Split from A&I Yukon thread: Gas Rules in OW Solo Dives

[kanonfodr]

The only reason I can see diving thirds for OW solo diving (something I have done) is simply being cautious: 1/3 out, 1/3 back, 1/3 for a f***up (entanglement, lost, etc). And I had an AL40 for a pony, which was a little less than half my backgas (was diving single LP95s at the time.)

However, that was for shore diving where I would be traveling longer distances. I've never dove the Yukon, but if it's anything like any other wreck/artificial reef I have dove then I would instead reserve 1/3 of my backgas for the ascent, preferably with a sizeable (19cuft+) redundant air supply for a f***up. So using an AL80 I would start my ascent at 1000 PSI, which is about where I start my ascent anyways when buddy diving. My main objective would be to be aware of where I was in relation to the upline, and be constantly monitoring my gas supply.

Granted, my numbers for solo diving are super conservative, but since most of my solo diving was shallow reefs with no overheads it worked out fine, even if I did come back with half a tank. When I did solo, it was usually to accomplish some type of objective that a buddy would either have interfered with/been a liability or just refused and called me a lunatic.

This is a pretty simple explanation, but it's basically how I ran my solo dives.

Peace,
Greg

 

[AndrewA]

I am also not a solo diver but know many divers who like to dive solo (especially on commercial dive trips). I have noticed that all of them have an octopus on their main cylinder. Given that they are diving alone (and as solo divers have an independant alternative air source!) who is the octopus for? Could it be that SSI are using the rule of thirds so that the solo diver can still safely assist another diver? (i.e.planning for the unexpected OOA from your "insta non-buddy")

 

[ScubaSteve]

I am also not a solo diver but know many divers who like to dive solo (especially on commercial dive trips). I have noticed that all of them have an octopus on their main cylinder. Given that they are diving alone (and as solo divers have an independant alternative air source!) who is the octopus for? Could it be that SSI are using the rule of thirds so that the solo diver can still safely assist another diver? (i.e.planning for the unexpected OOA from your "insta non-buddy")

Most solo divers are just divers that may dive with a buddy on their next dive. There is no issue with having an octo as part of your kit when diving solo. As long as it is not part of the gas supply (normal, emergency or redundant) then it is a non-issue IMO.

I think what is being missed on why people have issues with the rule of thirds for OW dives is the fact that most OW dives the diver does the following: (direct) Descend, Dive, (direct) Ascend. The rule of thirds, as used by cave divers (because there is no "(direct) ascend" option, is good because they usually follow the same path (or similar) as they did to get into the cave meaning they should need basically the same amount of gas if nothing goes wrong. Rule of thirds could be more applicable to an OW dive if the profile was: Descend, dive bottom to a point, turn and dive bottom to where you descended to, Ascend. This still is an overkilled gas plan IMO because the diver still has direct access to the surface but it is better than a drop, dive, ascend profile.

FWIW, I am not a cave diver so I am perhaps over simplifying this, but I think it works for what it is intended.

 

[Cave Diver]

but why 1/3? Why not 1/4 out 1/4 up, 1/2 reserve? I imagine that was awap's point.

The problem with the application of thirds is that the assumptions behind it don't necessarily apply to openwater profiles, so it's bound to be questioned (or have fun poked at it).

1/2 + 200!!!! :d

 

[Cave Diver]

Rule of thirds could be more applicable to an OW dive if the profile was: Descend, dive bottom to a point, turn and dive bottom to where you descended to, Ascend. This still is an overkilled gas plan IMO because the diver still has direct access to the surface but it is better than a drop, dive, ascend profile.

Correct.

There are some OW situations where a direct ascent at any point is not a good idea, such as areas with heavy boat traffic or surface currents that make it preferable to stay submerged during the return to entry point, in which case a 1/3 rule makes more sense. For most diving it's overkill if for someone who monitors their gas supply.

 

[WetDawg]

First off, Thal, your reputation and experience in the dive industry are beyond reproach, more respectful I could not be.

As an SDI Solo Diving Instructor I thought I would jump in and attempt to answer your specific question;

I've never really thought out gas management for solo diving. What is SSI's reasoning? I hope it is something better than, "just in case."

First off, I don’t think the actual math behind the rule of thirds in ever explained in the course, unlike the “Rock Bottom” calculations that are explained in other courses by other agencies.

In fact the quote straight from the SDI Instructor Guide is this: “We have settled on the rule of thirds as the appropriate reserve volume for the purposes of this course. However, even though this would give a diver ample volume for most emergencies – such as emergency decompression or losing up lines – solo divers must still be configured with a complete redundant gas source to safely manage the unlikely event of catastrophic failure somewhere in our primary gas system.” (Copyright credit to Scuba Diving International)

Frankly, I would agree that the rule of thirds is ridiculously conservative for an open water dive, however, it is for that very reason that is becomes most appropriate for the Solo Diver. Because you are entirely self reliant on only one set of brains to both recognize and solve any problems that crop up, it behooves the solo diver to be ultra conservative in every facet of their dive planning especially in gas management as one does not have a handy backup gas supply swimming nearby.

 

[Tortuga68]

What is the SDI recommendation for solo diving - twins, pony?

 

[idive2]

They also teach that a higher level of situational awareness is required when solo diving.
Observing more closely for entanglement issues and other possible what-ifs is even more
important when diving solo. As has been mentioned the absence of anyone else to help with
an entanglement or provide air if a situation arises is the reason for the more stringent air
management guidelines.

 

[Dyno Bill]

I feel it all varies depending on dive profile and style. If you do a jump down to a specific spot or item then it's relatively predictable. I always did rec diving in shallower water,maybe 80 to 100 max and many times shallower. I like to explore coves and walls in the general areas a boat may be at anchor in. I have many times been a third of a mile from the boat when hitting 1000 lbs. In my opinion that's a good time to head for home. I usually hit the area of the boat around 500 and can goof off a bit more if something of interest is seen but I have done really long surface swims before due to poor gas management and it's not fun. A couple of times I have taken my BC off,inflated it and paddled back lying on top of it. Thats actually really a lot easier than surface swimming. When diving with others I commonly use a larger tank and am back at the boat with a lot more gas than needed but I like to have extra should someone else need a breath. Over the years I have picked up a few hitch hikers not even with my group as they were in need of something to breathe. Thats the fabled insta buddy in my opinion.

 

[Tortuga68]

Eh, the fact that the conseqences may be more dire when you're solo isn't a reason to pay less attention to entanglement or OOA because you have a buddy IMO