The Wonders of Radar
<HTML><P><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8></TD><TD vAlign=top align=left width=328><IMG height=237 src="http://www.sailnet.com/images/content/authors/copeland/030701_lc_hr53.jpg" width=328><BR><DIV class=captionheader align=left><FONT color=#000000><B>There are so many good reasons for having a radar unit on board your boat that it's not difficult to justify the expense. </B></FONT></DIV></TD></TR><TR><TD colSpan=2 height=8></TD></TR></TBODY></TABLE>Radar is one of those toys you can always manage without until you have one. One of those items that, when you become aware of its many uses, it becomes indispensable! At night, in fog and rain, this aid inspires confidence and helps monitor other traffic movements. For landfalls on unlit coasts, for transiting passages between islands or entering a harbor in poor visibility, we consistently use our radar. Radar bearings and distances are true and do not rely on the accuracy of charted positions like GPS. We can even gauge the severity of tropical line-squalls coming up to us and, in areas such as Indonesia and the Malacca Strait, we have used radar to warn us regarding the approach of unlit and possibly hostile craft. <P>For both the long distance and coastal cruiser, radar is one of the most useful tools for navigation, and in our opinion, of major importance for safety at sea. Small vessel radars are increasingly affordable, reliable, and have relatively small electrical power needs. </P><P>Aboard <I>Bagheera</I> we have a Raytheon SL72 24-mile LCD unit with a seven-inch screen in a waterproof display, which is mounted under the dodger where it can be seen from anywhere in the cockpit. We didn’t put it on the binnacle, since thanks to self-steering we spend little time behind the wheel when on a passage. The rotating antenna is housed in a fiberglass pod and is mounted 12 feet high on a stainless steel spar at the stern. (This does double duty by also supporting our solar panels.) We put it here to avoid a blind spot aft, which results if the radar is mounted on the mast; also, because there is less movement there, scans are more stable on the screen in rough conditions. In addition, this location makes tuning and servicing easier, particularly if, when installing, enough cable is coiled below the deck to enable the antenna to be lowered to the deck without fully detaching it.</P><P><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8></TD><TD vAlign=top align=left width=328><IMG height=237 src="http://www.sailnet.com/images/content/authors/copeland/030601_lc_8c.jpg" width=328><BR><DIV class=captionheader align=left><FONT color=#000000><B>On board the author's boat, the radar display unit is mounted under the dodger where it's easily visible from anywhere in the cockpit.</B></FONT></DIV></TD></TR><TR><TD colSpan=2 height=8></TD></TR></TBODY></TABLE><P>Definition can be lost abeam when heeled, so it is advantageous for the antenna to be mounted on a platform that can be tilted up to 20 degrees from the horizontal. This platform is easily held in position using a locking extension. To do this, we use a handle such as those used by window cleaners. Gimbaled units are also available, but these can lead to chafe in the complex wiring harness as a result of the constant movement. </P><P>As a navigation tool, we use our radar when we're within range of a coast to obtain accurate fixes, to identify charted features, to transit a channel, or enter a harbor at night in poor visibility. We also use the unit to locate aids to navigation. This is particularly helpful where charting is not accurate, which is the case in much of the world. In northern Australia, for example, some coastal surveys date back to Flinder’s time, a British navigator who charted the area in the early 1800s. Even in the Caribbean and Mexico (often the first offshore experience for many cruisers), some of the islands are inaccurately positioned. The popular Isla Isabela, close to Mazatlan, with its hundreds of nesting birds and lovely diving, comes to mind from our last cruise. Using our GPS position we found that it lay one and one third nautical miles to the east and one and one half miles south of its charted position. With these existing errors, piloting by GPS is no longer accurate, but with radar one can still make a safe entry. </P><P><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8></TD><TD vAlign=top align=left width=292><IMG height=229 src="http://www.sailnet.com/images/content/authors/copeland/030701_lc_radar.jpg" width=292><BR><DIV class=captionheader align=left><FONT color=#000000><B>It takes some practice to properly interpret what you see on a radar display screen, so before you get proficient, don't jump to conclusions about what might be out there.</B></FONT></DIV></TD></TR><TR><TD colSpan=2 height=8></TD></TR></TBODY></TABLE><P>As a safety tool, radar’s ability to pick up vessels before they become visible to the watchkeeper enables their track and speed to be assessed. In addition, we use the radar to locate and follow storm cells, estimate the severity of tropical squalls approaching at night, pick a passage through a static fishing fleet, and keep a watch on vessels in the vicinity if we're in areas where there are concerns about security. </P><P>Features that our unit shares with most other small radars include: automatic ‘timed’ scans, after which it reverts to standby; an alarm that sounds if a ‘target’ is detected within a set zone; the ability to bring up on the screen navigation information from other instruments such as GPS readings, waypoint information; depth, wind speed and direction; two separate range/bearing cursors and a man-overboard position. </P><P>The reliability of this unit has been good, our only problem (still unresolved) being an intermittent, momentary loss of the picture when the ambient temperature is over 80 degrees Fahrenheit. </P><P>Our use of radar depends on the circumstances. When we're in familiar waters with good visibility it is rarely used, except perhaps to check whether we are gaining on our friends in another sailboat, to satisfy our racing jones. In busy or unfamiliar coastal waters and known shipping lanes, the radar is on full time in anything but perfect visibility. Offshore by day in good conditions it will only be used if a vessel is sighted, but as the weather deteriorates, or at night, it will be on intermittently or full time, depending on conditions and traffic. Like all sailors, we like to conserve electrical power, but because <I>Bagheera’s</I> radar only uses 38 watts (about three amps) when it's on (and only half that when on standby), the available power is not a big concern regarding our battery bank, which has 690 amp hours. </P><P><TABLE cellSpacing=0 cellPadding=0 align=right border=0><TBODY><TR><TD width=8></TD><TD vAlign=top align=left width=328><IMG height=237 src="http://www.sailnet.com/images/content/authors/copeland/030601_lc_sunset.jpg" width=328><BR><DIV class=captionheader align=left><FONT color=#000000><B>When the daylight wanes and so does visibility on the water, radar becomes an even more important aspect of your navigation arsenal.</B></FONT></DIV></TD></TR><TR><TD colSpan=2 height=8></TD></TR></TBODY></TABLE>It’s important to know the limitations of radar. A radar just shows objects in direct line of sight for the scanner. It will not show vessels in a bay obscured by a headland, for instance. Nor will the shape of a ship’s echo show its size or direction. Operator knowledge is important. Anyone unfamiliar with radar use should seek instruction, since a misreading of the picture or lack of understanding of the principles can be disastrous. The radar-induced collision is a well-known phenomenon in commercial shipping circles, and even the professionals make mistakes. New crew need to be given time to learn its use, and we never allow them decision-making responsibility until they have shown competence with the unit. Until then Andy or I will always be with them on deck if a vessel is on a collision course and/or if one is closer than five miles, to walk them through the interpretive process. In particular we make sure that they are still making use of all the other clues available, such as the ship’s lights. <P>Also, be sure your boat has a good radar reflector and check that it works at all points of the compass. We found a blind spot in our Firdell, which is mounted on the forward side of the mast. Because ships dead astern were unable to pick us up, we now carry a second reflector aft. Remember too that other wood and fiberglass vessels lacking radar reflectors may not show on your screen; radar was never meant to be a substitute for keeping a a regular visual watch. </P><P>There are so many useful products on the market today for cruisers. Most have some merit, but with the increasing traffic on the oceans of the world and in unpredictable weather, we find radar contributes hugely to our peace of mind and safety at sea, making it a very desirable addition for successful cruising. </P></HTML>
|All times are GMT -4. The time now is 09:06 AM.|
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2015, vBulletin Solutions, Inc.
User Alert System provided by Advanced User Tagging v3.1.0 (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
(c) Marine.com LLC 2000-2012