Ratlines are the “rope ladders” that allow sailors to climb the masts of sailing ships. Making these can be intimidating to new ship modelers. Here’s a short video clip showing the process of tying ratlines using the tried and true “clove hitch” knot that used on the full-sized ships.
In the video description on the Youtube sight, the poster says:
The model in the clip is Mamoli’s 1/54-scale English royal yacht Mary, 1660. This ship has only 1 mast with 4 shrouds on each side, limiting the number of ratlines needed. The ratlines are about 16″ scale inches apart. The card with the lines on it was created as a visual guide. Once the knots are done, I touch each knot with matte acrylic varnish to help hold the knot in place. Other modelers may use watered-down PVA glue for the same reason. You’ll notice I stretch the knots by grabbing the ends of the ratline and pulling outward. This tightens the knots, stretches the line, and prevents the “pulling in” of the shrouds that you see on some models.
This is, of course, just one way to add ratlines. Some modelers, especially at smaller scales, may use a sewing needle to run the ratlines through each of the shrouds, using no knots, then use glue to secure them. Others may simply glue each ratlines directly to the shrouds, again, using no knots.

Photo from ModelShipWorld forum, showing clove hitch knots in the middle, with cow hitch knots on the ends.
On real ships at full size, the ends of the ratlines are not knotted, but an eye is formed in each end, and those eye are lashed to the outer most shrouds. However, some modelers simulate this by tying the outermost knots using what is called a “cow hitch”.
You should use whatever method you find works best for you! Ω