Question Multiple Deco Dives in One Day Experience and Rules

[lizardland]

Personally I don't really have any hard and fast rules on it. A lot of it comes down to what the first dive has been, how it went and how I'm feeling afterwards. And how much life is left in my lime, how much dil and O2 I have. And largely, can I be bothered? Most of the 50m+ diving I've done is on boats with other technical divers and the charter is for one specific wreck. It's very rare to see an OC trimix diver here so most people are doing this kind of dive on CCR, doing decent bottom times and will generally be either too tired or out of scrubber time for anything else. Just the deco commitment alone for a repeat dive will make a second dive pointless. Add to that just the sheer amount of time that a skipper needs to set up for the dive, deploy 10 or 12 gas divers and recover them again. A second dive is just not realistic.

It's more a question for mid-range diving where you can often find yourself on a mixed boat. Generally I'd have no real issue doing two <50m dives with a good chunk of deco in a day, especially if I can get a long interval between the two. If the second dive is a site that I've dived a lot or isn't particularly interesting then I'll happily sit it out. If it's a submarine I will happily swim back to land.

I think the most I've ever done was 5 deco dives in one day when caving in the Jura mountains in France which also involved some substantial changes in altitude as well. Oh to be that young and stupid again.

 

[mr_v]

You can do multiple deco dives on the same day provided that you know what you're doing, are staying conservative, and spending plenty of time on surface resting and hydrating.

My limit is boredom. I've done dives with ~100 min of deco twice per day. My gradient factors are 50/70 but I usually don't get out of the dive unless my SF GF is 60. Here are some things that I've learned.

These dives were a lot, and I was bored out of my mind. My new rule is that every dive with > 100 min deco requires an iPad with some movies. Also, I am not sure if doing multiple deco dives per day is good for your body. I never got bent but always was more time than usual, which some attribute to signs of decompression stress.

 

[LFMarm]

I don’t follow rules based on # of dives. I just make sure to stay within a GF curve that I feel conservative enough for me. Depending on the PrT of the first dive and the surface interval, the second dive may require significant more deco than if it would be the first one of the day but this is not an issue for me as long as the deco and bailout is properly planned.

My most significant deco happened on a shallow (45 m) 4.5h dive in the afternoon after a very deep dive in the morning. I got out of the second dive with a GF of 40 after an extensive shallow deco.

 

[DiveLikeAMuppet]

Why would you make that assumption? Are you talking about test conditions or simply by the dives people have been doing for decades?

Purely test conditions, so I pad my deco a bit - which seems to be the consensus in this thread.

People have been doing many things for decades, that doesn’t mean there are no issues. Maybe repetitive deep recreational bounce decompression diving (what the studies call our hobby ) is the new cigarettes - I think that with these dives you get to a point where fitness, thermal comfort, exhaustion and many more factors matter, so the outcomes become random and the DCI hits more unpredictable. And outside of an occasional DAN study there is little monitoring.

 

[kensuf]

For stuff shallower than 75m/250', my general rule is maximum 2x dives a day with a minimum SI of 90 minutes, and once I've clocked more than 30 minutes of "oxygen" time (6m/20'), I'm done for the day.

If I'm at a bucket list destination (ex. Bikini) and want to go beyond the 30 minute limit, I'll bump the SI up to 3 hours. But even if I'm a bucket list, I'll only do one dive on days where I'm going deeeeeeeeeeeeep.

 

[macado]

I am content doing 2 x 180-200ft (~55-60m) with runtimes up to ~90-120 minutes. It is not uncommon for me to do this 5-7 days straight although usually we have an off-gassing day (bad weather day) thrown in here somewhere.

I do this type of diving fairly regularly and have good solid empirical evidence this works for me. I usually feel very good, not achy, not super tired. I try to get at least a 2+ hour surface interval between dives but unfortunately sometimes this doesnt always happen.

As others mentioned, this is a pretty common Great Lakes pattern and dive profile in other places in the world.

The line for me gets blurred around 250' (~76m). Over this depth and I am usually a one and done unless I have a good reason to get back in the water (.e.g., conditions are excellent and I have a long surface interval). I wont get into the Gradient Factor discussion as I've mentioned what I run on here several times. I would say there are no hard and fast rules, only personal experience and judgement will help here.

The other consideration is "shallow" decompression dives. For example, cave dives in the 100ft (~30m) range or even one long dive at 100-130ft (30-36m) on a wreck like the Spiegel Groove. I feel these dives in some cases are more risky and more aggressive than deeper dives since you are saturating your slow loading issues. A ~2-3 hour dive in the 100ft (30m) range in my opinion carries more risk / decompression stress than a 200ft (60m) dive where you spend only 25-30 minutes on the bottom

What's important to note here is these profiles may bend other people like a pretzel. You should ideally ramp up slowly and see what dive profiles work for you. I have dive buddies who are perfectly happy and content with one decompression dive a day and that is perfectly fine.

 

[SelfDiver]

For stuff shallower than 75m/250', my general rule is maximum 2x dives a day with a minimum SI of 90 minutes, and once I've clocked more than 30 minutes of "oxygen" time (6m/20'), I'm done for the day.

If I'm at a bucket list destination (ex. Bikini) and want to go beyond the 30 minute limit, I'll bump the SI up to 3 hours. But even if I'm a bucket list, I'll only do one dive on days where I'm going deeeeeeeeeeeeep.

This has my vote.
75m is my soft rule for two dives.
2x50m dives in a day for multiple days should be OK for decompression, but the logistics are more problematic. Captain needs to approve this way ahead of time and don't complain if sea conditions change and you get what you get.