You'd have to keep in mind though that on a typical boat schedule 1 hour SI happens with the 2 tanks before lunch. Then you have a lunch break with 1.5-2 hours SI, and so far I've not seen 2 tanks after lunch offered. You really need to be someplace that's "all you can dive" and is relatively deep at that: e.g. on Bonaire you can easily finish your dives in the shallows with your computer crediting that towards off- rather than on-gassing. (Bubble models tend to imply that off-gassing is more efficient at safety stop depth than at the surface.) Liveaboards would be one example I guess.
Like
@scubadada said, typical boat where? In NC and NJ, the boats I've been on do a dive, an SI where people may eat something if they brought it, a second dive, and then head back in. If both dives are on the same site, the SI could easily be "encouraged" to be 45 minutes. Even if the boat moves to a new site for the second dive, the sites seem to be normally chosen so that the boat is at the second site and ready for divers to enter after a 1 hour surface interval. It is also common to hear the boat captain start to tell people "okay, folks, it's been an hour," meaning they have had a 1 hour surface internal, so they should be getting in again, if they want to do a second dive.
People frequently eat their lunch after the second dive, on the 1 - 2 hour ride back into the dock. Those boats don't usually go out for afternoon dives.
I do have a nagging question, which I'll throw ope, but will also direct at
@scubadada &
@stuartv
Cold water diving - completely alien to me as you know:
I was taught (and it came up in my DM theory) That for cold water diving, using the PADI RDP, you add 10' to your max depth for added conservatism.
Is this still considered normal practice?
How do people do this on a computer? Do they increase the conservatism by 1 step, or just dive the NDL with no modification?
I'm always assumed that that dive computers don't use the temperature in their calculations (but happy to be corrected)
I did SDI OW, which really just focused on using computers for diving. I do not recall anything about using tables and picking the next depth level for determining NDL in cold water. I also do not recall anything specifically said along the lines of "if you're diving in cold water, bump up your computer's conservatism."
So, in my very limited experience, I'd say the answer to your specific question is no, that doesn't seem to be normal practice.
And, I do not know how people handle cold water diving, in this regard. I believe tech divers will generally use lower GF numbers. But, I really don't know what, if anything, "typical" rec divers do in this regard. I have never talked to any of them regarding that subject. However, my suspicion would be that those recreational divers diving in cold water do not make any adjustments to their computer based on it being cold water. I suspect they either dive in the cold for as they long as they can stand it, or as long as their gas holds out, and if all that is as long as their NDL, then they just dive their NDL.
I haven't done a comprehensive survey, but the only computers I can think of that take temperature into account are the ScubaPro ones with their biometric factors that they incorporate. I think they claim to factor in water temp, skin temp, heart rate, and gas consumption. I would GUESS that they would only use those factors to shorten NDLs, never lengthen them. But, I guess that information is proprietary and it's moot for me as I won't be using one of those computers in the foreseeable future.
The only published, peer-reviewed deco algorithms that I know of - at least, that are in use in commercially available computers - do not include any kind of temperature in their parameters. I'll be sticking to computers with those kind of algorithms in the foreseeable future and managing my own conservatism parameters.