Ratlines hark back to visions of sailors deftly climbing the rigging of large sailing ships, checking the sails and the horizon as they go. In modern times, ratlines are used to climb above the level of the deck, up into the sails of a ship to check for obstacles in the water. When sailing in wide open waters , ratlines are not so necessary, but tropical waters with coral require checking the water every so often, and ratlines are a useful tool for this purpose.
Sight the horizon and use it as a level guide to set your ratlines. Decide on the height of the first ratline based on where you will climb from. Mark the point for one side of the first rang of your ratline with a permanent marker on the aft shroud. Mark the forward shroud for the opposite end of the first rang.
Parcel the shroud lines with friction tape for several inches above and below the marks for the rungs. Transfer the marks to the friction tape. Parcelling is wrapping a cushioning material around the shroud lines to keep moisture out. Self-stick friction tape works well in this application, as it can be wrapped for several inches and sticks on its own.
Apply service to the parcelled shroud lines with the waxed sail thread or tarred marline. Service means wrapping several inches of tightly wound line around the core line, which will serve as a rest to keep the ratline rang from sliding down. Double service is recommended for the most secure lines.
Tie a constrictor knot by looping the line around the shroud and cross the ends in the front. Take the short end back around the line again below the cross over, then over the top of the other section of line. Take the end and slide it beneath the "X" where the two lines crossed, but above the shroud line, between the two. Pull it tight. Finish the service by twining the line around the shroud for 3-inches in very tight loops. For the last few loops, loosen the loops then slip the end of the line back up through the loose loops and tighten. Add the service to the opposite shroud in the same manner and continue for each rang all the way up.
Attach the wood rungs above the service. Hold the piece of wood to the shroud lines. Mark where the rang will align with the shroud on each side. Mark a cut line for the end of the rungs leaving an inch on the rang past where it meets the shroud. Make this line match the angle of the shroud. Rout grooves on the line where the shroud lines will attach to the wood rang so it fits snugly.
Attach the wood rang on the shroud lines aligning the grooves you routed to the shroud lines, fitting them just above the service and resting on the top edge of it. Clamp the wood rungs with stainless steel strapping folded over the rang and shroud, then screwed in place. Another way to connect them is to attach a sta-lock bar toggle to the shroud, then screw it in place to the wood rang.
Repeat the parcelling, service, and custom marking the rang for fit all the way up the shroud, to the height you want the rungs to reach. Place a rang every 12-inches, and calculate the number of rungs you need by the height. For example, if you want a 15-foot ratline, you will need 15 rungs or one every foot.