- Highlight the charts which you have on board with a highlighter pen in the correction log (NP 133A). An example of how to fill the log is shown to the left.
- Note down in the correction log correction numbers from all ANM’s, that are to be corrected, in an ascending order.
- Voyage charts must be corrected first, followed by all charts on board.
- Pull out the affected chart and confirm from the notice number, whether the last correction affecting the chart is entered at the bottom left hand corner of chart.
- It may be prudent to check if the chart has actually been corrected for the last notice.
- A ‘tracing’ is often used to position a correction accurately and quickly. If tracings are available on board, use them as they are more accurate and less time consuming when correcting charts.
- Only proper chart correction pens, ink and pencils should be used as shown in the section above.
- Chart blocks must be aligned carefully. When pasting chart blocks it is recommended to use “Positionable Mounting Adhesive Rolls”, as glue causes distortion within the block.
- 9. Only standard chart symbols as mentioned in Chart 5011 should be used.
- After completing each correction:
- Note down the correction number at bottom left hand corner of the chart.
- Strike out the correction number written in Chart Correction Log by pencil.
- Strike out the chart number at the correction in ANM or the tracing.
- Before moving to the next chart, correct all corrections (as noted from all ANM’s) affecting the chart.
- “Cumulative List of Admiralty Notices to Mariners” is published every 6 months and lists correction numbers affecting each chart for the last 2 years. This should be used to verify that all corrections affecting a particular chart have been carried out. It also gives the date of issue of the current edition of each chart.
- Temporary and Preliminary (T & P) notices are corrected in the following way:
- Only voyage charts to be corrected.
- Look up the list of T’s and P’s in force (This is published monthly in ANM)
- The T & P notices are printed on one side of the page. This is to facilitate them being cut out and filed, by area in the ship’s T & P file. The index of this file should be the “Monthly T & P’s in force” list. This has to be renewed monthly when the new one is received.
- Correct voyage charts with the T’s & P’s in force, in pencil, and note the correction number in the bottom left hand corner of the chart, as well as in the correction log.
Correction for a new chart:
When a new chart or new edition of a chart is received on board this procedure must be followed:
- Highlight the chart number in the correction log. Erase all the old corrections (in case of new edition and write the edition date in pen).
- Enter the Chart Folio and sequence number, from the index. In case of a new edition, this information is already present.
- Correct the chart for any pending corrections. Record these corrections in Chart correction log in pencil.
- Correct the Admiralty Chart Catalogue (NP 131) if affected.
- Cancel the old edition of the chart by writing boldly on top “CANCELLED” and remove it from the bridge.
Corrections to old charts:
If a chart has not been kept up-to-date and the last correction effected on the chart is very old, use the following procedure to correct it:
- Check that the edition is current in the Cumulative Notice to Mariners.
- Check in the latest Cumulative Notice to Mariners against the chart number, the number of uncorrected notices. Note them down in the correction log.
- Start by correcting the latest correction first and proceed backwards until all the notices are corrected.
Navigation warnings in force:
Usually only the voyage charts are corrected for Navigation Warnings. A proper log of all Navigation Warnings should be maintained with individual sections for each area. The log is maintained in the following way:
- All Navigation Warnings in force until the year end are published in the Annual Notices to Mariners.
- All relevant sections of Navigation Warnings are removed from Admiralty Notices to Mariners and filed in the Navigation Warnings log in serial order.
- A complete list of all navigation warnings in force is published quarterly, in the weekly notices to mariners. This list forms the first page of the log.
- The above list is kept updated, as the new notices are received. Old lists are removed on receipt on new list at the end of quarter.
- Obsolete or cancelled notices are removed from the log, as required.
- All Nav warnings are removed at the end of the year, when new Annual Notices to Mariners received.
- Navigation Warnings in force must be corrected on voyage charts in pencil and number to be noted in the left hand corner of the chart also in pencil.
Admiralty Digital Notices to Mariners (ADNM) service:
Very recently the United Kingdom Hydrographic Office has introduced the Admiralty Digital Notices to Mariners (ADMN) service. Here all the Notice to Mariners are available along with tracings and block corrections on a 3.5″ floppy disk. The text is arranged in such a way that there is only one notice per page. This assists in electronic transmission of the notices using the latest communications systems. For further details refer to publication number NP 294 (How to correct your charts the Admiralty Way).
All navigational charts on board are generally grouped into folios which can be divided in to three categories:
- Standard folio which contains all navigational charts, including latticed charts, for the world. These may be grouped in one of the following ways:
- a) Each folio contains charts of a particular geographical location, in a serial order. These are given in Catalogue of Admiralty Charts (NP 131) and in publication number NP 133A (Chart correction log and folio Index).
- b) All charts should be kept in serial order and grouped by serial order e.g. BA 1000 to BA 1500 etc.
- Local Folios which contain charts for local services and for particular requirements not met by standard folios, such as US or Canadian charts.
- Special Folios which contain Routeing charts, Loran/ Omega charts.
Types of chart corrections:
The following corrections are listed in Weekly Notices to Mariners (ANM):
- Permanent corrections are listed in serial number, from beginning of the year. A minor correction can be corrected by pen and areas of chart known as “blocks” are issued for major corrections.
- Temporary and Preliminary (T & P) corrections are carried out in pencil and are erased after they are cancelled or superseded by permanent correction.
- Navigational warnings are listed under Navareas.
- A New edition of chart is issued when the major portion of a chart is revised.
Charts must also be corrected for Local Navigational warnings and Local Notices.
- Notice the basic colour difference between a Metric chart and a Fathom chart as mentioned above.
- Look below the title of the chart which has a phrase stating “Depth in Metres” or “Depth in fathoms”. Sometimes you may also find statement like “Soundings in metres” or “Soundings in feet and fathoms”. These statements also indicate whether the chart is metric or fathom chart.
- Now look at the title of the chart which gives the name of the chart or the area where the chart is applicable. The name or the title of the chart is at the most conspicuous place and it is placed in such a way as to not to interfere with any navigational information given on the chart. Do you see it – What is the title of the your chart ?
- See below the title of the chart for some additional information like unit of height and depths (have explained earlier), references datum used, type of projection and natural scale of the chart.
- Do you know what a natural scale of the chart is? It is the ratio of unit distance (length) on the chart to the corresponding distance on the earth’s surface (both measured in same units) For e.g. if the natural scale is 1 : 25,000 – this means that 1 cm of chart corresponds to 25,000 cms on the earth surface.
- Look at both the metric and fathom chart you have removed and note down the natural scale of both the charts.
- Do you know how to identify a chart? Each chart is identified by its chart number which is printed on left top and right bottom corners outside the margin. Note down in your technical diary the numbers of both the charts which you have removed.
- Can you locate the compass rose on the chart? These are the compass engravings to facilitate plotting of bearings, directions and courses. Some of these have two concentric rings – the outer one representing the true north directions and the inner one representing the magnetic north
- Apart from the above you have dimensions of the basic plate from which the chart is printed on the lower right hand corner outside the margin and the Date of publication of the chart (shown outside the bottom margin in the middle) along with the name of the Hydrographer.
- New edition indicates the date when this chart was partly or completely revised and published. This is printed to the right of the date of publication.
Note down the new edition of both the charts which you have picked out.
- Corrections to charts both small and large are printed on the left hand corner below the bottom margin. This will be discussed in details further in this module when dealing with correction of charts.
- The vertical scale on the left and right hand side is known as the Latitude scale and the scale on the top and bottom is known as the Longitude scale. Distance on a Mercator chart is taken on the latitude scale. The latitude and longitude are marked in degrees and minutes (1º = 60 minutes) and each minute of the latitude scale corresponds to 1 nautical mile on the chart (at the same latitude).
For example: If the ship is at 20ºN latitude and if you have to measure a distance in the same place, then you should use the latitude scale at 20ºN. Similarly distances on a chart between two positions are therefore measured along the latitude scale in between the corresponding latitudes of the two positions.
- On modern metric charts depths are given in metres and sometimes in meters and decimetres. Heights are always printed in metres.
For example: 86 on a metric chart indicates a depth of 8 metres and 6 decimetres
On a fathom chart 94 indicates depth of 9 fathom and 4 feet. (1 fathom = 6 feet).
- Source data: On all modern charts, the Source data inset is placed in a convenient location indicating source of hydrographic information used in the construction of the chart. This includes the year, name of the agency and scale of hydrographic survey of each section of the chart.
- Chart datum: It is the lowest level of water that is reached in that location. Charts datum is defined as a level so low that the tide will not frequently fall below it. Modern practice is to establish datum at or near the level of Lowest Astronomical Tide or L.A.T.
- A.T. – is the lowest level predicted to occur under average meteorological conditions and under any combination of astronomical conditions. Sometimes storm surges may cause lower levels to occur.
- · All depths and Drying heights are measured from this somewhat arbitrary level.
Some features of the coast are exposed during low water or low tide. Such features are generally referred to as drying heights and is usually indicated with numbers underlined. For example: 5 (meaning on a metric chart drying height is 5 metres – also meaning that this particular area is 5 metres above chart datum so during low tide this portion of land may be dry).
- Continuous lines with sounding figures, circling an area or a line zig zagging along the coast represent depth contours. These are lines joining areas with the same depth measured from the chart datum.
- Height of mountains may cover a large area but the point at which the height is measured is indicated by a point. For example: 245 means the height of the point is 245 metres.
- Soundings below 5 metres are indicated by light blue colour on a metric chart and a light blue colour strip (ribbon) is printed towards shallow side of 10 metre depth contour.
- · Blue tint, in one or more shades and tint ribbons, are shown to different limits according to the scale and purpose of the chart and the nature of the seabed.