RBT Time too low Scubapro G2

[Kokodive]

Hello. Does anyone know why my RBT time would be so low - 7 min - just 3 minutes into the dive? I tried ascending a little bit but that didn't help as much as I thought it would. I had to end my dive at about 10 minutes with plenty of air left. Is there a setting that makes this too conservative or was it really that low? Thank you.

 

[Whitrzac]

Because you burned through a lot of gas in 3min. The computer calculates that value based on the past few min of air consumption.

 

[Kokodive]

Because you burned through a lot of gas in 3min. The computer calculates that value based on the past few min of air consumption.

Thank you. Assuming I was at 3000psi at the beginning was this air consumption too much for this depth at this timepoint?

 

[inquis]

Assuming you had an AL80 tank, you were consuming gas at about 1.7 cuft per min per atm, which is above average, but you need what you need. That rate usually comes down after you get to depth because you're not adding much to your BC after that. In other words, the remaining gas time is initially on the low side.

When you say you had "plenty" left, it's common to end with a fair bit, because you must maintain a reserve in case your buddy needs to share. There is usually a setting for the reserve pressure on most computers, and I would guess it's set to 700 psi. However, that's actually too low to get 2 stressed divers to the surface with a safety stop and normal ascent rate if you're at 90 ft.

Search for "Minimum Gas" or "Rock Bottom" for more details about reserve amounts. Check your computer manual to understand the reserve pressure setting.

 

[crofrog]

Assuming you had an AL80 tank, you were consuming gas at about 1.7 cuft per min per atm, which is above average, but you need what you need. That rate usually comes down after you get to depth because you're not adding much to your BC after that. In other words, the remaining gas time is initially on the low side.

The tanks cooling off too can have a big impact. It's pretty common to see a few hundred PSI drop from hot sun to in the water. Here is example of tanks cooling going from 80 degree day to 60 degree water. My SAC for the rest of the dive was around .6

When you say you had "plenty" left, it's common to end with a fair bit, because you must maintain a reserve in case your buddy needs to share. There is usually a setting for the reserve pressure on most computers, and I would guess it's set to 700 psi. However, that's actually too low to get 2 stressed divers to the surface with a safety stop and normal ascent rate if you're at 90 ft.

Just to put some of the math right here:

On a single AL80 to bring 2 divers up to the surface at 10fpm with 1 minute of problem-solving time with the divers SAC at .75cuft/min time, you'd need 35cuft of gas, which means you should be leaving the bottom with 1400 psi in your AL80.

 

[Kokodive]

Thank you all. I will download the dive profile later after work and will look into it in more detail. Will upload the data and see if I can get any more insight. Appreciate your responses.

 

[Kokodive]

Assuming you had an AL80 tank, you were consuming gas at about 1.7 cuft per min per atm, which is above average, but you need what you need. That rate usually comes down after you get to depth because you're not adding much to your BC after that. In other words, the remaining gas time is initially on the low side.

When you say you had "plenty" left, it's common to end with a fair bit, because you must maintain a reserve in case your buddy needs to share. There is usually a setting for the reserve pressure on most computers, and I would guess it's set to 700 psi. However, that's actually too low to get 2 stressed divers to the surface with a safety stop and normal ascent rate if you're at 90 ft.

Search for "Minimum Gas" or "Rock Bottom" for more details about reserve amounts. Check your computer manual to understand the reserve pressure setting.

Assuming you had an AL80 tank, you were consuming gas at about 1.7 cuft per min per atm, which is above average, but you need what you need. That rate usually comes down after you get to depth because you're not adding much to your BC after that. In other words, the remaining gas time is initially on the low side.

When you say you had "plenty" left, it's common to end with a fair bit, because you must maintain a reserve in case your buddy needs to share. There is usually a setting for the reserve pressure on most computers, and I would guess it's set to 700 psi. However, that's actually too low to get 2 stressed divers to the surface with a safety stop and normal ascent rate if you're at 90 ft.

Search for "Minimum Gas" or "Rock Bottom" for more details about reserve amounts. Check your computer manual to understand the reserve pressure setting.

I wanted to provide a little more context now that I have downloaded the dive. After seeing RBT 7 minutes at 90 ft I decided to ascend a little to see if that gives any more time. I didn’t try to to go back down to depth as I didn’t feel comfortable with the RBT. There was nothing to see at shallower waters so decided to go back up for a safety stop and surface. It shows that consumption was 1800psi so assuming it was 3000psi at the beginning I must have surfaced with about 1000 psi at least.