What is safety spool in diving?
A safety spool is a small hand-held spool of line, typically 15 to 30 m, used to send up an SMB or to run a short jump off a guideline. It has no handle, no brake and no moving parts, which is why it jams far less often than a reel.
A safety spool — a finger spool — is a flat disc of Delrin or aluminium with a groove full of line and a hole through the middle for your finger. It carries far less line than a reel and has nothing on it that can go wrong: no handle, no ratchet, no lock. That simplicity is the whole reason the word "safety" is in the name.
What is the difference between a spool and a reel?
- A spool holds 15–45 m, has no moving parts, and is deployed by letting it hang and spin on your finger or on a double-ender. Drop it and it stops. Cheap enough to carry two.
- A reel holds 50–150 m or more, has a frame, a handle and usually a brake, and is what you use to lay a long primary guideline. More line, more control, and more that can jam.
Divers carry both for a reason: the reel does the long work, the spool does everything short.
What is a safety spool for?
- Sending up an SMB — by far the commonest use, and the reason every recreational diver should own one.
- Jumps and gaps in a cave, where one line is connected to another.
- A short search pattern, or marking a spot to come back to.
- A backup way out. In an overhead environment a spool with a few tens of metres on it is a spare exit line if the primary is lost, and that is where "safety" spool comes from.
How much line do you need?
Match it to the depth you actually dive, plus slack. 15 m is enough for a recreational profile inside 20 m; 30 m is the common all-rounder; deeper or decompression diving wants 45 m or more — a line that runs out before the buoy reaches the surface is a line that pulls you with it.
How do you use one without tangling it?
- Wind it under tension, evenly, in one direction. A loosely wound spool birds-nests the moment you let it run.
- Let it spin, don't feed it. Hold it by the finger hole or by a bolt snap and let the line pay out on its own.
- Never clip a loaded spool to yourself — the double-ender goes on the spool, not on your harness.
- Take up the slack last, once the buoy is up and the line is vertical.