Well, we use a locking box with an interesting geometry on Afterburner...the halyard is pulled through the box until a swaged on stainless slug passes into the box...then drops into a notch & locks in place. To disengage, we apply more tension to the halyard, pulling the slug further through the box until it clears the notch. It is now unable to re-engage in the notch as we release the halyard.
I like this system. Works well. Easy to engage and disengage.
However, there was an interesting point made about compression on the sheave. Unfortunately this system does not unload the sheave when it is engaged. The halyard still carries the load over the halyard sheave.
