Mo2vation:
What is the best way to minimize the risks that are inherent with solo diving? Is it a 30 ft pony clipped off like Fido on the left Dring? Should I leave the pony in the stable and get a baby doubles with an isolator? Is it staying at reasonable depths (like 60 and up?), keeping the dive duration short (like 45 minutes or less?) Maybe solo only from boat dives? Im looking to speak with people who have given this a lot of thought, and have taken rational steps to enter safely into solo diving.
The first step is to recognize that a Buddy is merely a tool in managing risk. What this means is that if you choose to do nothing else, the reprocussion is an increase in risk, which is your choice to accept or not.
From there, it merely boils down into specifics as to what provides the greatest risk reduction benefits. IMO the first and most important "precaution" is within yourself: the willingness and ability to minimize your reliance on others (sometimes called 'self-sufficiency').
On the specific questions you asked:
1. Redundant Air. Manifolded twins are obviously the best, but a major hassle for travel-by-air trips. A pony works better here, if you feel that its risk-reduction is worth carrying. I've carried an AL13 at times; ask me for the technical details on the DOT CFR for flying with a pony (or just do a web search to find the webpage I have on this subject).
1a. Pony mounting location. What works best will have to be determined experimentally, and also on your requirements. For example, mounting options change if you're working with rental AL80's at a tropical resort versus a tank that you own at home and can permanently bolt an adaptor to. FWIW, I first tried a sling mount on my pony, but found that it physically interfered with my UW camera's use, particularly when in non-horizontal shooting postions. As such, I tank-mount it, and because I want a rig that allows for use of rental tanks on the road, my pony mount was chosen with this in mind (I went with the PonEase by SeaLutions).
2. Depth. Always a risk. Generally speaking, I dive a little shallower when solo, but not really by all that much because IMO its important to be completely in control regardless of if I'm with a buddy or not. My depth is also influenced by other environmental factors - for example, I'm willing to go a bit deeper when there's a hard bottom than when off a wall. Overall, I'd personally consider 60fsw to be very conservative, but then again, I've been diving for a long time and have a couple hundred solo dives.
3. Duration. IMO, its more of a risk when its coupled with Nitrogen Ongassing. For easy, shallow tropical reef dives, the concession I make is to do a "flower petal" pattern which navigationally brings me back to the center (where the diveboat is) every 750-500psi or so. I will always know exactly where the exit is at 1000psi, and will generally burn the last 500psi in healthy proximity to said exit.
3a. Decompression. Generally, I prefer to do no-deco profiles, but if there's something worthwhile to extend into deco, I'd do that, with or witout a buddy. I try to be more conservative in how "deep" I'll go into deco because there might not be a redundant air supply around...essentially, I'll not do a profile that ends up with more deco than I'll be willing to risk DCS by skipping if there's an equipment malfunction. As I said at the beginning, it all comes down to risk recognition and what level of risk you're willing to accept.
4. Platform (boat dives). Generally, most of my solo dives are from boats, because most of my dives are boat dives. I'd examine the risk potential of a solo shore dive due to the environment it is in. I've not made shore dives in places like Monterey to personally know if its conditions are acceptable/not, but as we all know, there's good days with minimal risk and bad days with unacceptable risk. One plus I will give for boats is that you'll have someone topside who's aware that you're down, which is less likely to be the case for solo shore dives, so there is some surface support which helps reduce risk for some of the accident permutations.
5. Weighting. You didn't ask the question, but IMO, there is absolutely no substitute for having some weightbelt-configured ditchable weight. If you are solo, the surface is your only friend (regardless of DCS risk) and weighting systems such as Weighted Backplates and Weight Integrated BC pockets are not as easily/quickly ditched to gain postive buoyancy.
6. Surface Buoyancy. Similarly, you should critically examine how your system floats you at the surface in case you come up either weak, in need of surface aid, and/or lose conciousness. If you end up face-down or have to extert significantly keep rolled back (such as a BP/W), this adversely affects your ability/capability for self-rescue and odds of survival. Since it stems from equipment, it is not an unavoidable risk.
-hh
On a shorter trip, I love to show newer divers want shipwrecks in cold, fresh water look like.
