As I gradually replace all the gear on my sailboat, I've come across a consistent problem. Rope, winches, blocks, anchor chain, cleats, etc. are often rated with a "safe working load." Great to know, but this information is useless unless I know what kind of load these components will be under once installed on my boat. Right now I'm clueless as to how strong something like my headsail halyard needs to be, or what kind of load my winches will encounter. I just take peoples advice on what I need, but this is inconsistent and I'd like to know more. Any thoughts? Anybody know a website or book that gives a way to figure out what kind of loads & forces are happening on my boat so I can more accurately buy gear?