what is bottom time?

[Diver0001]

Safety stop would be Interruption in direct ascent the way I was taught which means on tables I would be doing a bounce dive at 130 fsw. My SSI tables show 5 min at 130 3min safty sxtop means 2min for down and up. I have always wondered if this was correct

your safety stop is not considered an interruption to the normal ascent.

It's a little out of scope in the current discussion but any time you spend shallower than 8 metres (for example, a your 5 metre stop) can't cause any significant ongassing...so not only does your safety stop not count as part of the bottom time, you can extend your safety stop practically indefinitely without incurring any additional ongassing.

R..

 

[SteveFass]

Bottom Time

 

[H2Andy]

steve, i'm usually pretty good at jokes and such...

but i must say... this one ... zooom

over my head

 

[SteveFass]

Darned if I know why the boat says, "Coconut Tree" on its side. The name of the boat is "Bottom Time". It's the same boat as in Undefined's pic above, but shot from the side.

 

[diver 85]

I was trained & taught BT is the moment you start your descent till the time time you start your ascent.....In your example it will be 22 minutes, 10 going down & 12 on the bottom).......nothing more nothing less.......btw, PADI here.......btw II, also it's the name of my 1st boat.......

 

[Charlie99]

It depends on what table/algorithm you are using. If using PADI RDP/wheel, then bottom time is defined as the time between the beginning of yoru descent and the beginning of your ascent. (10 min descent + time at depth before making a direct ascent)

i.e.

10 + 12 = 22 mins

Is this still true if it takes 15 minutes to ascend? How about 30 minutes of ascent? (Although I quoted Rakkis, the question is for anybody that says that the 10 minute ascent doesn't count as bottom time)

I don't have the instructions for any of the tables handy, but I'm pretty sure you will find words like beginning of "DIRECT ascent" or "UNINTERRUPTED ascent" as the point where the bottom time clock stops. An ascent much slower than the ascent rate around which the table was designed will end up loading the slower tissues heavier. In the extreme example is a diver "riding the NDL" back to the surface. The bottom time definitely does not stop at the beginning of the ascent in cases like this.

My rough rule of thumb is to figure out how long it would take to get to surface at the ascent rate of the table. Any excess ascent time beyond that I count as bottom time. This is a bit conservative, but if you don't like that, you should calculate the dive as a multilevel profile, use a dive computer, or try to estimate your deco status by averaging depths.

The original poster doesn't say how much of the 10 minute ascent was shallower than 20' so we have no idea how much time was spent down in the 80' and 90' range.

 

[Nemrod]

The question was proposed pretty much as a square profile. If you spend 30 minutes ASCENDING when the table calls for a 60 or 30 foot ascent rate your not following the table and your no longer on a square profile--your doing a multilevel dive and it should be broken into segements for computation for us non-computer users.

Time spent under water during "ascent" in excess of the recommended ascent rate and safety/deco stops should be counted as bottom time---it is a multi level dive.

N

 

[Meng_Tze]

I thought BT was the time you spent lying on the bottom?

 

[divingjd]

Crawfishdiver's answer was correct under the definition of bottom time SSI uses and he said he was using SSI tables. Bottom time is the time from the beginning of the descent to the beginning of the direct ascent to the surface. The ascent to the safety stop and the safety stop itself are counted as bottom time. The direct ascent to the surface only begins after the safety stop. Other agencies may define it differently. The point of the "direct" ascent idea is to cover multi-level dives. The safety stop example is almost the trivial case, but it is consistent with the definition.

 

[H2Andy]

I thought BT was the time you spent lying on the bottom?

whatever it is, i sure as heck don't get enough of it