chapter 6 - landmarks

8/14/2019 Chapter 6 - Landmarks

1/20

Landmarks 6-1

brief list, landmarks are artificial features.But landmarks also include prominent natural features such as a mountain peak, glacier,volcano, cliffs, or other suitable natural ob-

jects. 1

This chapter provides information on thetype and utility of landmarks and how theseare depicted on nautical charts. This chapteralso identifies sources of additional informa-tion (e.g., the U.S. Coast Pilot, Chart No. 1,United States of America Nautical Chart Ab- breviations and Terms and the Light List ) ,

which supplement that provided on the nau-tical chart. Finally, the chapter concludeswith practical pointers on the selection of land-marks for navigation and why landmarks aresometimes not seen or identified when under-way.

Importance of Landmarks in CoastalNavigation

All mariners, with varying degrees of for-mality, employ landmarks for navigation.Used in conjunction with seaman s eye orinformal navigation, landmarks serve to de-termine an approximate position, define haz-ardous areas, provide directions for harbor

1 It is important that natural features have clearly defined reference points that can be accuratelylocated if these are to be charted as landmarks. Mountains with rounded peaks would probably not becharted as landmarks, although the topography would be shown.

CHAPTER 6

Landmarks

Introduction and OverviewAccording to accepted NOAA Nautical

Chart Manual nomenclature, a landmark

...is any fixed natural or artificial object on land which is prominent fromseaward and can be used in determin-ing a direction or position. The termexcludes objects expressly erected fornavigational purposes such as lights ordaybeacons. Prominence is the firstrequisite for a landmark, but ease of

positive identification is also impor-tant. The unusual or unique featuremay qualify as a landmark because it iseasy to identify although not particu-larly prominent.

A more complete list of landmarks typicallycharted is provided later in this chapter.Briefly, however, landmarks include such ob-

jects as buildings, stacks, tanks, domes, tow-ers of various descriptions, spires and radioantennas. (Not all of these objects in a givenarea would be charted as landmarks, however.)Often, as in the examples presented in this

Even with the best charts, we are cautious about fixing our position, for it is so easy to goof.And the easiest way of all is by taking a mark,assuming it is the right one, and ignoring any

others that may be in sight. Patrick Ellam


2/20

NOAA Chart User's Manual6-2

entry, etc. For example, directions to a favor-ite anchorage based on recent local knowledgemight be given as:

Stay in the main river channel until

passing the red brick pump house onthe left (when northbound) then altercourse to starboard until the bow isaligned with the blue A-frame buildingbetween the flagpole and the marinaand the stern with the pump house.Continue along an imaginary line join-ing these two landmarks until well pastthe small island on the right-hand side,then turn to port .

More formally, landmarks are charted ob-

jects used for determining LOP (e.g., with ahand-bearing compass or radar) 2 and circles of position (e.g., with radar or an optical rangefinder for landmarks with charted height in-formation) so as to determine a fix or estimatedposition for the vessel. Table 6 1 providesboth general and specific illustrations of howinformation derived from landmarks can beused for marine navigation. As with ATONs,discussed in Chapter 5, landmarks can be usedto fix the vessel s position, to serve as the vi-sual equivalent of radio beacons for homingor tracking purposes, to evaluate whether ornot a vessel is in dangerous waters (e.g., byuse of a danger bearing or danger circle), toidentify turn points, and for a variety of spe-cialized purposes such as compass calibrationor to determine whether or not the vessel sanchor is dragging. Included in the list of ref-erences at the end of this chapter are textsthat discuss these topics in detail. Names en-closed in parentheses (e. g., Bowditch) denoteparticularly pertinent references.

In short, charted landmarks are the logi- cal equivalent of shore-based ATONs for use

2 Landmarks are generally selected so as to be detectable and identifiable from the sea by visual means.Some may be detectable and identifiable by radar, but charting as a landmark offers no guarantee that theobject can be detected and identified by radar. In particular, landmarks in built-up areas, such as cities, areoften lost among many land returns.

GENERAL:

Used for determining range or bearing byvisual means (or radar) in coastal watersso as to determine a fix or estimatedposition;

SPECIFIC ILLUSTRATIONS:

Used for determination of fix, running fix,estimated position, set and drift of cur-rent;

Used for plotting danger bearings, danger circles, horizontal danger angles;

Used (in conjunction with danger bearing

or circle) for evaluation of vessel's posi-tion with respect to unobservable hazardsto navigation;

Used for establishing vessel turningbearings;

Used as visual equivalent of RDF beaconfor homing or tracking purposes;

Used for compass calibration; and

Used for determining whether or not ananchor is dragging. a

a The landmark need not be charted for this purpose.

in coastal waters. If accurately charted (morebelow), detectable, and readily identifiable,these can be superior to the use of floatingATONs (buoys) recall that fixed structuresare preferable to floating structures for posi-tion determination. In some areas of highpopulation density or numerous conspicuousnatural features, charted landmarks are ac-

tually more numerous than charted ATONs.

Table 6-1. Utility of Landmarks Shownon Nautica l Chart


3/20

Landmarks 6-3

Types of LandmarkTable 6 2 provides a list of the more com-

mon artificial landmarks depicted on nauti-cal charts, together with pertinent brief re-marks. Refer to the Glossary given in appen-

dix A for more complete definitions. It isworthwhile to study these and to gain practi-cal familiarity with landmarks by systemati-

cally comparing the chart representation of landmarks in your area with the physical ap-pearance of the object. These training ses-sions can be made an enjoyable part of eachcruise. An experienced navigator can often

form a highly accurate mental picture of landmarks to be found in unfamiliar wa-ters merely by studying the chart.

Continued on next page

ANTENNA Usua lly reserve d for those re -flec ting antenna s which arelarge in size a nd of o pe n or grid-type c onstruction.

BUILDING Se e HO USE.

CHIMNEY A rela tively sma ll, up right struc-ture p rojecting above a buildingfor the conveyance of smoke.

CUPOLA A turret or sma ll dom e-shapedtow er whic h rises from a b uild -ing a nd is small compa red to thebuilding.

D O M E A large, hemisphe ric al c upo la,or a roof that is round ed or manysided . Their app ea ranc e lookslike a large go lf ba ll.

DOME (RADAR) A dome known to contain rad artype of equipment shall bec ha rted a s DOME (RADA R). Ifthe radar use is not know n, sim-

p ly c ha rt a s DOM E. The ir a p -pearance looks like a largego lf ball.

FLA G PO LE A single sta ff flagpole rising fromthe ground and not attached toa building.

FLA G STA FF A flag pole rising from a buildingis not necessarily the mostprominent pa rt of a b uilding forlandma rk rec og nition p urpo ses.

FLAG TO WER Any scaffoldlike tower on whichflags are hoisted, such as aCoast Gua rd Skeleton stee l flag-pole.

GAS TANK Since a gas or oil tank differs insha pe and size from a w a tertank, the compound name is

or OIL TANK used . The se a re usua lly c ylin-drical.

Table 6-2. Illustra tive Landmarks


4/20


Table 6-2. Illustrative Landmarks (continued )

Continued on next page

OIL TANK See GAS TANK.

RADIO MASTRADIO TOWER Rad io tow ers a nd rad io ma sts

are meta l structures used to e l-eva te antenn a s. A RADIOTOWER is a ta ll struc tu re usu-ally of op en lattice -type c on-struc tion a nd a lwa ys self-sup -p orting . A RADIO MAST is avery ta ll slim struc ture he ld verti-

ca l by guylines.

RADIO TOWERK A G T1340 kHz

RADIO MAST 1015 FT(TV, FM)( STROBE, R LTS)

RADIO TOWER 215 ft(MICROWAVE) orMICRO TOWER

H O U S E Cha rted when the building itselfor BUILDING is the land ma rk.

LOOKOUTTO W E R Any tower, usually of op en c on-

struc tion, surmounted by a sma llhouse in which a wa tch is hab itu-ally kept, such as a Coast GuardLooko ut Tow er or a Fire Loo k-out Tow er.

LORAN-CSTA TIO N S (See: Ap pend ix A. Glossary.)

MICRO TR A tow er whic h c ontains micro-wa ve transmitters and rec eivers,used in the transmission of com -munication signals.

M O N U M E N T A structure, suc h a s a build ingor sc ulpture, erec ted as a me-mo rial. A lso used to d eno te aboundary ma rker for surveyingor other p urposes. The re is nostandard size or shape to amo nume nt. Som e, suc h as theWashington Monument, re-sem b le an ob elisk (i.e., a four-sided shaft that ta pers to a pyra-mida l po int), others a ssume avariety o f shapes.


5/20

Landmarks 6-5

Table 6-2. Illustrative Landmarks (continued )

TO WER; TR Tha t p a rt o f a struc ture hig herthan the rest, but ha ving verticalsides for the g rea ter pa rt o f theheight.

Any enclosed structure, whetheror no t its side s a re vertic a l, withba se on the g round a nd high inprop ortion to its ba se.

T R E E Lon e tree or conspicuoustree, are not used since the ad -

jec tive is a ssum ed . O the rwisethe tree wo uld no t serve a s alandmark.

WA TER TO WER A decorative structure enc losinga ta nk or stand pipe . Its ap pe ar-anc e ma y prevent its be ing rec-ognized as a water tank orstandpipe.

WINDMILL A self-explana tory term.

S P I R E A slender point structure sur-mo unting a build ing. It is rarelybroken b y stag es or other fea-tures. The te rm SPIRE is no t a p-

plic ab le to a short p yram id-sha p ed struc ture rising from atower or belfry. Spires are oftenseen atop churches.

STAC K This term is a p p lied to a ny ta llsmokestack or chimney, regard-less of c olor, sha pe, or materialwhe n the stac k is mo re promi-nent as a land ma rk than a nybuilding in connec tion with it.

STANDPIPE; A tall cylindrica l struc ture in a w a-te rworks system, the he ight ofwh ich is seve ra l time s grea terthan the diameter.

TANK A water tank elevated highab ove the ground by a tall skel-eto n framework or support. The

word elevated is om ittedsince a tank would not b e

a landmark unless el-evated.

O THER EXAM PLES O F LANDM ARKS NO T ILLUSTRATED A BOV ETHAT M AY BE USED O N C HA RTS:

Battery, Bloc khouse, Buddhist Tem ple, Camp ing Site,Ca pitol, Ca stle, Cemetery, Chape l, Church, ChurchTower, Church Spire, Church Cupola, Company, Court-ho use, Cross, Eleva to r, Fa c to ry, Fla re Sta c k, Fort,Fortified Structure, Gable, Governme nt House, High

Sc ho ol, Hote l, Institute, Jossho use, Ma g a zine,Marabout, Minaret, Mine, Mosque , Pagoda, Pavilion,Qua rry, Sc ho ol, Shinto Shrine, Silo, Sma ll Fort, Tele-grap h, Telephone , Tem ple, Tomb , University, Well,Windmotor.

SPIPE

Sources: Desk Reference Guide, Bowditch, Chart No. 1.


6/20


For most landmarks (e.g., buildings,churches, radio towers), object definitions arefamiliar and the mariner should have little orno difficulty correlating the chart represen-tation with the physical appearance of the ob-

ject. In some cases (e.g., cupola, dome, chim-ney, stack), the definitions are more subtleand/or the objects may be less familiar so morestudy and on-the-water comparisons are ap-propriate.

Objects Not Normally Depicted As Land-marks

There are also several classes of objectsthat are not typically selected as landmarks on nautical charts. (These objects may beshown on certain charts in areas where suit-

able landmarks are few and far between.)Table 6 3 provides a list of those either inten-tionally or unintentionall y omitted. In themain, the reasons for not selecting these ob-

jects as landmarks are obvious. For example,objects of a temporary nature, such as a con-struction crane, would be a poor choice for alandmark since the object would probably bemoved to another location by the time that thechart was printed.

Trees are another example of an object notnormally charted as a landmark. Think of theconsequences, for example, if the tree werestruck by lightning or chopped down. Evenworse, suppose there were another tree stand-ing one-half mile away!

The charting of movable objects as land-marks is generally avoided. A gantry crane ata shipyard may be a very prominent feature,but it would not have a fixed geographic posi-tion and, therefore, would have little utilityfor precise fixing of a vessel s position.

Signs are not typically charted as land-

marks. However, an unusually conspicuoussign, especially in an area without other suit-able landmarks, may be charted. The eleva-tion and lighting of the sign are considered inmaking the determination of whether or notto select the sign as a landmark. Signboardsdisplaying navigational information may beconsidered as landmarks if they displaynavigationally relevant information, for ex-ample, signboards used to mark distances

INTENTIONALLY NOT SELECTED:

Objects of a temporary nature (e.g., verticalconstruction crane, exploratory oil-drilling rig,dredge);

Inconspicuous objects, unless specificallyrequested by a competent authoritative source(e.g., survey tower or target, object used by theUSCG in buoy placement);

Objects which move in position;

Classified military objects for which no releaseby competent authority can be obtained;

Signs, unless unusually tall, large, or otherwiseconspicuous or in an area devoid of other objects of landmark value;

Multiple objects of the same type very closetogether or in a relatively small area (in thiscase only the tallest or largest items, and/or those on the outer limits of the complex will becharted);

Trees unless (in exceptional circumstances) noother visual references are available to the

mariner; or Omni stations, unless recommended by areliable source.

UNINTENTIONALLY OMITTED:

Objects missed in a previous survey or thosewhich have been constructed since the lastsurvey.

Table 6-3. Items Ge nerally Not Cha rted asLandma rks on the Na utica l Chart

along a waterway. As another example, signsproviding water-level information are nor-mally charted even if not visible from a dis-tance.

It may come as a surprise to some readersthat not all items potentially suitable as land-marks are actually charted. To be sure, insparsely populated flat land areas, nearly allsuitable landmarks would be charted. But inbuilt-up areas, only a few otherwise suitable


7/20

Landmarks 6-7

objects would be plotted as landmarks. 3 Forexample, large cities, such as Boston, NewYork, and Philadelphia, have literally thou-sands of buildings that might be suitable land-marks. However, in practice only a handful

those believed sufficient for safe and efficientnavigation are actually depicted as land-marks on the chart. Figure 6 1 provides suchan illustration for the Philadelphia, PA Camden, NJ, area. Indeed, one of the criteriafor charting landmarks in the Desk Reference Guide, is that consideration should be givento the number and quality of other chartedlandmarks or reported objects of landmarkvalue in the area. Therefore, the marinershould not expect that the nautical chart willdepict al l possible structures as landmarks.

Generally, this poses no particular problemto the informed mariner. But while underwaythis can sometimes lead to confusion and iden-tification problems. For example, several wa-ter tanks may be visible in an area in whichonly one or two are charted. In this case, themariner might be faced with the problem of

which of the tanks in view are those charted?

How Landmarks Are Depicted on theChart

Landmarks are charted in the exact posi-tion reported on source documents. Both asymbol and one or more labels usually accom-pany a charted landmark.

SymbolsIn certain cases, the outline shape of a

prominent structure may be charted to scaleif it is relatively large or of particular inter-est and of landmark value (e.g., the Pentagon,Fort McHenry). More typically, however, land-marks are charted with standard symbols.

Landmark symbols are shown in Section E of Chart No. 1. According to the accuracy with

which the landmark s location is known, thesymbols include:

An accurate landmark symbol, consist-ing of a black circle 1.18 mm (0.047") inradius with a center dot 0.25 mm(0.010") in diameter in cases where theposition of the landmark is consideredto be located within 10 feet of its cor-rect geographic location.

An approximate landmark symbol, con-sisting of a smaller black circle 0.5 mm(0.020") in radius without any centerdot in cases where the landmark is lessaccurately located than above, but gen-erally considered to be within 100 feet

of its correct geographic location.An approximate landmark symbol ex-plained above, but with the letters PA(position approximate) as part of the la-bel in cases where the location of theobject is considered to be within 101 to300 feet of its correct geographic loca-tion. Such landmarks, sometimes re-ferred to as inexact position landmarks,are only charted if they serve a criti-cal navigation need.

In some cases a landmark, such as a build-ing, will be drawn to scale and, additionally,have some contained feature depicted with theaccurate or approximate position label. For ex-ample, the Customs House in Philadelphia,shown in figure 6 1 is drawn to scale. Addi-tionally, the tower atop this building is shownas a landmark with the accurate position sym-bol. Identifying particular portions of struc-tures as landmarks makes it possible to takeaccurate bearings.

Excepting those landmarks which aredrawn to scale, charted landmarks are shown

3 Aside from the logistics and compilation problems of charting all possible landmarks, the resultantchart (with requisite labels) would be physically impossible to produce. Moreover, NOAA is actively seek-ing ways to reduce chart clutter and make more user-friendly products.


8/20


Fig. 6-1. Excerpt from NOSChart No. 12313 (Philadelphiaand Camden waterfront). Of thethousands of buildings in thePhiladelphia, PA-Camden, NJ,area, only a few are chartedas landmarks. This inset fromChart 12313 illustrates stacks,spires, tanks, and towers aslandmarks. The Camden CityHall Tower is a primary label.Less well-known, the CustomsHouse in Philadelphia is writ-ten TOWER (CUSTOM HO).Three hospitals and a fireboatstation are shown in this chartextract. These are not chartedfor their landmark value, butrather for their functional value.


9/20

Landmarks 6-9

in only one of two sizes (1.18 mm radius circleand 0.5 mm radius circle) regardless of actualdimensions. In this sense, all landmarks arealike. Something more is clearly needed tohelp the navigator identify the landmark. This

additional information is provided in labels that are printed next to the landmark symbol.

LabelsAccompanying the landmark symbol is one

or more labels. Labels are used to provide ad-ditional information useful in identifying thelandmark. The label also provides a redun-dant indication of the accuracy with which alandmark is located.

The first label depicts the primary natureor descriptive term most likely to identify the

object (e.g., TOWER, STACK, CHIMNEY) setin 6 pt. Newton Medium type and placed inclose proximity to the landmark symbol.Landmarks charted with the accurate landmark symbol are labeled entirely in vertical capital letters, those charted with the approximate landmark symbol are labeled with initial capitals only. Thus, for example, a tower con-sidered to be located within 10 feet of its cor-rect position would include the accurate land-mark symbol and the label TOWER, whereasone located to within 100 feet of its true loca-tion would have the approximate landmarksymbol and the label Tower. 4 A tower witha location uncertainty greater than 100 feetwould carry the label Tower PA. A partiallist of standardized labels and authorized ab-breviations are shown in table 6 4.

Secondary and descriptive labels may beadded for clarity and are enclosed in paren-theses to the side or underneath the primarylabel. The capitalization convention for thesecondary label(s) is the same as that for the

primary label. Consider a lighthouse, for ex-ample. If operational, this would not be con-sidered a landmark rather it would be in-cluded as an ATON (see Chapter 5). However,

Table 6-4.Labe ls and Authorized Abbrevia tions

ANTENNA (ROUND, PARABOLIC, ORRECTANG ULAR)

CHIM NEY (CHY)CUPOLA (CUP)DOME (a dome known to contain rada r equip-

me nt shall be labeled DOME (RADAR)FLAGPOLE (FP)FLAG STAFF (FS)FLAGTO WER (F TR)GAS TANK or O IL TANKHOUSE or BUILDING (HO or BLDG) (if the

structure e ncloses eq uipme nt of naviga -tional use, a one- word de scription shallfollow the primary level (e.g., BUILDING(VOR))

LOOKOUT TOWER (LOO K TR)LORAN STATIONSMICRO TRMO NUMENT (M ON)RADIO MAST (R MAST) followed by, if known,

radio freque ncy, height, call letters. Also(TV, FM, AM, STROBE, or RLTS).

RADIO TOWERSPIRESTANDPIPE (S'PIPE)TANKTO WER (TR)TREEWATER TO WERWINDMILL

if no longer used as a lighthouse, it would beclassed as a tower. But, because the term

tower includes many different types of struc-tures, it is desirable to add a secondary ordescriptive label, abandoned lighthouse, tosupplement the primary label. Accordingly,such a landmark (if accurately located) would

be labeled TOWER (ABAND LT HO).Names of certain locally well-known build-

ings may be shown as secondary labels to fa-cilitate identification. For example, DOME

4 The lone exception to this rule is the case where an acronym is used in the primary or secondary labelof an approximately determined landmark. Here the acronym would be included in capital letters, e.g.,Tower (USCG). The primary label would be shown in initial capitals only.


10/20


(STATE HOUSE) or BUILDING (RITZTOWER) or TOWER (CUSTOM HO) might beshown on secondary labels. Well-known andunusually prominent landmarks are, on occa-sion, depicted using the name of the landmark

as the primary label. For example, EMPIRESTATE BUILDING and WAS HINGT ONMONUMENT are shown on nautical charts.

Descriptive labels that identify the relative size or location or other distinguishing characteristics of the landmark may also beshown in parentheses following or below theprimary name. When only one object of a groupof similar objects is charted, the descriptivelabel includes the number of objects in thegroup. Examples include STACK (TALLESTOF THREE), HOUSE (WEST GABLE), SIGN

( L I G H T E D ) .A descriptive label may also relate to the

shape of the object. Examples include TANK(OBLONG), TANK (BALL), or TANK (BALLON TEE). Color is not normally noted 5 in alabel because this may be only temporary.Painted names on objects are not normally shown unless the name or abbreviation is dis-played in very large and conspicuous lettersthat are easily identified. The material of construction is not described in a secondary label because the mariner usually cannot identifythe material from a distance.

In some cases both a secondary name anddescriptive label are included. For example:

STACK (FLARE)(TALLEST OF THREE)

might be found in a shore side petroleum re-finery.

The height of the object is also sometimesincluded. Heights can be used for determin-ing the vessel s distance from the landmark(see Bowditch) and, with bearing data, to fix

the vessel s position. In the case of landmarks,the height is given in feet (or meters for met-ric charts) measured from the top of the land-mark relative to mean high water except innontidal areas where these are measured rela-tive to the sounding datum. Height informa-tion is provided for only a minority of charted

landmarks, however.Aircraft obstruction lights are typically

regarded as secondary importance as an aidto navigation. Therefore, these are not nor-mally charted with a light dot and magenta

flare unless listed in the Light List and givena Light List number. Obstruction lights onlandmark objects are not labeled unless spe-cifically requested by a reliable source. Inthis case, no differentiation is made betweenocculting and fixed lights. For example, astack (with accurate location) with a whitestrobe and red obstruction lights would belabeled:

STACK (STROBE, R LTS).An obstruction recommended for charting

as a landmark that is identified only as an air-

craft obstruction light is charted with the ap-propriate landmark symbol and labeled:

OBSTN (R LT).Radio structures are labeled with the type

of function and height (when considered of sig-nificant importance for visual sighting). AMbroadcast stations will have the call letters andfrequency included in the label, as will otherstations known to be used for marine naviga-tion assistance. Here are a few examples:

RADIO MAST 862 FT(TV)(STROBE, R LTS)

RADIO MAST 483 FTW S S O1230 KHZ(R LTS)

RADIO TOWER 315 FT(FM, MICROWAVE)(R LTS)

In very congested areas, a list of stationsmay be provided elsewhere on the chart toavoid the elimination of important topographyand/or hydrography as a result of labeling.

The foregoing provides a useful summaryof key charting conventions for landmarks.

5 Color may be included, however, in U.S. Coast Pilot or Light List descriptions.


11/20

Landmarks 6-11

Other Sources of Landmark InformationIn most cases the position and the label(s)

shown on the chart will be sufficient for thenavigator to use the landmark for navigation.However, other sources may offer useful in-

formation as well.Pictures of selected landmarks are in-cluded on the back of certain conventional andsmall-craft nautical charts. These photographsare very useful in identifying landmarks. Forexample, the back of NOS Chart No. 13221(Narragansett Bay) contains several photo-graphs of landmarks and ATONs in the area.

Commercially produced cruising guides of the area sometimes provide descriptions and/or photographs of landmarks.

An important source of collateral informa-

tion on landmarks is the U.S. Coast Pilot. Im-bedded in the general text and, in some areas,highlighted in a special section called Promi-nent Features, the U.S. Coast Pilot providesinformation on the location, appearance, andsuitability of landmarks for navigation. Guid-ance for the preparation and revision of theU.S. Coast Pilot is provided in the Coast Pilot Manual. Here is an excerpt from this docu-ment regarding how Prominent Featuresshould be described:

Prominent Features. Describe thebest charted landmarks for navigation,such as land formations, lights, tanks,stacks, towers, buildings, etc. Note thecolor, form, and height of headlandsand peaks. Streaks of color in bluffsmay be useful in identifying features.If objects such as mountains, hills, cliffs,islets, or rocks are recommended aslandmarks, give their measured or es-timated heights .

In highly developed areas wherethere are numerous charted structures,the Coast Pilot supplements the chartsin two important ways: by identifyingthe best landmarks and by describingthe structures for positive identifica-tion. Give the height, color, and paint-ing pattern of prominent structures if available. Describe the general shape

of unusual objects .

Here are a few passages from Volume 3, At- lantic Coast: Sandy Hook to Cape Henry (1993)that illustrate the type of information pre-

sented:

When approaching Maurice River, mari-ners should use care and not confuse thestructure of East Point Light with a pri-vate house with a tower about 1.3 miles tothe east, both landmarks are similar inappearance.

In 1967, the monument on Liston Pointwas reported destroyed; and in 1983, themonument on the south side of the entranceto Hope Creek was also reported de-stroyed. Remains of the structure fromListon Point may exist up to 100 feet off-shore and may be covered during hightide.

A large, cylindrical water tank, about 1.5miles west of Ocean City Inlet, is promi-nent and is a good landmark while enter-ing the inlet.

Assateague Light and the lookout toweron the southern tip of Assateague Islandare good marks for approachingChincoteague Inlet.

Abandoned Navesink Lighthouse is in acleared space on the easternmost spur ata ground elevation of 180 feet; the two 73-foot brownstone towers, the north one oc-tagonal and the south square, are con-nected by a dwelling.

As a final example, consider this descriptionof the entrance to Bridgeport, CT, harbor,taken from Volume 2, Atlantic Coast: Cape Cod to Sandy Hook (1993):

Prominent Features. The large redand white horizontally banded stack of a power plant on Tongue Point is themost prominent landmark in this area.Other prominent landmarks include a


12/20


group of stacks on Steel Point: the tow-ers of a high-voltage line; several churchspires; a gas tank with a red-and-whitecheckered band at the top, on the westside of Pequonnock River; the radio

towers at Pleasure Beach; the Bridge-port Harbor Light 13A. The rays of anaerolight about 1.3 miles northwest-ward of Stratford Point can be seenfrom offshore.

The U.S. Coast Pilot is invaluable as asupplement to nautical charts for many rea-sons. These few examples illustrate why thisis so for the identification of landmarks.

Practical Pointers and LimitationsRelevant to Landmarks

The balance of this chapter provides somepractical pointers relevant to the use of charted landmarks in navigation. The firstpart of this section presents practical ideason the selection of charts and landmarks fornavigation. The second part addresses theimportant topic of why some charted land-marks may not always be able to be seen (oridentified) from the vessel.

PointersPerhaps the most important suggestion isto select the largest scale chart of the area for navigation. This point is made in severalplaces in this manual, but it is worth restat-ing here. Large-scale charts offer the great-est amount of detail for a small area, and offerthe greatest number of charted landmarks hence the largest number of options for posi-tion fixing. Any landmark shown on asmall(er)-scale chart will also be shown on thelarge(er)-scale chart of the area, but many land-marks shown on large-scale charts are not de-picted on small-scale charts because it is nec-essary to generalize charted features fromlarge scale to small scale. As well, the latest edition of this chart with corrections given in the NM should be used. Although landmarksare relatively permanent (recall that perma-nence is one of the criteria for charting a land-mark), they do change on occasion. Structuresare torn down, and new ones are periodically

constructed, so it makes sense to have the lat-est information at hand.

Another important point to reemphasizeis that all sources of information should beused to fix the vessel s position not just land-

marks. Maintenance of a dead reckoning plot,use of depth information, ATONs, and othermeans should all be used. Knowledge of eventhe vessel s approximate position can be help-ful in identifying landmarks that might be usedfor more exact fixes. Moreover, other informa-tion (e.g., the depth of water at the vessel slocation) can be used to increase the confidencein or rule out the tentative identificationof a landmark.

Selecting Landmarks For UseIn low-lying land areas of low population

density (e.g., portions of the Delaware and Vir-ginia coast) landmarks may be few and far be-tween, and the mariner may have little choiceas to which landmarks to use. Selection guide-lines for landmarks are not relevant in thiscase.

However, other coastal areas offer manymore charted landmarks, and the mariner of-ten has a choice of which to use for naviga-tional purposes. Here are four useful selec-

tion criteria for suitable landmarks in caseswhere choices are available:

Objects should be selected that are detectable and readily identifiable. Manyfeatures might be used for position fix-ing, but objects selected by cartogra-phers as landmarks are likely to be con-spicuous (see below). Landmarks de-picted with the accurate position sym-bols are to be preferred over those de-picted with the approximate location

symbol. Refer also to the U.S. Coast Pilot or commercially produced cruis-ing guides for information on the ap-pearance of conspicuous landmarks.

Objects selected should be in a geo- metrical configuration suitable to their intended navigational purpose. For ex-ample, if a landmark is to be used toestablish a danger bearing, it should be


13/20

Landmarks 6-13

Fig. 6-2. Excerpt from NOS Chart 13218 (Martha's Vineyard to Block Island). The TOWER (ABAND LT HO) off Sakonnet Point is ideally situated to define a danger bearing to avoid Schuyler

Ledge when approaching from the south. The accurately known landmark is likely to be conspicuous.Indeed, the lighthouse was probably there precisely for this purpose.


14/20


Fig. 6-3. Excerpt from NOS Chart 13218 (Martha's Vineyard to Block Island). The DOME and S PIPE nearWoods Hole would offer a poor crossing angle for a vessel attempting to fix its

position in the vicinity of the Middle Ground. Use of either landmark and the CUPOLA at the east end of Naushon Island would be preferable.


15/20

Landmarks 6-15

appropriately positioned relative to thehazard to be avoided as illustrated infigure 6 2. If more than one landmarkis to be used as, for example, to plot atwo or three bearing fix the land-

marks should be chosen so that the re-sulting crossing angles of the lines of position are best. For two objects, acrossing angle of 90 is optimal, andcrossing angles less than 20 or 30should be avoided. (Refer to figure 6 3for an illustration.) For three objects,60 crossing angles are best. (Bowditch,Maxim.) Selection criteria for horizon-tal sextant angles are more complex,and the reader is directed to some of the references (Bowditch, Admiralty Manual of Navigation ) for details.

Landmarks closer to the vessel are generally preferable to those further away.This is because errors in bearing (takenwith a hand-bearing compass or radar)are nearly independent of the distance,and the position error associated witha given error in azimuth increases di-rectly with distance. If a compass bear-ing is inaccurate by 5 (a plausible fig-

ure, see Dahl), for example, the linearerror is approximately 5,300 feet if thelandmark is 10 miles distant, but onlyabout 260 feet if the landmark is 1/2mile distant. (For more detail, seeDahl, Moody, or Brogden.)

Taller landmarks should generally be chosen in preference to shorter objects.Other things being equal, taller objectscan be seen at a greater distance thanshorter objects due to the curvature of the earth. If He is the height of theobserver s eye (in feet) and Ho is theheight of the object in the same units,then maximum distance, D (in nauti-cal miles), at which the object can beseen (as a result of the curvature of theearth (Bowditch)) is given by the equa-

tion, D = 1.17 He + 1.17 Ho .Assuming a height of eye of 10 feet, a20 foot object would be just visible overthe horizon at 8.9 nautical miles, a 100foot high object might be seen at 15.4

nautical miles. (See table 3-1.) Of course, use of this criterion dependsupon the height of the object beingknown and recorded on the chart.Height information is not provided forall landmarks and certain tall land-marks, such as radio towers, may bedifficult to see (Eyges) in hazy condi-tions because these are generally slen-der objects.

Limitations

Even experienced mariners occasionallyhave trouble detecting and identifying chartedlandmarks (Graves, Eyges). So it is worth-while to enumerate some of the reasons whylandmarks may not be seen. These include:

The landmark may no longer be there.Although landmarks are selected so asto be relatively permanent, artificialstructures are occasionally destroyedby natural disasters or demolition ac-

tivities. Ultimately, this fact is re-ported to NOAA and the chart is up-dated to delete the landmark, but thisprocess takes time, and even the latestcorrected chart of the area may show

phantom landmarks. 6 Along withdemolition, new construction may cre-ate problems regarding landmarks, be-cause new structures (see below) maybe confused with charted landmarks.

The landmark may not be visible as a

result of horizon geometry (see above)or poor atmospheric visibility. Knowl-edge of the vessel s approximate posi-tion and the prevailing visibility, as wellas the landmark s height, can be help-ful in determining whether or not alandmark is likely to be visible. Statis-tical visibility data for various locations

6 In cases where changes in landmarks are viewed as critical to navigation safety, landmark changes willbe reported in the NM. Such listing is relatively rare, however.


16/20


can be found in the U.S. Coast Pilot .These data can be useful for trip plan-ning purposes. Table 6-5, for example,shows the average annual number of days with visibility less than or equal

to 1/4 mile for selected locations in theUnited States, ranked in descendingorder. In Nantucket, MA, for example,poor visibility occurs an average of 96days out of each year approximatelyone day out of four. St. Croix, San Juan,Hilo, and Honolulu enjoy nearly totalfreedom from episodes of 1/4-mile vis-ibility. Data in the U.S. Coast Pilot alsoshow the distribution of reduced vis-ibility episodes by month. Figure 6-4shows this information plotted for Nan-

tucket, MA. As can be seen, the worst

months at this location are June, July,and August.

The landmark may be masked by other structures, terrain features, or vegeta-

tion. At the time that an object is se-lected as a suitable object for chartingas a landmark, a determination is madethat it is conspicuous. However, inthe years since originally charted,events may have occurred which limitthe visibilit y of the object. For land-marks in built-up areas, such as cities,new construction may have taken placewhich masks the landmarks from someor all approach angles. In rural areas,trees or other vegetation may obscure

the structure at least from some ap-

LOCATION

NANTUCKETBLOCK ISLANDSAN FRANCISCOTATOO SH ISQ UILLAYUTEEUREKAATLANTIC CITYLOS ANGELESSEATTLEASTORIAPORT ARTHURHOUSTONSAVANNAHWILMINGTONMOBILEPENSACOLASACREM ENTOJACKSONVILLEPORTLAN DNEW YORKDAYTONANEW ORLEANSHA RTFORDBRID G EPO RTBALTIM O RERICHMOND

STATE/TERRITO RY

MARICAWAWACANJCAWAO RTXTXGAD EA LF LCAF LO RNYF LLAC TC TMDVA

ANNUAL DAYSWITH VSBY.

LESS THAN OREQUAL TO 1/ 4 M

9679645949494844434341414039393735353333323130303029

LOCATION

CORPUS CHRISTICHARLESTO NSAN DIEGONEW HAVENAPALACHICOLABROWNSVILLEPROVIDENCEPHILADELPHIAWILMINGTONTAMPANO RFOLKFT M EYERSBOSTO NJUNEAUNEWARKCAPE HATTERASANNETTEWASHINGTONWEST PALM BEAC HMIAMIKEY WESTST CROIXSAN JUANLIHUEHILOHONOLULU

STATE/TERRITO RY

TXSCCAC TF LTXRIPANCF LVAF LMAAKNJNCAKDCF LF LF LVIP RHIHIHI

ANNUAL DAYSWITH VSBY.

LESS THAN OREQUAL TO 1/ 4 M

29292828282725252424232323222019161387100000

SOURCE: U.S. COAST PILOT

Ta ble 6- 5.Annua l Da ys With Visibility Less Tha n or Equa l

to 1/ 4 Mile for Sele cte d Loc a tions Ra nked in Descending Order


17/20

Landmarks 6-17


18/20


proach angles. (In this case, landmarksmay be visible in certain seasons e.g.,winter and not in others.) Rememberalso that landmarks are selected to bevisible from the sea, but not necessar-

ily from all possible approach angles.(Inspection of terrain features and el-evations can sometimes help to iden-tify terrain masking.)

The detectability of an object by visual means is a complex function of atmospheric visibility, background contrast,and lighting. Landmarks may be cam- ouflaged as a result of limited contrastwith background areas or because of lighting conditions at the time of obser-vation. (See Eyges for several illustra-tions.)

The mariner may be disoriented and looking in the wrong place on the chart.It is commonplace in navigation that itis much easier to determine your posi-tion if you already know where you are.On reflection this statement is not astrivial as it seems. A practical tip inidentifying landmarks is to plot the

vessel s dead reckoning position (orestimated position if one LOP is avail-able). Then, based on this position onthe chart, plot the bearings to each of the charted landmarks. Next (binocu-lars with a built-in compass are best)look along these plotted bearings forthe landmark. If the vessel s assumedposition is nearly correct (and the vis-ibility is sufficiently great and the land-marks are above the horizon), the land-marks should be visible on bearings

within a few degrees of those plotted.This technique will not work if thevessel s position is grossly in error, butcan be very helpful otherwise. (Foradditional details, see Bright (1990).)

The mariner may actually see the land-mark, but not be able to establish positive identification. This may occur be-cause of confusion among several pos-sible objects (see below), but may also

occur because of ambiguity over theidentity or appearance of the object.For example, the term tower may beused to describe many related but dif-ferent objects. Towers (not otherwisedistinguished) could include structuresas diverse as aircraft control towers,tall buildings (the John Hancock build-ing in Boston, MA), and abandonedlighthouses. (In some cases a second-ary label will be included to narrowdown the possibilities.) The marinershould study the definitions of each of the landmark terms to maximize thepossibility of correct identification.

Finally, it sometimes occurs that sev-eral objects can be seen from the ves-sel, but it is not immediately apparentwhich is the charted landmark. Inother words, the landmark may be detectable but not identifiable. For ex-ample, only some of the many water

tanks in the Philadelphia Camdenarea are charted as landmarks. De-pending upon the vessel s position, itis not always possible to identify whichare the charted landmarks. In suchcases the mariner is well advised tosearch for other identifiable landmarksthat could be used to fix the vessel sposition. Even an approximate fix maybe sufficient to enable correct identifi-cation of the original landmark. Thistechnique is known as shooting up

measuring the bearing of each of sev-eral candidate landmarks and choosingthe one that provides a line of positionthat passes closest to the vessel s posi-tion. (For additional details, see Mellor.)


19/20

Landmarks 6-19

The competent mariner regards each voy-age as a learning experience. In cases where a landmark is missed, or misidentified, the mariner should make every attempt to determine the reason(s) why this occurred. If the

reason is that the landmark was improperlycharted, the mariner should bring this matterto the attention of NOAA and USCG so thatappropriate corrections can be made. Everyerror offers the opportunity to learn a valu-able lesson.

Concluding CommentsLandmarks are very useful for coastal navi-

gation and serve to complement the system of

Exhortation to Apprentices of the Art of Navigation

When so ever any Shipmaster or Mariner shall set forth from land out of any river or haven, dili- gently to mark what buildings, castles, towers,churches, hills, downes, windmills and other marks are standing upon the land all of which, or many of them, let him portray with his pen, how they bear and how far distant.

A. Ashley, 1583, quoted in Naish

ATONs. Careful study of the chart conven-tions presented in this chapter and the defi-nitions presented here and in the Glossarywill pay dividends in improved navigationalskills. Student navigators and that includes

all of us would do well to take the opportu-nity of comparing the chart presentation of familiar areas with what is observable fromaboard the vessel. Finally, prudent marinersdo not rely on any one aid or technique fornavigation. The navigator should use all avail-able data (e.g., dead reckoning positions,AT0Ns, depth information, electronic positiondata, and visual or radar observation of land-marks) to navigate safely.


20/20


Bright, C., Danger Bearings and TurningMarks, Ocean Navigator, Issue No. 45,March/April 1992, pp. 69, et seq.

Bright, C., Identifying Visual Targets,Ocean Navigator, Issue No. 33, June 1990,pp. 63, et seq.

Brogden, B., Accurate Bearings: How to GetBetter Visual Fixes for Coastal Naviga-tion, Ocean Navigator, Issue No. 51, Janu-ary/February 1993, pp. 78, et seq.

Carr, M., Update Charts For Coastal Pilot-ing, Ocean Navigator, Issue No. 50, No-vember/December 1992, p. 33.

Dahl, N., The Yacht Navigator s Handbook,Hearst Books, New York, NY, 1983.

Defense Mapping Agency Hydrographic/Topo-graphic Center. American Practical Navi- gator, An Epitome of Navigation (Bowditch), Publication No. 9, DMA StockNo. NV PUB 9 V1, Bethesda, MD, 1995.

Ellam, P., Yacht Cruising , W.W. Norton &Company, New York, NY, 1983.

Eyges, L., The Practical Pilot, Coastal Navi- gation by Eye, Intuition, and Common

Sense, International Marine Publishing,Camden, ME, 1989.

Graves, F., Piloting, International MarineCompany, Camden, ME, 1981.

Human Technology, Inc. Desk Reference Guide: Specifications Unit, Chart and Map,Feature: Buildings. Report developed forNational Ocean Service, Charting and Geo-detic Services, Marine Chart Branch, Un-der Contract OPM-85-77, McLean, VA, Oc-tober 1985.

Human Technology, Inc. Desk Reference Guide: Specifications Unit, Chart and Map,Feature: Landmark. Report developed forNational Ocean Service, Charting and Geo-detic Services, Marine Chart Branch, Un-der Contract OPM-85-77, McLean, VA, Oc-tober 1985.

Kals, W. S., Practical Navigation, Doubleday& Company, Gordon City, NY, 1972.

Maloney, E. S., Chapman Piloting, 60th Edition,Hearst Marine Books, New York, NY, 1991.

Markell, J., Coastal Navigation for the Small Boat Sailor, Tab Books, Blue Ridge Sum-mit, PA, 1984.

Maxim, L. D., Advanced Coastal Navigation,Second Edition, United States Coast GuardAuxiliary, Coast Guard Auxiliary NationalBoard, Inc., Washington, DC, 1990.

McClench, D. and D. B. Millar, Mixter s Primer of Navigation, Sixth Edition, VanNostrand Reinhold, New York, NY, 1979.

Mellor, J., The Art of Pilotage, Sheridan

House, Dobbs Ferry, NY, 1990.Ministry of Defence, Directorate of Naval War-

fare. BR 45(1) Admiralty Manual of Navi- gation, Vol. 1, Her Majesty s Stationary Of-fice, London, UK, 1987.

Moody, A. B., Navigation Afloat, Van NostrandReinhold, New York, NY, 1980.

Naish, J., Seamarks , Their History and Devel-opment, Stanford Maritime, London, UK,1985.

Toghill, J., The Yachtsman s Navigation Manual, John DeGraff, Clinton Corners,NY, 1975.

U.S. Department of Commerce, Coast and Geo-detic Survey. Nautical Chart Manual, Vol- ume One: Policies and Procedures, SeventhEdition, Washington, DC, 1992.

U.S. Department of Commerce, National Oce-anic and Atmospheric Administration, Na-tional Ocean Service, and Department of Defense, Defense Mapping Agency Hydro-graphic/Topographic Center. Chart No. 1United States of America Nautical Chart Symbols Abbreviations and Terms, NinthEdition, Washington, DC, January 1990.

U.S. Department of Commerce, National Oce-anic and Atmospheric Administration, Na-tional Ocean Service. Coast Pilot Manual,5th Edition, Rockville, MD, 1994.

References

chapter 6 - landmarks

Documents