Low cost GPS compass
A GPS compass is probably the best form of heading sensor available because it provides a direct read out of a vessels heading with no corrections to apply. It works by having two GPS receivers mounted a fixed distance apart and measuring the angular distance between them. Because the two receivers are both subject to the same errors created by outside sources these errors are cancelled out so that the heading obtained from a GPS compass is both accurate and reliable.
Up till now GPS compasses have been both expensive and quite large which has restricted their use to ships rather than boats. Now a new GPS compass has come on to the market that opens up the use of this new technology to boats of all sizes. The Seapilot made by Swedish company True Heading AB is a compact unit weighing under half a kilo and just 25 cms long which can offer a heading accuracy of 1.7°making it adequate for most navigation purposes.
One of the main attractions of this new unit will be its low cost and it is offered with a price tag of €800 which makes it comparable with many advanced fluxgate compasses used today but with the added advantage that there are no corrections to apply to the heading read out to get a true course. In addition to its steady heading information, the Seapilot will also give you GPS positions and speed read outs in the normal way of a GPS receiver.
Because the heading is obtained by interpreting the readings between the two GPS receivers there can be a slight delay in the calculations and to overcome this when making sharp turns a rate gyro is incorporated. This senses the angular turning of the boat and updates the heading readings until the boat is back onto a steady course thus maintaining the heading accuracy. It also allows for the heading readouts to continue in the event of a short term break in GPS reception.
True Heading is a Swedish company that has been a pioneer in GPS compass technology. They have developed a range of GPS compasses for ships offering an accuracy of 0.1° and it is from this experience that they can offer this new low cost boat unit. This Seapilot compass is likely to revolutionise the compass market and it should provide a much better autopilot heading reference as well as providing reliable heading information to other on-board electronic devices. However it does require a power supply to keep going so the original magnetic compass should still be carried on board as a back up.
By Dag Pike
