I wrote it and was not only thinking the way down, but the way up too. I know divers that use a 15/55 as an intermediate gas. When I read it back, yes, I had maybe explain that or did not mention the 15/55
And I agree that 15/55 is not the best choice for a travelgas on the way down direct from surface. You can then choose to go down on a 50%, switch at 18m-20m most times you can directly switch to bottomgas then. On way up you choose the 15/55 as intermediate gas. For a 100m dive, I would use an 18/45, and not an 15/55, but I know divers that take that extra gas, so they do that 100m dive with 4 stages. I prefer to do it with 3 stages and still have my reserves. The problem is not taking a breath at surface in calm waters and go down then on a 15/55. The problem is if you have to work and you still have the 15% reg in your mouth at surface.
On oc you are limited in the amount of gas you can carry yourself. I have done a 17 minute bottomtime to 110m depth on a wreck, oc. The reserves could not be taken by ourselves, so they where on the anchorline.
Even on cc you have to take bailout and are limited too on such depths, you really have to think about safetydivers if you want to do such dives. And safetydivers have to be paid too, so they make a dive more expensive too.
Decotimes depends on the depth and on the bottomtime.
If you do a bounce to 100m, that can be done in 45-50 minutes, really fast go down and then up again, stupid bouncing. A nice wreck with a 60 minute bottomtime at 58m with 2 hours deco will give a much longer runtime. But you have to make in both cases a proper gasplanning. And both dives will not be really cheap. Remember that always something can goes wrong and that you have all your gases paid, you are in the water and then you have to cancel a dive.
A few weeks ago I mentioned that I was breathing faster than normal at 132m, I was afraid of CO2 with my rebreather, so I went up again with my buddy. 10 minutes down to reach the 132m and a 80 minutes deco already. Around 110m I feeled ok again, but with such dives you go back to the surface then. The reason for the possiblity of CO2? Diluent was was a 6/73, so END was ok. The EADD was 48m (equivalent air density depth), so yes you feel that breathing gets harder at such depths. Scrubber was used in 4 degrees C water at such depths. So CO2 was possible. I have dived home the same scrubber (this was last dive of the trip) on 2 dives to 10m max and no problems. But I still think that there was some CO2 at that depth. That was a 150 euro dive where I have seen nothing
But happely the bailoutgases are still in my tanks and nothing went wrong.
