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THE CHARTMAKING PROCESS WHERE DID THE REEF GO? MIXED MES­SAGES

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The sa­loon is quintessen­tially Azimut; with luxe ma­te­ri­als and high lev­els of fin­ish, no amount of com­fort was spared. Far left: Win­ning fea­tures of the lower helm: slid­ing glass panel to bring in the sea air and com­fort­able helm seats. Left: Keep­ing beat with the ex­cel­lent fur­nish­ings, the lower helm sports twin Ray­ma­rine MFDs.

It’s a dark and squally night in Novem­ber 2014. Ves­tas Wind, one of the boats par­tic­i­pat­ing in the roundthe-world Volvo Ocean Race, is romp­ing along at 16 knots in the In­dian Ocean. There is a loud crack—the dag­ger­board has sheared off. The boat piv­ots hard to port; the keel strikes the bot­tom and Ves­tas Wind is aground in 6-foot break­ing seas on the Car­ga­dos Cara­jos shoals, 240 miles north­east of Mau­ri­tius in the In­dian Ocean.

As waves wash over her, Ves­tas Wind pitches and rolls vi­o­lently, and starts to break up, los­ing both rud­ders, the keel, and large sec­tions of the hull. Wa­ter floods be­lowdecks and the ship’s lithi­u­mion batteries be­gin to smoke, threat­en­ing to go up in flames. In the early hours of the fol­low­ing morn­ing, the crew scram­bles off the back of the boat onto the shel­tered side of the reef from where they are res­cued later that day. All are safe and un­harmed.

No one aboard was aware the reef ex­isted, in spite of the fact that the area had been resur­veyed from 2008 to 2010 by the In­dian Hy­dro­graphic Of­fice. The elec­tronic charts in use were ac­cu­rate and cur­rent, and a highly ex­pe­ri­enced nav­i­ga­tor was in charge of route plan­ning. So how could this hap­pen? This ac­ci­dent dra­ma­tizes a fun­da­men­tal weak­ness in many of the elec­tronic chart­ing sys­tems in use on re­cre­ational boats. To un­der­stand it, we have to look at how charts are made. Hy­dro­g­ra­phers take sound­ings by run­ning straight lines and ac­cu­rately po­si­tion­ing these and any sub­merged land­masses. In shal­low and in­shore wa­ters these lines are closely spaced to en­sure that no in­ter­ven­ing fea­tures are missed. The deeper the wa­ter and the far­ther off­shore, the sur­vey lines get more widely spaced, be­cause miss­ing the fea­tures be­tween them is less rel­e­vant.

Up un­til the wide­spread use of sides­can sonar (start­ing in the 1960s), there was lit­tle or no lat­eral vi­sion when tak­ing sound­ings, and prior to 1939, none at all, es­pe­cially if the sound­ings were col­lected with a lead line. Prior to the ad­vent of satel­lite nav­i­ga­tion sys­tems, the po­si­tion­ing ac­cu­racy used to plot sound­ings was sig­nif­i­cantly less than what any off-the-shelf GPS can de­liver to­day. Over half of the sound­ings on cur­rent U.S. charts were col­lected us­ing pre-sides­can-sonar and non-satel­lite-po­si­tion­ing tech­niques. In other parts of the world, it can be any­thing up to 100 per­cent (for ex­am­ple, much of the Pa­cific, Ba­hamas, and Caribbean; even sub­stan­tial sec­tions of the UK’s coast­line).

Hy­dro­g­ra­phers typ­i­cally con­duct sur­veys at a larger, more de­tailed scale than those used to pro­duce the charts de­rived from the sur­vey. As many sound­ings as pos­si­ble are col­lected and crammed onto the sur­vey sheet, to the point that tra­di­tional, pre-dig­i­tal sur­vey sheets can be al­most il­leg­i­ble. The car­tog­ra­pher has to re­duce this mass of data to a leg­i­ble level with­out los­ing the es­sen­tials.

For ob­vi­ous rea­sons, the first pri­or­ity of car­tog­ra­phers has al­ways been to display ar­eas of shal­low wa­ter to­gether with haz­ards, such as rocks and reefs. Large-scale charts that cover a small area in great de­tail have room to add plenty of sound­ings, such as nar­row chan­nels be­tween shoal ar­eas. Small-scale charts (cover­ing a large area in lit­tle de­tail), on the other hand, do not have the space to leg­i­bly add fine de­tail once the low-wa­ter ar­eas have been inked. As a re­sult, the more you zoom out with paper charts, the larger the shal­lowwa­ter ar­eas get. There is ab­so­lutely no mis­un­der­stand­ing con­cern­ing haz­ards. There are two types of elec­tronic charts: raster and vec­tor. A raster chart is an elec­tronic pho­to­graph of a paper chart, so the same shal­low-wa­ter fea­tures are re­pro­duced: Shal­low wa­ter is al­ways clearly iden­ti­fied, re­gard­less of scale. A vec­tor chart is an en­tirely dif­fer­ent an­i­mal. All of the data on the most de­tailed (largest scale) chart or sur­vey sheet is cap­tured in a data­base and is avail­able to be dis­played at any chart scale. When you zoom in, at some point you get all this in­for­ma­tion. When you zoom out, if this in­for­ma­tion were to be re­tained, the chart would rapidly be­come so clut­tered that it would be un­read­able. This is where the tra­di­tional car­tog­ra­pher re­moves de­tail to make the chart leg­i­ble, pre­serv­ing the shal­low-wa­ter sound­ings. Re­duc­ing the clut­ter on vec­tor charts is done in the soft­ware.

It is not un­com­mon for vec­tor soft­ware to re­move the shal­lowwa­ter sound­ings. Given the zoom level at which the nav­i­ga­tor aboard Ves­tas Wind planned his route, and at which the dig­i­tal charts were be­ing used while at sea, the reef sim­ply dis­ap­peared from view. The shal­low­est wa­ter dis­played was 130 feet. The nav­i­ga­tor plot­ted a course di­rectly across the reef. Had the nav­i­ga­tor con­sulted a paper chart at any scale, the reef would have been clearly vis­i­ble.

Note that most of the cur­rent crop of mul­ti­func­tion display de­vices (MGD) can now display world­wide raster charts in ad­di­tion to vec­tor charts, which was not pos­si­ble in the past due to higher mem­ory re­quire­ments of raster charts). While a ben­e­fit, raster charts of­ten still don’t in­clude ac­cess to im­por­tant paper chart el­e­ments, such as the source map. On a dark night in Jan­uary 2013, the minesweeper USS Guardian pow­ers at 7.5 knots di­rectly onto the Tub­bataha Reef in the Philip­pines in 4- to 6-foot seas. All ef­forts to free her fail. Later, in ris­ing seas she swings broad­side onto the reef, break­ing her keel and punch­ing nu­mer­ous holes in her wooden hull. Waves sweep over the deck and drive her far­ther on, and she is at risk of break­ing up. The crew is evac­u­ated. Guardian is sub­se­quently cut into three pieces, each small enough to be lifted off the reef by a gi­ant salvage crane.

How could this hap­pen on a navy ves­sel with its mul­ti­ple nav­i­ga­tional checks and bal­ances, es­pe­cially given the fact that the reef was clearly dis­played more or less in its cor­rect po­si­tion on the small scale (gen­eral) vec­tor chart? The prob­lem here was the navy’s large-scale (coastal) vec­tor chart had the reef 7½ miles out of po­si­tion, based on er­ro­neous satel­lite im­agery. This had been known since 2011 but had not been cor­rected due to “hu­man er­ror.”

Guardian’s skip­per and nav­i­ga­tor noted the dis­crep­ancy be­tween the small-scale and large-scale charts and sim­ply as­sumed that the more de­tailed chart must also be the more

ocean, sur­vey lines can be many miles apart, miss­ing mas­sive de­tails in be­tween.

These sorts of things don’t just hap­pen in re­mote cor­ners of the world. In 1992 the Queen Elizabeth II ( QE2) cruise ship, at that time the flag­ship of the Cu­nard Line car­ry­ing over 2,800 pas­sen­gers and crew, struck an un­charted ledge off Cut­ty­hunk Is­land in Rhode Is­land Sound when trav­el­ing at 24 knots. A long gash was cut in the ship’s star­board side. The QE2, with a draft of 32 feet, was sail­ing in wa­ters charted to a depth of 40 feet. The ledge fell in be­tween sur­vey lines.

A cou­ple of other fac­tors may have been at work in the QE2 ground­ing. We have a se­ri­ous anom­aly on all U.S. charts (paper and elec­tronic). The dis­played sound­ings are based on some­thing known as Mean Lower Low Wa­ter (MLLW). This does not equate with ex­treme low-wa­ter events, such as those that oc­cur dur­ing spring tides. The wa­ter level can, on oc­ca­sion, be sig­nif­i­cantly less than the charted depth, some­times by sev­eral feet. Most of the rest of the world uses a more con­ser­va­tive low-wa­ter chart da­tum, known as Low­est As­tro­nom­i­cal Tide, or LAT, so this prob­lem does not oc­cur. Many U.S. paper charts have a ta­ble some­where on the chart that has an Ex­treme Low Wa­ter col­umn that in­forms you by how much the wa­ter level can go be­low the charted depth. These ta­bles do not show up on vec­tor-type elec­tronic charts, and are likely to be hard to find on raster charts.

The other cir­cum­stance that may have been rel­e­vant in the QE2 ground­ing is the fact that when you power a boat with lit­tle wa­ter be­neath the keel, the pro­pel­ler tends to suck the wa­ter out from un­der her, low­er­ing the boat rel­a­tive to the sur­round­ing wa­ter. This is known as squat­ting, and if the clear­ance be­neath the keel is small enough, you can suck out the wa­ter un­til you are drag­ging the bot­tom, at which point the faster you try to go the more you drag, and the slower you ac­tu­ally go. We learned this long ago when we built and lived on canal boats in the U.K.’s shal­low in­land wa­ter­ways.

We ex­pe­ri­enced the squat­ting ef­fect dra­mat­i­cally one night when head­ing up the Mis­sis­sippi Gulf Out­let Canal (now closed, be­cause of the dis­as­trous role it played in the flood­ing of New Or­leans dur­ing hur­ri­cane Ka­t­rina). A fully loaded con­tainer ship passed us drag­ging the bot­tom and mov­ing just fast enough to main­tain steer­age­way. We edged over to the side of the chan­nel to get out of the way. As the ship came past it sucked the wa­ter out of the chan­nel leav­ing us tem­po­rar­ily hard aground and heeled way over. It’s the sum­mer of 2003, the sun is shin­ing and a fresh breeze is blow­ing—a great day for a cruise. My neigh­bor has just bought a cata­ma­ran. He calls: “Nigel, let’s go boat­ing.” I am work­ing on the page proofs of a new book called How to Read a Nau­ti­cal Chart (pub­lished by McGraw-Hill and now in its sec­ond edi­tion). “I’m sorry Mike, I can’t. I have to fin­ish these page proofs.” His swift re­ply, “Bring them with you.” So here I am, at the wheel of Mike’s brand-new pride and joy, read­ing the page proofs of How to Read a Nau­ti­cal Chart, when I run his boat onto a rock at 7 knots. We are both thrown across the boat. Sub­se­quent in­ves­ti­ga­tion re­veals a crushed keel.

The fault here? Mike did not have an elec­tronic chart­ing sys­tem on board so we were us­ing paper charts. The first time I had sailed these Maine wa­ters (years be­fore) I had made a men­tal note that if I stayed out­side of a line be­tween Had­dock Is­land and Western Egg Rock, I would clear the rock with room to spare. Sub­se­quently, I did not bother to look at the chart, which was un­for­tu­nate, be­cause I had mem­o­rized the rock on the wrong side of the line. For years I had sailed over this same rock and never struck it be­cause the tide had been high enough to clear it. On this day, we caught it at low tide. In all like­li­hood, if we had elec­tronic charts on­board and dis­played at the helm, we likely would not have run aground.

My point here is that ul­ti­mately, most ground­ings are the re­sult of hu­man er­ror rather than chart er­ror. Like most re­cre­ational nav­i­ga­tors to­day, to avoid the kinds of mishaps il­lus­trated above, I now rely heav­ily on elec­tronic charts both for route plan­ning and for nav­i­ga­tion. There are nu­mer­ous ben­e­fits as com­pared to paper charts, in­clud­ing real-time display of the boat’s po­si­tion (typ­i­cally to a greater de­gree of pre­ci­sion than the display of the chart data) with­out the pos­si­bil­ity of nav­i­ga­tor er­ror, over­laid AIS and radar dis­plays, and var­i­ous “added value” fea­tures, such as the abil­ity to pull up in­stant tide ta­bles. I have evolved a set of pro­cesses to min­i­mize the as­so­ci­ated risks.

We al­ways carry paper charts, typ­i­cally at a scale of some­where be­tween 1:80,000 and 1:150,000. This is not de­tailed enough for dif­fi­cult har­bor en­tries, but is good enough for most other nav­i­ga­tional pur­poses and as a back-up to the elec­tronic charts with­out break­ing the bank. It also en­sures that all shal­low-wa­ter ar­eas are clearly dis­played and gives me ad­di­tional data, such as notes and source di­a­grams that are un­likely to show up on the elec­tronic charts.

Be­cause of the rel­a­tively small size of even the largest elec­tronic chart display as com­pared to a paper chart, and also the fact that the screen res­o­lu­tion on elec­tronic dis­plays re­quires you to zoom in to some ex­tent to make any chart leg­i­ble, fur­ther re­duc­ing the cov­er­age area, I do my ini­tial route plan­ning for all but short and un­com­pli­cated pas­sages on the paper charts. This de­ter­mines whether or not I have a rel­a­tively straight shot be­tween the de­par­ture and ar­rival points. Let’s as­sume it is a straight shot.

I zoom out the elec­tronic chart un­til I have my two way­points, and then I lay down a track be­tween them. Then I zoom in and look for haz­ards and other fea­tures that might re­quire an ad­just­ment to the track, scrolling from one end of the track to the other, mov­ing the track and adding way­points as ne­c­es­sary. The fi­nal step is to zoom in to the level at which all avail­able data is dis­played. I scroll along the en­tire track once more, recheck­ing all the sound­ings and other fea­tures along the track and in its vicin­ity. I make ad­just­ments as ne­c­es­sary, high­light­ing po­ten­tial dangers, and re­view­ing al­ter­na­tive tracks (which I of­ten add to the chart) and emer­gency an­chor­ages in case con­di­tions change. This route be­comes our pri­mary nav­i­ga­tional tool.

There are in­creas­ingly so­phis­ti­cated soft­ware pack­ages that au­to­mat­i­cally per­form many of the func­tions just de­scribed, with Navion­ics’ Dock-to-dock Au­torout­ing be­ing the best-de­vel­oped at this time. The Coastal Ex­plorer PC chart­ing pro­gram has a

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