Besides the mariner's compass, all mariners must have up-to-date maritime charts and the standard equipment for plotting course.
Maritime charts provide topographic and hydrographic information. In the upper corner is the name of the chart and general information; in the right bottom corner the chart number; the name of the institution which published it, date of issue, name of institution which drew up the chart (in the middle below the frame of the chart); it also gives the ;magnetic rose+ with annual declination (in several places in the hydrographic part); details of ;minor corrections+ (left bottom corner); linear measurements in miles (M) and km (in a suitable place on the chart) etc.
Before the chart is used the information in the title should be read carefully.
The charts published by the State Hydrographic Institute in Split give depths and heights in metres, i.e. depths to level of the chart (Chart Datum) and heights from the medium sea-level. The State Hydrographic Institute in Split takes as level of the chart the medium height at low water during periods of maximum tidal activity (Mean Lower Water Spring). The sea in the charts is printed in several shades of blue for maximum ease of reading. Depths of less than 5 m are in deep blue, between 510 m in light blue and the rest of the sea section is white.
The scale of the chart is expressed in ratio or fractions (e.g. 1 : 100 000 or 1/100 000). Beside the numerical scale the linear scale may also be shown.
The outer border of the chart contains the numerical coordinates of latitude and longitude. Latitude is used in measuring distances (1 M = 1 minute). The length of minutes on the latitude scale of the chart increases as the latitude increases and thus in calculations account must be taken of the position of the vessel. This is because of Mercator's projection of the chart. Distance cannot be calculated by minutes of longitude.
The magnetic roses, usually found in several places on the chart can be used to plot course and azimuth with aid of parallel rulers or set-square. Inside the rose numbers of the magnetic declinations (variations) are drawn-in which should be corrected according to year.
The relief of the land sections of the chart is shown in contour lines (horizontals; usually 40 or 20 m apart), by crosshatching or a combination of both, some charts are colour-shaded, usually in ocre.
All details important for plotting the course but too small to be convincingly shown on the chart have special identification marks. The exact position of details so marked is taken from the middle of the base of the topographic sign or the centre of a circular mark (for cliffs, buoys etc.). With marks for symmetrical objects (churches, floating docks etc.) the exact position is the centre of the mark. The State Hydrographic Institute in Split has published a summary of all marks and shortenings entitled Symbols and Abbreviations on Maritime Charts (Znakovi i kratice na pomorskim kartama).
The largest scale and numerically detailed charts recently published and corrected are the best to use. Authorized sellers of nautical charts are bound to sell charts corrected to the day of sale, mariners must further correct them themselves.
Classification of charts
Charts of the State Hydrographic Institute in Split are divided in three classes: informative, navigational and supplementary.
Informative charts give information important for navigation such as currents, meteorological and hydrological details etc.
Navigation charts are designed for practical navigation, i.e. the plotting of courses, the plotting of a vessel's position. According to scale they may be: general, course, coastal charts and plans.
General charts present larger area, of whole seas with their adjacent shores and they are usually small scale. General charts no. 100, 101, 102 show the Adriatic as a whole or in part (scale of 1 : 1 000 000 or 1 : 750 000. Chart no. 103 shows the Ionian Sea and no. 108 and 109 the Mediterranean Sea (scale 1 : 2 500 000) etc.
General charts can be used for navigation outside Croatian territorial sea if the boat's safety allows it. But their main purpose is to give a more comprehensive view of cruising areas for planning routes and calculating the total distances and duration on the voyage to be covered.
Course charts show smaller areas of sea and include all important details needed for navigation. They are drawn to a scale of 1 : 300 000. The course charts of the Adriatic bear the numbers 30031 to 30037.
Coastal charts show in detail smaller stretches of the coast and the basic aids to navigation. Their use is obligatory in the immediate vicinity of the coast, and they contain most of the important details to facilitate the navigation. The newest editions (published by the State Hydrographic Institute in Split) have the number 100 plus an additional number which denotes the area covered by the chart (e.g. 10021: Šibenik Split), drawn to a scale of 1 : 100 000. They often include in larger scale the plans of certain harbours, anchorages and dangerous or important areas, straits, channels etc.
The State Hydrographic Institute in Split publishes special charts for small craft.
Plans cover small areas, usually ports, harbours and anchorages. They are drawn in great detail and to a larger scale (1 : 50 000). They bear separate scales of measurement for longitude and distance, as they do not indicate latitudes and longitudes at border.
Supplementary charts are drawn for certain special purposes and are not needed for normal navigation.
Charts cannot be used properly without the necessary navigation equipment. The most important items are navigational triangles (protractor) or parallel (slide) rulers for drawing in the vessel's course and azimuth, compasses for plotting distances and coordinates, a magnifying-glass, a soft pencil and soft eraser.