It doesn’t matter if you’re a wreck diver, scenic diver or a cave diver. The use of line is important to lead us back to the exit, mark our position to the surface, or to connect one guideline to another in a cave. We can choose either reels or spools, and the application generally dictates which choice to make.
In caves, we tend to use large primary reels to run line into the cave, tie it off regularly, and essentially allow us to exit the cave in zero visibility by following the line. The ability to deploy the line smoothly, and also to retrieve it if necessary it important, so reels tend to be preferred here. Spools are used to jump from one permanently installed line to another. A side passage in a cave, off the main cave conduit, would be a good example of this.
For sending up SMBs,we prefer to use a spool, around 40m long. This is small to carry, and is very easy to deploy. Also, it is virtually impossible to jam. Reel jams while setting off SMBs are frequent causes of rapid ascent incidents, so the simpler we can make this process, the better. Obviously, if we need to set an SMB off from deeper than around 30m, then the use of a larger primary reel can be considered.