Deco behaviour

On my dive last Friday I went into deco, just. I hadn't planned it as a deco dive but I just ran out of NDL while doing what I needed to get done. I had two tanks (main and pony) and plenty of gas so it was a acceptable risk. The behaviour of the descent was "interesting".

I hit deco at the exact same time with both my Perdix and my Descent which shows they do track the NDL pretty closely. The Perdix displayed clear instructions with a 3 - 1 telling me I had to do 1 minute at 3 metres. My Oceanic Atom displays the required deco stop in the same way. The Descent was not so clear. In fact, the only thing that appeared to change was instead of saying NDL it said TTS (which I guess means Time To Stop) and 1:30 below it.

As it was, I cleared the deco before I even got to 5 metres. It cleared on both the Perdix and Descent at around the same time and I got a nice message with vibration on the Descent telling me I'd cleared deco. Once I got to 5 metres, my Perdix had me do a 5 minute safety stop. The Perdix by default requires a 3 minute safety stop but extends this to 5 minutes if you go close to the NDL (and in this case just into deco but clearing it). The Descent on the other hand had no safety stop at all which I think is wrong. i.e. I could surface immediately. Note that my Atom 3.0 has the same behaviour.

It doesn't seem right that I could go very close to my NDL but still require a safety stop but if I go over it - i.e. accumulate more nitrogen - I don't require one.

The other thing that is odd is that on most dives I get a message on the Descent: "Approaching NDL". When I get the message I look at the NDL and it is around 30 minutes. I don't get the message the first time it gets to 30 minutes but it seems some time farther into the dive. I only get the message once and I don't believe I got the message before I went into deco.

0 Garmin-Heath over 6 years ago

To clarify, TTS is "Time to Surface." TTS shows the minimum amount of time it would take to ascend to the surface assuming a safe ascent rate and making all prescribed stops. TTS replaces NDL on the Descent Mk1 when you go into Deco. Also, the Deco stop ceiling depth with show at the top right of the screen, and Deco stop time remaining will appear in the bottom right.

When you're in decompression and do a required Deco stop, it counts as a safety stop too. This is the why the Descent won't ask you to do another safety stop unless you go below 35 feet again.

We are evaluating enhanced safety stop logic in an upcoming update to provide greater flexibility to the diver on safety stop behavior, including the ability to add and disable safety stops during deco dives.

0 atj777 over 6 years ago

To clarify, TTS is "Time to Surface." TTS shows the minimum amount of time it would take to ascend to the surface assuming a safe ascent rate and making all prescribed stops. TTS replaces NDL on the Descent Mk1 when you go into Deco. Also, the Deco stop ceiling depth with show at the top right of the screen, and Deco stop time remaining will appear in the bottom right.

Why isn't this in the manual? The only mention of TTS is in a brief note on Multi-Gas dive mode.

Why does TTS get more prominence than the deco stop time and depth? My other dive computers put deco stop time and depth right in the middle.

I was at 12 metres and the Descent was telling me I could safely ascend in 1 minute and 30 seconds after exceeding the NDL. So basically, it is saying that I could ascend directly at 8m/min with no stop. That does not seem safe at all.

When you're in decompression and do a required Deco stop, it counts as a safety stop too. This is the why the Descent won't ask you to do another safety stop unless you go below 35 feet again.

But in my case as I had cleared deco before reaching 5 metres so no deco stop was required. It should have reverted to a safety stop.

If I had ascended a few metres a minute earlier I would not have gone into deco and the Descent would have had me do a 3 minute safety stop. But I didn't, and had a higher accumulation of nitrogen in my tissues so the Descent tells me I don't need a stop.

We are evaluating enhanced safety stop logic in an upcoming update to provide greater flexibility to the diver on safety stop behavior, including the ability to add and disable safety stops during deco dives.

This is certainly required. I would hate to be using the Descent as my only dive computer on occasions where I drift into deco.

0 bleiro over 1 year ago in reply to Garmin-Heath

Dear,

so why TTS isn’t mentioned in user manual?