Stability - the ability of the model not to tip over - is a function of hull design, and most models have ballast keels. Unlike many full-sized racing boats, centerboards are seldom found on racing models. Like full-size keel-boats, model yachts will sink if they fill with water. For this reason a fiberglass hull is a top choice for the beginner unless he has the skill to plank up a watertight hull. To insure that the hull stays dry inside so the model won't sink and, equally important, to keep the radio receiver and equipment dry, the hatch should be designed for easy removal and yet be sealed tight for sailing.
Within the hull space are: a standard radio-controlled receiver, batteries for the receiver, a sail winch for trimming the sails, batteries for the sail winch, and the two or more servo mechanisms which steer the boat and control the winch. Rechargeable batteries are in order, since the typical operation span of most systems is about one day's racing or two hours' continuous operation. Dry batteries have the disadvantage of needing frequent replacement (they are not rechargeable) but they offer the advantage of giving some warning that they are getting low since they drop slowly in voltage as they discharge. NiCds, although rechargeable, do drop suddenly in voltage once they get on the edge of discharge. One of the most common problems the model skipper encounters is the loss of battery power while his model is out on the pond. Very often what appears to be outside interference to the radio turns out to be low batteries in the radio-control system which causes the receiver to act weird.
