I've been reading the ratchet block threads with great interest. Reduce hand fatigue, improve safety, prevent embarrassment...yep, gotta have at least one of those.
Unfortunately, I haven't quite figured out exactly what it is they do. Let's say, for example, in a mainsheet: I *think* they allow you to leave the sheet uncleated most of the time, because they won't let the sheet run out all of a sudden unless there's a substantial load on it (like a gust of wind). You can let the sheet run out if you want to by "easing" it. Not quite sure what easing is, but I think it means pushing the sheet out of the block groove so it just slides around the sheave without turning it.
So far, maybe so good. Then come the variations: auto ratchets, manual ratchets, auto-manual ratchets, and switchable versions of these. Some Harkens allow ratchet tension to be adjusted; some Ronstans allow switching from manual to auto.
I think that on-off switchable manual ratchets act like a conventional block in the off position, that is, they're free-running all the time. I also think that in the on position they allow the sheet to run out if the load exceeds a set amount. I'm not quite sure how auto ratchets differ from this; do they allow the sheet to run out when the load exceeds a set amount, and do they somehow determine this load themselves?
If anyone can recommend a good book on the subject, I'll gladly read it and write a book report.