What is a centrepin reel
A centrepin is a drum on an axle. There is no gearing in it at all, so one turn of the handle is one turn of the spool. The simplicity is not poverty but a way of building a reel in which there is almost nothing to break.
How it is built
A frame, an axle, a drum and the simplest of brakes — a ratchet or a tension screw. The handle sits directly on the drum, so you recover exactly what one turn gives you.
Some do without a brake entirely and control the drum with a finger: on a reel like this that is more precise than any drag.
Trotting
In a current a centrepin lets you release the rig downstream at exactly the speed the water is moving. The drum turns freely and the float travels naturally, without being checked.
This is precisely where a spinning reel loses: the bail and roller add resistance that shows in the drift.
The fly reel
A fly reel is a centrepin too. In fly fishing it plays almost no part in the cast: the line is thrown by hand, and the reel is there to store the backing and absorb a fish’s runs. On the method itself, see the fly rods section.
The ratchet
The classic centrepin brake is a ratchet: a sprung pawl bearing on a toothed wheel. It does not so much brake as stop the drum overrunning on its own, while announcing by sound that line is going out.
Fly reels take this further with a disc drag and an adjustable setting. There it genuinely absorbs runs rather than simply clicking.
Why it survives
The centrepin was never fully displaced, and the reason is plain: it has no component that twists the line. No bail, no line roller — and therefore no twist. Line lasts longer on it than on a spinning reel.
The second argument is direct contact with the fish. Nothing sits between the hand and the line, so a bite registers sooner than any line would show it.
Advantages and limits
The advantages are simplicity, feel and reliability. The limits are a short cast and a slow retrieve. Casting a light lure a long way with one is hard, and that is exactly why it is rarely fitted to a spinning rod today.