I went to Fiji early in my diving career, and I did a series of dives with a large group of instructors and dive shop owners from New Zealand. One of the shop owners was obese, and he was an air hog. He managed to get in full dives through an interesting technique. He would swim up behind another diver, reach around and very skillfully take the alternate air. He would breathe off of it for a few minutes, completely undetected, then return it. Then he would wander off in search of his next donor. He was so good at it that he was rarely caught. They all knew he did it, and they joked about it on the surface, but they usually did not know when he was actually doing it.
Another reason to use primary donate and a necklaced secondary. No way to pull shenanigans on someone with that configuration.
People have mentioned using larger tanks, which is fine if they are available. At dive resorts, I occasionally would find a 100 CUF tank, but usually nothing more than that.
On the recent boat dives I have asked for larger air tanks. Here are the outcomes. I'm leaving the operator names out to protect the guilty.
* Operator #1: AL100s short-filled to 3000 PSI, so I actually got 90 cf. No extra charge
* Operator #2: AL80s overfilled to 3300 PSI, so I actually got 84 cf. No extra charge
* Operator #3: HP100s with 32% because they didn't have any with air. At the time I was not nitrox certified. Upcharge of around $10 a cylinder
* Operator #4: I was nitrox certified before this dive and asked for 100 cf of Nitrox. Got a short-filled AL100 at 3100 PSI, around 93 cf. Upcharge for nitrox but nothing extra for the AL100
I've only been on one boat where AL100s would actually fit in the tank holders.
My SAC is typically around 0.60 and I find I need fully 100 cf to avoid being "that guy" on deeper dives. I dive HP120s at home. I have, at considerable expense, shipped two of my HP120s ahead for a trip next week, because the op I'm using doesn't really offer larger cylinders in a useful way (you can request it but they won't guarantee it, no nitrox, AL100s, probably short filled, etc).
Another option is a stage bottle. This is basically a pony bottle but it's not used for redundancy, it's part of the gas planning (although it does provide some degree of redundancy in case of a failure early in the dive).
I do that while shore diving but it is hard to pull off in practice on a boat.
A question unrelated to etiquette but related to air hogs.
On a busy diving schedule (say, a 7-10-day liveaboard, 3-4 dives per day), will an air hog increase his/her chances of getting DCS if he/she dives with a larger tank or often steals air from other divers, like the Kiwi diver mentioned here earlier? The time spent underwater is the same but the volume of air (and nitrogen) consumed is not. The NDC limits are based on an average diver; will high rate of air consumption multiplied by the same underwater time make a diver an outlier? Is the higher air consumption rate pushing the diver to nitrogen saturation faster, or is it only time that matters?
As indicated upthread, there isn't any evidence to suggest that higher air consumption contributes to DCS.
Well said but air hogs are not necesary big. It would be interesting to see the profile of a typical air hog, though.
I weigh 240 pounds and while I am perhaps 20 pounds overweight, I'm mostly just a big guy who goes to the gym regularly. I believe my air consumption has much to do with muscle mass.
The 120s are great. Even if they're short filled, I get a nice long dive and have a truly sufficient amount of reserve air at the end of the dive.
