How to choose and use radar for your boat

18th March 2016

Choosing the right radar system

An essential addition to any boats electronic navigation system, radar has been around for over a hundred years but what is it, how do you choose the right one and, more importantly, how do you use it?

What is radar?

Dating back to early experiments performed by Heinrich Hertz in the late 19th century it was discovered that radio waves transmitted from an antenna could be reflected off metal and thus the identification of remote targets could be ascertained without the aid of a positive visual sighting. So began the development of radar as we know it; a basic technology of bouncing radio frequencies from solid objects to determine their relative position (using time and frequency) to the antenna.

The basic principle is similar to the analogy of standing in a dark environment with a flashlight on a narrow beam. If you simply point the beam in one direction you will not know what targets are around you; however if you stood still and turned around 360 deg, shining the torch as you go, your beam will briefly show any object within its range. Radar uses a microwave pulse to replicate this scenario and, when it receives the reflection of a solid object, it calculates the distance to the target (the exception to this is broadband radar which uses a continuous pulse rather than intermittent signals).

During the early part of the 20th century a German inventor, Hülsmeyer, designed a system specifically for the detection of boats to try and avoid collisions in poor visibility and, although the technology has since advanced, the marine industry has relied heavily on radar for navigation ever since.

In short, radar is one of the single most important pieces of technology you can buy for your boat and can eliminate the guesswork and stress caused by boating under restricted and difficult visibility conditions. However, it’s commonly recognised that many boats aren’t fitted with suitable radar capability either being under-fitted with low cost devices not much better than using a pair of binoculars or vastly over-fitted with equipment so powerful that half of the functionality would never be used.

How to choose the right radar?

With such an essential piece of kit it’s important to make sure that you choose wisely to ensure that a) you invest in a radar system that delivers the best performance to suit your intended application and b) you get the best value for money.

So here are our six top tips to consider when weighing up your choice of radar:

1) Horizontal beam width – radar is broadcast from between one and six degrees with a narrow beam being capable of more focused pulses and thus able to differentiate between targets more accurately, delivering better bearings. However when waters are rough narrow beams are prone to losing their targets as the boat pitches and rocks. Compare this to a wider beam which has a far better tolerance of listing. Beam width should be considered in parallel with power as narrow beams can limit visibility at close quarters. Large vessels often require secondary radar onboard strictly for this purpose.

2) Antenna size – because it operates at microwave frequencies and with the limitations of the Earth’s curvature you will receive a better picture for even a small increase in antenna size. Simply put, the longer or larger the element of your antenna the more detail you are likely to receive on your screen. That said, if you don’t need to pick up targets further than five nautical miles away then there’s no point in strapping a tall mast to your vessel that is capable of picking up objects at much greater distances.

3) Power output – this is a simple factor; the more power to your antenna the stronger the signal. However, many people believe that they can buy a lower powered radar because they don’t require long range visibility but a more powerful radar can significantly increase the detail of close range targets and thus improve navigation at close quarters.

4) Size and weight – these factors will largely be dependent upon your mounting position as well as your wallet. You should ensure that the antenna or enclosed dome you are considering will be adequately supported at the required height on your vessel. It’s also worth pointing out that, wherever you position the antenna, you will need to ensure that the cable can be secured safely without leaving it exposed.

5) Screen display – the bigger the display and greater pixel resolution then the easier it will be to interpret the radar signal. Most radar signals are now digital and, as such, screens can offer high definition, ultra high definition and also DSP.

6) Integration – many radar systems on the market are designed to plug and play with additional marine electronics and you might want to couple your radar with your chart plotter or other devices.

There are plenty of radars available on Find A Fishing that may be suitable for your application. Check here for further details.

Safety first

Due to the fact that radar works in microwaves and high radio frequencies there are some important factors to consider to reduce the risk of radiation. Whilst the risk is unlike-rays which penetrate the human skin, radar radiation can cause the temperature of the skin and eyes (especially the cornea) to be raised. The UK Health and Safety Executive (HSE) recommends that the antenna is located at least a few metres from human contact, the radar is not used in dock or if it is required to be then it is pointed out to sea and that no one is able to position themselves between the reflector of larger scanners and the output horn of the transmitter. In the instance that an open box type scanner is installed it is further recommended that no one looks directly into the emission side of the slotted wave guide.

How to use radar?

So, you’ve found the best system for your boat but it’s simply not enough to have it fitted. As with most controls it is the user who must interpret the data being received and knowing how to use your radar could make a huge difference to the safety and operability of your vessel.

Most modern units now come with automatic imaging which translates the received data into more understandable information and provides suitable alarms as required. However, every good mariner should have a basic understanding of how to interpret the data received by radar.

Broadly, radar will display a ‘blip’ of size, corresponding to the strength of signal received from a known location. This image may vary in size than the actual target depending on the material, shape and height of the object being picked up. As such, a 50’ sailboat could appear larger on your screen than a 100’ motor yacht whereas something like a small fibreglass boat with little metal to reflect the pulse may not even show up. That aside most objects which are designed to be seen (such as shipping lane markers) are designed with radar in mind and show up clearly. Moving objects or those that reflect only the weakest of signals may require some user translation. Watching a radar screen for several minutes will help you to identify what is being picked up by how the signal is being communicated; calculating an objects speed and heading can all help distinguish what you are seeing on the radar. Many modern units allow you to tag such targets and will therefore calculate this for you; however you can also do this the old-fashioned way by monitoring an image for several minutes and tracking its course. The distance it covers over the time you monitor (including any changes in your vessels relative bearing) will allow you to determine the speed and likely source of the object and thus whether you are in danger of collision.

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