Tec Dive computers and dive plans

[J-Vo]

If "wet notes work" then surely a display page on your dive computer with "the plan" showinng helps too doesn't it? It can show exactly what your wet notes show

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.

 

[napDiver]

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!


If "wet notes work" then surely a display page on your dive computer with "the plan" showinng helps too doesn't it? It can show exactly what your wet notes show

O ok.

If you are using a "notes" function in your computer. The slate/wetnotes is for when your computer fails. You can argue, if you have two independent diving computers with a "notes" function do you really need a backup location for your dive plans. However, until its been used, abused, and failed many times over... most people won't be comfortable using the computer's "notes" as the ONLY location where they can get their dive plan. It's the same reason why I wouldn't trust an electronic slate to be the only location of my plan. When hit shits the fan, I want to know I have a way to deal with 100% certainty.

Now would it be my primary location for looking at my plan? 100% it definitely would.

 

[Wibble]

Plan your dive for the gas types quantities you need for the depth and amount of decompression time required for your breathing rate. Factor in a failure of one gas, redundancy, oxygen times and narcosis (amount of helium required).

This will yield your gas volumes required to dive, your minimum gas (to get to the second gas switch), your max Time To Surface (decompression time), maximum operating depth (for the oxygen content) and dive time (for the boat skipper).

Go diving.

Don’t exceed the MOD (max operating depth). Just before you hit minimum gas, maximum TTS, or max runtime (sum of dive time + TTS), thumb the dive and ascend to your first decompression stop and follow your computer (you do have a backup), switching to your decompression gasses as required.

CCR is slightly different but is working against your max TTS for your bailout (as per comment 6-ish)

Yes, there’s a lot to it which is why you need to study and progress deeper and longer, which is why it's called technical diving. Don’t underestimate the skills required to hang around at 6m/20' for ages -- zen-like meditative abilities combined with buoyancy control.

 

[rjack321]

@MaxTorque
Following two PDCs in my opinion is safer than trying to force myself into perfectly following the plan or try to "catch up" to it. Once you deviate in the slightest your plan is essentially invalidated and it is impossible to perfectly follow your pan.

I might add that the plan almost never matches precisely before you even get to the bottom. I don't know anybody descending smoothly and evenly at 60ft/min from the surface to e.g. 200ft

 

[boulderjohn]

I might add that the plan almost never matches precisely before you even get to the bottom. I don't know anybody descending smoothly and evenly at 60ft/min from the surface to e.g. 200ft

The number of vagaries in a dive are significant, and the written table approach is going to miss them all. Descent is a good example. I knew someone, a tech instructor, who was 100% opposed to computers, as was the agency for which he taught. He loved to descend rapidly, and he frequently had to wait at depth for the more normal descenders to get down to him. His normal descent rate was about 100 FPM.

So let's compare two divers doing the same preplanned dive with the same written profile. Diver A descends at 100 FPM, and Diver B descends at 50 FPM. They do a 300 foot dive. Diver A reaches the bottom in 3 minutes. Diver B reaches the bottom in 6 minutes. During the first 3 minutes of their "bottom time," diver A has an average depth of 150 feet. Diver B has an average depth of 75 feet. After 6 minutes of diving, diver A has an average depth of 225 feet. Diver B has had an average depth of 150 feet. They then do 12 more minutes for a total bottom time of 18 minutes. Diver A has an average depth of 275 feet. Diver B has an average depth of 250 feet. They then ascend, using the same written profile.

 

[KenGordon]

I might add that the plan almost never matches precisely before you even get to the bottom. I don't know anybody descending smoothly and evenly at 60ft/min from the surface to e.g. 200ft

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.

 

[MaxTorque]

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! ;-)

 

[Wibble]

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.

A computer, unlike your plan on a slate, adjusts the deco time according to your actual depth timings and selected gasses. A slow ascent simply increases TTS; if you’re happy with that, no probems.

 

[Wibble]

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! ;-)

A plan is simply a guide. Your computer monitors your dive progress which you follow. The two aren’t linked except for your overall dive parameters.

Example, diving on the Couvier. Depth 32m/105' to 48m/150'; what’s your plan? Unless you’ve dived it, you won’t know that the bow is down a slope and that the ship's holds are circa 38m/120'. Dive times are fixed 70 mins due to the tides and it is a must return to shot line as it’s in the middle of the busy shipping lanes (Dover, UK).

A realistic plan is to simply gas up for 48m/150' MOD, then keep monitoring your dive time and TTS until it gets to 65 mins. It's a classic rebreather dive as you can have your helium and breathe it too.

A written plan is more or less useless unless you’re exceedingly strict with depth constraints or happy with a wildly conservative plan.

 

[DiveClimbRide]

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! ;-)

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.