Hydrographics

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Paper Charts

Paper charts are still considered the gold standard of navigation, and many cruisers rely on them exclusively. In this day of decreasing cost of electronics, even cruisers who rely almost exclusively on electronic chars usually have a set of paper charts as a backup.

Paper charts are produced directly by the above agencies, and are frequently sold through retailers such as chart agencies. A quick search of the business telephone directory or local internet business search guide, or google, will reveal a list of chart agencies in your area. In general, Admiralty paper charts or the USA charts from NOAA are the best to aim for, although the smaller national agencies also have a useful range of charts. For example the LINZ charts from New Zealand have a good reputation for the South Pacific region, where coverage is available (e.g. Samoa, Cook Islands or around New Zealand).

An increasing number of chart agencies now produce charts on demand, where the latest chart including any updates, notes to mariners, or other annotations, are produced via a high speed chart plotter directly from the agency when the paper chart is ordered. This provides some clear advantages in terms of accuracy of navigation.

The Title Block

When first using a chart, several items of information on the chart require close scrutiny. Read the chart title block carefully for:

Scale

The scale of a chart indicates the degree of detail available. Small-scale charts are generally in the range of 1:40 000 to 1:80 000. On a small-scale chart you will notice that some aids to navigation are not shown or are shown by a small dot. There is a chart that covers the whole of the North Pacific. It shows a very large area, but very little detail. Large-scale charts are required for entering harbours and anchorages. They will show much more detail. All rocks and aids to navigation will be included. Remember small-scale charts have little detail while large-scale charts have lots of detail.

Type of Projection

The projection used will affect how distance is measured on the chart. On a polyconic chart, look for a distance scale. On a Mercator projection use the latitude scale.

Depths and Elevations

In considering depths two factors must be considered: chart datum and unit of measure. Chart datum is the point from which depths are measured. Canada and the United States use different reference points, the Canadian being shallower that the American. If using an American chart, use American tide tables; Canadian charts require Canadian tide tables. The units of measure can vary. Older charts may be in fathoms and feet; newer charts will be metric with depths in metres and tenths of metres. A typical sailboat has a draft of 6 feet. That is either one fathom or 2 metres. Be careful. Elevations and clearances are generally measured from the highest watermark. This adds a measure of safety. Again, Canadian and American charts use different reference points. As an aside, the areas of the chart shown in green (foreshore) are between chart datum and the high watermark.

Horizontal Datum

If you are using a GPS ensure that you have set the horizontal datum to coincide with that of your chart. The most common is WGS 84, which is equivalent to NAD 83.

Special Notes and Cautions

These call attention to the appropriate Vessel Traffic Services, restricted areas, and other similar information.

Date of issue and corrections

The date of issue is printed on the chart. A stamp indicates the date up to which the chart has been corrected using Notices to Mariners.

Chart Formats

Electronic charts come in two basic formats: raster and vector charts.

Raster charts are a scanned copy of the paper charts, usually geo-referenced so that they can be loaded into and managed by navigational software such as OpenCPN or similar.

Vector charts are digitised copies of the paper charts, or perhaps completely newly made charts, done in a scalable (vector) format. They generally scale better than raster charts but may not be as easy to use in large scale mode.

Where a computer with software such as OpenCPN is being used, the charts can come in a number of different formats. The Chart Sources Page for OpenCPN discusses the various chart formats that are available, which formats are compatible with OpenCPN, and where to obtain the charts.

There are a number of proprietary chart formats, most of these are vector formats. For example:

Proprietary charts are usually designed for use with a chart plotter of a particular type, or a particular piece of software. For example the Navionics charts are designed for use only with the Navionics software, while C-MAP charts can be used on some pieces of software for computers as well as certain types of chart plotter. Imray charts come complete with a piece of software that can read those charts.

Generally speaking the various chart agencies appear to be moving away from proprietary formats towards standard formats such as S57 / S63 (S57 refers to the chart format, S63 refers to the encryption format used to preserve copyright owner's rights). This allows software developers to concentrate on developing features for their software and retaining compatibility with many different chart formats, whereas chart producers can focus on the detail and accuracy of their chart data.

For more information see the OpenCPN chart formats page which gives a good summary of the available digital chart formats and their compatibility.

C-Map

Available as either a plug-in memory module for stand-alone Chart Plotters or as a DVD for installation on a notebook computer. C-Map uses the CM-93 vector format for charts, which exists in a number of different versions. The included chart plotter software supplied by Jeppesen on the DVD - called ECS 4.01 - is well out of date but free alternatives like OpenCPN and Software On Board are readily found on the internet and can use various versions of the CM-93 chart format (version 2 for OpenCPN, version 3 and later for other packages).

Cost

Although all charts cost money, and electronic charts are often more expensive than their paper equivalents, prices of electronic navigational charts has been dropping of late.

Many of the national chart agencies now make at least their raster charts freely available. Those include USA and New Zealand charts.

Web-based charts

  • OpenSeaMap project is developing a world-wide free nautical chart. Although there is still only significant levels of detail in the data for northern Europe and limited depth data, the project is progressing.
  • Navionics currently provides free access to their web-based chart client. Additionally they provide WebAPI for embedding these charts into websites.

Chart Segments in this Wiki

Above all, be careful with copyright when using charts in the wiki. A scanned image of a copyrighted paper chart, or a copy of an electronic chart from a commercial charting package, will almost certainly be subject to a copyright which means it cannot be used in this wiki. If you are going to take a screen shot of an electronic chart to use on a wiki page, the following are useful options:

  • OpenSeaMap -- although the coverage is limited in various places around the world, the data is free and coverage is increasing slowly.
  • Google Earth
  • Google Maps
  • One of the freely available raster charts, for example those issued by LINZ in New Zealand. See the section on Chart Sources by Region below.

It's possible to use a Google Map directly in a wiki page, using a code like this:

<googlemap lat="-23.159029" lon="150.788269" zoom="14" width="350" height="335" />

... although it's not preferable to do that, because the Google Map segment can be slow to load. A better idea is to take a screen shot of a map such as OpenSeaMap and incorporate it into the page. First of course you need to Upload the screen shot file and then incorporate the image as follows:

[[Image:Rosslyn_bay.png|center|thumb|350px|'''Map''' ]]

Note: If screenshots of Google Maps are used, these MUST be saved in .png format to preserve the Google Logo layer (to show the copyright details). Upload as .png to the Wiki with the logo intact.

Selecting Which Charts to List (for Charts sections)

Google Earth will allow you to find a city or port on the world globe. From there, a neat tool called GeoGarage will allow you to find maps for most places of interest, just by zooming in on that location and looking at the numbers on the chart overlays. These are not the latest charts, but those that the various agencies are happy to release to the general public, and Notices to Seamen should still be consulted for the latest variations. Coastlines don't change much over time, but navigation aids and channel markers do. Once you have that chart number, try UKHO search engine to get the full title and scale for your webpage.

If an area isn't covered by these tools then a Google search usually reveals some useful data.

Try to list the smallest scale for the terrain being discussed, there's no point listing large scale maps at the level of a continent. Australia, for instance, is completely covered by one chart at 1:10000000 scale and six charts at 1:3500000 scale. As we drill down to view state coastlines and even further to individual ports, the maps get more detailed.

Multiple sources can be listed on a wiki page if they are available. Often there is a British Admiralty chart for a region when nothing else can be found, and you can be sure that the US government has most charts as well. Both NOAA and NGA charts can be viewed online here.

Chart Categories

The Danish Hydrographic Office (KMS) categorizes the charts thus:

Passage/landfall Charts
Scale: 1:2.000.000 to 1:350.000.
These charts cover very large areas and are only to be used when navigating across open seas or oceans. These charts contain very limited amounts of nautical and hydrographical information. Close to shore, this information is sometimes omitted completely.
Coastal Charts
Scale: 1:350.000 to 1:75.000.
These charts contain detailed nautical and hydrographical information, enabling safe navigation through main waterways and straits.
Approach Charts
Charts in the scale between 1:75.000 and 1:30.000.
These charts contain detailed nautical and hydrographical information in order to safely approach the harbours shown in the area. In narrow straits or confined areas or in areas where a special scale chart covers the area, a simplification can have been done.
Harbour charts & Special scale charts
Charts produced in a scale larger than 1:30.000.
These charts covers areas which are difficult to navigate such as narrow straits, harbours or anchorages.

Chart Sources by Region

Australia

The Australian Hydrographic Service publishes both paper and electronic charts for the Australia region.

An index of the AHS paper charts is here: http://www.hydro.gov.au/webapps/jsp/charts/chartlist.jsp

AHS electronic charts are available in the AusENC product. This is S63 format which is compatible with OpenCPN versions 3.3 and later. Details are available about AusENC and about electronic charting.

AusENC charts are not purchased from the Australian Hydrographic Service directly but can be obtained from chart retailers such as Boat Books Australia.

Canada

The Canadian Hydrographic Service (CHS) produces charts of Canadian waterways. CHS does not sell charts directly to the public, they are sold through a network of dealers and distributors.

CHS publishes a paper chart index and a digital chart index. CHS produces vector based Electronic Navigational Charts (ENCs) and raster (BSB) charts. Both charts are available on CD. CHS BSB charts are in the BSB-4 format which is not compatible with OpenCPN -- for more information see the OpenCPN chart formats page.

CHS ENC charts meet the S-57 standard.

Canadian digital charts are quite expensive due to a complex arrangement that the government has with a single monopoly chart supplier. Apparently due to this arrangement the CHS does not own the copyright to its own charts and cannot make the charts available any cheaper.

New Zealand

Land Information New Zealand (LINZ) publishes both paper and electronic charts for New Zealand and much of the South Pacific region. Due to New Zealand's close ties with many Pacific Island states such as Samoa, Cook Islands and Tonga, these charts are often the best available for the waters of those nations.

LINZ make available a chart catalogue on line and both raster and vector formats. The raster charts are available for free download in a format that's compatible with OpenCPN. The vector charts have an on line catalogue and are available for purchase on line.

UK

The UK Hydrographic Office is arguably the world's largest producer of charts and has been for hundreds of years. Their chart coverage is world-wide. Their charts are often referred to as Admiralty or BA (British Admiralty) charts.

Note that some BA charts haven't been updated for some time. Especially in areas of the South Pacific, it's often the case that the LINZ charts are a better and more accurate source.

BA charts are produced in both digital and paper formats, digital charts are available in both raster and vector format. These are sold under the ARCS (Admiralty Raster Chart Service) and AVCS (Admiralty Vector Chart Service) brands. Note that both brands incorporate charts from other agencies such as the Australian Hydrographic Service. The vector format is S-63 / S57 which is compatible with OpenCPN.

An on line catalogue is available for download. Due to the number and breadth of BA charts, it's a significant download just for the catalogue.

BA charts can be purchased from a network of distributors world-wide. One such distributor with a comprehensive range of both vector and raster charts is Euronav in the UK, and another is ChartWorld in Germany. The producers of the OpenCPN plugin for the S63 format have an agreement in place with ChartWorld for the sale of compatible digital charts. In addition to the charts, a list of other digital publications is available including list of lights, radio signals, and tides.

USA

The agency in the USA responsible for producing charts is the Office of Coast Survey of the National Oceanic and Atmospheric Administration (part of the Department of Commerce).

Variously referred to as US, NOAA, NGA (National Geospatial-Intelligence Agency) or NIMA (for the former name of NGA) charts, these also have world-wide coverage although the same caveats apply as to Admiralty charts.

Charts are available in paper and digital formats, the digital formats are raster RNC and digital ENC. Both format charts are freely downloadable for US waters only -- although US charts are available for foreign waters these are not freely downloadable. There is an on line catalogue of digital charts available.

Both the paper and digital formats are available from distributors such as Maryland Nautical. The freely available charts can be downloaded direct from NOAA here for RNCs and here for ENCs.

SailorSmiley.gifContributors to this page

Names: Haiqu, Delatbabel


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