rick00001967

hope it is ok to post this in this section. seems appropriate....
what are your thoughts out there about calculating bottom time?? we were taught (about 15 yrs ago) that BT was from the time you begin desent to the time you reach the surface. i would like some opinions on a few things.
first - do most of you include your 3-5 minute safety stop at 15 feet or not??
second - do some of you end your BT time when you begin your asent??
third - if you answer yes to the second question, how do you properly preplan your dive if you know the asent will be a very slow one. for example.... asending along a reef that gradually gets shallower and may take 15 or 20 minutes to reach 15 feet for your stop.
i know some of these answers are easy if you use a computer but i have often wondered about the complex calculations it must take to preplan a dive with a gradual asent.
the reason i am asking this is because most of my dives used to be going down to a certain depth and staying there for a certain time and then asending. simple. but lately it seems that a lot of my dives (with guides) have been these so called "multilevel dives" which i am sure are probably safer but without a computer i don`t see how doing a proper plan is possible using only a simple dive table. anyway.....curious on all your thoughts. thx rick

James Goddard

PADI defines it as the time from the start of your decent to the start of your ascent.

I do not.

I use the bottom time reported on my computer, minus the safety stop time.

rick00001967

i guess the real question to me that has never been fully answered is "what constitutes an ascent"?? is it when you begin getting shallower no matter how slowly, or is it when you decide to head direct to the surface. the definitions i find in all the literature is not very clear. most people i talk to about this have different ways of doing it depending on who taught them.
the use of a computer makes life a lot easier of course, but how do you preplan your dives. for example.... if you want to dive to 80 feet and only need to be at that depth for 5 or 10 minutes with the rest of the dive being a tour around a reef that gets gradually shallower, at what point in the dive do you stop counting your BT. is it as soon as you begin rising from 80 feet no matter how far or how slow. is it when you reach your 15 foot stop. or is it at some point in between. i do not use a computer but i do not see how you could use it to preplan a dive like that. there are too many variables. what do you think??? thx rick

MgicTwnger

I dive my computer. It turns on when I submerge and turns off when I surface. That's my bottom time. Let the computer do the figuring about gradual ascents, etc. It's a lot better at it than I am.
BTW, I use a mechanical SPG and have a timer/depth gauge on my arm for backup. However, if the computer fails, up I go.

Hi, James. Havn't heard much from you lately. Too busy with Karioke?

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Scuba Mama

PADI does teach from the time you beginning your descent until you begin your ascent. Yes, that means using the tables you can dive 60feet for 55 minutes and return back to the surface. It should take 1 minute 60feet per minute. In theory you should be fine. I like to give myself more time and the example is at the max for the table. If your using tables, 55 minutes for 60feet does not mean if I started up at 35 minutes I can hang out past 25 minutes at any of the new level. This is why computers are better. They allow adjustments while for diving and its your profile not a flat table. Hope this helps.

James Goddard

For calculating bottom time, your ascent begins when you thumb the dive. Safety stops are part of the ascent time but if you're not heading to the surface it's a multi-level dive, not an ascent.

James

rick00001967

it is very interesting to see the subtle differences in the way we were all taught. i guess that is to be expected with the vast number of different instructors out there. they all have their own way of doing things. the "bottom" line is(hahaha)get it.... sorry that was bad....anyway.... the bottm line is that if you do not have a computer you are stuck using the tables and must follow stricker guidlines to ensure safety. if you want to get the most time out of your dive time you need a computer. you can still preplan the dive as best as possible with the tables and then adjust your dive accordingly as you go if the computer lets you. does that sound about right???
after just buying a new set of regs and a bcd it will be awhile before i can afford a computer (if ever). thx for all the advise. if anyone else has a new spin on this topic let me know. thx again rick

glynneco

[quote=MgicTwnger]I dive my computer. It turns on when I submerge and turns off when I surface. That's my bottom time. Let the computer do the figuring about gradual ascents, etc. It's a lot better at it than I am.
BTW, I use a mechanical SPG and have a timer/depth gauge on my arm for backup. However, if the computer fails, up I go.
QUOTE]

Yeah, I do the same. For table profiles it's start of descent to when you start up the anchor line (or it's virtual equivilent). Tables and multilevel diving are a pain. Square profiles are simple and keep you out of trouble.

Bite the bullet and get a computer you'll be soooooo much happier and less stressed!

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Resqdivemedic

Computers are the way to go. I just purchased one afetr 20+ years diving analog. Took some time to learn it, but I dont think I can switch back. Makes life a whole lot easier. I also dive using my watch as a backup. As most of the previous post, my bottom time starts from the time a descend to the time I surface.
Dive safe.