Computer says ...10' Deco Stop 3 minutes?

[plclark196]

I recently completed a dive with max depth about 105' with most of the dive ranging between 85' and 100'. I was diving with 2 computers - a Tusa IQ-800 and an older Oceanic Data Plus. The Tusa put me in Deco while I was still in a comfortable range on the Oceanic. Both computers on SF-0. My instructions on the Tusa were to do a 3 minute Deco Stop at 10'...that depth seemed strange to me as that is shallower than even a normal Safety Stop. On my ascent I decided to do a Deep Stop for a minute at 50'. While doing this Deep Stop my Tusa started adding time to my 10' Deco Stop ..and in fact actually got up to a 5 minute Deco stop at 10'. After my minute expired at 50' I decided to do a slow ascent to about 20 - 15' and see what adjustments my computer might make. Once in that range my computer was still telling me to make a 4/5 minute Deco Stop at 10'.... so I ascended to 10 ' and hung out and sure enough I was able to wait out the 4 minutes (a big rock ledge aided in this) and then my computer gave me a 3 minute Safety Stop.
This is only my 10th dive with this Tusa IQ-800. The manual sheds no light on this. Does this seem normal to anyone out there? Anyone with any light on this? Thanks!

 

[redacted]

That's why I retired my Scubapro and TUSA computers and only use Oceanic now. They just tend to be more (sometimes much more) conservative.

It is pretty easy to make a liberal computer more conservative. Not at all easy to make a conservative computer more liberal.

 

[don Francisco]

The 10'/3min deco stop was based on the normaly optional safety stop being mandatory on dives over 100'.

The 10' depth is the ceiling, though you can do it anywhere between 10' and 20' or split the difference at 15 feet as you usually do. You might also add a deep stop at 50' for 1 minute, but many computors aren't programmed for it, and will consider this an extension of the dive, possibly adding to the required deco time as yours did, or if not, still require the full 3 minutes at 15'.

 

[Jim Lapenta]

Oceanic computers are known for using a more liberal algorithm. My veo is pretty close to the tables v-planner gives me when set to be less conservative. There is nothing wrong with being conservative but I prefer to set the level of conservatism. Any time I question if my comp will be ok I cut tables as a backup. As for the 10 feet this is a normal decompression stop depth. I have never seen a 15 foot deco stop. And remember a safety stop is different than a deco stop as it is recommended as opposed to being mandatory. When it is mandatory it is no longer a safety stop.

 

[RJP]

Does the TUSA have an algorithm that gives you credit for Deep Stops? (I'm guessing not)

 

[MaxBottomtime]

First of all, you're in Cave Country. You shouldn't be using a computer.
Some computers can be programmed to remove the safety stop requirement. If you have the computer interface, check the settings. Some don't begin to credit you until around 13-14 feet. I had an Oceanic that would stop crediting my required deco if I was at 16 feet. Most older computers were programmed for 10 foot stops. PADI began suggestion 15 feet instead because they felt divers couldn't maintain a 10 foot stop.

 

[Mr Carcharodon]

Dive computers give wildly different answers, and in general the manufactures will not tell you what they are doing or why. You are already smarter than your computer is by stopping at 50 fsw and doing a slow ascent from there. Putting undue faith in an electronic box on your wrist that is spitting out numbers that come from who knows what algorithm is just irrational. If you want to spend an extra 5 minutes between 10 and 20 fsw that will do no harm and is probably a good idea if you are pushing NDL limits at all, or are cold or physically stressed.

 

[TSandM]

Most of the recreational dive computers, if you put them into deco, use pretty much a pure Buhlmann approach to deco -- drive the gradient by getting as shallow as possible, and then sit there until you clear the obligation. Many people now approach decompression rather differently, including deep stops for bubble control. Buhlmann computers don't recognize deep stops as beneficial, but in fact penalize you for doing them, on the theory that you are still ongassing some compartments.

I highly recommend buying and reading Mark Powell's Deco for Divers, which is a very readable explanation of decompression theory, and sheds a great deal of light on why certain computers produce the results that they do.

 

[RonFrank]

It is unfortunate that your manual does not show the tables that the computer is based on. My Aeris Epic does. I also get credit for multi-profile dives where I may have a bit of a deco obligation, but after a very slow ascent that obligation is gone.

It helps to have the tables that the computer uses, and the rules as well. A 105' dive is within rec limits, so I'm not sure why you incurred a deco obligation unless you were down there past your NDL.

You may try contacting TUSA to see if you could get more info on what models their computer are based from. It is a shame that it's not available in your manual...

 

[vshearer]

.

I highly recommend buying and reading Mark Powell's Deco for Divers, which is a very readable explanation of decompression theory, and sheds a great deal of light on why certain computers produce the results that they do.

What she said

Get ready for a wait on Powell's book, I just got mine after a 5 week wait off of Amazon. It is worth it though.

There are also a multitude of sites that can lend understanding on the web, just don't confuse understanding with experience.

Something I learned a long, long time ago in a galaxy far, far away.