More or less random ice diving and equipment thoughts
I think the whole issue surrounding the hole should be an integral part of any ice diving class. In ice that is not excessively thick, up to about a foot thick, you cut a triangular hole and slide the piece of ice under the ice, then when done diving slide it back into the hole. It will have melted a bit and be slightly undersize, but it helps the open hole freeze closed much faster. You also mark the hole so that skaters, snowmobilers, ice fisherman driving across the ice etc, do not fall in. In thicker ice, you may have to cut it into chunks and lift it out. that gets complicated as the pieces freeze together once out of the hole - makes for a messy lake with large thinly frozen over holes all over the place.
Cutting the hole and setting up is 90% of the work. It makes the point that ice diving is a group activity that requires at least 4-5 people. Placing the hole in shallow water seems to make sense as deep diving under ice strikes people as "dangerous". But the other point of view is that the area of interest is often the ice itself and no one is gonna go to 100' anyway. And it is a group activity. When one of the divers in the group stirs up silt, the viz goes to hell pretty much permanently and the magic of ice diving evaporates. If you put the whole in shallow water, put the crappy divers with poor buoyancy skills last in the group. Threaten those going before you with death if they rototill. Personally, putting the hole in 60-90 feet of water if possible makes more sense to me as it keeps people off the bottom.
Spreading sand or gravel around the hole can make it easier for tenders - unless it is sunny out and not too far below freezing. In that case, the darker gravel will absorb heat and melt ice and the melt water can then be problematic in addition to all the other water that ends up out of the hole.
I have seen lines secured and tended two ways.
1. One with the lines secured with ice screws so that they are still secure if a tender drops them. The up side is obvious, the downside is that multiple lines can get tangled as the divers circle the hole so it limits you to one diver in the water at a time.
2. The divers just hold unsecured lines. The downside is obvious in that the line could be dropped with the diver moving off under the ice with no way home, and or the tenders walking around on the ice as potential slip and fall accidents waiting to happen. The upside is that the tenders can move around the hole and keep the lines straight and tangle free - essential if you have 2 divers in the water at once.
Traditional ice diving uses a fairly short line of maybe 100' in lenght. A safety diver will have a slightly longer line.
Some instructors advocate having two divers in the water for immediate support/buddy system reasons. That philosophy pretty much requires line tending approach number 2.
Other instructors advocate one diver in the water with another diver sitting on the edge of the hole ready to go acting as a safety diver and hooked into a slightly longer line. Maybe 150'. In that case approach number 1 makes a lot more sense.
Both are pretty dated from a technical diving standpoint. If you are cave certified or advanced wreck certified, you have a couple more options. My favorite method of ice diving occurs early and late in the season when ice forms or remains in bays with open water in the middle of a lake. Ideally you find a point with open water on the end, then dive back under the ice using a primary reel and cave pentration techniques from a tie off in open water and a continuous guideline to open water. All the fun of diving under the ice, with a lot more to see and zero work cutting the hole. The longer distance however does require redundant gas supplies.
In that case, unless you are able to shut down both the left and right valve or the isolator on your manifolded doubles in a dry suit with heavy underwear, heavy gloves, etc, redundant doubles are not adequate as a freeflowing reg could result in you losing all your gas. If you can't isolate dive independent doubles or dive your manifolded doubles with the isolator closed and manage the gas like you would independent doubles. A single tank with a large 30 or 40 cu ft pony also makes sense when ice diving. A slung pony can be unclipped and handed out of the hole, and is a bit easier than getting out with doubles.
If the lake is fully frozen over, tying off to an ice screw outside the hole and doing a secondary tie off immediately under the hole (perhaps on an anchor or cinder block lowered carefully for that purpose) lets you use the same cave diving approach to ice diving.
If you dive wet, pre-flooding the suit with luke warm or tepid (not hot) water helps a lot (very warm or hot water will expand capillaries and actually promote heat loss) to reduce the initial chill as your body does not have to warm that initial layer of water in the suit. Also, when you get out, immediately cover the suit with a wind proof rain suit or simialr garment to prevent evaporative cooling. Other wise the wet outer layer of the wet suit becomes a big swamp cooler. The same applies to neoprene or crushed neoprene dry suits - cover them quickly until you get out of them or get into a warming house.
Neoprene dry suits are ideal for ice diving - much warmer than a trilam or a crushed neoprene suit. And whatever you use, keep enough air in the suit to fully loft the underwear. Diving partially squeezed may be good form in comparatively warm "cold" water, but in the 35 degree water you find ice diving, a partially squeezed suit is just a recipe for getting colder sooner.
A sealed reg is nice, but use good cold water technique anyway. Never inflate or breathe the reg until it is fully submerged (check the reg at home if it worked then, it will still work at the dive site) using the reg at all above the water, just supercools the first stage. Pull back any hose covers to expose the metal fittings - it improves heat transfer. Don't inflate and inhale at the same time. Use small blasts on the infator, not one big long one.
The foldable geodesic shaped tents utility companies use are ideal for an easy to set up warming house. They set up and take down in about 2 minutes and are big enough to dress in and accommodate a propane heater. Find one, or befriend someone who works for a utility company who can borrow one from work.
Know the water depth before you make the hole. Nothing like going to all the work to make the hole and discovering you have 2 ft of water between ice and bottom. Guess how I learned that one. Yep, some days I have stupid attacks. I am gonna make that part of a side mount ice diving course some day.