down to the 70 foot ledge and then back up to the 40 foot one.

But almost all of my diving is what I call "terrain" diving -- we go down, swim further down, swim back up along the bottom and often all the way to shore. There are no definable "levels" per se. Using max depth in most of these cases would be absurd -- yesterday's first dive, with a max depth of 78 feet (where we didn't stay long) would have gone LONG into deco if I just used the RDP tables with total time at depth, but my computer was never even remotely annoyed with me. I could use the average depth as a second level, but I often don't know what it is until I am out of the water, at which time I don't think the word "planning" is applicable any more . . .

Yesterday's dives were all new sites to me, so unlike places I go frequently, I did not know the terrain profile or exactly what we were going to be able (or want to) do.

Does anybody have any advice on how to be more proactively responsible with planning of such dives?

 

[Tod]

So why is the computer so bad in this case? I understand the logic about not becoming dependent upon something that could fail (dead battery) during the dive. But if you cannot establish a perfect dive profile (due to venturing into an unknown area), then you are stuck with either limiting the area of exploration (to avoid a sawtoothed profile) or being realistic (within your outside limits) and sticking with your basic training and keeping within your basic profile (while using the computer to keep track of your nitrogen loading (or PPO if going deeper).

How "far into deco" do you think you really would have been if you were solely diving tables based upon your maximum depth? To me, this is where the computer can be helpful - as long as you don't push it each dive.

Basically, if you dive tables then you should stick with them and be cautious about profiles that cause you to get into the "gray area." If you dive computers, you should still be realistic and keep within a sensable profile range, but have a plan in place should the computer fail on you. (And be prepared to reconsider any repetitive diving carefully if you do dive a computer and it goes south on you.)

Not sure I answered your question, but I think if you are going to stress over the use of the computer, you should be prepared to restrict your diving profiles (especially in unknown areas).

 

[in_cavediver]

I'm a fairly anal and compulsive person, and I absolutely buy the arguments that blindly diving a computer algorithm is not the most responsible way to dive. And I should be able to come up with a satisfactory answer to the question I am about to pose, but I haven't.

I think everybody would pretty much agree that standard dive tables were designed for square profile dives -- go down to the wreck, poke around, come back up. Given that there are various tables created using various algorithms, they are still the best tool we have for planning such dives.

The PADI wheel is an attempt to create a tool that will give divers a little more realistic planning for multi-level dives. This works if you are, for example, diving ledges, and go down to the 70 foot ledge and then back up to the 40 foot one.

But almost all of my diving is what I call "terrain" diving -- we go down, swim further down, swim back up along the bottom and often all the way to shore. There are no definable "levels" per se. Using max depth in most of these cases would be absurd -- yesterday's first dive, with a max depth of 78 feet (where we didn't stay long) would have gone LONG into deco if I just used the RDP tables with total time at depth, but my computer was never even remotely annoyed with me. I could use the average depth as a second level, but I often don't know what it is until I am out of the water, at which time I don't think the word "planning" is applicable any more . . .

Yesterday's dives were all new sites to me, so unlike places I go frequently, I did not know the terrain profile or exactly what we were going to be able (or want to) do.

Does anybody have any advice on how to be more proactively responsible with planning of such dives?

I have heard of individuals planning many levels to model that. I have also heard of individuals using this rule: 1/2 time or less spent from max depth/2 to max depth. At least 1/2 of the dive time spent above the max depth/2.

Personally, I just would use a computer and be done with it. If it fails on the dive, spend lots more time in the 15-25 foor range and enjoy the dive and call it the last dive of the day. Or (not generally recommended), take the repetive dives all shallow with long SI's (IE less than 40' deep and a couple hours between dives)

Just my take

Mike

 

[TSandM]

As a result of another thread that just came up, I ran into a couple of threads addressing depth averaging which really go in quite a bit of detail into the pros and cons of some strategies for doing what I want to do. Another example of the wealth of information and opinions available on SB!

 

[Doc Intrepid]

T,

FWIW, IMHO it comes down to dive planning - there is nothing wrong with using your computer on dives such as those you describe. Computers shine at precisely this sort of multi-level dive analysis, in terms of tracking real-time nitrogen loading (e.g. "predicted" loading, in accordance with whatever algorithm is programmed into the computer).

With an unknown site, there is going to be a paucity of data to use for planning purposes anyway. But you can estimate your profile based on your past experience, personal data (SAC), and rules of thumb such as the 120 rule, as well as tools such as tide tables.

The point is that you don't simply allow the computer to dictate the dive. Your plan incorporates data you DO have access to, such as your gas supply, your RMV, your buddy's gas supply, your buddy's RMV, max depth, Rock Bottom based on that max depth, projected time outbound based on estimated current, projected time back toward your point of entry, etc. etc. You can state something like "we're going down to X depth, turning left, compass heading Y degrees, proceeding in a loop down not deeper than Z depth. We will turn at either 30 minutes or at 2000 psi, whichever comes first..., depending on how much time/gas we have remaining at 20' we'll do three drills, A, B, C. Afterwards, we'll shoot a bag then surface" (etc. etc.)

In other words, you can formulate a plan based on the data you DO have access to, and insert limits on the variables you don't know about. Then allow the computers to go do that voodoo that they do so well!

Just don't let the computer dictate the plan. It complements the plan, rather than being the ONLY plan... IMHO...

Other diver's mileage will most certainly vary.....

Regards,

Doc

 

[gcbryan]

I'm a fairly anal and compulsive person, and I absolutely buy the arguments that blindly diving a computer algorithm is not the most responsible way to dive. And I should be able to come up with a satisfactory answer to the question I am about to pose, but I haven't.

I think everybody would pretty much agree that standard dive tables were designed for square profile dives -- go down to the wreck, poke around, come back up. Given that there are various tables created using various algorithms, they are still the best tool we have for planning such dives.

The PADI wheel is an attempt to create a tool that will give divers a little more realistic planning for multi-level dives. This works if you are, for example, diving ledges, and go down to the 70 foot ledge and then back up to the 40 foot one.

But almost all of my diving is what I call "terrain" diving -- we go down, swim further down, swim back up along the bottom and often all the way to shore. There are no definable "levels" per se. Using max depth in most of these cases would be absurd -- yesterday's first dive, with a max depth of 78 feet (where we didn't stay long) would have gone LONG into deco if I just used the RDP tables with total time at depth, but my computer was never even remotely annoyed with me. I could use the average depth as a second level, but I often don't know what it is until I am out of the water, at which time I don't think the word "planning" is applicable any more . . .

Yesterday's dives were all new sites to me, so unlike places I go frequently, I did not know the terrain profile or exactly what we were going to be able (or want to) do.

Does anybody have any advice on how to be more proactively responsible with planning of such dives?

It's more important that you control the profile...go deep first...spend more time shallow, slow ascent, deep stop, etc. It's also important to learn a little about deco (whether you use it or not), try playing around with Vplanner trying out various profiles. The point is to not rely on your computer. I don't see a problem with using it.

Gray

 

[SStrecker]

I agree with the advice provided by Todd and Doc. All of my non-vacation diving is in fresh water lakes and flooded quarries (where depths are moderate and visibility is relatively low). So I definitely hug the terrain for a relatively close examination of the bottom environment. While definitely not sawtooth, it does produce a meandering dive profile, that begins and ends from the shore. A dive computer is critical to making this strategy work effectively. Nevertheless, I do some advance planning, with fresh water charts (when available), to at least identify the prospective average and maximum depths to be encountered for the dive. I use both the tables and a computer to make the best of the situation. Good judgement bridges the gap.

 

[TSandM]

I've read several places people recommending learning a little bit about deco -- can anybody recommend reading material that would be useful? I have the Essentials of Deeper Sport Diving, but it talks at length about the derivation of the tables, but not about decompression theory.

 

[boomx5]

As usual, Doc has some great advise here. As you become more aware of your dives and are able to profile and track them in your head, then you can start to break away from the confines of a dive computer. However, at this stage of your diving, a computer will be a good learning tool to help you build that experience to see what is actually happening during the dive. Depending on where you would like to go with your diving, you can learn to plan and execute multilevel dives in your head and on the fly, but it will take some additional training.

 

[Don Burke]

You can rough out an approximation by using the fractions of the no stop limits used, but that is pretty shaky. I use that method to check if a computer is out to lunch when I am out diving. It certainly is not very precise.

For planning, a program like DecoPlanner or Vplanner can let you plot out several profiles. Since you have little idea of where the dive is going to take you, it could take some time to run through enough possibilities.