These look kinda cool, but I'm trying to imagine an application for them on my boat.
I think the inexpensive rings underneath the tramp are lightly loaded and work just fine as they are.
Perhaps the cunningham blocks up by the tack? Jib sheeting purchase? Spin halyard (up top)? Traps?
Haven't had trouble with any of these areas yet.
I can see how they might be useful in some of the bunji routing systems for the spin sheet take up and trap lines...but these are more expensive than Harkan's 16mm blocks and I would much rather use the real block with a sheave and bearings.
The advantage to this thing, however, probably is with entanglement. If it's in a system that often has slack in it I can see how this would be less likely to mis-orient itself. Perhaps on something like the mast rotation limiter or something.
