Unless they’ve added it recently, the instructor guides for neither the SDI Solo course nor the PADI Self-Reliant course require a spare mask. The PADI guide recommends one.
It is not required in the SDI course and I do not carry one. We did, in my SDI course, practice a dive with no mask and then demonstrate diving with a mask without the strap. Y'all realize, this used to be part of basic scuba, broken strap and lost mask.
During the class, about 10 minutes of one dive was done with no mask. Just continued the dive. No problem. I cannot recall actually loosing a mask. I have broken a strap and anyone who has difficulty retaining a mask, no hood needed, without the strap needs to get a better fitting mask. It is almost a non issue without a strap.
I just remembered, I had a skirt tear on a old (vintage rotten mask like 30 years old) and flood me out. Even with that I was able to keep a bubble in it long enough to read my gauges easily and continue the dive to a safe conclusion.
Now, my solo instructor did require a snorkel, which we never used, but I bought one especially for him and rolled it up in a little pouch and put it on my shoulder webbing way back by the plate out of the way. But I have no room for a spare mask and I will not be toting one for anything short of something like a cave or wreck penetration dive (which she who rules my life forbids now
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I have done actually dangerous things in my life (many times in the past), and largely, aside from cave diving and maybe spearfishing on the rigs, the sport of SCUBA is not one of those dangerous things.
After poo-poohing solo diving courses I would say that it did have merit. No, you cannot learn to solo from a course, I still hold that opinion, but for experienced divers who are about to go solo or who already have been, it was a useful exercise to bring a little focus and order to what I had been doing, which I plan to keep right on doing, thank you. Or, if one is not experienced then it would be useful. I guess I wrestle with the "how much experience does the solo diver need" question. In my case I have been solo from the beginning. Obviously I had no experience, but I was a strong swimmer, kinda smart for a kid, and my diving locations were limited to benign, shallow places. So, I guess, if one is going to solo, regardless, the course is useful.
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