First a little vocabulary. The heavy lines running from the sides of the ship to the mastheads are called shrouds. They're important structural parts of the ship's rigging. The ratlines, which are much thinner, run horizontally across the shrouds and serve as ladders for the crewmen going aloft.
I always encourage people to rig their own shrouds and ratlines. It isn't as hard as a lot of people seem to think - and once you've rigged a few of your own, you'll almost certainly conclude that those plastic-coated thread things that come in the kits are pretty hideous. (Besides, it's almost impossible to get them taut.)
The shrouds of the Cutty Sark are made of rope, and so are her ratlines. The shrouds are supposed to be looped around the mastheads; each shroud goes up from the deadeye, around the masthead, and down to the next deadeye on the same If you do a Forum search on "ratlines," you'll find quite a few posts that explain a couple of ways of doing it. If this is the first time you've tried it, I'd suggest the "needle through the shroud" trick. [later edit: somehow or other part of that last sentence initially got dropped. Sorry about that.] But tying them like the originals, with clove hitches to hold them to the shrouds, isn't really so difficult - and the Cutty Sark, with only a few shrouds per mast, isn't such a bad model to learn how to do it on.
Several Forum participants have urged newcomers to use overhand, or square, knots instead of clove hitches, but I've never been able to figure out why. The clove hitch is just about the easiest knot there is. Here's a web page that explains it: http://www.google.com/url?ysa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0CAcQjRw&url=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DHf6bbQKj1X4&ei=eZFQVKjVN8yxyATs-4CICQ&bvm=bv.78597519,d.aWw&psig=AFQjCNGXmZqq2JY81rwNdUxIjaOq48N6vA&ust=1414652664768479
I'll offer once more an observation I've made often in this Forum: rigging ratlines is pretty simple. It does have a learning curve, which is kind of steep but remarkably short. My guess is that, if you've never done it before, the first ratline you rig will take you ten to fifteen minutes. The second will take about half that. And by the time you get to the masthead you'll be tying one every minute or two, and wondering why people make such a fuss about tying ratlines.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.