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.

 

[chthonicly]

Hi Tech divers, so I have a question I know that in general the advice is that when conducting a decompression dive you should not do a 2nd dive on the same day, but I have been on multiple tec dives with a mix of technical and recreational divers on a boat and I am in the minority of the Tec divers who miss out on the 2nd dive. I have even seen tech divers conducting multiple decompression dives after 1hr surface interval and even 3 consecutive dives.

When I calculate using multi deco depending on the profile it looks like it’s technically possible so I am asking what other technical divers experience has been and any specific rules/ guidelines that you always adhere to.

Thank you and Happy Diving

I think a lot of this is personal -- so many factors go into this beyond tables/computers. We all know of folks who end up with a hit despite their computer/tables/planning sw saying it was technically possible. I think each diver needs to find their limits and also take into consideration any mutable factors (age, weight, fitness, sleep, hydration, etc) which affect this and change their conservatism to fit their current state of existing.

For my comfort level, my rules are: 1 deco dive/day, and I dive 50/70, and I do my last 3m very slowly. I like to do "surface deco" for a bit after surfacing, eg, debrief w/team in the water before exiting. I also dislike boats and their schedules and chaos of lots of other divers so most of my deco diving is shore or cave based where one has the luxury of no one else setting the dive schedule.

 

[clownfishsydney]

I have done six trips to Chuuk Lagoon, two trips to the Solomon Islands (Guadalcanal area) and six trips to dive the wreck of the SS President Coolidge (in Vanuatu). All these trips were two decompression dives a day. However, they all had very long surface intervals, at least two or three hours. Second dive was always shallower by 20 metres and only light decompression. No-one on the trips ever had a problem.

 

[bipolarbear]

I regularly will do trips doing 2x 50m or 60m dives in places where the dive sites are just a short boat ride away. If I do anything >75m or with more than 60 mins of deco then it's a one dive day for me, although occasionally I'll jump in for a no-deco dive with my partner in the afternoon or evening if I've done a big dive in the morning.

I dive quite conservatively (30/70), but I have a historical shoulder injury that gets minor DCS symptoms on occasion (pain, sometimes nerve tingling radiating down to my forearm on that side) which is my sign that I have pushed things too far. If I'm in a place like Truk and doing 2x 50m and long dives a day, I'll give myself a day off halfway through the trip to completely off gas.