I think Diver0001 was just referring to how some technical divers (GUE, UTD) manage their ascents. In their profiles, they will often include 1 minute stops at 10 ft. intervals. In contrast, other divers may incorporate slightly longer stops (modified deep stop) at 1/2 max depth (or some variation on this theme) with shorter stops between the deep stop and the shallow stop (approx. 10 - 15 fsw).
For recreational divers, the optimal duration and depth of deep stops has not been worked out yet.
I like Diver0001's take on the value of being in total control of the ascent rate. A series of one-minute stops at specific depths demonstrates mastery of buoyancy control. That's a good thing...something that all divers should be able to do.
At least one venous gas emboli study has revealed higher bubble scores in divers who ascend at a "too slow" rate.
It's entirely possible that optimal ascent rates could be different depending on a diver's current depth.
No, it's not that complicatated and it's got nothing to do with DIR or any kind of technical voodoo. Those 1 minute rolling stops through 18-6 metres every three metres means you're ascending at 3m/min. That's about as slow as you can go without doing more ongassing during the ascent. If you make the stops any longer (like 3 min), then you'll actually still do a fair amount of ongassing during the ascent.
In itself, there isn't any harm in ongassing during a very slow ascent if (a) you account for that in your dive planning by including the the ascent time in your bottom time calculations (if you're using tables) and (b) in the context of recreational diving you stay on the safe side of the NDL throughout the whole ascent.
Don't forget, in terms of the table the bottom time is defined from the point the descent begins to the point an uninterrupted ascent to the 5 metre stop begins.
However, the PADI table uses this definition on the assumption that you are making your ascent at 18m/min.
What I tell my students is not to worry too much about the 18m/min ascent rate PADI defined for the table. It's just one of the parameters with which the table was tested but since the development of the table it's become quite clear that 10m/min is already fast enough so they should ascend slower and add their ascent time to their bottom time. I think if you play around with deco software that they will mostly confirm what I was saying that an ascent slower than 3m/min will give you longer hang times and certainly longer total ascent times than ascents in the 3-10m/min range. (now some smart-alec will go out and look for an exception to this but still, you can see it as a rule of thumb).
So to make a long story short:
Assuming you're using the PADI table, which I think the OP was suggesting because he mentioned the 18m/min ascent rate in the first post:
- If you want to count your bottom time up to the point where you start making an uninterrupted ascent to the 5 metre stop then you need to ascend fast enough not to get over the NDL during the ascent. That means about 10m/min and certainly not slower than 3min/min (ie, the 1 min rolling stops).
- If you want to ascend very slowly, any slower than 3min/min and certainly to ignore the ascent rate suggested by any given table then you really need to add your ascent time to your bottom time or in other words to count your bottom time until you *arrive* at your 5m (or 6m) stop. The reason being that you will continue to ongass somewhat during the ascent.
To put this in practice, IIRC the NDL for 18 metres on the PADI table is 56 minutes. If you are planning on making 1 min rolling stops at 18-6meters (or even better, to just put in a 1min stop at 1/2 depth to ensure you're in the 10m/min range) then you could leave the bottom at about 56 minutes and still be ok NDL wise when you get to 6m. However, if you're planning on making 3min stops from 18-6 meters then your ascent is too slow for the table and you'll need to leave the bottom earlier. 5, 3min stops is 15 min, so I would suggest planning on leaving the bottom at about the 41min mark in order to accomodate that ascent. (adding ascent time to bottom time).
I hope that didn't confuse things.
R..
