Know how: Radar 101

With today’s ever-increasing reliance on chartplotters with AIS overlay for collision avoidance, what role should radar play as a safety device? Duncan Kent investigates

While your chartplotter will (hopefully) show you where the land and sea should be, only radar can show you where everything actually is.

The invention of AIS has certainly made navigation simpler and a lot safer for small craft, especially now that many of the major marker buoys and beacons out there have real or virtual (more likely) AIS transmitters to indicate their position. Still, there are many vessels out there that either doesn’t have an AIS transmitter fitted or that switch it off at sensitive times (fishing and military craft, in particular), which can be a threat to safe navigation, especially in poor visibility.

While expensive and often underused, radar really should be the #1 must-have safety device for coastal and offshore navigation. Even when your collision risk is low, when crossing a wide-open ocean, for instance, radar can still be extremely useful when warning of bad weather approaching. Consider the following when deciding what makes sense for your boat.

Solid-state broadband radar

The latest type of radar equipment now available for leisure marine use is broadband, Pulse Compression (CHIRP) or Frequency Modulated Continuous Wave (FMCW) radar. All are the same (the names just describe certain aspects of their technology) and all utilize solid-state circuitry instead of the older, heavier, more power-hungry magnetron-based devices.

One of the main problems with having radar on small to medium-size cruising yachts has always been power consumption. Now, being solid-state, energy consumption has been reduced by a factor of 10. This, in turn, allows the radar to be left powered up in standby mode, knowing that it can be re-activated instantly with no warmup period. Better still, even when switched on for the first time the unit now takes just seconds to become fully operational, whereas before it could take up to five minutes before you could trust what you were seeing on-screen.

Yet another major advantage of solid-state radar is the massive reduction in the weight of the antennae, meaning their effect on a yacht’s stability is far less when mounted high up the mast.

CHIRP and broadband

When thinking about radar clarity/resolution, there are some primary features to be aware of. The first is a radar antenna’s horizontal beam width, which defines its ability to discriminate between two or more targets on close but different bearings and at a similar range. The narrower this beam the better, which in the past has always meant fitting the largest antenna possible. Put simply, the wider the antenna the narrower the beam width. Currently, Navico’s (Simrad/Lowrance/B&G) Halo 24 and Furuno’s DRS4D-NXT are the largest of the solid-state radar domes, but no doubt the others won’t be far behind with 24in models. Though the bigger domes can make installation a little more awkward, they are not much heavier and the additional sharpness of the picture is worthwhile compensation.

Other important factors in getting the best signal return is transmission power and pulse length, or at least it was in the days of the magnetron-powered radar. Since the introduction of broadband radar, however, this has changed. Today, emissions from solid-state radar transponders are below those for a regular cell phone, meaning (in addition to the fact they require far less power) that they no longer risk health problems for people close to the antenna. Also, due to their increased processing power and CHIRP technology, beam pulse lengths (ideally long for detecting long-range targets, but short for better discrimination) can now be processed to provide much more data and thereby noticeably improve target discrimination.

Note, as an added benefit, that while radars traditionally always had a blind spot around their antenna of around 150-200ft in circumference due to the time difference between transmitting and receiving signals, now that broadband radar does both simultaneously, ranges have reduced to around 20ft or less.

Latest features

The first to take the broadband leap for leisure use was Simrad, part of the Navico group, with its 3G broadband radar. This was rapidly superseded by the company’s 4G unit, which added a dual-range viewing capacity and improved target definition. Simrad’s latest models, the Halo 18 and 24, offer high-speed (60rpm) antenna rotation speeds at short range for much-improved collision avoidance. One sweep per second ensures even the movement of fast vessels is tracked smoothly and continuously.

The first to introduce CHIRP technology was Raymarine with its launch of the Quantum radar a few years ago. Since then Raymarine has added numerous other features to keep it fully up to speed with the competition.

First introduced by Furuno, for example, all the major radar manufacturers have now added Doppler technology, which allows the viewer to spot immediate threats at a glance. The way this works is that when signals bounce back off a moving vessel, the frequency of the returned signal varies depending on the direction the target is traveling in. These fluctuations in frequency can then be used to differentiate between those vessels that are moving away from or toward your ship. In practice, targets moving away from an antenna are usually displayed in green, whereas those moving toward it are shown in red.

Along these same lines, all but the Quantum 2 now offer dual-range viewing for compatible MFDs, in which the screen can be split–each displaying at a different range. MARPA, multiple-target tracking, is also now common, allowing users to simultaneously track up to 10 targets or more and automatically calculate their course, speed and Closest Point of Approach (CPA). A heading sensor must be included in the circuit, however, to enable this function to operate.

LATEST PRODUCTS

NAVICO 

Navico’s Halo 24 has a 24in dome, enabling a very narrow horizontal bandwidth to be created. Together with its excellent “Beam Sharpening” technology, this feature is able to provide sharper target images with better separation between vessels, navigation marks and land contours. It also boasts the fastest rotating antenna for target acquisition inside a 1.5-nautical mile range, allowing fast vessels passing close by to be followed much more consistently, as the signal can almost be seen moving on the screen in real time. Combined with its “Velocity Track” doppler technology, this greatly enhances the primary goal of collision avoidance.

The Halo 24 also offers Dual Range capability, enabling both short and long-range viewing on a single display, and a top range of 48 nautical miles. Other useful features include several preset modes, such as Harbor, Offshore, Weather and Bird, which automatically tune the necessary filters and optimise the parameters to suit the situation or requirement. navico.com

RAYMARINE 

Raymarine’s Quantum CHIRP radar set a whole new standard when it was released a few years ago. As well as being less than half the weight of older generation magnetron antennae and considerably less power-hungry, it also brought a level of definition and separation characteristics never before been seen in a compact leisure radar. For the first time, it became easy to pick out buoys and small boats on the radar screen, greatly aiding close-quarter pilotage in poor visibility or at night. In addition, it introduced Wi-Fi data comms (to Raymarine MFDs only) and much thinner cables, which facilitated installation and reduced weight aloft.

Quantum 2, just launched, has also added Doppler processing to help discern between harmless and threatening vessels for collision avoidance and automatic MARPA tracking of up to 10 target vessels simultaneously and vessel trails to indicate the historic movement of targets on the screen. raymarine.com

GARMIN 

Garmin often to follow where others first tread, which isn’t necessarily a bad thing. Renowned for producing reliable marine and aeronautic navigation kit, the company might not always be on the cutting edge, but when it does introduce a new model, it usually works as it should right out of the box.

The company’s latest Pulse-Compression Fantom radars, which were originally only available with an open-array antenna, now come in 18in and 24in dome versions for sailboats. They also boast all the features of the others, including “MotionScope” doppler definition, a range of up to 48 nautical miles, MARPA tracking and Dual Range operation. They even offer a 48rpm highspeed mode for smoother tracking of nearby vessels and marks. Ultimately, the only thing they appear to lack is a wireless data transmission option, and to be honest I’m not totally convinced that’s a game changer anyway. garmin.com

FURUNO 

Compatible with its NavNet TZtouch MFDs (4.2.1+) or TZtouch2 (3.0.1+), Furuno’s DRS4D-NXT radar was the first to incorporate the doppler effect via its “Target Analyzer” feature, which all its competitors have now adopted. The unit is only available in a 24in dome. Although the size makes it slightly more awkward to install, the system’s size is more than justified by its extremely narrow horizontal beam width, enabling the sharpest target images to be displayed.

In addition to this, the DRS4D also features “Fast Target Tracking” whereby it “locks on” to up to 100 targets within a 3-nautical-mile radius to provide accurate and rapid vessel movement reporting, plotting their course and speed while displaying a dotted heading vector for each target vessel. Another useful feature is RezBoost which, when set to maximum, increases the image resolution and greatly improves separation between smaller targets. furuno.com

Duncan Kent is a freelance technical writer who has been reviewing marine electronics for the past 30 years

February 2019