When I first looked at this post I actually thought it was me you were talking about. I just went on a boat dive with a couple people that were asking about our doubles some (in the great lakes area). Your profile pic looks like it could be one of the people on the boat. Then I saw the post date, and realized you posted this before I met those folks. Though, some of our group did a community fun dive a bit before you posted this, so maybe it wasn't me, but my friends
(probably not). That said, I feel like I can probably chime in a bit here.
Getting cold? Nothing to see?
This is a good point. When diving lake superior it can be cold. So calling a dive early can be a good way to make sure you dont get too cold when doing multiple dives throughout the day. Though, this wasn't the case for us last weekend. The water temps were great!
Swapping tanks sucks and it's usually not about volume, it's about redundancy.
I agree with this wholeheartedly. I know some people don't see it as a pain, but I hate swapping tanks. I'd rather get out, set my kit down, take a break then just put it back on and go. Though, we still do an equipment check, so one could argue that we're not really saving much time here.
Your second point is more important to me. I really like the redundancy that doubles allows. Especially when doing deeper dives or dives in cold water. I've never had an issue with my regs but I will some day. And I like the redundency that doubles provides.
I'm also diving the tanks that I got from
@lostsheep. This means nothing, just thought it was a fun fact.
Assuming these are not unusually small tanks, there is no technical reason for their early exits. My best guess would be that they were doing some kind of training exercise.
In my opinion, every dive is a training dive. Generally, my dive partners and I try to do some skills on every dive. Even if we spend an hour doing a "fun" dive, we'll try and sneak in some skill training somewhere. Could be something basic like deploying an SMB when we don't actually need to. Or something more in depth, like doing an s-drill. Often, its super basic, just finding a point of reference and practicing some back kicks or helicopter turns for a few minutes.
By diving the same exact kit every single time (that we can). We just keep building skill and confidence so that when we (eventually) do our deeper technical dives, we're comfortable with our kit. All the skills we've been practicing from the beginning translate to a 250' dive.
Diving doubles is so comfortable underwater, and extremely easy to acquire excellent trim, that you will forget about the burdensome aspects while on land: entry / exits and staging yourself. When I can dive doubles, I prefer to dive doubles.
This is another point I totally agree with. From day one of diving doubles I fell in love with the way they feel in the water. I won't go back to single tanks, unless I absolutly have to.
On top of all of that, I think it's a massive PITA to switch between singles and doubles, unless you have enough money to buy multiple sets of gear. If you dont have multiple reg sets, you need to switch all your gear around to work with one first stage. Plus, your doubles wing isn't ideal for a single tank. That doesn't bother some people. Which is fine, but if it does bother you, now you need another wing. I think it is just a lot.
I'd be willing to bet that those divers you were with weren't thinking about their bottom time, but rather they came up with a plan, dove their plan, then finished the dive, as planned. It just so happened that those plans only required a 30 min bottom time, or whatever.
