Subsurface Deco Ceiling Question

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

The green ceiling is computed by subsurface. Actually, the actual ceiling is the tiny dark green thing at the very top (the info box will report the actual value when you move the mouse there), the light green is the ceiling rounded to 3m/10ft as you have selected to show the ceiling in multiples of those. This ceiling of probably just a few cm/inches I would not lose much sleep over, it will be gone before you reach that depth at a decent ascent velocity.

A dive computer computed ceiling would show in red. Depending on the brand of your dive computer, you might get the gradient factors of the dive computer in the "Extra information" tab. You can change the gradient factors Subsurface uses to display ceilings in logged dives in the global preferences in the "profile" section.

Hope that helps.
 
Here's what it looks like with a computer ceiling and a Subsurface ceiling overlaid. The green is GF50/75 and the red is Suunto Fused RGBM.

fq5JCUr.png
 
Correct me if I am wrong, but Shearwater computers (at least Perdix and Teric) do not account for safety stops in their NDL calculation (which makes perfect sense if you ask me). I am only using OC Tec mode, but I am 99% sure it's the case for OC Rec as well.

Yes, you are correct. The definition of an NDL dive is that you can ascend directly to the surface without stopping so safety stops will not be included. In rec mode the Perdix will advise the diver to make a safety stop at 15 ft if the dive, at some point, exceeded 35 ft in depth. There are various options for the safety stop. I don't know if this behaviour is the same for the Teric.
 
Quote from Teric manual regarding safety stops can be found earlier in this thread.
 
So your computer is saying your ceiling is 10 fsw? That sounds like they think you should really do a safety stop if you approach within 10 minutes of the limits implied from the 120 rule. Your dive was not particularly deep but it was longish which in combination with a moderate depth merits some caution. Most dive computers without explicit algorithms are black boxes with unknown parameters. Most, if not all, of those will err on the side of caution. Learning something to gauge your dive computer against is worthwhile. That could be 120 rule, ratio deco or a review of dive tables. Don't take those as gospel, but don't take what your dive computer says as gospel either.
 
The green ceiling is computed by subsurface. Actually, the actual ceiling is the tiny dark green thing at the very top (the info box will report the actual value when you move the mouse there), the light green is the ceiling rounded to 3m/10ft as you have selected to show the ceiling in multiples of those. This ceiling of probably just a few cm/inches I would not lose much sleep over, it will be gone before you reach that depth at a decent ascent velocity.

I.e. you're saying subsurface does not factor in ascent time in its ceiling calculation, correct?
 
The displayed ceiling is about the current tissue loadings not those in the future after some potential ascent with some assumed ascent velocity. It tells you: with your current inert gas loadings your model does not like you being above this depth.

It is not the statement: if you start ascending now, you will hit a stop at this or that depth (if the ascent is not instantaneous)
 
It is not the statement: if you start ascending now, you will hit a stop at this or that depth (if the ascent is not instantaneous)

I think that should be in bold in section 6.5.3 of The Fine Manual. And in the Fine FAQ too. (Perhaps omitting the "beam me to the surface Scotty" bit :wink:

This is the 2nd time this comes up in recent memory and maybe a some future somebody will read it there (I know, I know) and not post here. And if they do we can look down at them and smugly say "RTFM".
 
https://www.shearwater.com/products/perdix-ai/

Back
Top Bottom