The life of a radar on board a cruising yacht is an easy one. Aside from a few hours of action when it’s misty or foggy, its younger sibling, AIS, does the heavy lifting of collision avoidance for most yachts. Once the preserve of large yachts and commercial vessels, however, radar is increasingly found on yachts under 40ft. It’s become more affordable, easier to install and more intuitive to use, but how about its operators? Have we advanced with it and are we using it to its full potential? I suspect not.
Like many cruising boats, the Challenge 72 that I co-skipper, CatZero, constantly receives and transmits AIS data. Since it runs in the background the volunteer watch leaders soon become familiar with it. The all-new B&G Halo 24 radar is turned off until needed. I took the opportunity of a light airs delivery from Cherbourg to Portsmouth after the Fastnet Race to introduce the crew to the new tool, and become better acquainted with the latest technology myself.
HOW IT WORKS
With radar, more than any other equipment, it’s important to understand how it works – what it can do and, more crucially, what it can’t. Radar stands for RAdio Detection And Ranging. It works by emitting a powerful radio wave and then listening for the echo as the signal bounces off objects in range. By timing how long the echo takes to return it can calculate distance with precision. Angles are harder to differentiate: the beam width of a traditional radar is 3-4° wide, which makes bearings less accurate than range.
Not everything makes a good reflector. Metallic surfaces are best, GRP and wood are poor reflectors and carbon fibre lies somewhere in between. Shape matters too: a curved or irregular surface is more likely to return some of the signal in the right direction than a single plane, hence the angular, slab-sides of stealth ships. Water is a good reflector which can be problematic, given the sailor’s operating environment.
RANGE
Radar range is limited by height. The radar horizon is 2.2 x √height in metres. Although is a 72ft boat, the radar is mounted on a 4m high arch giving a horizon of only 4M to low-lying
