Radar Revolution Page 2 - Sail Magazine

Radar Revolution Page 2

For the past 60 years or so the basic principles of marine radar have not changed. A radar transmits very short pulses of microwave energy and receives echoes reflected back from solid objects. The direction of an object is indicated by the direction from which the echo returns, and its range is determined by the time interval between when the pulse was transmitted and when
Author:
Publish date:
Social count:
0

Low clutter: pulsed radar shortens its pulse length at short ranges; the pulse length is what gives the unit the ability to discriminate between objects that are on more or less the same bearing but at slightly different ranges. The longer the pulse length, the bigger the gap between two objects must be before they show up as separate blobs on a radar screen. Usually this is about 50 feet at short range and about 500 feet at long range. Because FMCW radar doesn’t use pulses, it can distinguish between objects separated by a gap as small as about six to ten feet.

Another benefit is that FMCW radar is less affected by echo clutter from the sea surface or from rain. The clutter effect is more pronounced with rain and clouds because pulsed radar can often receive a return that is strong enough to register as a large mass on a radar screen. Navico says that its Broadband radar is at least five times less susceptible to rain and sea clutter than a conventional radar and that it can be removed altogether, using two automatic settings, harbor and offshore. There’s also a manual option for those who like to have something to tweak, or who like to use visible rain clutter to dodge squalls or showers.

To listen for echoes while still transmitting, FMCW radars need two antennas, one mounted above the other; one transmits and the other receives. This means that the radar has almost no minimum range. If you need to pick your way through piles or closely-moored boats you can do so without losing sight of the one you may be about to hit.

Power consumption

A 4kW-pulsed radar doesn’t use much power because it’s transmitting for such a small amount of time, but considerable power is consumed by heating the magnetron and lighting up the display. While FMCW units have no magnetron they do turn an antenna, run a processor, and illuminate a display. That is why power savings aren’t quite as much as you might like. But a power draw of 17 watts is still a useful saving compared to the 25 watts consumed by a conventional 2kW radar. For many users the biggest power savings will come from the instant on feature that allows a FMCW radar to be ready for use within about 20 seconds, rather than two or three minutes. This almost puts an end to the need to run the radar in “standby.”

A conventional pulsed radar can still do some things better than a FMCW unit. For instance, long-range performance is perhaps the most significant advantage of a conventional radar. No matter how clever FMCW technology may be, there’s a point at which a 100mW transmitter simply runs out of power. I can’t put a number on exactly what the maximum range might be as it depends entirely on the target. But Navico does say that the long-range performance of its FMCW radar is closer to their conventional 2kW units than it is to their 4kW models. Even so, I would say we’re seeing the start of a technological revolution that will forever change the way marine radar works.

I went out on the water with Navico’s new BR24 unit and, with some judicious tweaking of the controls, I could see large ships about twelve miles away and I could also get intermittent echoes from large targets on land over 20 miles away. The boat was not large and the antenna was less than fifteen feet above the surface of the water. Because it doesn’t transmit high-power pulses, FMCW radar will not trigger a response from radar transponders such as RACON’s (on navigation marks), SARTs (on liferafts), or any other active radar responder.

But most people will probably never see a SART used in earnest, and chart-overlay technologies and AIS are already making RACONS and radar responders less relevant. Unfortunately, the day I went out the seas were calm and the sky was clear. That meant I didn’t get a chance to see any rain clutter and not much in the way of sea clutter, either.

sea_trials

Related

180615-01 Lead

A Dramatic Comeback in the Volvo

After winning three of the last four legs in the Volvo Ocean Race (and coming in second in the fourth), Dutch-flagged Brunel is now tied for first overall with Spanish-flagged Mapfre and Chinese-flagged Dongfeng following the completion of Leg 10 from Cardiff, Wales, to ...read more

MFS-5-2018-Propan-SP02

Tohatsu LPG-powered 5hp Propane Motor

Gassing it UpTired of ethanol-induced fuel issues? Say goodbye to gasoline. Japanese outboard maker Tohatsu has introduced an LPG-powered 5hp kicker that hooks up to a propane tank for hours of stress-free running. Available in short-, long- or ultra-long-shaft versions, the ...read more

TOTW_PromoSite

SAIL's Tip of the Week

Presented by Vetus-Maxwell.Got a tip? Send it to sailmail@sailmagazine.comThink Deeply When chartering, I am always maddened to be told that the echo sounder is calibrated “to depth under the keel, plus a bit for safety.” Such operators seem to imagine that the instrument’s sole ...read more

180612-01 Landing lead

Painful Sailing in Volvo Leg 10

It’s looking to be a case of feast or famine for the 2017-18 Volvo Ocean fleet as it continues the epic struggle that has been Leg 10, with it having been all famine thus far. Painful is the only word to describe the light-air start in Cardiff, Wales, on June 10, as the 11-boat ...read more

01-13_07_180304_JRE_03695_4605

Tips From the Boatyard

Within the Volvo Ocean Race Boatyard sits a communal sail loft which provides service and repairs for all seven teams sailing in the 2017-18 edition of the race. The sail loft employs only five sailmakers who look after 56 sails in each stopover. If you’re thinking, “wow, these ...read more

sailCarwBasicsJuly18

Sail Care for Cruisers

Taking care of your canvas doesn’t just save you money, it’s central to good seamanship  Knowing how to take care of your sails and how to repair them while at sea is an important part of overall seamanship. The last thing any sailor needs is to get caught on a lee shore with ...read more

Ship-container-2048

The Danger of a Collision Offshore

This almost happened to me once. I was sailing singlehanded between Bermuda and St. Martin one fall, and one night happened to be on deck looking around at just the right time. The moon was out, the sky was clear and visibility was good. Still, when I thought I saw a large ...read more

New-MHS-Promo

Multihulls on the Horizon

Fountaine Pajot New 42The French cat powerhouse has been on a roll these last few years, cranking out new models that not only replace their older line but take a step forward in design and user-friendliness. The New 42’s “real” name had not been revealed as we went to press, but ...read more