I have some spare time that I want to spend. Hence, I will reply to this post. Please note that I am only reacting to these exact words, not to the whole discussion. So, just isolated comments. I am not taking sides. Just my opinions below.
2) navigation in caves on the mainline is done with cookies,
Yes
when you live the mainline you usually put an arrow
You meant a personal cookie to count the team?
- Surely at every fixed T there are arrows already installed.
- If visibility is good and jumps are done instead, then you had better add your arrow where needed, that is true. And cookies to count your team.
3) What are you saying? In a cave, often you CANNOT choose your diving profile
Correct
4) I have no idea of how lines are placed for ice diving;
They are placed at the bottom.
Right, you can always try something like this:
but as far as I know I am about the only person to have attempted something like that at least in my home town +100km
I imagine they are usually far from the bottom
No. A permanent (or personal) line runs along the bottom even in ice diving, unless you follow the ceiling.
If you have a line tender, then there is no line belaying, of course!
If the line gets broken far from the entrance, the other part may fall towards the bottom
It is plain
stupid to use a negative rope when following the ceiling or while doing ice wreck dives with a line tender. A negative line in ice diving is perfect when... let me think... never? Neutral or positive.
Our ice diving rules tell us to ascend to the ceiling when we get lost (to save air and to facilitate rescue by circular search pattern). This obviously applies to dives along the ceiling or to dives with a line tender. Cave diving technique ice dives follow usual lost line procedures.
if it is negative, like in the figure on the right, or towards the ceiling if positive, or moving around a lot if neutral. In all these scenarios, the usual techniques used in cave diving would be WAY less effective
(indeed, in a cave the natural obstacles would stop the line to move around that much
Walls. That is a point. Remember though, that the walls do form a pipe, and if there is a current, the broken line disappears at the horizon. In ice diving a current is less common.
Ice diving in a current in low viz is a STUPID thing to do unless you are on a rescue mission.
And I wouldn't be surprised to find other aspects that are specific to ice diving
1. Free flow --> brain freeze --> urgent need to exit --> hold your breath --> trash your lungs
2. No backup mask. See #1
3. Loss of buoyancy --> sudden stop at the ceiling may hurt
I can for sure attest that #1 is actually a real risk.
If a novice asks a cave diver "how do you navigate in a cave?" and the answer is only "Continuous guide line to the surface. Compass... and know how to use it." That novice will understand almost zero of cave diving navigation. Could you give more details?
Details: "This thread is your life line. If you loose it you will never find your way out and you will have but two options: suffocate or inhale water. I recommend the former. Now choose."
There is a whole lot more to say about visual clues in navigation, about compass use, about lost line drills, about buddies etc etc etc but healthy fear is good. Heroes fall.
- is the no-visibility due to particles (like in cave diving) in the water a common scenario in ice diving?
A good point. Probably not, except for some public safety diving.
- is the darkness a serious problem like in cave diving?
At certain sites the abyssal zone starts at 20m/60ft
"If I am right, it is better to take an ice diving course before going under the ice".
Certainly. And do make sure that the instructor has more ice diving experience than the minimum. Why would one need a cave course for ice diving when there are dedicated ice diving courses?
Just make sure the courses cover the chosen technique. Line tender / fixed line / own reel and suitable emergency procedures.
Cold water comes with its own risks that are quite different from the risks of cave or sump diving.