Ocean depth chart

Ocean depth chart DEFAULT

OCEAN CHARTS

This page contains links to online bathymetric and ocean charts and several online indexes for the UC San Diego Library's print chart collection.

  • The Chart indexes that are available online are noted on this page. Charts are not cataloged and do not appear in the library catalog.
  • Access & questions: access to the print collection of charts is by appointment only, contact Amy Butros to request an appointment, email:  [email protected]

NOS/NOAA Charts

Covers US and territorial waters. A complete collection, that is not updated with Notice to Mariners; therefore this is a reference collection and unsuited for navigation.

NGA Charts

The UC San Diego Library owns a complete collection, until NGA (the National Geospatial-Intelligence Agency) discontinued paper chart distribution in June 2010. Our charts were not updated from Notice to Mariners; therefore this is a reference collection and unsuited for navigation. Paper indexes to the collection are still available, please contact [email protected] for an appointment to view these charts

General Bathymetric Chart of the Oceans - GEBCO

British Admiralty Charts

Worldwide waters. Not a current or complete collection. British charts usually offer better detailed coverage for waters around Commonwealth countries, e.g. Fiji, British Virgin Islands, etc. Paper index to the British charts is available, please contact [email protected] an appointment to view these charts.
  • INDEX (select 'commercial')

Mexican Charts

A fairly complete collection, including older charts in an earlier numbering scheme. Paper index to the Mexican charts is available, but the index linked below is easier to use than the print index. 

  • INDEX (downloaded from www.semar.gob.mx)  
  • INDEX 1 & INDEX 2 to OLDER charts with the earlier chart numbering scheme
  • Sea of Cortez Charts & Cruising Guides: Charlie's Charts have unique charting details and information for the Gulf of California, that you won't find in the government-produced charts. They recently added Gerry Cunningham's naviagation charts for Baja and the Sea of Cortez, and have great cruising guides for purchase also.

Australian Charts

Coverage of Australian waters, Torres Strait, Papua New Guinea, & Antarctic water. A strong collection

Canadian Charts

Canadian Hydrographic Service's website for digital and print publications.  They do not sell to the public, but provide a Dealer Locator to find the chart and dealer in areas closest to you.

French Charts

Not a complete collection. French charts usually offer better detailed coverage for waters around French territories than U.S. charts, i.e. French Polynesia.

Iranian Charts

Coverage of Iranian waters & Persian Gulf. A fairly complete collection

Indonesian Charts

Coverage of Indonesian waters. We collect in areas where the Indonesian charts offer better coverage than the U.S. and British charts.

Japanese Charts

Coverage of Japan & East Asian waters, Pacific & Indian Oceans, and Japanese area of Antarctica. Not a complete collection.

SIO-Produced Charts

Historically SIO produced many paper charts and maps relating to research interests. These are filed within the collection's geographic filing arrangement. Some of the better known SIO produced maps include:

  • Bathymetry of the North Pacific. J Mammerickx, SM Smith, IL Taylor, TE Chase. UC Institute of Marine Resources Technical Report 3,6-15. Scripps Institution of Oceanography, 1970.  Ten sheets.
  • Surface Sediments and Topography of the North Pacific Ocean. J Frazier, DL Hawkins, A Arrhenius, J Mammerickx, TE Chase, HW Menard. UC Institute of Marine Resources Technical Report 27-36. Scripps Institution of Oceanography, 1972.  Ten sheets.
  • Bathymetry of the South Pacific. J Mammerickx, SM Smith, IL Taylor, TE Chase. UC Institute of Marine Resources Technical Report 45A-54A. Scripps Institution of Oceanography, 1971-1974.  Eleven sheets.
  • Topography of the South Pacific. J Mammerickx, SM Smith, IL Taylor, TE Chase. UC Institute of Marine Resources Technical Report 45A-56. Scripps Institution of Oceanography, 1975.  1:6,500,000

Other Chart Resources

CHART VENDORS
Sours: https://library.ucsd.edu/research-and-collections/collections/notable-collections/sio/charts.html

Chart Reading 101

Nautical Chart

Except aboard the shallowest of craft, venturing beyond narrow or familiar waters means you need a chart. If you are not acquainted with charts, they can look intimidating, but their mystery cannot survive 10 minutes of study. To learn about charts, buy one for the waters you want to navigate. The chart seller can tell you which one you need.

Don't Ask For A Map

By convention a map showing coastlines, water depths, and other information of use to navigators is always called a chart. Calling it a map is like calling the bow the pointy end.

Scale

When you are buying a chart of specific waters, you typically have a choice between a chart that covers a smaller area in greater detail or one that covers a larger area in less detail. The scale of a harbor chart, for example, might be 1:20,000, meaning that 1" on the chart represents 20,000" of the earth's surface, or about 0.27 nautical miles. That makes a mile on the water a little less than 4" on the chart. Harbor charts will be very detailed.

Small-craft charts come folded like a road map for more convenient use on smaller boats. The scale of small-craft charts is often 1:40,000, so a nautical mile is about 1.8" on this scale chart.

The scale designation on charts is a fraction (1/40,000), so the larger the number after the colon (or slash), the larger the area the chart shows, but the smaller the scale. So-called coastal charts, for example, typically use a 1:80,000 scale. That makes a nautical mile less than an inch, and lets a single chart cover a 30 mile by 40 mile area, but with less detail than a large-scale chart. General charts with scales as small as 1:1,200,000 cover huge areas — 600 miles or more — but with little detail. Such small scale charts are useful primarily for route planning.

Depths

Numbers printed on the water areas of the chart indicate the depth of the water at that spot. However, a 2 on the chart might mean two feet, two fathoms, or two meters. It is essential to know which unit of measurement is used. This is always shown on the face of the chart in large print — SOUNDINGS IN FATHOMS AND FEET, for example. A fathom, by the way, is six feet, so on a chart with soundings in fathoms, a number such as 03 means zero fathoms and three feet. The water at this spot is three feet deep at MLLW. A sounding of 55 would be 35 feet (five fathoms and five feet). In 1992 U.S. charts began switching from feet and fathoms to soundings in meters. If your brain hasn't made that switch, you can divide soundings in meters by 0.3 to get the approximate depth in feet.

The soundings printed on the chart normally represent the depth at mean lower low water (MLLW), so the actual depth is usually more than the charted depth. However, when the tide table shows a negative low-tide entry, actual depths will be less than the chart indicates. When the depth of the water is a concern, you will need to know the height of the tide.

Contour Lines

In addition to numerical depths, charts show depth contour lines. The 10-fathom contour line on a small scale chart, for example, indicates that all the waters inside this line are no more than 60 feet deep. On larger scale charts, contour lines are often shown for three fathoms, two fathoms, one fathom, and sometimes even three feet. Typically, the area inside either the three fathom or one fathom contour line is tinted blue to provide quick identification of shoal water.

Symbols And Abbreviations

In addition to water depths — including the shoreline — charts show the location of rocks, reefs, wrecks and other submerged obstructions, anchorages, channels, lighthouses, buoys, and even tide rips. The symbols and abbreviations for these features are often obvious but sometimes less so. All are illustrated and explained in NOS Chart No. 1: Symbols, Abbreviations and Terms, which isn't a chart at all, but a booklet. It used to cost about two bucks from the government, but today a hard copy, available only from a commercial vendor, will set you back about $10. Or you can download an electronic copy to your computer for free from NOAA. Either way, reading through Chart No. 1 will reveal new and useful details that charts often include.

Aids To Navigation

Red daybeacons are shown on your chart as small triangles. The green ones — any color but red, actually — appear as small squares. Lighted markers have a magenta flare symbol — like an exclamation mark. A variety of symbols are used for buoys. Lighthouses are generally shown as a dot inside a magenta disk, sometimes with the flare symbol. All are illustrated in Chart No. 1.

Prominent land features, such as towers, buildings, and even hills may also be shown on the chart if they might be valuable to the navigator. Many older charts also include Loran-C time distance lines.

Compass Rose

At various locations on the chart you will find groups of three concentric circles of ruler-like hatch marks. This is called a compass rose, and it indicates true north — the outer circle — and magnetic north — the inner circles. Since you are almost certain to be steering by magnetic compass, you will nearly always use the inner circles, normally the one marked in degrees from 0 to 360.

Plotting Course And Distance

The list of essential plotting tools is short. You need a sharp pencil, a pair of dividers, and a parallel rule.

To see how easy plotting is, draw a straight line between two points on your chart. Let's call them A and B. The parallel rule is a good straightedge. We want to know the direction and distance from A to B.

Begin by aligning one leg of the parallel rule along the A-to-B line. Holding that leg tightly against the chart to keep it from moving, move the other leg out until its outside edge is at the center of the small cross in the center of the nearest compass rose. If the ruler doesn't extend far enough in one motion, then press the moving leg of the rule tightly to the chart and bring the other leg to it. As long as you move only one leg at a time, holding the other down, you can "walk" your course across the chart. When the rule finally reaches the center of a compass rose, it will still be parallel to the original A-to-B course. Now where the edge of the rule crosses the magnetic compass rose is the magnetic course from A to B. This is the course you would steer, assuming no compass deviation and no current. Of course, where the rule crosses the opposite side of the compass rose is the course from B to A.

Measuring distance is even easier. Put one point of your dividers on point A and the other on point B. Now, without altering the spread of the dividers, move the tool straight to one side or the other of the chart and place the points on the latitude scale. Count the number of minutes between the points. One minute of latitude is equivalent to one nautical mile. You can also place your dividers on the distance graph printed on the chart, but the latitude scale is usually more convenient.

If the distance between A and B is wider than your dividers will spread, then set the dividers to some convenient distance — say five miles — using the latitude scale. Starting at point A, walk the dividers along the course line. In other words, rotate the dividers on the forward point to move the back point from five miles behind to five miles forward. Continue this until the forward point is beyond B, then squeeze the dividers to place the point on B. Read this last divider spread from the latitude scale and add it to the miles already accumulated five at a time. If you stepped off five miles three times, with the remaining distance measured at 3.5 miles, the distance from A to B is 18.5 miles.

If you are thinking you do not need to know any of this because you have a GPS chartplotter aboard, you are wrong. Lots of things can disable electronic navigation, many of which will be out of your control. The more you understand about navigation, the more comfortable you are likely to feel on the water and the safer you and your guests and crew will be. Comprehensive navigation texts run to 1,500 pages or more, but having a paper chart aboard and knowing just this much about how to use it can get you there and back without electronic guidance. It is a valuable hold card.

For a more complete understanding of charts and navigation, I recommend Boat Navigation for the Rest of Us by Captain Bill Brogdon.

Sours: https://www.boatus.com/expert-advice/expert-advice-archive/2012/july/chart-reading-101
  1. Minnkota trolling motor
  2. Scott surname meaning
  3. Wandering synonyms
  4. Monterey salmon season

Ocean Depth Map

Bathymetric Map

This is a Bathymetric Map. It shows the depth of the Ocean Floor around the world.

Bathymetry is the measurement of the depth of the water in oceans, rivers, or lakes.

Bathymetric maps or charts look a lot like topographic maps. They use lines to show the shape and elevation of land features. On Bathymetric Maps, the lines connect points of equal depth.

The depth in feet looks arbitrary, but it corresponds to depth in meters. The gaps or distances between depths is 1000m. The only gap that has a different value is the first one which is 200m. This is the the continental Shelf or Epipelagic Zone.

The colors on this map are not continuous. They are just different shades of blue to highlight the different features of the sea bottom.

Affiliate Disclosure

Databayou.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com. Databayou.com also participates in affiliate programs with Clickbank, CJ, and other sites.

Vertical Divisions of the Ocean

As the depth in the ocean increases, the water column has different characteristics and light penetration. These are the Ocean Zones.

The table below shows the depth in meters and feet. It also shows Ocean Zones and Seafloor features. Each one of these zones is explained below.

ColorDepth in FeetDepth in MetersOcean ZonesSeafloor Features
00Epipelagic ZoneContinental Shelf
656200
3280 1000Mesopelagic ZoneContinental Slope
65612000Bathypelagic Zone
98423000
131234000Continental Rise
164045000Abyssopelagic ZoneAbyssal Plain
196856000
229657000Hadalpelagic ZoneOceanic Trench
262468000
29527 to 360899000 to 1100

Seafloor Features

Continental Shelf

The Continental Shelf is the part of the continent that is submerged under water. This area is relatively shallow. It starts at the coastline of a continent and ends at the shelf break.

Continental shelves are part of the continent even though they are underwater.

The continental shelf was exposed by drops in sea level due to glacial periods. Marinebio.

The average depth of the Continental sea Shelf is 150m. The width varies across continents but it can average 80km.

If you look at this map, the light blue colors next to the continents show the sea shelf.

South America next to the Pacific has a narrow shelf, while the Bering Sea has a wide Continental Shelf.

Sunlight penetrates the shallow waters of continental shelves which makes this areas rich in sea life from microscopic algae to big mammals like sealions. Another reason this area is rich in organisms is because it receives nutrients from river runoff.

Continental Slope

Continental Slope is the slope between shelf break and the deep ocean floor. About 8.5 percent of the ocean floor is covered by the continental slope.

The continental slope is part of the Continental crust.

The average angle of the continental slope is 4°. The Continental Slope on the Pacific Ocean tends to have more than 5° because it is an active Margin. The Atlantic Coast is more passive and usually has less than 3°.

Continental slopes can be cut by submarine canyons, an example is the Congo canyon which follows the mouth of the Congo River.

Close to the continents the sea shelf slope increases dramatically. This is why it is not prominent in the map. It is quite difficult to find this depth on it as it is very narrow.

Continental Rise

The continental rise is a wedge of sediment that has accumulated at the base of the slope due to the change in gradient from the steeper slope to the virtually flat abyssal plain. This build-up of sediment is similar to the debris that accumulates at the base of a cliff.

It is mainly silts, mud and sand that has been deposited by turbidity flows.

Continental rise is almost absent where there are sea trenches due to active subduction zones.

Abyssal Plain

Abyssal Plains are underwater plains on the deep ocean floor. They are usually 4500 and 6000 meters deep. They are some of the flattest places on Earth.

Trenches

Trenches are long and narrow canyon like features, parallel to continental margins. They are the deepest parts of the ocean floor.

Trenches are associated with intense volcanic activity, usually in the form of volcanic arcs, or volcanic island chains, that develop above the descending side of the subducting plate associated with a trench. Most tranches are in the Pacific Ocean. Source: Geologycafe.com

Deep Sea Submersible

Mid Ocean Ridges

The Ocean Ridges are another visible part of this map. They are not in the table but they are visible in the areas where the continental plates are separating. Specially visible in the Atlantic Ocean, between South America and Africa.

Mid Ocean Ridges are underwater mountain ranges formed by plate tectonics.

These ridges are uplifted because of the convection currents that rise in the mantle beneath the ocean crust. Therefore forming underwater mountain ranges, throughout the globe. Source: Science Daily

The latest measurements of the ocean seafloor were made with satellite information. These estimates keep updating as we get more information from the seafloor.

Ships like NOAA's Okeanos Explorer, are required to fine tune satellite data. So far only 10% of the bottom of the ocean has been mapped, so these estimates will keep changing. NOAA.gov

If you are interested in learning more about the ocean floor, I suggest the following books found on Amazon.

Ocean Zones

Epipelagic Zone

Epipelagic or upper ocean, is the part of the open ocean above 200m.

This is the part of the ocean where there is enough sunlight for algae to make photosynthesis (the process by which organisms use sunlight to convert carbon dioxide into food)

Photosynthetic organisms are primary producers. They are the base of the food chain that sustain the rest of organisms.

Therefore this zone is home to all sorts of sea life, like dolphins, tuna, and starfish. This zone also contains most of the fisheries.

Mesopelagic Zone

The mesopelagic zone (or middle open ocean) stretches from the bottom of the epipelagic down to the point where sunlight cannot reach. This zone is below 200m and above 1000m.

Sunlight decreases rapidly with depth. Photosynthesis is not possible in this zone.

This zone is a major player at removing carbon dioxide from the atmosphere by storing it for centuries.

The organisms in this zone are not well known. This area is also subject to one of the largest migrations. Fish and zooplankton come here to retreat at dawn after feeding at night in the photic zone.

Bathypelagic Zone

The Bathypelagic zone is below 1000m and above 4000m, this zone has no sunlight.

The water above creates incredible pressures.

Only Bacteria and soft bodied organisms can thrive in this conditions.

Some organisms have bioluminescence and they use it to attract prey or to find a mate. Some species have lost their ability to see anything at all.

The main food source is the organic material what drops from the Mesopelagic zone.

Other organisms live from the bacteria that thrive in the methane and sulfides seeping from the ocean floor.

Abyssal Zone

It refers mainly to the waters above the continental rise, which are between 3000m to 6000m. It is hard to define exactly where the top limit of these waters is, but the best way to describe it is the area where the water hits 4 degrees Celsius (39.2F).

The waters are calm and unaffected by sunlight or storms on the surface.

No oxygen is produced as there is no photosynthesis. The oxygen present comes from horizontal flow derived from when the water left the polar regions.

Salinity is also constant and higher as there is no direct introduction of freshwater from rain or rivers above. Nutrient concentration is higher as there are no plants to absorb them and dead organisms on settle to the ocean floor.

The average depth of the ocean is 4000m (2.5miles) making this zone the largest living environment on Earth! "It covers over 300,000,000 square km (115,000,000 miles)–about 83% of the ocean’s total area and 60% of Earth’s surface." Untamed Science




Sealab-1, billed as the world’s first working underwater habitat

Hadalpelagic Zones

These zones are the deepest in the ocean. They are mainly deep ocean trenches and troughs.

This is the deepest marine habitat that goes from 6000m to 11000m or 3.7 to 6.8 miles deep.

People used to think this areas had no life. So far they have discovered about 400 species, and the discoveries keep increasing with more research and better technology.

There are 21 trenches around the world. These are the darkest blue in the map. Some of them include the Marian Trench, Japan Peru-Chile, Tonga, Puerto Rico and Java. Hades

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Resources Ocean Depth

The Bathymetry shapefiles to create this map where downloaded from Natural Earth.

If you are interested in the history of diving and would like to learn more about the progress of underwater technology, from the earliest days of diving to the most modern underwater habitats, and if you happen to be close to Panama City, I suggest you go to the Man in the Sea Museum.

Seafloor Map Inspiration

I made this map as a first attempt at visualizing seafloor for a fisheries chart. The map was never finished but I really liked how the bathymetry of different depths looked. I wanted to make it interactive and detailed so the viewer could see how deep is each area under the sea.

To receive updates on this and more nature maps join my email list!!!!!!!

Bathymetry map of the world showing seafloor depth
Sours: https://databayou.com/ocean/depth.html
How Close Are We to Completely Mapping the Ocean?

Nautical chart

Topographic map of a maritime area and adjacent coastal regions

A nautical chart is a graphic representation of a sea area and adjacent coastal regions. Depending on the scale of the chart, it may show depths of water and heights of land (topographic map), natural features of the seabed, details of the coastline, navigational hazards, locations of natural and human-made aids to navigation, information on tides and currents, local details of the Earth's magnetic field, and human-made structures such as harbours, buildings, and bridges. Nautical charts are essential tools for marine navigation; many countries require vessels, especially commercial ships, to carry them. Nautical charting may take the form of charts printed on paper or computerized electronic navigational charts. Recent technologies have made available paper charts which are printed "on demand" with cartographic data that has been downloaded to the commercial printing company as recently as the night before printing. With each daily download, critical data such as Local Notices to Mariners are added to the on-demand chart files so that these charts are up to date at the time of printing.

Sources and publication of nautical charts[edit]

Nautical charts are based on hydrographic surveys. As surveying is laborious and time-consuming, hydrographic data for many areas of sea may be dated and not always reliable. Depths are measured in a variety of ways. Historically the sounding line was used. In modern times, echo sounding is used for measuring the seabed in the open sea. When measuring the safe depth of water over an entire obstruction, such as a shipwreck, the minimum depth is checked by sweeping the area with a length of horizontal wire. This ensures that difficult to find projections, such as masts, do not present a danger to vessels navigating over the obstruction.

Nautical charts are issued by power of the national hydrographic offices in many countries. These charts are considered "official" in contrast to those made by commercial publishers. Many hydrographic offices provide regular, sometimes weekly, manual updates of their charts through their sales agents. Individual hydrographic offices produce national chart series and international chart series. Coordinated by the International Hydrographic Organization, the international chart series is a worldwide system of charts ("INT" chart series), which is being developed with the goal of unifying as many chart systems as possible.

There are also commercially published charts, some of which may carry additional information of particular interest, e.g. for yacht skippers.

Chart correction[edit]

The nature of a waterway depicted by a chart may change, and artificial aids to navigation may be altered at short notice. Therefore, old or uncorrected charts should never be used for navigation. Every producer of nautical charts also provides a system to inform mariners of changes that affect the chart. In the United States, chart corrections and notifications of new editions are provided by various governmental agencies by way of Notice to Mariners, Local Notice to Mariners, Summary of Corrections, and Broadcast Notice to Mariners. In the U.S., NOAA also has a printing partner who prints the "POD" (print on demand) NOAA charts, and they contain the very latest corrections and notifications at the time of printing. To give notice to mariners, radio broadcasts provide advance notice of urgent corrections.

A good way to keep track of corrections is with a Chart and Publication Correction Record Card system. Using this system, the navigator does not immediately update every chart in the portfolio when a new Notice to Mariners arrives, instead creating a card for every chart and noting the correction on this card. When the time comes to use the chart, he pulls the chart and chart's card, and makes the indicated corrections on the chart. This system ensures that every chart is properly corrected prior to use. A prudent mariner should obtain a new chart if he has not kept track of corrections and his chart is more than several months old.

Various Digital Notices to Mariners systems are available on the market such as Digitrace, Voyager, or ChartCo, to correct British Admiralty charts as well as NOAA charts. These systems provide only vessel relevant corrections via e-mail or web downloads, reducing the time needed to sort out corrections for each chart. Tracings to assist corrections are provided at the same time.

The Canadian Coast Guard produces the Notice to Mariners publication which informs mariners of important navigational safety matters affecting Canadian Waters. This electronic publication is published on a monthly basis and can be downloaded from the Notices to Mariners (NOTMAR) Web site. The information in the Notice to Mariners is formatted to simplify the correction of paper charts and navigational publications.

Various and diverse methods exist for the correction of electronic navigational charts.

Limitations[edit]

In 1973 the cargo ship MV Muirfield (a merchant vessel named after Muirfield, Scotland) struck an unknown object in the Indian Ocean in waters charted at a depth of greater than 5,000 metres (16,404 ft), resulting in extensive damage to her keel.[1] In 1983, HMAS Moresby, a Royal Australian Navysurvey ship, surveyed the area where Muirfield was damaged, and charted in detail a previously unsuspected hazard to navigation, the Muirfield Seamount. The dramatic accidental discovery of the Muirfield Seamount is often cited as an example of limitations in the vertical geodetic datum accuracy of some offshore areas as represented on nautical charts, especially on small-scale charts.

A similar incident involving a passenger ship occurred in 1992 when the Cunard liner Queen Elizabeth 2 struck a submerged rock off Block Island in the Atlantic Ocean.[2] In November 1999, the semi-submersible, heavy-lift shipMighty Servant 2 capsized and sank after hitting an uncharted single underwater isolated pinnacle of granite off Indonesia. Five crew members died and Mighty Servant 2 was declared a total loss.[3] More recently, in 2005 the submarine USS San Francisco ran into an uncharted sea mount (sea mountain) about 560 kilometres (350 statute miles) south of Guam at a speed of 35 knots (40.3 mph; 64.8 km/h), sustaining serious damage and killing one seaman. In September 2006 the jack-up bargeOctopus ran aground on an uncharted sea mount within the Orkney Islands (United Kingdom) while being towed by the tug Harold. £1M worth of damage was caused to the barge and delayed work on the installation of a tidal energy generator prototype. As stated in the Mariners Handbook and subsequent accident report: "No chart is infallible. Every chart is liable to be incomplete".[4]

Map projection, positions, and bearings[edit]

A pre-Mercator nautical chart of 1571, from Portuguese cartographer Fernão Vaz Dourado(c. 1520 – c.1580). It belongs to the so-called plane chartmodel, where observed latitudes and magnetic directions are plotted directly into the plane, with a constant scale, as if the Earth's surface were a flat plane (Portuguese National Archives of Torre do Tombo, Lisbon)

Historically the first projection, invented by Marinus of Tyre ca. AD 100 according to Ptolemy, was what is now called equirectangular projection (historically called plane chart, plate carrée, Portuguese: carta plana quadrada). While it is very convenient for small seas like the Aegean, it's unsuitable for seas larger than Mediterranean or an open ocean, even though early explorers had to use it for want of a better.

The Mercator projection is now used on the vast majority of nautical charts. Since the Mercator projection is conformal, that is, bearings in the chart are identical to the corresponding angles in nature, courses plotted on the chart may be used directly as the course-to-steer at the helm.

The gnomonic projection is used for charts intended for plotting of great circle routes. NOAA uses the polyconic projection for some of its charts of the Great Lakes, at both large and small scales.[5]

Positions of places shown on the chart can be measured from the longitude and latitude scales on the borders of the chart, relative to a geodetic datum such as WGS 84.

A bearing is the angle between the line joining the two points of interest and the line from one of the points to the north, such as a ship's course or a compass reading to a landmark. On nautical charts, the top of the chart is always true north, rather than magnetic north, towards which a compass points. Most charts include a compass rose depicting the variation between magnetic and true north.

However, the use of the Mercator projection has drawbacks. This projection shows the lines of longitude as parallel. On the real globe, the lines of longitude converge as they approach the north or south pole. This means that east-west distances are exaggerated at high latitudes. To keep the projection conformal, the projection increases the displayed distance between lines of latitude (north-south distances) in proportion; thus a square is shown as a square everywhere on the chart, but a square on the Arctic Circle appears much bigger than a square of the same size at the equator. In practical use, this is less of a problem than it sounds. One minute of latitude is, for practical purposes, a nautical mile. Distances in nautical miles can therefore be measured on the latitude gradations printed on the side of the chart.[6]

Electronic and paper charts[edit]

Conventional nautical charts are printed on large sheets of paper at a variety of scales. Mariners will generally carry many charts to provide sufficient detail for the areas they might need to visit. Electronic navigational charts, which use computer software and electronic databases to provide navigation information, can augment or in some cases replace paper charts, though many mariners carry paper charts as a backup in case the electronic charting system fails.

Labeling nautical charts[edit]

Automatically labeled nautical chart

Nautical charts must be labeled with navigational and depth information. There are a few commercial software packages that do automatic label placement for any kind of map or chart. Modern systems render electronic charts consistent with the IHO S-52 specification.

Details on a nautical chart[edit]

Many countries' hydrographic agencies publish a "Chart 1", which explains all of the symbols, terms and abbreviations used on charts that they produce for both domestic and international use. Each country starts with the base symbology specified in IHO standard INT 1, and is then permitted to add its own supplemental symbologies to its domestic charts, which are also explained in its version of Chart 1. Ships are typically required to carry copies of Chart 1 with their paper charts.

Pilotage information[edit]

Detail of a United States NOAA chart, showing a harbour area

The chart uses symbols to provide pilotage information about the nature and position of features useful to navigators, such as sea bed information, sea mark, and landmarks. Some symbols describe the sea bed with information such as its depth, materials as well as possible hazards such as shipwrecks. Other symbols show the position and characteristics of buoys, lights, lighthouses, coastal and land features and structures that are useful for position fixing. The abbreviation "ED" is commonly used to label geographic locations whose existence is doubtful.

Colours distinguish between man-made features, dry land, sea bed that dries with the tide, and seabed that is permanently underwater and indicate water depth.

Depths and heights[edit]

Depths which have been measured are indicated by the numbers shown on the chart. Depths on charts published in most parts of the world use metres. Older charts, as well as those published by the United States government, may use feet or fathoms. Depth contour lines show the shape of underwater relief. Coloured areas of the sea emphasise shallow water and dangerous underwater obstructions. Depths are measured from the chart datum, which is related to the local sea level. The chart datum varies according to the standard used by each national Hydrographic Office. In general, the move is towards using lowest astronomical tide (LAT), the lowest tide predicted in the full tidal cycle, but in non-tidal areas and some tidal areas Mean Sea Level (MSL) is used.

Heights, e.g. a lighthouse, are generally given relative to mean high water spring (MHWS). Vertical clearances, e.g. below a bridge or cable, are given relative to highest astronomical tide (HAT). The chart will indicate what datum is in use.

The use of HAT for heights and LAT for depths, means that the mariner can quickly look at the chart to ensure that they have sufficient clearance to pass any obstruction, though they may have to calculate height of tide to ensure their safety.

Tidal information[edit]

Tidal races and strong currents have special chart symbols. Tidal flow information may be shown on charts using tidal diamonds, indicating the speed and bearing of the tidal flow during each hour of the tidal cycle.

See also[edit]

Further reading[edit]

  • Calder, Nigel (2008). How to Read a Nautical Chart. McGraw-Hill Professional. ISBN .

References[edit]

  1. ^Calder, Nigel. How to Read a Navigational Chart: A Complete Guide to the Symbols, Abbreviations, and Data Displayed on Nautical Charts. International Marine/Ragged Mountain Press, 2002.
  2. ^British Admiralty. The Mariner's Handbook. 1999 edition, page 23.
  3. ^"Maritime Casualties 1999 And Before". The Cargo Letter. 2007. Retrieved August 25, 2018.
  4. ^Marine Investigation Accident Branch (2007) Report Number 18/2007.
  5. ^See, for example, NOAA 14860 - Lake Huron 1:500,000 and NOAA 14853 Detroit River 1:15,000.
  6. ^Nautical charts on sailingissues.com

External links[edit]

Sours: https://en.wikipedia.org/wiki/Nautical_chart

Chart ocean depth

Nautical Charts

Plan your next trip with our online nautical charts. We have assembled links to NOAAonline nautical charts. Jump to the bottom of this page for tips and information on how to get free nautical charts. pda iconNOAA printable nautical charts by area

Boaters you should use a GPS and have area nautical charts onboard, especially if you are not familiar with the local waters. Staying within nautical markers is encouraged to protect both wildlife and our waterways, and to keep you from getting lost in the back waters.

Collier County Angler GuideThe waters on the Gulf of Mexico, The Keys, and inshore waterways can be shallow, so knowing your depth is very important to avoid grounding. Frequently check the depth reference on your chart and watch the color of the water - the darker the water appears, the deeper it is. Always keep in mind charts are not always up to date due to our shifting substrate. The coastal waters of the Gulf and The Keys have little structure, so the sandy substrate is constantly shifted around. Sandbars change locations often - an area could be 4 feet deep this month and sandbar or island the next month. It is also very easy to get lost in the 10,000 Islands or the mangrove islands in and around Florida, so use your charts!

The Boating and Angling Guides by FWC are a great resources consisting of area waterway maps and includeinformation on speed zones, marinas and public access boat ramps, and seagrass and mangrove locations. Get your Guide at the Florida Fish & Wildlife website or pick one up locally.

DISCLAIMER: We provide information on this website for your convenience. This information is provided as a guide for Florida fishing & boating and is not conclusive. We will not be responsible for the accuracy of information on referring websites. We will not be held liable for any damages if you rely on the information or regulations listed on this website.

Sours: https://www.floridagofishing.com/info-nautical-charts.html
Learning Your Marine Charts

How to Read a Nautical Chart

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