No Drop Bottles for 30M+

[seeker242]

My point is that in my AOW deep dives there was always one just in case.

Around here, there are never bottles, not even for 200' dives. I have never seen one, ever.

 

[Blackcrusader]

The situation you described was 40 min at 30 m on Nitrox 32%. Not the ones you mentioned in your latter post. With a SAC of 12 L/min, you would use 1920L on the bottom. That would leave 212L from the 2132L you stated. Ascending at 9 m/min directly to the surface, with a SAC for both you are your buddy of 12 L/min that would take 200L of those 212L.

As such, it results that you did not consider:
1) Time to solve issues at depth;
2) Safety or deco stop;
3) Any increase in SAC due to stress (even if not double) - the world is not black and white: there is a wide range of reactions between business as usual and full blown panic.

No I would not use 1920 liters at the bottom to get to 40 minutes I would have used 1838 liters at 12l/min at the 40 minute mark. That is based on a rate 50% more than my normal rate. To ascend and complete deco I need less than 300 bar at 12l/min to ascend and complete the safety stop from the 40 minutes at 30m. 2132L is the total used at 12l/min it is not 2132 liters for the amount the tank holds.

Also an AL100 holds 2600 liters at 200 bar. I would get my AL tank filled to at least 210 bar 2730 liters for this dive maybe 220 which would give me over 2860 liters of air.

2132L would be the total dive completed including the deco stop at the safety stop level. A sac rate of 12l/min I have not done in the last 250 dives. Not even ten. So even if I calculated at 10L/min which I am certainly capable of then I would only need 1780 liters for this dive. On an AL100 with 2730 liters would mean I complete the dive with 950 liters remaining which would be around 60 bar.

If I calculated and used air at my normal sac rate 8l/min I would need less than 1430 liters for this dive from an AL100 tank with 2730 liters. So I already calculated the dive using 50% at 12l/min

 

[David Novo]

No I would not use 1920 liters at the bottom to get to 40 minutes I would have used 1838 liters at 12l/min at the 40 minute mark. That is based on a rate 50% more than my normal rate. To ascend and complete deco I need less than 300 bar at 12l/min to ascend and complete the safety stop from the 40 minutes at 30m. 2132L is the total used at 12l/min it is not 2132 liters for the tank.

Also an AL100 holds 2600 liters at 200 bar. I would get my AL tank filled to at least 210 bar 2730 liters for this dive maybe 220 which would give me over 2860 liters of air.

2132L would be the total dive completed including the deco stop at the safety stop level. A sac rate of 12l/min I have not done in the last 250 dives. Not even ten. So even if I calculated at 10L/min which I am certainly capable of then I would only need 1780 liters for this dive. On an AL100 with 2730 liters would mean I complete the dive with 950 liters remaining which would be around 60 bar.

If I calculated and used air at my normal sac rate 8l/min I would need less than 1430 liters for this dive from an AL100 tank with 2730 liters. So I already calculated the dive using 50% at 12l/min

View attachment 636086

I was not discussing your tank choice. I was trying to understand your statement that the dive could be done safely with 2132 liters of gas.

40 min of bottom time at 30m with a SAC of 12L/min equals 40 min x 4 bar x 12 L/min/bar = 1920 liters. The fact that what you said was not what you meant does not change that.
It is clear in your picture that you are not accounting for the gas your buddy would need in case of emergency.

 

[Blackcrusader]

I was not discussing your tank choice. I was trying to understand your statement that the dive could be done safely with 2132 liters of gas.

40 min of bottom time @30M at 12L/min equals 40 min x 4 bar x 12 L/min/bar = 1920 liters. The fact that what you said was not what you meant does not change that. It is clear in your picture that you are not accounting for the gas your buddy would need in case of emergency.

Yes the dive can be done safely using 2132 liters of gas. Not even 1800 liters for this dive would be required for myself or dive buddy I just calculated at a much higher rate than our normal air consumption and his sac rate is less than 9l/min.

Of course you could use a steel 120 with 230 bar for this dive.

 

[Gareth J]

Around here, there are never bottles, not even for 200' dives. I have never seen one, ever.

Just a point here.
In almost all the cases where we have either had a bottle attached to the trapeze, attached to the shot or rigged on the boat on a drop line and buoy. They have always been OUR bottles. WE provided the spare cylinder, WE rigged the trapeze, shot or drop buoy.

If yo are doing deeper diving, then you need to be suitably equipped.

 

[David Novo]

Yes the dive can be done safely using 2132 liters of gas. Not even 1800 liters for this dive would be required for myself or dive buddy I just calculated at a much higher rate than our normal air consumption and his sac rate is less than 9l/min.

Just out of curiosity as I am not familiar with it, is that BSAC's standard to calculate required gas? Increase SAC by 50%, ignore gas needed by a buddy or time to solve issues in case of emergency?

 

[Blackcrusader]

Just out of curiosity as I am not familiar with it, is that BSAC's standard to calculate required gas? Increase SAC by 50%, ignore gas needed by a buddy or time to solve issues in case of emergency?

Join a BSAC club take the sports diving course so then you will know.

 

[David Novo]

Join a BSAC club take the sports diving course so then you will know.

I just asked for the sake of clarity, so that, given this is the "Basic Scuba Discussion" forum, any reader less familiar with gas calculations would not be misled by thinking some statements are the rule and not the exception.

 

[Degenerate]

Your reply does confirm that is can be done on a single tank even if you say not for most people. This does not make what I wrote incorrect. It can be done safely on a single tank. Single tank 120 with 230 bar would be more than enough for a lot of divers.

You're not wrong.
But this is in the basic scuba forum, and most newer divers won't be close to a SAC of 12, and most of them will probably typically dive 80s or something similar.
It's a pretty bad idea to be telling newer divers that such dives are perfectly fine on a single, when they in fact will leave pretty much zero room for error in their case.
Add the gas needed for an emergency ascent from the bottom while buddy breathing to the calculation I posted and you'll hopefully see why I think it is a bad idea to say stuff like that in the basic scuba forum.

 

[Blackcrusader]

You're not wrong.
But this is in the basic scuba forum, and most newer divers won't be close to a SAC of 12, and most of them will probably typically dive 80s or something similar. It's a pretty bad idea to be telling newer divers that such dives are perfectly fine on a single, when they in fact will leave pretty much zero room for error in their case.

Add the gas needed for an emergency ascent from the bottom while buddy breathing to the calculation I posted and you'll hopefully see why I think it is a bad idea to say stuff like that in the basic scuba forum.

Also divers who are novices or newer are not doing 30m deco dives either I would assume? It's a bit more than basic diving when you have to gas plan for deco dives yes? Yes I should have written in it a different thread however I was replying to a comment about deco being "light deco" which again newer divers are not doing.