Smaller Scale boats, up to 40 inches long will still need strong rigging line, such as Dacron, which can be bought from the Kite shops.
The line must not stretch, lots of fishing lines do stretch, so be very sure when buying line, to ask if it stretches.
Bigger Scale boats can use fishing Trace Wire, it is usually Nylon covered and is available in very many strengths, do not underestimate the strength of wire required.
The Nylon covering on the Trace Wire magnifies the actual wire size, so it looks a lot stronger than it is, use the breaking strain figures, do not let your eyes fool you.
The Trace Wire is joined with metal Crimps, which are easy to use and fit.
I initially rigged Bluenose using 40 Kg wire, it snapped first time out!, she now sails with 80 and 100Kg wire which lasts a fair time – – BUT, it does snap!!.
If the shiny finish on the Trace Wire is not to your liking, use a Waterproof Marker Pen to colour the line to your liking, the same can be done to the Dacron line too.