First dive at 40 meters - Newbies recreational

[Dody]

If I had done this on a Suunto I would expect something like 12. I see stops at 20 and 11 on a 39m wreck dive I did in Gozo. I distinctly remember deciding to actually do the 11m stop while the other two on regular Suuntos carried on up the reef.

if the scheme is essentially Pyle stops then this is what you would expect. The Aqualung manual could give more detail but I am sure it would become very obvious after a couple of bounces to depth.

Honestly though, going to 40m on a 80 or 100cuft cylinder, the risk isn’t from deep stops or deco but something like a freeflow or leak at 40.

Good one. I did not think about a free flow. Would such a problem arise, I think that the best solution would be buddy breathing and ascending to 5 meters for the tank at the safety stop or worse (straight to the surface). With 150 bars for two, a controlled ascent could be possible, right?

 

[Raphus]

Good one. I did not think about a free flow. Would such a problem arise, I think that the best solution would be buddy breathing and ascending to 5 meters for the tank at the safety stop or worse (straight to the surface). With 150 bars for two, a controlled ascent could be possible, right?

This depends on the depth and sac rate.
If a problem occurs the sac will rise.
In really stressful situations sac 5 times the normal rate is reported. I usually calculate with 2 times for the entiry ascent, because on the way up the breathing should normalize. So faktor 2 is a good median i think.

You can calculate this yourself. Just google for mingas calculation. Its not that hard.

If both divers are in a stress situation. 40m deep with only one tank. 150 bar in 80cft tank is not that much air.
For my and my gf sac, we need 120 bar for 30m.
Which is nice, because its close to the rule of half. 150 bar usable air /2 =75 bar.
200-75=125 bar turn pressure.

And on the way back we normaly start to ascent, so we see different thinks on the way back.

 

[David Novo]

Good one. I did not think about a free flow. Would such a problem arise, I think that the best solution would be buddy breathing and ascending to 5 meters for the tank at the safety stop or worse (straight to the surface). With 150 bars for two, a controlled ascent could be possible, right?

You mean donate air (with an octopus). Buddy breathing is both divers taking turns from the same regulator.

A theoretical controlled ascent would be possible. The ascent that you did would not.

 

[Blackcrusader]

Honestly though, going to 40m on a 80 or 100cuft cylinder, the risk isn’t from deep stops or deco but something like a freeflow or leak at 40.

Again the likely hood of this happening is pretty rare. Knowing how to deal with it is another thing at 40m. A leak can be minor and not stop a dive you see many people with a leaking o ring complete dives. A free flow is an inconvenience but not life threatening and recreational divers are diving with buddies. Not at lot of NDL time at 40m on air so you have to get there quickly. Thousands of divers do it safely on an AL80 every year.

 

[David Novo]

This depends on the depth and sac rate.
If a problem occurs the sac will rise.
In really stressful situations sac 5 times the normal rate is reported. I usually calculate with 2 times for the entiry ascent, because on the way up the breathing should normalize. So faktor 2 is a good median i think.

You can calculate this yourself. Just google for mingas calculation. Its not that hard.

If both divers are in a stress situation. 40m deep with only one tank. 150 bar in 80cft tank is not that much air.
For my and my gf sac, we need 120 bar for 30m.
Which is nice, because its close to the rule of half. 150 bar usable air /2 =75 bar.
200-75=125 bar turn pressure.

And on the way back we normaly start to ascent, so we see different thinks on the way back.

If you need 120 bar of reserve and assuming you have 200 bar at start, your usable gas is 80 bar and your turn pressure 160 bar.

 

[David Novo]

Again the likely hood of this happening is pretty rare. Knowing how to deal with it is another thing at 40m. A leak can be minor and not stop a dive you see many people with a leaking o ring complete dives. A free flow is an inconvenience but not life threatening and recreational divers are diving with buddies. Not at lot of NDL time at 40m on air so you have to get there quickly. Thousands of divers do it safely on an AL80 every year.

Gas planning should consider scenarios, such as a freeflow, no matter how rare they are.

 

[Raphus]

If you need 120 bar of reserve and assuming you have 200 bar at start, your usable gas is 80 bar and your turn pressure 160 bar.

In a cave yes. But i dive mostly quarrys, where i can ascent any time. I just need enough air to bring me and my gf back to the surface. So at 120 we start to ascent and usually go back during the ascent.

But you are right, this might confuse other readers..

 

[Blackcrusader]

If you need 120 bar of reserve and assuming you have 200 bar at start, your usable gas is 80 bar and your turn pressure 160 bar.

On this planned dive to 45m to retrieve a camera, we descended at a decent speed I could see the camera from around 35m depth which helped and we were told where is should be so did not have to really do a search. My turn pressure is just over 180 bar. We then ascended to around 25m for a short time then to a shallower depth where we caught up with another dive group from out boat.
As we had gone off the boat first we had a longer dive time than the other group who had a 55 minute dive. If you know how to manage a stressful situation you can still maintain a decent sac rate. In the last 30 minutes of this dive we had to swim against a current to get back to the dive boat. Good exercise. So made sure I had enough air should an issue have cropped up.

 

[Dody]

You mean donate air (with an octopus). Buddy breathing is both divers taking turns from the same regulator.

A theoretical controlled ascent would be possible. The ascent that you did would not.

Yes, with an octopus. I thought that everyone had those nowadays.
I have made myself a very simple excel spreadsheet computing breathing minutes and depths relative to the SAC. With 75 bars and a SAC at 30, you have 6 minutes at 40 m. With a SAC at 50, almost 2 and half minutes but you don’t stay at 40.

 

[Raphus]

Yes, with an octopus. I thought that everyone had those nowadays.
I have made myself a very simple excel spreadsheet computing breathing minutes and depths relative to the SAC. With 75 bars and a SAC at 30, you have 6 minutes at 40 m. With a SAC at 50, almost 2 and half minutes but you don’t stay at 40.

Yes right, but breathing from an octupus is not called buddy breathing. Buddy breathing is breathing from 1 reg.
But you meant the right thing.

Yes but you have 2 divers on that tank. So a sac of 50 for both divers is realistic (30 +20 for example).
Ascent rate of 10m/min needs 4 minutes to surface from 40m.

Average depth during ascent is 20m so 3 atm.
+ some time at 40m to start air sharing and solve problems