Greenham Regis marine electronics advice and service

Kings Saltern Rd

Lymington

Hants.

SO41 3QD England

lymington@greenham-regis.com

Tel : 01590 671144

Fax : 01590 679517

Greenham Regis

Shamrock Quay, William Street,

Southampton

Hants.

SO14 5QL England

Tel : 023 8063 6555

Fax : 023 8023 1426

Greenham Regis Chichester

Itchenor Shipyard

Itchenor

W. Sussex

PO20 7AE England

Tel : 01243 511070

Fax : 01243 511070

Greenham Regis Emsworth

Emsworth Yacht Harbour

Emsworth

Hants.

PO10 8BP England

emsworth@greenham-regis.com

Tel : 01243 378314

Fax : 01243 378120

Greenham Regis Poole

Unit 3, 23 West Quay Rd

Poole

Dorset

BH15 1HX England

poole@greenham-regis.com

Tel : 01202 676363

Fax : 01202 671031

www.greenham-regis.com

Thirty years ago, marine electronics, or at least, leisure marine electronics, was in its infancy. A typical yacht had maybe an echo sounder and possibly a radio direction finder. GPS and chartplotters were unheard of, radar was rare and an expensive luxury, and logs were mainly mechanical.

Advances in marine electronics have given owners access to an array of evermore sophisticated equipment. It undoubtedly improves the performance of their boats, increases the pleasure the boats provide, and enhances the safety and convenience of life on board, so long as the individual products are right for that particular job and have been properly installed.

Modern marine electronics depend on very sensitive radio receivers and data handling circuits. They have to amplify and process the weakest of signals, while at the same time being able to cope with radio and electrical interference from the engines boat charging systems, from domestic services such as boat fridges and cabin fluorescent lights, and, increasingly from other marine electrical equipment. There’s no room in this high tech environment for poor installations, or for materials which corrode or fatigue when they are exposed to water, sunlight, or repeated movement.

Leisure marine radar

Radar prices have tumbled over the past few years. Technological improvements have come hand-in-hand with falling prices, making modern small marine radars more capable, yet easier to use than ever before.

The most obvious leap forward in small marine radar technology came in the early eighties with the development of the raster scan “daylight viewing” displays. Until then, all radars had such dim pictures that in daylight they could only be seen by peering through a cowl.

Raster scan no longer builds up the picture in stages. Using a rotating scanner, a raster display uses the same information to update a picture stored now in its electronic memory. Twenty five times a second, it flashes the latest update onto a small CRT screen.

Multi-function electronic displays

Multi-function electronic displays are one of the Greenham Regis specialities. These use the second major advance in marine radar... the application of raster pictures to liquid crystal displays (LCDs). LCDs are slimmer, lighter and use less power than CRTs and are less vulnerable to water.

The introduction of colour liquid crystal displays that are suitable for viewing in bright daylight and the multi-purpose display screen are the developments that Greenham Regis have exploited, allowing the user to select radar, chartplotter or fishfinder pictures depending on the sensors or antennas connected to the system. The enhancement of data and video interfacing using high speed bus technology, waterproof repeater displays for radars or chartplotters are now a reliable and readily available option, bringing the necessary navigation information direct to the helmsman, inside or outside the yacht.

The biggest improvement has been in the definition of the display.

Beamwidth has improved, the width of the radar beam, and ranges from 7 degrees down to less that a degree, great if you are looking for a narrow harbour entrance.

Pulse length has similarly improved when it comes to discriminating between objects that are on the same bearing but slightly separated in range. Short pulses give better definition, but a long pulse may be required to produce an echo from small or distant targets. Manufacturers solve the problem by making yacht radars that automatically change the pulse length to suit the range scale in use.

Spot size related to the graininess of the display. All raster pictures are made up of a huge number of spots called pixels. The pixels have become smaller, the human eye can’t distinguish them, so the picture can show smooth curves and fine detail.

Noise and interference

Other factors affecting the clarity of radar pictures can be unwanted blips that don’t relate to anything you want to see, but which can obscure real contacts. Manufacturers build extra controls into their radars, allowing their performance to be subtly adjusted to eliminate clutter, but unfortunately anything that eliminates clutter can also eliminate weak targets.

To overcome this, manufacturers have developed ever more sophisticated automatic controls to take over from the human operator.Radio noise is all around us, from the sun, onboard electrics, and even the radar itself. It’s most obvious on radar when you turn the gain up too high, when it appears as a snowstorm of speckles that are the visual equivalent of the background hiss you get when you turn up the volume on a radio of tape player. A high quality receiver will avoid picking up extraneous noise and won’t make much of a contribution itself: a lesser one will amplify everything, with the result that you have to turn the gain down to lose the noise, and risk losing weak contacts as well.

As you move up the price range, one obvious change is that you’re likely to get a more powerful transmitter. In most cases, this is matched by an increase in nominal range, but it’s important to appreciate you can't buy range, because range is limited by the radar horizon, just as the distance you can see is limited by the visual horizon, so a 48-mile radar probably won’t detect a ship any further away than a 24 mile set. The real virtue of power is that it enables the set to detect small targets without cluttering the screen with noise.

With a higher price you are also likely to get a bigger antenna. This is important because beam width is largely determined by antenna size. A good big one will always beat a good little one.

The other obvious change is the display. A bigger price is likely to give you a bigger screen, a choice of CRT, colour or monochrome LCD, and a dramatic increase in the number of pixels. But whether you need that extra quality depends on the size of your boat, the power available, and the use you make of it. Bear in mind, though, that any radar needs to be properly installed and set up if you are to get the best out of it, especially if it is to be interfaced with other equipment such as a compass, GPS or chart plotter.

Radar transmitters, inside their radar scanner units, produce very short pulses of super high frequency radio waves (microwaves), which are focused into a narrow beam by the rotating antenna. Pulses reflected back from solid objects such as land or other vessels are collected by the antenna, and passed to the receiver where they’re amplified and processed. This involves measuring the time between the pulse being transmitted and the returning echo being received. Radio waves travel at a constant speed of 300 metres per microsecond, so that the time interval is directly related to the distance the pulse has travelled to and from the target.

Echoes are only received when the scanner is pointing straight at a target, so the direction in which the antenna is pointing when an echo is received corresponds to the target's bearing.

The distance and bearing are then passed to the display, which uses them to build up a picture of a boat’s surroundings.

AIS radar

AIS radar has become the latest development. AIS stands for automatic identification system and is really anti-collision radar.

Greenham Regis recommends Comar Systems AIS radar, Easy AIS, NASA Marine Instruments or MX-Marine AIS.

AIS radar offers lots of benefits in that it can often operate where radar cannot function, such as seeing around bends on a river or estuary, or even where bad weather may obscure a radar display. The system can track up to 128 targets and picks up signals from both Class A and Class B (leisure) transponders.

Sea-Me active radar target enhancer offers increased radar visibility and consequently, safety.

Generally, manufacturers Raymarine Electronics, for example, have product ranges that incorporate most electronic instruments and not just radar. They work closely with manufacturers of ancilliary equipment, for inctance, Scanstrut radar and antenna mounts.

This is why the service offered by companies like Greenham Regis has become so valuable.

Sonar and fishfinders

Multi-function electronic systems

Multi-function electronic systems are all about networking yacht instruments. Link them together so that they can exchange information and the capability of the system becomes very much greater than the sum of its parts.

It was American autopilot manufacturers who first thought of using a position fixer to control an autopilot. 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 0183 is 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 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.

NMEA has developed and introduced two new interface systems and protocols known as NMEA 0183-HS (High Speed) and NMEA 2000. The latter 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.

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.

GPS Navigation Equipment

Electronic position fixing can relate our present position to the world around us easily, accurately and instantaneously.

GPS (Global Positioning Systems).

GPS receivers cost as little as £100 and offer better than 20 metres accuracy wherever you may be. Garmin GPS and Magellan GPS are both recommended by Greenham Regis. Garmin GPS now extends to touchscreen handheld GPS for multi-activity use.

DGPS

There are plenty of reasons for wanting accuracy better than 20 metres, so Differential GPS (dGPS) provides.

A Differential Beacon Receiver (DBR) receives position correction signals. The DBR may be integrated with the GPS, but many are separate “black boxes” designed to enhance the performance of existing GPS sets.

All GPS receivers, for instance, can store planned positions as “waypoints”: you can tell it where you want to go, and it will tell you the direction and distance you have to travel.If you need to zigzag round obstructions, you can make up a route by stringing several waypoints together like a join-the-dots picture.

By using what is know as the Doppler Effect and also comparing your present position with your position a few seconds ago, a GPS set can calculate your direction and speed of movement over the sea bed.

By reducing positioning errors, dGPS makes the speed and direction displays so much more accurate that sailors can use them to assess the true effect of tidal streams.

Marine Plotters

Greenham Regis supplies Garmin chartplotters,, Seiwa chartplotters, Standard Horizon chartplotters and Yeoman chartplotters.

Knowing where you are is one thing: relating that to the real world is another.

Navigators have traditionally done the job with paper charts. It was almost inevitable that charts and compasses should develop side by side, because without a compass, it would have been impossible to produce a chart, and without charts, the value of a compass would have been pretty limited.

GPS is as dramatic a development as the compass was in its day, and is making us look at new ways of storing, organising and displaying navigational information.

Setting up a computer to display a GPS position on a lat-long grid is no great problem, and it’s easy to make a few fixed points on the grid represent buoys or landmarks. The clever bit is in expanding this idea to show entire coastlines and contours.

Marine electronic charts

Popular brands include Navionics electronic charts and C-Map electronics.

Raster Charts

In effect, a raster chart is an electronic photograph, produced by scanning a paper chart in much the same way as a fax machine scans a letter. The image is broken down into coloured dots, and information about the colour and position of each dot is stored on a computer disc or memory cartridges. When it’s needed, this mass of data can be reassembled to produce a picture on the screen.

Vector charts

A vector chart is more complicated to produce because it involves electronically tracing a raster chart to produce and image in which lines are stored as lines, rather than as strings of unconnected dots. The process is largely automated, but is still takes time, skill, and sophisticated equipment; in return, it produces charts that typically take up only a hundredth of the memory occupied by equivalent raster charts. This makes vector charts particularly well suited to dedicated chart plotters, whose memories and processor speeds may not match that of the latest personal computers, but whose internal organs are built to withstand life afloat and whose controls are more appropriate for the job.

Vector charts have other advantages, too. One is that they can be enlarged or reduced as much as you like: one minute you can be looking at a map of the British Isles, the next you can zoom in to individual pontoons in a marina. Another is that the chart can be “layered”, as though it were built up of a series of transparent sheets. Each sheet contains a different kind of information, so the picture can be de-cluttered by removing unwanted layers.

Of course there are drawbacks: the tracing process can introduce inaccuracies, or the chart editor may reduce “clutter” by omitting information.

At present, we have two broad classes of electronic charts, raster and vector, with several incompatible brands competing in each class. Each has its own particular strengths, so different hardware manufacturers have adopted different brands.

It pays to look carefully at all the options and take our expert advice before committing yourself to one particular system.

Ring Andy Haines on 01590 671144