Dive computer differences

[kneptoon]

I recently dove using my Suunto Spyder with a dive master using a Uwetec based computer. We did 2 multi-level dives. The first dive was to 90' for 44 minutes. We had a 47 minute surface interval. The second dive, also multi-level was 62' for 55 minutes. I know that the logarithms for the Suunto are the most conservative, however on the second dive I needed 8 minutes of decompression to his nil. I realize it is impossible to know the exact profile we each did. But I dove a shallower profile than his throughout the second dive. Are the differences in the programmed logarithms that great or was he just in a hurry to get back to lunch? In my 8 minute wait I did discover that Sargasso weed has thousands of juvenile trigger fish hanging about underneath.

 

[AlexMDiver]

Yes, I believe the difference between Uwatec and Suunto can be quite large. It also depends I think on how tec versus rec each computer is.
Some new types do deep stops that give you more credit later on. I am still often amazed at the differences in decompression software between computers and this shows how fuzzy this science still is (or it proves that there are very good and very bad computers out there. Which is which is sometimes difficult to assess).
When I deco dive and I see that in my group (with everyone on very similar profiles) some divers are either way above me or below me it makes me wonder what is right. Good thing is to always plan and check with tables where you are at. Don't just rely on the computer. More difficult with multi-level, but still useful.
Of course a different profile between two divers can then make large differences in your decompression times. Just one or two minutes extra at depth and you have much larger differences in deco stops.
Was it 8 minutes of deco or 5 plus an automatic safety stop included?

I have a VR3 and am very happy with it. It is expensive, but very felxible and the algorithm is modern. My Suunto Stinger is nice and I use it as a bottom timer. I got annoyed that you cannot plan deco dives and that it is too restrictive.

 

[DiveMaven]

Depending on your perspective, this seems to be why people either perfer Suuntos or not. Some folks believe that the Suunto's conservatism is safer, though there is no scientific or statistical evidence to back them up. I guess it's like the folks that believe that Nitrox makes them less tired...no scientific evidence to back them up, but they still prefer Nitrox because of that perception.

No right, no wrong, just perceptions and preferences.

 

[divingjd]

I use a UWATEC computer and had the same kind of thing happen diving with a buddy using a Suunto computer. He went into deco and I didn't. Our profiles were not identical, but the algorithm difference accounts for a lot of it. There are lots of different algorithms used by various computers. When you learn tables in OW class, you get the impression there is only one decompression model, but there are actually many.

 

[Fastmarc]

... however on the second dive I needed 8 minutes of decompression to his nil. I realize it is impossible to know the exact profile we each did. But I dove a shallower profile than his throughout the second dive. Are the differences in the programmed logarithms that great or was he just in a hurry to get back to lunch?

So basically you went into deco and he didn't? Was it you intention to do a deco dive?
If it wasn't, you should have adjusted your dive when you saw you NDL running low or even call the dive to avoid going over.
You would be suprised how differently two divers vary even when on the same logarithms. My buddy dives using the same rgbm and quite a few times we end up with different NDLs by mins. Him just stopping to snap a few pictures at a different depth made the difference.
Did your DM leave you while you did you deco stop?
Did he do a safety stop?

 

[TSandM]

There was actually a thread not too long ago where we spent a long time talking about the differences in NDLs depending on the model/algorithm used. They can be substantial. This really goes to the fact that decompression is a mathematical model of an incompletely understood physiological process. Different assumptions are made in the construction of different models. Some look only at dissolved gas, some look at bubbles. Some mix the two.

The bottom line is that where you go into deco is imprecise.

What's important about your opening post is that, according to your dive information, you are a new diver. You really shouldn't be pushing your limits to put yourself into deco, whether real or a figment of your computer's imagination. Do you know how to calculate whether you have enough gas to be as deep as you were for as long as you were, and still DO your 8 minutes of deco? Do you have the buoyancy control to be able to do the deco? Do you know whether you should have done deep stops, or why one would do deep stops, or where you would do them?

There is a ton of stuff to know about diving with decompression obligations. Being caught between the necessity to decompress and an inadequate gas supply to do so is a recipe for an accident. The best way to avoid that is not to push your limits so hard, so early on. If your divemaster was working for a commercial operation, he should have stressed that you watch your computer and let him know when you were approaching your NDLs. If your divemaster is a friend, he should know better than to let you go into deco at your stage of the game.

Now, we could also get into dive planning, and whether you checked to see if the profile proposed for the second dive was going to fly from an NDL standpoint, but from experience, I know that planning multi-level dives is difficult because there aren't many tools with which to do it. If you use the tables, the first dive put you into deco and would make you stay out of the water altogether for the second one. I don't know what you would come up with if you used the PADI wheel, because I've never used it.

Anyway, I think there are some more important questions to be asked here than what the differences between the computer algorithms are.

 

[kneptoon]

Your assumptions are just that. But mostly incorrect, tending to pedagogic. I know you mean well but...come on. Please read my post again. Are your assumptions warranted?

 

[kneptoon]

5 minutes plus 3. thanks for your input.

 

[Scubaguy62]

however on the second dive I needed 8 minutes of decompression to his nil.

While it is undeniable the Suunto is more conservative than the UWATEC, I'm curious; judging by the logged dives on your profile, and not knowing your buddy's experience, I wonder if he may have been breathing a different percentage of O2 than you. If he was breathing 32% and you were breathing 21%, that might also be a factor why you needed a deco stop and he didn't. Want to elaborat on this????

 

[kneptoon]

The dive master did hang out with me. I was diving my dive. Safely.