Magnetic compasses are still the standard device for determining a boats direction. Nearly unchanged in hundreds of years, they are relatively easily constructed and inexpensive, and need only the power of the Earth's magnetic field. However, they point to the magnetic north pole, which is slightly different from the true north pole, and only indicate the direction your boat points. Yachts, especially multihulls, tend to slip sideways across the water, and currents can push any boat off course.
Electronic depth sounders are standard equipment on yachts, though they come in several forms. The most common ones, like Ocelot's, are a simple form of sonar that sends sound pulses straight down, and electronically computes the depth based on the time for an echo to return. This information is then displayed in either a digital readout or an analog gauge. Ocelot has both displays, mounted up by the helm. Some other boats have more fancy displays, showing bottom contours and soft echoes that may be fish. Depth sounders also detect water temperature.
A knot log, or hydrospeedometer, is another common instrument, though some boats rely instead on the more accurate GPS speed readouts. Knot logs work by means of a small paddlewheel that sticks into the water under the hull. As the boat moves through the water, the knot log detects how fast the wheel spins and displays the boat speed digitally. However, knot logs can be strongly affected by current, showing considerable error at times.
Anemometers, which measure wind, are less common on yachts, especially monohulls, since wind strength can be felt with reasonable accuracy. However, knowing the wind is important on a catamaran, and the wind in Ocelot's cockpit is often very different from the wind in the sails. For this reason, instruments which measure wind force and direction are mounted on top of our mast. The readout, which is located in the cockpit over the helm like the others, can show the apparent speed and direction (what the boat feels) or can electronically compensate for our forward speed to show the true wind.
One instrument that almost no yacht is without now is a GPS. GPS, which stands for Global Positioning System, uses satellites to provide accurate and real-time position information. A good GPS can determine latitude and longitude to within a few feet, and do so one or more times per second! By comparing different fixes, a GPS can determine speed and direction that is accurate despite currents or magnetic variations. A GPS can also hold waypoint information, and calculate the distance, bearing, and time to arrival. When a GPS is connected to electronic charts, you can view a boat's position relative to the chart, making it easier to plot courses and avoid dangers. Ocelot has two GPSs mounted above the main switch panel, and another which is hand-held and battery operated.
One of our more recent major projects was mounting the radar. This one was a bit interesting for us because, ideally, the radar screen is visible from the helm station, but inside, away from the sea spray. The problem for us is that we don't have any spaces that fill both those categories and are not in anybody's way. We considered raising the main switchboard and mounting the screen underneath it, but decided instead to attach the screen near the ceiling above the switchboard. The other consideration, of course, was where to mount the antenna. We had a mast radar mount, but instead put the radar on our first spreader. This makes it partway up the front of the mast to give us the best possible angle for observation.
Although an autopilot is essentially a convenience item, and not really an instrument, they can be very useful. Ocelot, like most yachts, came with an autopilot. However, it was an old model and didn't work very well. Specifically, the electronic fluxgate compass that it used to determine our heading was stuck on saying we were going one way. The problem was in the computer, not the compass, and replacing it is so expensive that for a long time we did without an autopilot. However, on the crossing between Curacao and the San Blas, we had to do so much hand steering, we decided we wanted to have a functional self steering system before we made any more passages. Although many sailboats can use a wind steering device which uses no electricity, it is not practical to mount one for a catamaran. Therefore, we bought a new electric autopilot made by the same company (Raytheon Autohelm.) Although it draws approximately four amps continuously, a considerable amount of electricity, it simplifies passages greatly. Connected to our other instruments, the autopilot can maintain a constant wind heading so we don't need to trim the sails, or keep a steady course to a GPS waypoint, as well as simply maintain one magnetic heading. Furthermore, our new autopilot has a gyro that allows it to compensate for rough seas, keeping the boat as smooth as possible.
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