Gas Consumption Rant

[Rick Inman]

Another option is always stay a little more shallow than your dive buddy.

Keeping together and aware of your buddy's location is the most difficult if he/she is above you.

Here's a question to ponder: if you are doing a dive at 66', how much gas/time will you save by being 10' shallower?

 

[ScubaSteve]

........On an AL80 I usually have to surface due to nitrogen loading rather than running out of air..........

How does this work? A computer is built on algorithms that determine how much nitrogen has been absorbed into the system and what should have been passed from your system based on the depth and duration (and O2 content of course) of your dive profile. Unless you have more repetitive dives than the group, I do not see how you would have to call a dive due to reaching or approaching your NDL.....the only thing that I can think of that would get you there quicker is a more conservative computer (like mine...a Suunto) but this is minutes not tens of minutes and it is a cumulative effect not immediate. I do agre with you though....talk to people up front and determine which diver best suits your ideal profile for a dive buddy. Sometimes this will work because of the number of solo divers and sometimes it will not. Bottom line is, make sure the pre dive discussion is complete and happens, and make sure the DM knows what your plans are.

 

[scubadiver888]

TSandM - I respect your opinion more than about anyone else on this board. You make a valid point. And if I'm at 100 feet I definately agree. But if it's toward the end of a dive and we have multi-leveled up to 50 feet or less I am willing to trust my gauge or CESA if needed. But I'd never let my wife surface alone.

This is selfish. Think about why you will not let your wife surface alone. I would guess you would feel horrible if something happened to her. Don't you think she would feel the same way if something happened to you? What is good for the goose is good for the gander.

I consider the dive op we go with in Coz very high quality and safety minded, yet on many dives they would have divers ascend solo, once they dived with the diver a few days and were comfortable with their experienc level. I quess many disagree with that practice and I can understand that position. I have always ascended with my buddy when they want to go up first, but I am willing to ascend on my own.

You sign a piece of paper that says the dive op is not responsible for most things and that diving is inherently dangerous. If you are diving 2 to 4 times a day, every day and nothing happens you start to become complacent. I dove with an operator in Aruba in December '06 then again in April '07 (4 months apart). The first dive was like your dive operator in Coz. In April they were more stricked. Turns out someone got hurt in February.

 

[BDSC]

Keeping together and aware of your buddy's location is the most difficult if he/she is above you.

Here's a question to ponder: if you are doing a dive at 66', how much gas/time will you save by being 10' shallower?

OK. I tried to calculate this out. Not sure if I did it right but here goes.

Lets assume that at 66ft you will get 50 minutes of bottom time. I am just using this number because I have to use some number. If all conditions were the same but you were diving at 56ft, I calculate that you would get 58 minutes or an extra 8 minues.

BDSC

 

[scubadiver888]

Keeping together and aware of your buddy's location is the most difficult if he/she is above you.

Here's a question to ponder: if you are doing a dive at 66', how much gas/time will you save by being 10' shallower?

If I'm diving at home or not on a cattle run I am usually right beside my buddy and within 3' (if I know them well I stay within 6"). If I have a good buddy on a cattle run I dive properly. If I have an insta-buddy and he is not paying attention to me I'll do the 10' above. Usually on these sort of lead dives we are above 60'. The viz also has to be 70'+.

I would never dive below 60' with an insta-buddy that I was not sure of.

When I first started diving, the group at 60' and me at 50' saved enough that I didn't have to be the first person up.

This is a temporary solution. My ultimate solution was to get better at gas usage.

 

[BDSC]

OK. I tried to calculate this out. Not sure if I did it right but here goes.

Lets assume that at 66ft you will get 50 minutes of bottom time. I am just using this number because I have to use some number. If all conditions were the same but you were diving at 56ft, I calculate that you would get 58 minutes or an extra 8 minues.

BDSC

After looking at this again, I think you would only get 56 minutes and not 58. So an extra 6 minutes.

 

[scubadiver888]

How does this work? A computer is built on algorithms that determine how much nitrogen has been absorbed into the system and what should have been passed from your system based on the depth and duration (and O2 content of course) of your dive profile. Unless you have more repetitive dives than the group, I do not see how you would have to call a dive due to reaching or approaching your NDL.....the only thing that I can think of that would get you there quicker is a more conservative computer (like mine...a Suunto) but this is minutes not tens of minutes and it is a cumulative effect not immediate. I do agre with you though....talk to people up front and determine which diver best suits your ideal profile for a dive buddy. Sometimes this will work because of the number of solo divers and sometimes it will not. Bottom line is, make sure the pre dive discussion is complete and happens, and make sure the DM knows what your plans are.

I was saying that NOW I end a dive because I approach my NDL. I used to run out of air and have to call the dive early (30 minutes for a 50' dive for example). NOW I almost never call a dive due to air.

I have noticed however that I hit approach NDL before most other people on a dive. Either they are going into deco or my computer is more conservative.

 

[ScubaSteve]

I was saying that NOW I end a dive because I approach my NDL. I used to run out of air and have to call the dive early (30 minutes for a 50' dive for example). NOW I almost never call a dive due to air.

I have noticed however that I hit approach NDL before most other people on a dive. Either they are going into deco or my computer is more conservative.

OK thanks for the clarification....that makes more sense.

 

[Rick Inman]

After looking at this again, I think you would only get 56 minutes and not 58. So an extra 6 minutes.

Well, it depends on your sac.

Let's say you breathe a .8 sac. At 66', that would be 2.4cf of gas consumed per min.

At 55' (10' shallower) that would be 2.14cf of gas per min.

At 66' for 30 mins you would breathe 72cf of gas. At 55' you would breathe 64cf of gas. So on this dive, the 10' saves you 8cf of gas, or, approximately 3 mins. A lower sac means less savings.

 

[BDSC]

Well, it depends on your sac.

Let's say you breathe a .8 sac. At 66', that would be 2.4cf of gas consumed per min.

At 55' (10' shallower) that would be 2.14cf of gas per min.

At 66' for 30 mins you would breathe 72cf of gas. At 55' you would breathe 64cf of gas. So on this dive, the 10' saves you 8cf of gas, or, approximately 3 mins. A lower sac means less savings.

Hey Rick, I'm having a hard time putting faith in your numbers if 55' is 10' less than
66ft.