A beginners' guide to RC sailboats

Radio Control Boat Modeler, Jun 2000 by Houle, Tom

You can make a light, strong radio board out of 1/8-inch poplar plywood. Make this board removable from the hull. See Figure 3 for the sheeting arrangements for single- and double-purchase sail arms. I recommend the double-sheeting arrangement; it offers more travel than a single-sheeting arrangement. Futaba sail winches come with one arm extension rather than two, but this arm is easy to replace or extend with a new, double arm cut from either 1/16-inch aluminum or G-10 fiberglass board.

SAILS

* Sail basics. To understand how sails work, we need to review elementary aerodynamics. Only when running straight downwind does the wind "push" the sails. During a broad reach (wind on the beam of the boat) or while beating (boat moving into the wind), the sails develop lift through their airfoil-like shape. Sail panels are cut (broad seamed) to develop a specific three-dimensional airfoil depth when sailing to windward. The air flowing over the jib and main sails generates a lift vector on their tee side. This lift vector drives the boat more sideways than forward. This is where the fin keel beneath the boat, with its own symmetrical "airfoil," comes into play. Without the fin keel, the boat would simply move sideways and make no forward way. The fin keel resists sideways Oee) motion, and at the same time, it develops hydrodynamic lift that keeps the boat tracking forward.

When the sail and fin-keel forces are working together, they maximize the speed of the boat in your chosen direction. When this happens, we smile broadly and say the boat is balanced, sailing as if it were on rails. Some kits come with sails or there will be instructions where to buy them. If you're scratch-building a scale model, you can find a sail maker who will make sails that fit your spars and are cut to match your wind and pond conditions.

* Installation. In Figure 5, note that the comers of both the jib and main sails are attached to a wonderful little gizmo called a bowsie (see Figure 6). A bowsie enables you to tune your rig for the day's sailing conditions. You can buy bowsies or make them out of 1/32-inch aluminum or brass strip or even 1/16-inch plastic. The bowsies should be at least 1/2 inch long with three holes drilled approximately 3/16 inch apart. (Bigger bowsies are acceptable.) You'll use a bunch of these on your boat. You can buy them from Pop-Up Mfg., George Ribeiro, Victor and other companies. I make my own and drill them to barely clear the diameter of woven 20- to 30-pound fly line, which is what I use for my main and jib sheets, backstay and jibstay. Fishing snaps are nice for attaching the jib swivel to the deck, the sheet ends to the spars, the jibstay and backstay to the mast crane, and so on.

* Making your own sails. About 12 years ago, our sailboat club was convinced that we could make our own sails and save a lot of money Well, we did make sails, and we did save money; but one Sunday, a guest came to race with us. His U.S. One Meter wore a suit of commercially made sails, and he won every race, roundly trouncing our boats with their pretty but, oh, so inefficient sails. Since then, our club has progressed to the oint where nearly evervone uses commercially made sails. If you want to go fast, you either become a competent sailmaker (a dastardly black art) or buy sails.