Abstract: An autopilot system for a vessel such as a boat receives a pre-set heading direction set by e.g. the user and also receives the apparent orientation (heading) from a heading sensor. The difference between the pre-set heading direction and the actual heading is then determined and a correction signal is generated in dependence on that difference, which correction signal is then used to control the orientation of the vessel by e.g. generating a rudder correction signal which varies the position of the rudder. In the present invention, the correction signal is further dependent on the difference between the actual heading and a reference direction such as magnetic North or South. In this way errors due to differences between the apparent orientation as detected by the heading sensor and the actual orientation of the vessel may be corrected.

Abstract: An autopilot system for a vessel such as a boat has an autopilot unit connected via a drive to the rudder or other direction determining means of the vessel. When the autopilot unit is operating normally, direction information from e.g. a heading sensor is processed by the autopilot unit and the drive is controlled by the autopilot unit to determine the appropriate position of the rudder. The rudder is also linked to a steering wheel or other manual steering arrangement. When the steering wheel is moved during normal operation of the autopilot unit, this causes an interference with the control of the rudder by the drive and, if this interference has sufficient magnitude and duration, this triggers override of the autopilot unit, returning the vessel to manual control via the steering wheel. The override may alternatively be triggered by detection of rudder movement by a sensor.

Abstract: A hand bearing compass comprises an electronic direction finding sensor fixed in a flat rectangular compass body. An actuating button causes the sensor to measure a magnetic bearing in dependence on the orientation of the compass body in a horizontal plane; measured bearings are stored in microprocessor memories for subsequent sequential recall to a display. To align the sensor horizontally in use the compass has longitudinal sights for visual alignment with a mark and a flat upper surface of the compass body for alignment with the horizon to facilitate levelling. Actuator and longitudinal sights are laterally spaced to avoid obscuring the latter, and arranged symmetrically about a median plane of the body so that use is possible in either hand.

Abstract: A drive circuit applies an oscillating signal to the drive coil of the fluxgate thereby generating output pulses from the detection coils of the fluxgate, which pulses have an area proportional to the magnetic flux through that coil. The output pulses are integrated sequentially by an integrator. The output may be used directly to obtain the orientation of the fluxgate, and hence of a vessel in which the fluxgate is mounted but it is preferable on the grounds of accuracy and speed of response to apply a predetermined number of pulses from each detection coil, apply a constant signal to the integrator and measure the times between the application of that constant signal and the integrator output attaining a predetermined value. This may be measured digitally giving a more accurate measurement of the fluxgate orientation. Suitable error elimination means may be provided.