bottom time definition?

The dive was unsafe because the poster left the planning for the entire dive in someone elses hands, and was plainly beyond his level of training and understanding.

 

Which is what every student doing every course at every level does when diving with an instructor.

The only way to expand experience and training is do go outside your previous limits under supervision.

I dont see a problem with such a conservative dive profile.

 

I disagree, yes by definition you are often extending your limits whilst training. However since it wasn't a training course, and the very questions posed by the original poster suggest they haven't a scooby how it works, means they haven't done enough for it to be safe.
If I'm training someone, or guiding a diver to extend his/her limits, I'll make absolutely sure they understand what they are doing and why, the risks involved etc etc and only then take them in. Under no circumstance would I just announce we're doing xyz and jump in.
I agree its only a few minutes of stops, less if done on an appropriate mix, but that's not the point - it is patently beyond their experience _and_ understanding

 

And im still disagreeing . Once certified you gain experience by diving. You dont normally dive with an instructor after that so you are again by definition diving outside your experience with a non certified instructor (although it will normally be a more experienced diver).

Im not familiar with the syllabus but surely the basics of decompression and theory of nitrogen loading etc are taught at the very basic level so SHOULD be understood (?)

Even if a new diver has never done a dive that deep i dont think it should be beyond their understanding as im sure they should have learnt at least the basics during the course.

The other issue here is from the information supplied this looks more like a multi level dive as opposed to a square profile 100ft dive so it may well have been well within the NDLs anyway.

 

But he clearly didn't, and remember in the US decompression is still taboo, whereas here it isn't. There is a world between tdi and padi training.
Anyway, enough of semantics I'm finished work now, kits in the car, I'm going diving to catch some tea

 

flw is right. The diver should know better than to go to 100 feet and stay underwater til their computer read 30 minutes. Plan your dive, dive your plan. Obviously no planning occurred here, and the diver had no idea whether they were incurring any kind of deco obligation. That's unacceptable for someone who has been taught better (I would assume they have, since it's in the minimum course standards).

 

Interesting article about lobster divers on the Moskito coast.. check out their no-decompression dives and the results!

http://www.sonic.net/~rocky/Moskito 2003/Moskito2003Situation.htm

 

(btw, who said "we went to 100 feet until the comp said 30 minutes?)

I think it could be argued that the dive was planned and followed. It sounds like a conservative profile with multiple stops planned and made. The planner? The divemaster. Whether the diver was right or wrong to trust the planner is different argument, I think. (Why is vplanner trusted? This can lead to a heavy discussion about basis for trust.)

Sounds like some great experience was gained, some great questions were brought to light, answers and understanding sought, hmmm...

Just trying to see a positive here.

 

We run into the situation quite often here where divers aren't really aware of the concept of "multi-level" diving....we'll get back to the shop, and maybe we've gone to the Blue Hole, which is about 120'/37m at the exit, and do...depending on the diver's air consumption...maybe a 50~55 minute dive. Of course, we spent about 4 minutes from descent to the deepest part of the dive, then most of the dive around 40'/12m, then maybe 15 minutes or longer quite shallow....5~8m/15~25'. Sometimes these divers then try to "log" this as a 120' dive for 55 minutes and get a confused expression when they think they've exceeded the NDL by 40 minutes or so! We tell them the dive profile before the dive, but they sometimes forget about that when it comes time to log it. So then I'll explain how you can do multi-level diving with the "wheel" or a computer (and I've played around using the standard dive table for it, just comparing results with the wheel...very close, but I don't tell them or recommend it since it's not "legally defensible" and all that.)

Anyhow, the bottom time question: in calculating pressure groups, it's from descent until you start your ascent towards your safety stop (or surface, if you don't do a safety stop.) In the manual, it says that you can add in your safety stop time if you want to dive more conservatively (this would give you a "higher" letter at the completion of the dive.)

The only problem I have with that definition is when people use that "bottom time" as the entire "dive time" (where they total their cumulative bottom time at the bottom of the log book) because on certain reefs, I might do 15 minutes or longer basically at safety stop depth, swimming along the top of the reef...but as long as I can see fish, it's all "dive time" to me and should be counted in the log book.

 

We DON'T trust decompression software. We cross reference the output with our own past experience and other models and softwares before we choose to use the profile on a dive. Even then we often use the software output as a starting point and modify the progile from there to suit out tasts. At least we do that until we gain some confidence in a model or piece of software.

Also Rass hemmingway, the author of vplanner maintains a data base full of real life diving results to reack the performance of the model and application.

A little more solid than the judgement of an unknown DM I think