Using This Chart, You Can Conclude That in Australia's Economy

Whether yous're on your dream vacation, heading out for a short weekend, or dreaming over the wintertime, you'll be looking at charts. Large-scale charts, small scale charts, harbor charts - what are all those symbols and how do you lot employ them to find your mode in the world?

How to read a chart, plot a course and navigate?

In order to read a chart, you interpret longitude and latitude lines to determine your coordinates, which is your position.
Yous have to empathise and interpret different symbols like depth, calibration, and navigation marks.
Using these symbols, you find a safe course and plot information technology on the chart.
Find the direction of this form using a compass.
Maintain management using the compass readings.

If you're new to navigation this tin overwhelm, especially if yous're looking at a crowded electronic vector chart. This guide gives yous all the basics on how to read a chart and use it to plot a safe course from where you are to where you lot want to go.

In this commodity:

Navigation Nuts
Reading a Chart
Using a Chart - Plotting a Grade
Dead Reckoning - Pulling it all Together
Chief Chart Navigation with One Course

A nautical chart is similar a road map. Information technology shows you the expected lay of the land and gives references for finding your way to somewhere when don't know the path.

On country you've got roads, which limit where you tin bulldoze and how much trouble you can get into. If you're on Interstate 95 and you know the adjacent exit number, you're expert for figuring out where you lot are and how to get where you're going. No one will put a big rock in the middle of the highway that yous won't see until you lot hit it.

But 1 patch of h2o looks a lot like another. When you can come across land it's easier to figure where yous are. If you go fog or it'due south nighttime fourth dimension or you're far out to bounding main, you have goose egg to brand one patch of blue look any different from another. And even if you can see landmarks, they won't help you if you can't identify them. And the water may cover hazards similar rocks and shoals that y'all need to avoid. Eyeballing a lighthouse on land won't help you miss a shoal unless y'all know where the shoal is relative to your gunkhole.

A nautical chart shows things nether water and describes the landmarks and references you lot can see. Navigation is traveling a planned course from start to finish, using the chart to avoid obstacles and hazards. To empathise how to do this, y'all demand to empathise how we refer to places in the globe.

Geographic Coordinates

Centuries ago cartographers devised Geographic Coordinate system to locate any place on the globe. Lines of breadth range from 0° at the equator to ninety° at the poles and run parallel to the equator. Lines of longitude run from the due north to the south kickoff at 0° in Greenwich, England and run to 180° West and Eastward.

Nosotros express Geographic Coordinates every bit Degrees/Minutes/Seconds (east.g. 35°43"25'), or with a decimal instead of Seconds (eastward.yard. 35°43.424). There volition also be a letter at the end to designate the hemisphere. They are always in pairs, with breadth followed by longitude.

An instance of a complete coordinate is:

41° 39' 48" N
071° 26' 44" Westward

This will be a little over 41° North of the equator, and a little more than 071° West of Greenwich, England. If a longitude is only two digits (like the example), add together a zilch to the front of it to avoid confusion.

With a road map, I tin give you lot directions to that place by saying "From Post Road, take a left on King Street, and so another left on H2o street." But coming by h2o those directions are useless. Coordinates tell yous where something is, and so you tin find it with your charts.

Latitude Lines

Breadth lines will be North or South of the equator and are always parallel to each other. One minute of latitude is equal to ane Nautical Mile. So every degree of latitude is always sixty nautical miles from the next. If you take two latitude positions, you can judge how far apart they are in a n/due south management.

We'll notice this very convenient later on when nosotros're measuring distances and plotting courses.

Longitude Lines

We designate lines of longitude West or Eastward, relative to Greenwich England. For example 071° West is a line running roughly through Cape Cod on the U.S. East Declension. But 071° East is near Kabul, Afghanistan.

Because they run from the Northward Pole to the South Pole, lines of longitude are non always the aforementioned distance apart. Picture slicing an orange into sections - a two directly cuts from the "poles" on a curved orange result in a department of peel pointy on each end and fat in the eye. You tin not use longitude lines to measure altitude.

Using Degrees and Math

Degrees, minutes and seconds may seem counterintuitive when you piece of work with geographic coordinates. But it's all based on circular geometry, or "clock math." Just like an hour has sixty minutes and a minute has sixty seconds, a degree also has sixty minutes and a infinitesimal has threescore seconds. Electronic navigation tools often use decimals instead of 2d, only the concept is the same. Thirty seconds is half a minute (.500), forty-five seconds is .750, etc.

The merely error you have to watch for is calculation minutes and seconds. While 50 seconds plus 20 seconds equals seventy seconds, with "clock math" that's one minute and ten seconds, or 1"x' or ane.167".

The Poles

Outside of latitude and longitude lines, another other key component of navigation are the earth's poles. The True North pole as a geographic location is at breadth ninety° North at the very pinnacle of the planet on the axis of rotation of the earth where the longitude lines converge.

Merely the North pole we use for navigation with compasses, known as Magnetic North, is virtually 500 Km away from true north, and information technology drifts. When you're thousands of miles from the north pole, a compass will point to the magnetic pole, not the true due north pole. This may be a difference of xv degrees or more, and the amount of variation is different depending on where you are in the globe.

This information is well tabulated and predicted, and we can make adjustments then what you lot plot on paper matches what you see on your compass.

Reading a Chart

This article teaches reading paper charts, since paper charts are the basis of navigation for chart plotters and electronic charts. There are variations in how electronic charts may brandish information, specially vector charts, only in one case you lot know paper charts due east-charts are easy. We'll accept y'all through each function of the chart, explaining the fundamental information needed for basic navigation. Raster charts on your plotter look just like paper charts.

Latitude and Longitude Lines

At the top and bottom of the chart, you'll come across a scale of numbers for longitude. On the left and correct edges of the chart, you'll discover the latitude scale. At sure points on the chart, reference lines will run from n to s and east to west at fixed intervals. The corners will evidence you the degrees and minutes where the scale starts, though points on the scales may be marked with minutes or even seconds.

Near the edges of the nautical chart you will often detect a distance measuring scale to measure a mile, one-half a mile, a kilometer, and so on. As we learned already, we don't need that since we have lines of latitude running down the sides of the chart. Every infinitesimal of latitude is ane nautical mile, and so every nautical chart has a built in scale even if they don't add together a separate one.

Scales, Depths, and Notes

Somewhere on the nautical chart will exist a scrap of text describing in some particular what the chart is. Non all of this applies to plotting a basic road, but it'southward practiced to know things like how erstwhile the chart is.

Some critical pieces of information include:

Scale. The chart scale volition be a ratio, for example "1:25,000" or "ane:500,000". With this ratio, one unit as measured on the chart equals 25,000 of the same units in the actual earth. If you measure out a centimeter on the chart, it'southward 25,000 centimeters (or 250 meters) in the real world. I inch on the chart is 25,000 inches in the world, or 2,083 feet.
Depth soundings. Numbers will be sprinkled over all areas covered in water to show depths. Somewhere you will discover the notation "Depths in UNIT" where Unit of measurement is feet, meters, or fathoms. This is significant, brand sure you understand what the soundings mean or you may finish up ashore. Soundings are taken for low tides, in that location may be water on a spot at high tide.
Navigational Marks. Any notes on the marker organization used and information technology volition probably notation the buoyage system.
Tides and Currents. In areas with noteworthy currents and tidal swings, they may provide critical details.
Special Marks, Notes or Considerations. Denoted with blackness, red or purple text, special notes may pertain to anything from fish trap locations, anchorages, military machine restrictions zones, or anything else which may affect navigation through the covered areas.

Compass Rose

Every chart will have a compass rose. Some may have more than one. The compass rose should accept 2 circles, the outer denoting true n, and the inner showing magnetic north. At that place will also be variation data to calculate magnetic n from true, and information about the almanac expected change in the position of the magnetic north pole.

We will utilize the compass rose afterwards when we plot lines and courses and measure angles to determine numeric directions.

Depths and Contours

A good nautical chart will take many depth soundings - small numbers on the bottom of the water parts of the chart. But not also many, for readability. It will also have contour lines. These lines connect soundings of the same depth to prove you the relative shape of the bottom. Contour lines at ten-human foot intervals, for instance, will show you how the bottom shallows out or drops off. The closer the lines, the steeper the drop.

Many charts with country on them likewise evidence contour lines on land, showing hills and land structures. These are useful to determine where you are from the hills and valleys you expect to encounter.

Nautical chart colorations are the opposite of what a novice might expect - shallows are bluish, shading to lighter colors, and then white for the deepest places on the chart. The darker the blueish, the shallower the water.

Symbols, Marks and Lights

The well-nigh useful data on the nautical chart is the various marks and symbols. Every sailor should have a copy of U.Due south. Chart Number 1, the master list of all symbols, signs and objects you will come across on any U.S. government chart. Some details may vary on charts from other countries, merely about of the symbols and abbreviations are used on most all English language linguistic communication charts. It'due south a not bad reference to larn chart reading and is available equally a free download. You tin can also club a paper re-create for your nav station.

Download the US Nautical chart Number 1 here (pdf)

Aids to Navigation

Permanent regime or private marks will be on a chart with a detailed abbreviation describing their markings and how to identify them. Most aids are showing the way around a hazard, or the way to the all-time navigation channels. Pocket-size scale charts without much particular may not show all marks in an area. It's important to have detailed charts for harbor approaches and coast lines.

Aids to navigation include buoys, day marks, lights, beacons and a few less common marks. The symbols and lettering at each mark describe how yous tin can place them with colour, shape, lighting, and low-cal patterns.

In this example, you tin observe government two marks and a lighthouse.

G "i" Fl 1000 ii.5s means green mark,. numbered "1", with a flashing green light every 2.v seconds.
R "viii" Fl R 4s BELL is a ruby mark with the number "8" and a blood-red calorie-free that flashes every four seconds and a bell.
WARWICK Oc G 4s 66Ft 12M is Warwick Lite, with an occulting (mostly on) green lite with a 4s cycle. It is 66ft tall and visible for 12 nautical miles.

Most of the descriptions aren't difficult to puzzle out once you become the pattern downward, but now and then you accept to go take a await at Chart Number 1.

Hazards

A chart will besides show a variety of permanent hazards and dangers. The example to a higher place shows "Round Rk" every bit a rock awash at low tide. You tin also see "Bound Rk," "Old Pier Rk," and "Barden Rk" which exercise not evidence as being brimful simply are shallow plenty to be notable. They should testify anything which may pose a hazard. Changes since they printed the chart will not be on there. Most chart authorities produce a periodic Find to Mariners reporting whatsoever changes.

Landmarks

When country shows on a chart, it may show standpipes, towers, flagpoles and other permanent structures if they may exist helpful to navigation. You can sight these with a compass to become your position and use them to get your bearings. In the sample below, you can find a monument, a tower, and a chimney as visible landmarks from the water.

The Gloucester Fisherman's Memorial shown on the chart sample.

Putting it Together

You've got the latitudes and longitudes, depths, landmarks, and aids to navigation. You should be able to read the chart samples to run across how you might discover your exact location fifty-fifty without a GPS. It the sample chart above from Gloucester, MA, if y'all sail right to that G "ix" marker almost Babson Ledge, yous will know exactly where you are.

Practice if you can, sitting on your boat or on shore with a nautical chart and trying to pick out the landmarks and aids. As well endeavor information technology at night.

Using a Chart - Plotting a Course

Plotting a course from one place to another isn't complex, it'due south a affair of breaking the trip downwardly to segments, or legs, each with a known form and distance and safe to navigate. When you string a series of legs between waypoints effectually known hazards and land masses to reach your destination, you've plotted a course.

To do this practise, yous will need a paper nautical chart, a sharp pencil (non a pen), a parallel ruler, a set of dividers (sometimes called a "compass"), a starting point and a destination.

Learn to Plot Your Get-go Class

If you have never plotted a course before, nosotros recommend beginning reading our full guide on how to plot your first form. It will walk you through the entire process step-by-stride.

Laying in the Course

To plot a form, first look over the chart to see what is between your starting time and your destination. Y'all can even trace a rough course with your finger, noting hazards similar islands, shallows and rocks you lot desire to avoid.

Brand a mark at the beginning of your course, a buoy exterior your marina is a common starting point. From there, pick a point in the full general management of your destination with no hazards between the start and the get-go marking. Placing a mark near a government aid is convenient, but practise not put your marking ON the assist to navigation. For ane, y'all don't desire to hit the mark, so don't aim right at information technology. Second, everyone else is plotting to that mark too, and yous don't desire to pile up on the h2o if visibility gets poor.

Place your mark a niggling away from the regime mark on the condom navigation side. With the direct border of your parallel rule, depict a line from the starting mark to the first mark. Check the line to brand sure it doesn't run over whatsoever hazards or depths shallower than your draft. If yous find problems, erase the line and pick some other point and repeat.

Once you have a safety first leg, find another marker on the way to your destination from the beginning leg. Draw another line to the new mark and check for hazards. Repeat this procedure for each leg until your last leg ends at your destination. Your course shouldn't run through any shallows or hazards.

When the line is complete, it still needs to me measured and marked before you know what courses you take to steer to get where you're going.

Measuring Lines and Marking Your Course

We utilize parallel rules to create lines with a known compass heading, or to measure the compass heading of line you drew on your nautical chart. The compass rose is the gauge to measure and draw your lines. Nosotros will use the parallel rules and the compass rose to measure out the form to steer on each leg, and the dividers to measure the length.

The Course to Steer

Take the outer edge of your parallel dominion and place information technology along the beginning leg of your course. At present, pressing gently on the rule on the grade to hold it in place, motion the other ruler away from the line towards the compass rose. With luck, you'll reach it in the offset move. Most of the time you will have to "walk" the ruler across the nautical chart to the compass rose. The goal is to maintain the same bending on the rulers as the line yous're measuring, then accept it slow and shine and don't brand jerky motions. If you wiggle the rulers, start over.

Maintaining pressure on the first ruler, open the rulers toward the compass rose. When you lot tin't move it any more than, put pressure level on the leg you simply moved, move the other leg upward until it'southward touching the leg you're holding down. Then put pressure on the commencement leg again and open the rulers towards the rose. Repeat and walk the rulers until you achieve the middle signal of the compass rose with the outside edge.

Once the edge of the ruler is through the center of the rose, read the headings from the points on the outside of the rode. The outer circle volition evidence numbers for the true bearing, the inner circumvolve is for magnetic. Note the bearing on a scrap of paper.

In the eye of the compass rose, you lot volition see a measure for variance on the northward line of the compass. This is the difference between true and magnetic north on the current chart. Next to that volition exist a twelvemonth, with a number and direction. For example, it may read 18°35'Eastward 1994 2'E. This tells you your compass will read virtually 20 degrees from true, and it the variance changes two seconds every yr.

In most cases you can ignore that, unless your chart is very old or the annual alter is large. In 2020, the chart above has 26 x 2' = 52' of additional variance, or almost a degree change in heading. If (years ago ten annual change) is less than a minute you tin unremarkably ignore it for short legs. A degree change in course on a v or ten mile leg won't take you out of sight of your next marking. If information technology's significant, for East variance, you Add together the annual change to the magnetic course you lot recorded, otherwise subtract it.

When y'all accept the final magnetic course measurement, write it over the course leg with a "C" for course, the course, and "G" for magnetic. If your form is less than 100° put a leading nil on it to avoid ambivalence. For example, record a 92° magnetic course equally C 092M, or 273° nosotros write as C 273M.

Leg Altitude

There are several was to utilize dividers to mensurate your leg lengths, you'll figure out which works best for you and some techniques piece of work meliorate in some situations than others.

The easiest is, if your leg is short plenty, to spread the dividers between the ii points on the leg. Then move them to the latitude scale on the side of the chart and run across how many minutes of latitude they spread out. That is the leg length in miles. You may take to interpolate or make a crude judge at partial seconds on large-calibration charts.

Another method is to open the dividers a fixed, measured distance such as a mile. The option depends on the length of your leg. Put ane divider leg on the starting point of the leg, and the second leg on the course line. Now rotate the dividers around the 2nd leg and put the beginning leg on the mark. Walk the dividers down the course line while counting how many lengths y'all measure, then you have the miles in the leg.

Except for the last rotation, that will exist a fractional distance and the divider leg volition go past the mark. Push the dividers together until the leg is on the mark, and so measure on the breadth scale how long the fractional corporeality is.

Tape the leg distance under the course like with "D" plus the length of the leg and the units you measured. A vii.8 mile leg we write as D vii.8 NM. If you lot apply a unlike unit, notation it. But most sailors do navigation with nautical miles.

Yous will want to complete these steps for each leg of the trip. I too like to tape the course details and the Lat/Long of each waypoint on a separate sheet for easy reference during navigation.

Measuring and Plotting Points

To measure a point and get the geographic coordinates, find a government marking on your nautical chart, like the "R8" in the get-go example chart. You can meet 2 reference lines on that nautical chart, one for one for longitude and one for latitude. Find the reference lines on your nautical chart and follow them to the edge; and you will see the actual latitude or longitude.

With the divider, put one leg on the mark you picked to measure. Expand the dividers to put the other leg on the nearest breadth reference line, measuring shortest departure betwixt the two. If you drew a line from the marking to the line, it would be perpendicular to the line so visualize that as you measure out. If you rotate the dividers on the leg on the mark, the measurement will be right when it only touches the reference line in one identify.

At present motility your dividers to the latitude scale on the chart and put the reference line leg on the aforementioned line on the scale. Exist careful not to change the divider measurement; most will be tight enough to stay fixed. The other divider leg will sit on the actual breadth reading for the mark. The scale will vary with the detail of the chart, but you should be able to tape a full latitude reference from that betoken. If it only shows minutes or seconds, wait at the summit or bottom of the calibration for the degrees and minutes. Write it all down.

Echo the process with the longitude reference line. When you finish, yous will have the Lat/Long coordinates of the point yous measured. You don't have to practice this for a manually plotted class, but it's not a bad idea on principle. And you will demand to do it if you lot plan to enter the transmission course into a GPS or chart plotter.

Desire Another Form Plotting Example?

If you have never plotted a grade before, nosotros recommend kickoff reading our full guide on how to plot your first course. It will walk you lot through the unabridged procedure step-past-step.

Dead Reckoning - Pulling information technology all Together

At present that you lot can read a chart and plot a course, it's time to put this knowledge to work. Before chart plotters and the GPS, sailors navigated past dead reckoning. When old-time sailors used a sextant to get a position, they could merely use it to calculate their latitude. We cannot derive longitude with angelic navigation, and few sailors knew the math to make it work, anyway.

Expressionless reckoning is nada more than than estimating your position on a chart using your known speed and course. There is a specific notation to record this, and techniques to refine the accuracy when you tin can gear up a position. Y'all demand a speed log and a compass, with that you lot can estimate your position from a known starting indicate.

Annotation - many consider Dead Reckoning an obsolete skill in the age of the GPS. While there is some truth to this, it is an important skill to take in example you find yourself without a GPS or chart plotter. It's an first-class fill-in, and similar plotting a class on a paper nautical chart, it keeps you in tune with and alert well-nigh the waters yous're sailing through. Electronics neglect; when nosotros're offshore we record our position hourly on paper, just in case we need to start a DR plot due to musical instrument failure.

Making the Basic DR Plot

Somewhere in your plotted grade, you lot will pass known authorities marks or a reference that will give you an exact position fix. You lot can cheat and use a GPS if yous must, but don't refer to it after that in this exercise.

The general process is:

Every hour on the hour, annotation your speed through the water and magnetic course on a piece of paper.
On your paper chart, find the last dead reckoning bespeak (or known fix).
With your parallel rules, motility a line with to your magnetic course to the final known marker. This is the reverse of measuring the line. Put your parallel rules on the class through the center of the compass rose, then walk that line to your concluding DR mark.
Draw a line on your course the aforementioned length equally your boilerplate speed in knots from the last mark.
Put a dot on the mark, and a half circle around the top half to show it's a DR position.
Record the time nether the DR mark and note speed and distance on the line between the points.

There are a few more specifics, just that general process will give y'all an estimate of roughly where you are.

If you brand a form change, add a DR plot at the modify. If you don't change course on the hr, you will take to do a little math. Depict the grade line to the course alter in the same way, but the length of the line volition take to be a fraction of your gunkhole speed. This is the number of minutes since your last DR position divided by threescore minutes. Multiply this fraction by your speed to become how many miles long the DR line needs to exist at the course change.

Dead Reckoning Errors and Inaccuracy

At its all-time, DR plotting is a good estimation of your position. You want the best estimate you can, and at that place are factors which will push your DR plot abroad from your actual position. Do not treat dead reckoning positions every bit an bodily gear up, DR is a tool to get you lot to a place where yous can get a better fix from an aid to navigation or a landmark for accurate navigation.

Some factors which tin reduce the accuracy include:

Electric current. Tidal currents may be invisible to you, only a i knot current sweeping y'all sideways or pushing you backwards will make your DR judge off by a mile after an hour. If you know the currents for an area, you can correct for this by calculation a vector for the current to your DR grade and speed line and plotting that every bit the DR position. Note the correction on the plot.
Leeway and migrate. Similar to current, but leeway is sideslip in your boat. All sailboats sideslip a piffling, it's the nature of the forces that make a gunkhole sail confronting the wind. The heading on your compass will not fully lucifer your frontwards progress equally your boat slips a little away from the wind.
Variable Speeds. The best you can exercise for your estimates is the average speed of your gunkhole over an hr. If the wind is variable this may be difficult to figure. Do your best, just if yous accept a big lull for half an 60 minutes, remember earlier using the full boat speed if the wind picks up before y'all record your DR.
Compass Departure. Metal objects on a boat can affect a compass heading. The effects vary with the management the boat is heading. Imagine a compass with a magnet a human foot abroad. The compass volition indicate mostly north, merely a little towards the magnet. At present move the magnet in a circle around the compass; the readings will change slightly only still stay mostly due north. On your gunkhole, the magnetic interferences will alter equally the gunkhole sails in different directions. A profession can "swing" a compas and give you a deviation card for your boat. You use this to build the known deviation into your courses to eliminate this inaccuracy. Well-nigh electronic compasses calculate difference during calibation, consult your manuals and calibrate if you aren't sure if your compass is calibrated.

Correcting the DR Position

The longer yous sail on dead reckoning, the more inaccurate your estimated position volition be. If you're sailing near shore, yous can correct this by fixing your position, or getting a known position to correct your DR plot and get-go plotting from the new accurate position.

A simple manner to fix your position is to sail near a mark on your chart. For littoral navigation, you lot've probable plotted your course relative to government marks because they are convenient. This is to give you a periodic fix equally yous pass waypoints on your grade. When you come shut to the mark, tape your position with the fourth dimension, and circle the position dot to prove information technology'due south a "fix" and a proficient known position.

Another fix technique needs at least two visible landmarks or aids to navigation you tin identify, and a manus bearing compass. To commencement, take a bearing on the first point and record information technology. As quickly every bit you can, tape a bearing to the second marking. If y'all have fourth dimension, repeat the bearings. You want to hurry because the boat is moving and the more time betwixt bearings, the greater the error.

Find each marking y'all took bearings for on your paper chart, and then take your parallel rules and describe a line from each mark on the sighted heading. The marks should intersect, and the intersection is your rough position. If yous took multiple bearings, yous can describe more lines to get a sense of the dubiousness introduced by your boat speed. Circle the intersection and notation the time, then utilise this as the basis for your next DR plot. This is less accurate than finding a mark, but volition let you correct your DR plot for accuracy.
In that location are several other techniques such as the running set and more complex uses of a compass, landmarks, and math that are outside the scope of this guide.

Dead Reckoning and the GPS

GPS navigation makes all this DR plotting seem like a lot of unnecessary work. That doesn't mean it's not worth learning and doing. On coastal cruises information technology keeps us tuned in to the sailing, though we likewise record GPS fixes on shorter legs and at course changes.

Information technology is of import that sailors empathise not but how to push button the right buttons on the nautical chart plotter, but how navigation works. Not that we're expecting a calamity that volition take down your electronics or brand the GPS organisation unreliable, only it can and has happened.

Electronic navigation makes all of this very simple, but it'southward good to know how to find your way without it.

When you're set up to master nautical chart navigation, I recommend you lot check out the Coastal Navigation form at our partner NauticEd. It is quite excellent. They cover chart navigation in-depth and will guide you through multiple quality exercises to make sure yous really practise your new skills. Information technology is really affordable too.

You'll leave Littoral Navigation Clinic with an understanding of:

The Charts and how to use navigation tools
True north and magnetic north - and variation and departure
Determining your position using diverse techniques such as expressionless reckoning, running fixes and triangulation
What to exercise with your GPS position to get y'all to your destination
Set and drift from wind, tides and current
How to simply determine your heading based on Set and Drift

Cheque out NauticEd'southward Navigation Clinic now.

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Source: https://improvesailing.com/guides/nautical-chart-navigation