Originally Posted by Faster
... the furling line escapes the drum cage and locks itself, effectively 'jamming' the furler. It's only happened during sailing, never part way through a furl or unfurl. Requires a trip forward to straighten out. I suspect it happens at the end of an unfurl with too much slack in the furler line...
Faster, I have also assumed that to be the reason for Harken jams, the issue with part of the top being broken, is that the unit will consistently jam if any slack is permitted while unfurling.