'deep stop' experiences

[Celt]

Think I've got somewhere my PADI dive table (my very 1st one) advocating for a 60feet/min ascent. Some memories there !

If using US navy tables at 60fpm assent a delay deeper than 50fsw the extra time would have to be added to the bottom time which could put you on a new schedule considerably increasing deco time. We always went a bit quicker and would stop 10 feet below the first stop to hit the stop on time.

 

[EFX]

Invalid to rectify the '0' on your NDL, and how long ago it stopped counting down.

OK. I understand what you're talking about. Once the dive computer (DC) counts the NDL time remaining to zero the DC will start calculating the time needed in minutes at the shallowest deco stop, and you are at that point making a deco dive. The DC after some short delay will then show your stop depth with the time to stop. So, you are correct in that there is nothing you can do to go back to an NDL dive.

Just so we are on the same page, an NDL (no decompression limit) dive does not require any stops to decompress. The diver can go directly to the surface at a safe ascent speed of 30 ft/min (10 m/min). A deco dive in contrast, requires the diver to make stops for a certain amount of time at 10 ft (3 m) increments from the surface. This time spent at stops allows the tissues to off gas at a safe rate in order to ascend to the next shallower stop if one is required, or to finally ascend to the surface.

All of the boat charters I have been on are for recreational dives only, i.e. no deco. On some of those charters the captain sets a bottom time limit or will specifically state to be back on the boat with 500 psig (30 bar). On a few of those charters, where the first dive was deep, the captain emphatically said to watch our NDL. Most recreational divers with limited experience (<50 dives) will be gas limited as opposed to NDL limited where their gas consumption is too high to permit staying too long at depth and slipping into deco. But, I've seen it happen.

Since most boat charters are on a more or less fixed schedule, i.e. 2 dives in the morning and back at shore for lunch to reload the boat, the crew will be pissed if you go into deco. First, you are putting your safety at risk and possibly subjecting the crew to cancelling the second dive because they have to get you back to shore if you show DCS symptoms, and this will make for some angry customers. Second, you may be putting your buddy at risk if he feels the need to stay with you. Third, the extra time the crew and customers have to wait for you to complete your deco will not keep you in their grace, so expect to get a tongue lashing back on the boat and angry/disgusted looks from the other divers.

 

[Wibble]

OK. I understand what you're talking about. Once the dive computer (DC) counts the NDL time remaining to zero the DC will start calculating the time needed in minutes at the shallowest deco stop, and you are at that point making a deco dive. The DC after some short delay will then show your stop depth with the time to stop. So, you are correct in that there is nothing you can do to go back to an NDL dive.

Dive air at 30m/100ft for 20 mins and you’ll be over your NDL and in to deco. Ascend to, say, 15m/50ft and that deco obligation will clear an you’d see a NDL reappear as the fast tissues/compartment clear.

ASD doesn’t talk much sense, or at the very least struggles to explain things.

 

[tr3a]

They will if the Surface Interval is less than 90-minutes.

Bull---t

 

[Tassi Devil Diver]

For what it is worth I was treated for the bends in 2006 and 2007 in very similar circumstances, during the very early days of my deco diving journey. The dive profile on both dives was similar, a rec dive where we just went into deco, my dive computer then a Delta P VR2 instructed me to do a deep stop at 30m, I surfaced with a dull ache in my shoulder, my buddy on both occasions diving a Sunto did a 5min stop at 5 (as I did too) and did not get bent, only difference in profile was the deep stops I did. After the second event I started to think the deep stops were causing the issue. I could not disable deep stops on the VR2 so going forward I added the deep stop time on to my shallow stops (about 3min) and never experienced any further DCI issues. Using a Bulahman GF computer since 2010 I now us a GF of 60/70-80, moving from GF low from 15-30-40-50 and now recently 60 over the past 12 years.

 

[Hojo in SC]

Pretty much sums up deep stops for you and why they have gone out of style:

I've often wondered (non- tech diving) that if adding a deep stop after a 130 foot dive, if it really helps to blow off nitrogen or if I'm simply adding it to my tissues by staying at 65 feet for an extra minute.

 

[boulderjohn]

I've often wondered (non- tech diving) that if adding a deep stop after a 130 foot dive, if it really helps to blow off nitrogen or if I'm simply adding it to my tissues by staying at 65 feet for an extra minute.

You linked to Simon Mitchell's fine presentation, and I can give you Simon's answer to your question. He doesn't know either.

There is a significant difference between deep stops on decompression dives and deep stops on NDL dives, and there is no good, conclusive research to support or oppose them on NDL dives.

 

[EFX]

I've often wondered (non- tech diving) that if adding a deep stop after a 130 foot dive, if it really helps to blow off nitrogen or if I'm simply adding it to my tissues by staying at 65 feet for an extra minute.

I would not add any arbitrary deep stops. My advice to you is to follow your dive computer whether it includes deep stops or not. If your DC calls for a deep stop some slower tissues will on gas more nitrogen than if you were to make a continuous ascent to the safety stop. But, so what! What difference will it make for NDL, staying for that extra time at the depth of the deep stop? Those stops are only one or two minutes long. I know. I used to dive with a Mares Puck, a DC using the RGBM algorithm which called for a one minute stop if I did a dive within about 8 minutes of NDL. Often, the deep stop obligation would clear somewhere on the ascent.

Since the jury is out (actually there hasn't even been a trial yet) on whether deep stops mitigate the risk of DCS, especially for NDL dives, then it's just a matter of how much peace of mind you gain by doing them.

 

[scubadada]

Most rec dive computers allow you to opt in or out of deep stops, I have always opted out. As far as I know, there are no penalties for not completing deep stops if they are enabled. Of course, I know nothing about the RGBM computers, Suunto, Cressi, Mares.

 

[beester]

Think I've got somewhere my PADI dive table (my very 1st one) advocating for a 60feet/min ascent. Some memories there !

Well in my experience I haven't seen many people do blue water ascends anything close to 30ft/min let alone 60ft/min. I'm not talking about the theoretical part... I started diving when this was indeed the norm. I'm talking about the practical aspect of such ascends. People just can't do them.

30ft/min is already quite fast, specially if you know you 'll need to hit the brakes in a while to get to your deco stop. Most divers, even technical divers, are way more slow on their ascend... TOO slow.