bottom time definition?

[Pilaar39]

Thank you for the replies.. albeit, they are still a bit confusing. Once again, different people are giving me different definitions of bottom time. sigh.

No, I do not have a computer.. that is why I was trying to figure out how to use the tables to log this dive. Yes, I probably should invest in one, but as anyone knows in this sport, it ain't cheap; it will be my next investment, but for now I am still using the tables.. or trying to.

It has now been made very obvious that I made a mistake with this dive; fortunately, I am now home and have not suffered any ill effects.

 

[jonnythan]

Bottom time is from the time you start descending til the time you start your direct ascent. If you stop at 40 feet and swim around for 2 minutes, then your ascent, according to the tables, has not yet begun.

30 minutes at 100 feet is way, way beyond any table. Were you wearing a computer, or just trusting the dive leader for this?

 

[Al Mialkovsky]

In all seriousness, get a computer.

 

[sharkbaitDAN]

From what was written, this was not necessarily a deco dive. First, with as few dives as he has, he would have a very hard time spending 30 minutes at 100ft and having air to ascend.

Second, anyone can plan to do safety stops deeper than 15 ft, that is not the same as planned deco. I do them on every dive deeper than about 60ft.

This sounds to me like a multi-level dive, in which Pilaar39 did not know how how to do multi-level planning. I would suggest getting a computer, and if you can't afford it, learn how to calculate no-deco times for a multi-level dive. You can do it as part of an advanced class.

This illustrates the biggest problem with tables, which is that they plan square profiles, which are not how many recreational dives happen. Based on tables there are a whole lot of us who should not be alive many times over, i.e 110ft for 45 minutes if using the RDP, where the real profile only spends five minutes at 101ft.

Pilaar39, don't worry about writing in your letter groups, as has been mentioned before. I don't think your dive was unsafe, just not a very good idea. Hopefully you will go on and learn and dive more, so that you are never in a situation where you are unsure as to what happened on a dive. Dive Safe.

 

[Al Mialkovsky]

Yes it was a multi level dive. Something most don't learn to compute with the tables. Computers are getting cheaper and cheaper.

But the correct way to determine bottom time is that it starts from the moment you decend and ends the moment you begin your direct ascent to the surface. If 30 minutes was your total time, including a 5 minute safety stop your actual bottom time may have only been 20 minutes or so.

 

[Sideband]

Simple.
Max depth = (whatever your computer says)

Bottom time = (Your choice: total run time or run time minus safety stop and ascent time)

A computer assisted multilevel dive in which I reach a maximum depth of 102' and spend a total run time of 34min gets logged as 102' for :34. I don't worry about the pressure group.

ok. I guess that is what the comments section is for. That would look very misleading to me. Thanks

 

[String]

30 minutes at 100feet is certainly not "way, way beyond any table.".

Looking on my tables here its a deco dive requring a 3 minute stop at 6 meters only. Hardly into the realms of technical diving !
Yes you are outside NDLs but not massively and you dont suddenly die if clocking into deco.

It was by my tables definition a deco dive but only a very minor one.

(oh and if looking for definition, thats 30 mins from beginning dive to arriving at the 6m stop depth so allowing descent time and ascent time looking at 27 mins or so at maximum depth).

If it was a multi level dive chances are NDLs were never violated anyway or if ascent was slow the deco obligation would clear on the way up long before reaching stop depth.

 

[MikeFerrara]

Thank you for the replies.. albeit, they are still a bit confusing. Once again, different people are giving me different definitions of bottom time. sigh.

No, I do not have a computer.. that is why I was trying to figure out how to use the tables to log this dive. Yes, I probably should invest in one, but as anyone knows in this sport, it ain't cheap; it will be my next investment, but for now I am still using the tables.. or trying to.

It has now been made very obvious that I made a mistake with this dive; fortunately, I am now home and have not suffered any ill effects.

Log it as a trust-me dive. You followed some one and you trusted them with all your decompression planning.

Here's a vplanner VPM-A schedule for a 30 minute dive to 100 ft on air. The conservatism was set to 2 of 4. Note that VPM-A is a bit more aggressive for the shallow stops than the newer VPM-B

V-Planner by R. Hemingway, VPM code by Erik C. Baker.

DIVE PLAN

Surface interval = 2 day 0 hr 0 min.
Altitude = 0ft
Conservatism = + 2

Dec to 100ft (0) on Air, 130ft/min decent.
Level 100ft 29:14 (30) on Air, 0.83 ppO2, 100ft END
Asc to 40ft (32) on Air, -30ft/min ascent.
Stop at 40ft 2:00 (34) on Air, 0.46 ppO2, 40ft END
Stop at 30ft 4:00 (38) on Air, 0.40 ppO2, 30ft END
Stop at 20ft 19:00 (57) on Air, 0.33 ppO2, 20ft END
Asc to sfc. (57) on Air, -30ft/min ascent.

Off gassing starts at 72.7 ft
OTU's this dive: 22
CNS Total: 7.2%

83.3 cu ft Air
83.3 cu ft TOTAL

Note the run time of 57 minutes.

I don't know how much time you really spent at 100 ft but I doubt it was 30 minutes. but...it doesn't sound like you know either.

Many wrecks don't present much of an oportunity for a multilevel dive.

Here's the vplanner output for 20 minutes at 100 ft

V-Planner by R. Hemingway, VPM code by Erik C. Baker.

DIVE PLAN

Surface interval = 2 day 0 hr 0 min.
Altitude = 0ft
Conservatism = + 2

Dec to 100ft (0) on Air, 130ft/min decent.
Level 100ft 19:14 (20) on Air, 0.83 ppO2, 100ft END
Asc to 30ft (22) on Air, -30ft/min ascent.
Stop at 30ft 0:40 (23) on Air, 0.40 ppO2, 30ft END
Stop at 20ft 7:00 (30) on Air, 0.33 ppO2, 20ft END
Asc to sfc. (30) on Air, -30ft/min ascent.

Off gassing starts at 69 ft
OTU's this dive: 15
CNS Total: 4.9%

49.0 cu ft Air
49 cu ft TOTAL

 

[fan(t)a(s)tic]

P.S. You can't log it as a PADI dive. Just log it as a dive dive.

:06: Crispos, can you explain to me what the difference between a "PADI dive" and a "dive dive" is?

Always considered myself a diver, not a padier... :thinking:

 

[MechDiver]

ok. I guess that is what the comments section is for. That would look very misleading to me. Thanks

Not if you're used to using run time. The term "bottom time" as defined by OW standards starts to lose meaning once you progress beyond NDL dives, and RT is of much more use.

MD