Arguably the most powerful navigational tool that can fit in your pocket, the handheld GPS has become more than just a means of fixing one’s position. Matched with today’s data-filled digital charts, the modern handheld GPS is a chartplot-ter, marina guide, tide checker, and more. Alone, or interfaced with the ship’s navigational network, these tiny—and relatively inexpensive—devices can serve quite handily as the ship’s primary means of navigation. Compact enough to be kept in a Faraday cage where they are immune to lightning strikes, they are ideally suited for backup service on a cruising boat. …