DIY Boat­ing

Boating NZ - - Contents - BY NOR­MAN HOLTZHAUSEN

Un­der­stand­ing radar

An old naval salt once told me that noth­ing beats a ‘Mark 1 eye­ball’ for safely nav­i­gat­ing your ves­sel. He was right, of course, and many ac­ci­dents have been caused by peo­ple fail­ing to sim­ply keep a good look­out. How­ever, there are times when vis­i­bil­ity is re­stricted, and our eyes alone are not good enough.

At night, or when there is fog or heavy rain, tech­nol­ogy can help to dra­mat­i­cally up­grade our vi­son and en­able us to see things that would oth­er­wise be hid­den.

Ra­dio De­tec­tion and Rang­ing, or radar, has been around since the Sec­ond World War and is of­ten cred­ited with help­ing to win the Bat­tle of Bri­tain. This tech­nol­ogy, even in its prim­i­tive form, en­abled Bri­tish fighter planes to ac­cu­rately in­ter­cept in­com­ing Ger­man bombers at night.

Since those early days the tech­nol­ogy has de­vel­oped hugely, and com­pact dig­i­tal radar sys­tems are now read­ily avail­able and priced to suit even mod­er­ate-sized trailer boats and yachts.

Large com­mer­cial radar units, and larger recre­ational ones, are char­ac­terised by a hor­i­zon­tal an­tenna (called an open ar­ray) which spins slowly around. This trans­mits a strong pulse of elec­tro­mag­netic en­ergy, which then bounces off ob­jects in the dis­tance. By know­ing the ex­act an­gle of the ro­tat­ing beam and mea­sur­ing the length of time for the echo to come back, the soft­ware can build up a pic­ture of the sur­round­ing area. The strength of the re­turn­ing sig­nal gives an in­di­ca­tion of the size of the ob­ject and builds up a fairly ac­cu­rate pic­ture of dis­tant ob­jects.

One of the is­sues with radar has al­ways been that large ro­tat­ing an­tenna; an­other the rel­a­tively high en­ergy out­put of tra­di­tional sys­tems. Since radar tech­nol­ogy uses mi­crowave ra­di­a­tion, just like mi­crowave ovens, much has been said about the risks of ex­po­sure to that en­ergy. How­ever, while it is still not a good idea to stand in front of a large com­mer­cial radar unit, mod­ern units only trans­mit in­cred­i­bly short pulses of ra­di­a­tion and pose no threat to hu­mans.

Those in the in­dus­try joke that you are more at risk of be­ing hit in the head from a spin­ning open-ar­ray an­tenna than suf­fer­ing ill ef­fects from the en­ergy com­ing from it. And most recre­ational units mit­i­gate even that risk by us­ing a smaller an­tenna in­side a com­pletely en­closed cylin­dri­cal hous­ing called a radome.

So, given that you prob­a­bly al­ready have a com­pat­i­ble mul­ti­func­tion dis­play (MFD) on your boat, as dis­cussed last is­sue, what are the con­sid­er­a­tions when look­ing to add a radar? Prices start from just over $2000 (as­sum­ing you have an MFD), but there are a be­wil­der­ing num­ber of op­tions.

Even if you stick with just one man­u­fac­turer you will no­tice nu­mer­ous mod­els, each with dif­fer­ent acronyms, spec­i­fi­ca­tions and prices. At the time of writ­ing we counted no less than 40 dif­fer­ent mod­els from the four ma­jor marine elec­tron­ics sup­pli­ers, all aimed at the recre­ational sec­tion. To con­fuse mat­ters fur­ther, dif­fer­ent man­u­fac­tur­ers of­ten use their own pro­pri­etary name for the same fea­ture. Let’s try and make some sense of this.

The first de­ci­sion to make is around the base tech­nol­ogy, and the dif­fer­ence largely de­pends on the range you re­quire. Tra­di­tional ‘pulse’ radar uses a high-pow­ered mag­netron to gen­er­ate a very short du­ra­tion burst of en­ergy. These units trans­mit at high power out­puts, typ­i­cally 4kw to 25kw in

One of the is­sues with radar has al­ways been that large ro­tat­ing an­tenna.

recre­ational mod­els, and have a range close to 100 nau­ti­cal miles. For max­i­mum range, a pulsed unit is the best op­tion.

New solid-state tech­nol­ogy uses a dif­fer­ent tech­nique called FMCW (Fre­quency Mo­du­lated Con­tin­u­ous Wave). This ‘broad­band’ radar sends a con­tin­u­ous sig­nal wave (rather than a pulse) with an in­creas­ing fre­quency (hence called broad­band) and is roughly sim­i­lar to the CHIRP used in sonar. That wave trav­els out, re­tain­ing its fre­quency and bounc­ing back from any ob­ject.

At the same time the sys­tem con­tin­ues to out­put a wave at an in­creas­ing fre­quency. Some clever elec­tron­ics com­pares the dif­fer­ence be­tween the re­turn­ing fre­quency and that cur­rently be­ing trans­mit­ted and cal­cu­lates the pre­cise dis­tance to the tar­get. Since this hap­pens con­tin­u­ously over dif­fer­ent fre­quen­cies through­out its range, a broad­band sys­tem pro­vides far bet­ter tar­get de­tec­tion and dif­fer­en­ti­a­tion than a pulse radar.

Broad­band units also trans­mit at far lower en­ergy lev­els, mak­ing them safer for smaller boats. Nat­u­rally they also draw con­sid­er­ably less power, mak­ing them suit­able for smaller

run­abouts or sail­boats with lim­ited power. The down­side is they have lim­ited range. Ear­lier mod­els had very poor per­for­mance out­side the three-mile range, but new mod­els, no­tably the 3G and 4G mod­els from Nav­ico, now have an ef­fec­tive range of up to 36 nau­ti­cal miles.

And then, just to con­fuse things fur­ther, there is an­other new tech­nol­ogy called pulse com­pres­sion radar, of­fered in dif­fer­ent vari­ants by Sim­rad, Ray­ma­rine, Fu­runo and Garmin. Ba­si­cally a hy­brid be­tween tra­di­tional pulse and CHIRP tech­nolo­gies, this pro­vides lower-emis­sion sig­nals than a stan­dard pulse but which pro­duces ex­cel­lent range and tar­get res­o­lu­tion. This tech­nol­ogy is also su­pe­rior at de­tect­ing small mov­ing tar­gets, like a flock of fly­ing birds and fast-mov­ing run­abouts. As such, it is best suited to medium range, with op­tions of 24 to 72 nau­ti­cal miles max­i­mum range.

So, hav­ing cho­sen the base tech­nol­ogy you want, the next de­ci­sion is whether to go radome or open ar­ray. The radome en­closes all the mov­ing parts in­side a com­pos­ite hous­ing, leav­ing noth­ing to snag on rig­ging, fish­ing lines or sails.

Some man­u­fac­tur­ers of­fer equiv­a­lent mod­els in both radome and open ar­ray con­fig­u­ra­tions, but gen­er­ally open ar­rays are larger and there­fore have

a higher out­put and greater range. Broad­band units are gen­er­ally radome, and pulse units may only be avail­able as open ar­rays, but it is in that mid-range where the dif­fi­cult de­ci­sion comes. Note that the ef­fec­tive range is also af­fected by how high the an­tenna can be mounted above the wa­ter, with more height giv­ing greater range.

Apart from the max­i­mum range, the min­i­mum dis­tance is also an im­por­tant as­pect when de­cid­ing on a model, and units vary in this re­gard from as lit­tle as 10 me­tres to more than 100m. Boat­ies who have trav­elled out of Have­lock in the Marl­bor­ough Sounds on a foggy morn­ing will know how cru­cial this dis­tance is, since the nav­i­ga­ble chan­nel is only 20 me­tres wide and it is a hair­rais­ing ex­pe­ri­ence to hear an­other boat close by when you can­not see more than a few me­ters ahead of you. Vir­tu­ally ev­ery boat op­er­at­ing out of that har­bour has a radar in­stalled.

The soft­ware sup­port­ing the radar sig­nal is equally im­por­tant, and of course this de­pends on what MFD or ded­i­cated dis­play you con­nect your an­tenna to. Most MFDS al­low you to dis­play the radar ei­ther in its own sec­tion of the screen or over­laid di­rectly onto the marine chart, and some will in­te­grate AIS sig­nals to iden­tify ves­sels which the radar de­tects. If your MFD does not sup­port your de­sired radar unit, you can opt to add a ded­i­cated dis­play with spe­cific fea­tures for your cho­sen model.

An­other use­ful op­tion is MARPA (Mini-au­to­matic Radar Plot­ting Aid) Tar­get Track­ing, a col­li­sion-avoid­ance soft­ware fea­ture sup­ported by some mod­els. This en­ables the dis­play to iden­tify and track other ves­sels, show­ing their speed and bear­ing, warn­ing of clos­est point of ap­proach and the time to the clos­est point of ap­proach.

This can be com­bined with prox­im­ity alarms to sound a warn­ing if a ves­sel is too close and head­ing for a col­li­sion. This fea­ture would be im­por­tant to ves­sels op­er­at­ing in busy ship­ping lanes, such as cruis­ing boats and large com­mer­cial ves­sels.

A vari­a­tion on this is a fea­ture dis­play­ing an echo trail which shows where the radar tar­get has been, so you can eas­ily see the di­rec­tion it is mov­ing and work out what the risk is to your­self.

So, know­ing all this, how do you de­cide what unit to buy? A few fun­da­men­tal ques­tions should re­duce the op­tions con­sid­er­ably, leav­ing the fi­nal de­ci­sion down to per­sonal pref­er­ence and bud­get:

Large com­mer­cial radar units, and larger recre­ational ones, are char­ac­terised by a hor­i­zon­tal an­tenna (called an open ar­ray)

If you are in­te­grat­ing to an ex­ist­ing multi-func­tion dis­play, then nat­u­rally start with the same man­u­fac­turer and look at what mod­els are com­pat­i­ble. How­ever, avoid lim­it­ing your­self too early, as you may find that the fea­ture you re­ally want re­quires a new MFD, pos­si­bly even a dif­fer­ent brand.

Next de­cide on the max­i­mum range you re­quire, based on your typ­i­cal us­age. For recre­ational fish­er­man, 24nm (so, one of the broad­band mod­els) is most likely ad­e­quate. For pas­sage-mak­ing sail­ing boats a greater range may be vi­tal. This is where the great­est cost trade-off comes – gen­er­ally, the greater the range, the higher the cost.

Next, check how much power is avail­able on your ves­sel. A high-power pulse radar will quickly suck the bat­tery dry on a yacht that does not have an en­gine con­tin­u­ously charg­ing it, while a broad­band unit will draw a frac­tion of the amount of cur­rent.

Do you need close-range ca­pa­bil­ity? If your boat­ing re­gion reg­u­larly ex­pe­ri­ences fog then this may be more im­por­tant to you than the max­i­mum range. Also, if you of­ten go into busy an­chor­ages at night, then the close-range tar­get res­o­lu­tion ca­pa­bil­i­ties may be the most im­por­tant fea­ture.

For game fish­er­man, the abil­ity to iden­tify a flock of birds fly­ing far enough away to be out of sight would be an ex­tremely valu­able fea­ture. In that case look for a unit of­fer­ing ‘Bird mode’ or sim­i­lar. BNZ

BE­LOW LEFT An open ar­ray pro­vides more op­tions in terms of trans­mit­ting power and range.

LEFTEven mod­est run­abouts can ben­e­fit from a radar in­stal­la­tion.

BE­LOW RIGHT Some mod­els al­low dual range, zoom­ing in to show what is close to the boat.

OP­PO­SITE PAGE Most smaller recre­ational ves­sels and many larger ones opt for radomes.

LEFTIn­stalling the radome or open ar­ray at the higest po­si­tion pos­si­ble ex­tends its range.

BE­LOWThis open ar­ray is mounted out of the way and well pro­tected from in­ter­fer­ence. RIGHT, TOP TO BOT­TOMAn open ar­ray an­tenna; With the unit set in ‘bird mode,’ flocks of birds in the dis­tance show on the dis­play; A typ­i­cal radome in­stal­la­tion with a satel­lite TV an­tenna stacked above it.

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