So your lines don't chafe because they are chain. What keeps your boat from chafing because you're tied to a dock with chain?
The lines aren't chain, they are rope. The lines have a thimble spliced into the end of the line - exactly like you'd have on an anchor line - where it connects to the chain. The chain is secured to the dock, the chain is basically just a shackle on the dockside. The free end of the line is then attached to the boat as per normal; Bow, stern or spring line.
We are talking about chafe of the mooring line where it meets the dock so to answer your question specifically, it is the thimble spliced into the end of the line that prevents chafe.
Originally Posted by RhythmDoctor
Doesn't chain rust given enough time and exposure to the elements?
Yeah, I suppose it would. Far slower than line chafe and, since we're in Canada, they definitely outlast our sailing season - it's only a few months *sigh*