Tec Dive computers and dive plans

[Wibble]

What? No. That makes no sense. You want to look at your computer the whole dive to see if you're at depth? Do yourself a favor and do some tech dives with both plans and computers and both before you waste time on an application that you'll bin as soon as you get some experience.

Absolutely this.

For the OP, if you buy MultiDeco (Mac, iPad, iPhone), you need to 'play' with it to work through the patterns you'll see. If you're going to dive with decompression, then MultiDeco's a great place to start.

You need to know those basic properties of the dive: max depth, max TTS, full dive time and minimum gas (if OC). There's a lot to dive planning and reading about it will help greatly. Required reading is Deco for Divers by Mark Powell.

Get your basic skills sorted (buoyancy, trim, finning) -- you could even attend a GUE Fundies course.

Once that's done, get plenty of dives in then start looking at ANDP (Advanced Nitrox and Decompression Procedures)

 

[Wibble]

The less I have to faf with a PDC the better. Flipping up my wrist slate to reference the plan is way faster and easier.

What plan?

Max operating depth, Min gas, max TTS, total runtime. That's it. If you can't remember those four numbers, do question why you're diving. The computer does the constant calculation of the TTS. Backup computer does it too.

This isn't the 1990's or naughties. We have Shearwaters now.

 

[J-Vo]

operating depth, Min gas, max TTS, total runtime.

That is typically it with maybe some mission specific details as well. Writing things down commits them to memory. Why not write them where you have them on the dive?

There is a reason I use two Shearwaters rather than ratio deco and it's more to do with my cognitive falibilty then the profile.

 

[boulderjohn]

I find people are slow on ascents and don’t get near the planned ascent rate. A computer is not the solution to that but it busts written plans.

I was discussing this a few years ago with an instructor who talked about a situation (diving a rebreather) where she carefully followed the called for 30 FPM ascent rate, and in doing so she passed every other diver on the ascent line in getting to the first stop. On the boat, they got on her for her "fast ascent."

Back in the era of written plans, two friends of mine got bent after a mild deco dive. They insisted they had followed their written plans perfectly. One of them had used a computer in gauge mode, and he checked the profile in the log. They identified 3 ways they had not followed the plan perfectly, and one of them was a ridiculously slow ascent to the first stop.

On another deco dive, my buddy and I were the next to last to arrive at the ascent line from the wreck, with the last team only a few seconds behind us. We knew from the prior boat discussion that we were diving exactly the same plan with the same computers. When we reached our first stop, I looked down the line into the gloom, but they were not in sight. Because they were using rebreathers, I saw no bubbles, and I was worried. It was not until the 30 foot stop that I could see them coming into view. Back on the boat, the DM was worried. He knew their planned run time, and they were far beyond that. What had gone wrong? When they got back on the boat, they said they could not understand it. Their TTS leaving the wreck was exactly as planned, but the computer kept adding time for some reason. I mentioned that they had ascended very slowly, and they looked at me like I was a noob. "You're supposed to ascend slowly!"

 

[AJ]

Surely "not very consistent rates" are exactly where a computer with a plan can help! The plan tells the computer where you should be at this point in the dive, the computer knows exactly where you actually are, and therefore the delta is easy to both calculate and show. And all it needs to be is a "plan delta depth" single fingure, ie +3 or -1. there is no penalty (directly) for failing to keep that value at 0, because your deco is still being calc'd in real time by the computer.

This sounds useful to me, but i fully understand some may think it is additional and unnecessary and i reserve the right to change my mind and think that too at any point! ;-)

Maybe you should ask yourself: why? What's the benefit? There are very few things important being down there imho. Trying to follow an exact plan on your computer the whole time is at best distracting, at worst dangerous. Concentrate on your dive/team/surrounding, not your computer. Have the numbers memorized or written down, follow the plan and be prepared for unplanned circumstances (for instance deco on the fly when your plan goes haywire).

As a beginning diver I concentrated way to much on my computer. Now it's just a tool that tells me depth and time. The rest of the information (TTS, NDL, deco, clear time, etc.) maybe useful, but certainly not all the time. I get a distinct feeling you're making your computer dive plan almost the reason for the dive instead of using it as a tool. But I may be wrong?

 

[MaxTorque]

For the sake of clarity, i am in no way suggesting that having a dive computer that can vector you in to your preplanned profile means you have to either

1) look at it
2) follow it


All it does is give you a frame of reference. Like having a speedometer in your car, most people simply drive at a speed that "feels about right", very few drive along looking at their speed continuously, but sometimes, it's rather useful to have a known reference instrument where hitting a target becomes more important.

I'm already using multideco for a reference. My deco PC software is calibrated and compared against this, as it's a proven reference, and my embedded deco code (running on an std 32bit ARM development board) is validated by using a software in the loop type approach against the PC software referenced against multideco

 

[rhwestfall]

....but you aren't getting the fact that "situational awareness" should have you knowing where you are in regard to the plan (be it memorized or on a slate/page), and "close enough" is what is validated by a glance at your measuring devices.

 

[boulderjohn]

This sentence is driving me nuts boulderjohn

I keep waiting for a follow up explaining why.

 

[dmaziuk]

OTOH if you wanted your plan to be in the computer, then you wouldn't want to enter it using a couple of buttons and a 2" screen. Uploading from the desktop application would be the way to do it.

 

[boulderjohn]

That's exactly my plan, to do Tec diving. But in the meantime, asking the question on here gets some very interesting opinions up front to help me on my way!

OK, so now that your thread has generated 60 posts, mostly from experienced technical divers, can you summarize what you have learned from the interesting opinions up front that are helping you on your way? How has your viewpoint on your intended computer change been modified as a result of this extended converstion?