BMEA

Once upon a time, a log was a log and a sounder was a sounder.  They got on with their respective jobs and that was it.  Now behind the scenes, your instruments could be chattering away to each other, making new information out of the same raw data.

On their own, instruments such as a sounder, log, and wind indicator provide a lot of useful information.  So, too, do radar, a chart plotter, and a GPS.  Link them together so that they can exchange information between themselves, however, and the capability of the system becomes very much greater than the sum of its parts.

One of the clearest examples of this is the effect of feeding information from a log to a wind instrument.  Imagine, for instance, that you are motoring at 6 knots in a flat calm.  Your own forward motion will produce an apparent wind of 6 knots, dead ahead, which will be shown by your wind instruments.  They can’t tell you that there is no real wind.  Feed in the boat speed from the log and heading from a transmitting electronic compass, however, and it becomes capable of showing you the true wind speed and direction.

Linking a chart plotter to a GPS is an obvious application: one could even argue that without an input from the GPS, a chart plotter is wasted, and that without the ability to download waypoints from the chart plotter, the GPS is operating way below its capabilities.

Feeding heading information from a fluxgate compass into a radar immediately opens up the radar’s stabilised display facilities: use its course-up mode for accurate, reliable collision avoidances, or its north- up mode to help relate what you see on the radar with what’s on the chart.  Link in a GPS as well, to display your waypoint on the radar screen, or to measure the lat and long of identified contacts.

The ideas of exchanging information between yacht instruments goes back to the late seventies, when American autopilot manufacturer’s hit on the idea of using a position fixer to control an autopilot.  At first each company developed its own methods but as the idea became more popular, it became obvious that there were advantages in using a standard system.  In 1980, the first specification for a standard marine interface was published.  It was called NMEA 0180 because it was developed by the National Marine Electronics Association (the US equivalent of the BMEA).

NMEA 0180 served its purpose, but was limited in its capabilities: it quickly became obvious that a radical reworking would open up far wider applications, so NMEA 0182 was born, followed by NMEA 0183.

NMEA 0183 is still the current standard providing simple two wire connection between instruments, allowing them to send messages to each other as short, low-voltage electrical pulses – a kind of electronic morse code.  In theory, NMEA 0183 allows any instruments with NMEA (often pronounced “neema”) output to talk to any instrument with a NMEA input.  It usually works well, but occasional problems require expert attention to resolve.  Sometimes, for instance, one instrument listens for a particular piece of information but doesn’t recognise it when it comes from an instrument made by a different manufacturer: it’s like a Scotsman and Cornishman speaking the same English but sounding completely different.

As expectation grows and technology advances, NMEA 0183, although being accepted worldwide both in the leisure and commercial marine industry over many years is starting to show its age and, several manufacturers are using it only to communicate with other makes of equipment while adopting much faster  and more versatile interfaces for use between their own products.  NMEA itself has developed and introduced two new interface systems and protocols known as NMEA 0183-HS (High Speed) and NMEA 2000.  The latter system employs multitaker, multi-listener communication based on the CAN bus used in many road vehicles. It allows multiple displays to be controlled from a single remote panel and also simplifies the installation with a single power and data cable to all the interfaced products fitted.  The interface responses of such a system may be regarded as effectively instantaneous.

Computers

More and more yachtsmen are using PCs on board. A computer can be used as a tool for navigation, weather forecasting, communication or entertainment. First you need to decide on what hardware you need, how to install it, and the power and interfacing considerations.

The performance required depends on what you want to use a computer for. If you want it for email, web browsing, and for basic navigation software, then any new PC you’ll find in the high street is more than powerful enough in terms of processor power, memory and storage capacity. In fact, there are arguments for choosing a lower specification computer – to save power and have a smaller physical unit.

If you want to use the computer for graphics-intensive applications such as radar or 3D views in the chart plotter, video editing or 3D computer games, then you will want a high-performance CPU (possibly a dual-processor model), and as much memory (RAM) as you can install – usually 1–2GB. A high-performance graphics processor is also a big benefit, and this is one area where laptops lose out to a fixed PC.

Disk size is generally not an issue, unless you want to use the computer for video editing, or you have a very large collection of audio files and digital camera images that you want to keep on your computer.