I have TWO x bow rollers .. neither having any way to stop the chain "jumping off".
I have a windlass
, that I only use when the chain is "Up_&_down" (to break her out)
Then I just haul her on up: quicker
Problem is - with no "pin_across_the_top" , to stop the chain rising upward, it frequently happens that the chain 'jumps out of roller, slips out, down across the gunnell and headds back toward my feet,
taking / grinding the gunnell as she goes.
As with most else, I've not found swearing too effective.
A massive heave forward _ up _ & _ Over again gets the chain back on the roller, and I'm back pulling chain, ready for the farce to repeat.