Are dive computers making bad divers?

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mac64

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Modern computers are very reliable. As with everything, there are sometimes teething problems. Scubadada probably has the most detailed records. In his case, the computer is over 99% reliable. But, as I recall from previous posts, the majority of those failures were due to user error, or dead/bad batteries.

I don’t have nearly that many dives, but haven’t had a single in-water computer failure. I have had two failures out of the water. One was a computer that just died. Dead battery, and didn’t wake up after the battery change. One was a bad transmitter. I bought it used, and it just didn’t fire up.

Electronics tend to fail on startup, so if it fires up and works, there is a very good chance that it will continue to work during the dive.
Thank you, the computer I got has a CR2NP user replaceable battery with a battery low warning. I'll keep an eye on it.
 

Ucarkus

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Which was the point of @boulderjohn's post #366. If that was calculated with a square profile, it is very much a technical dive requiring ANDP skills.

The reality was it's not a square profile and a computer was used to inform the diver of the deco limits, i.e. to keep within NDLs.
Honestly, how hard is to plan a multilevel dive with max ndl to 100ft and a second level to 40 or 50ft ndl. This will give easily 80+ mins bottom time. You only need to know few values by heart in order to conduct safe diving.
Do the same for your repetitive dive, pick your most common SI and stick with it. If I sum up how I do my rec diving, it is so simple to find patterns that few profiles that I know by heart will cover very high percent of my diving.
I drive a lot with navigation sw, even the places I know well, I use it. It is convenient being told what to do and not think about it. I traveled to another country and downloaded offline maps for using in the rental car. Surprise, download was not complete and I was stuck without internet and with only address of my destination at a parking garage. If I checked and noted the very few basics information of my destination, I could at least follow the road signs and get to my destination. I congratulated my self not being able to navigate and plan ahead and promised my self that I will never ever travel without backup navi.
 

mac64

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It’s not the planning, it’s the reality you find when you’ve descended to the dive site. You plan for a scenario but then discover the site is nothing like that.

Computers give you huge flexibility compared with tables. If you’re diving a rebreather then this basically removes gas limits (given the right diluent and bailout). Your dive plan then becomes the max dive time, using your computer’s TTS as the guide.

Thus if you’ve been lurking 10m/33ft deeper it doesn’t matter.
I'm afraid trusting a computer to come up with a change of plan 33 feet deeper than my original is a bit away for me. I always plan for the deepest I might go and bring 3 run times. With my dives I'd have to dig a hole to get deeper than the plan. Unless I actually left the wreck I'd be shallower than the plan so I'm looking forward to tomorrow's dive on the Cunard Liner Folia, with the computer plotting actual depth. Thanks Wibble.
 

Wibble

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Honestly, how hard is to plan a multilevel dive with max ndl to 100ft and a second level to 40 or 50ft ndl. This will give easily 80+ mins bottom time. You only need to know few values by heart in order to conduct safe diving.
Do the same for your repetitive dive, pick your most common SI and stick with it. If I sum up how I do my rec diving, it is so simple to find patterns that few profiles that I know by heart will cover very high percent of my diving.
I drive a lot with navigation sw, even the places I know well, I use it. It is convenient being told what to do and not think about it. I traveled to another country and downloaded offline maps for using in the rental car. Surprise, download was not complete and I was stuck without internet and with only address of my destination at a parking garage. If I checked and noted the very few basics information of my destination, I could at least follow the road signs and get to my destination. I congratulated my self not being able to navigate and plan ahead and promised my self that I will never ever travel without backup navi.
But…how many times has your sat nav taken you via some convoluted route because of some quirk of the algorithm. The lesson being that the driver’s skills need to monitor the satnav
 

Ucarkus

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But…how many times has your sat nav taken you via some convoluted route because of some quirk of the algorithm. The lesson being that the driver’s skills need to monitor the satnav
Which implies you already know the better route and have planned with a reference in advance. Otherwise, you would not be able to decide whether route you were provided was convoluted or not.
 

Wibble

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I'm afraid trusting a computer to come up with a change of plan 33 feet deeper than my original is a bit away for me. I always plan for the deepest I might go and bring 3 run times. With my dives I'd have to dig a hole to get deeper than the plan. Unless I actually left the wreck I'd be shallower than the plan so I'm looking forward to tomorrow's dive on the Cunard Liner Folia, with the computer plotting actual depth. Thanks Wibble.
We come from different generations of divers. My mere 10 year diving career has very much been on the shoulders of giants where the techniques, training, equipment, algorithms and computers are well sorted before I started.

I’m well capable of doing a table planning exercise. For NDL dives the tables are very simple, not so with decompression diving.

For planning I use software such as MultiDeco. This makes decompression dive planning very easy.

I was taught to write a dive profile on a slate. Actually it was write 4 profiles: target, +3m/10ft, +5mins, +both. That is incredibly tedious and time consuming.

One very quickly learns to trust GOOD computers (e.g. Shearwater) as they reliably perform the real-time decompression calculations. Once relying on the computer you now need two for resilience.

Once that line has been crossed, planning becomes much simpler. It’s effectively calculating the maximum times and gasses required for a specific depth — the absolute maximum depth for that dive. You jump in knowing those maxima and run the dive off the computer.

This simplifies the entire dive giving you the freedom to enjoy it with a minimum of fuss.

I’ve a trip to Malin shortly (a world class dive site on the north-west of Ireland). Planning will be for max depth of 75m/250ft and max runtime of 3 hours on a rebreather. All dives pretty much regardless of depth will use that same plan but will be executed using the computer (effectively referring to the TTS). Little extra thought required.
 

mac64

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We come from different generations of divers. My 10 year diving career has very much been on the shoulders of giants where the techniques, training, equipment, algorithms and computers are well sorted.

I’m well capable of doing a table planning exercise. For NDL dives the tables are very simple, not so with decompression diving.

For planning I use software such as MultiDeco. This makes decompression dive planning very easy.

I was taught to write a dive profile on a slate. Actually it was write 4 profiles: target, +3m, +5mins, +both. That is incredibly tedious and time consuming.

One very quickly learns to trust GOOD computers (e.g. Shearwater) as they reliably perform the real-time decompression calculations. Once relying on the computer you now need two for resilience.

Once that line has been crossed, planning becomes much simpler. It’s effectively calculating the maximum times and gasses required for a specific depth — the absolute maximum depth for that dive. You jump in knowing those maxima and run the dive off the computer.

This simplifies the entire dive giving you the freedom to enjoy it with a minimum of fuss.

I’ve a trip to Malin (a world class dive site on the north-west Ireland) shortly. Planning will be for max depth of 75m/250ft and max runtime of 3 hours. All dives pretty much regardless of depth will use that plan but will be executed using the computer (effectively referring to the TTS). Little extra thought required.
Azores high starting to build off the west coast giving settled weather. Happy diving. So TTS is constantly updating on a computer and when it hits 3 hours ye will start the assent. How does that work with different divers and computers.
 

Wibble

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Azores high starting to build off the west coast giving settled weather. Happy diving. So TTS is constantly updating on a computer and when it hits 3 hours ye will start the assent. How does that work with different divers and computers.
TTS is the Time To Surface from 'now' assuming you will use the gases you’ve entered — and enabled — in the computer. The TTS number will increase as your decompression loading increases. You add that to the dive time to get the overall dive time.

Some (approximate & simplified) examples…. After 15mins on the bottom at:
  • 30m/100ft the TTS would be the travel time to the surface as there’s no decompression obligation— within NDL
  • 45m/150ft the TTS would be 15 mins (plus a few mins for the travel time)
  • 60m/200ft the TTS would be around 30 mins (plus…)
  • 75m/250ft the TTS would be around 45 mins (plus…)
The great thing about TTS is for a multi level dive, the TTS updates as your decompression obligation changes. Head up to the reef at 20m/70ft from the caverns at 75m/250ft at 15 mins and you'd be decompressing whilst diving, so the TTS would decrease, head back down and it starts increasing again. The Delta5mins time will show if youre on gassing or off gassin.
 

boulderjohn

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It’s not the planning, it’s the reality you find when you’ve descended to the dive site. You plan for a scenario but then discover the site is nothing like that.

I'm afraid trusting a computer to come up with a change of plan 33 feet deeper than my original is a bit away for me. I always plan for the deepest I might go and bring 3 run times.
This reminds me of a dive I did nearly a dozen years ago, in my pre-computer tech diving days.

We planned to dive to a wreck we had never visited before, with a max depth of 260 feet. We chose an appropriate bottom mix, 21/25 for travel and early deco, 50%, and O2 for our gases. As usual, we made 3 dive plans with 3 run times.

The wreck was actually 2 wrecks, one on top of the other, and when we got there, we saw little point in going to the maximum depth and looking at a hull. As a consequence, our actual depth was considerably shallower than what we had planned, and there was plenty to look at there. Unfortunately, though, we had to follow our plan, and we began the ascent accordingly.

If we were doing that dive today, we would still make a plan for the maximum dive so that we would be sure to have plenty of gas, but when we did the actual dive, we would be able to use our actual depth to plan the ascent. We could watch the TTS, knowing from our previous planning when we needed to start the ascent. It would give us considerably more bottom time to enjoy the dive.
 
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