Except from the nautical chart, in order to ensure the required safety, the mariner is obliged to use a variety of nautical instruments.
The appropriate use of the nautical chart requires certain “surveying instruments” that are mandatory in vessels.
(1) Parallel for shaping courses and bearings
(2) Pair of compasses for measuring distances
(3) Protractor for measuring angles
(4) Right- angle triangle for shaping astroposition lines
(5) Magnifying lens for magnifying the charts’ symbols
(6) A regular pencil, gum eraser and scraper
Depth Measuring Instruments
Nautical charts accurately register the sea depths. The mariner is mainly concerned about the depth under the vessel’s keel given that this is both the most important criterion concerning safety and a useful datum concerning anchoring. These data are registered by the bathymeters.
It consists of a lead counter- weight and the lead rope, which is subdivided into meters. In order to be discerned, the sub-division points are either colored or are differentiated via a piece of cloth or another piece of rope, which is tied on the lead rope with a knot. It is used for small depths, mainly in the harbors and the anchorage areas.
It is the modern electronic instrument which calculates the sea’s depth under the vessel’s keel. The principle of its function is based on the measurement of time which intersects between the transmission of supersonic signals which are transmitted by an apparatus located on the vessel’s keel.
The supersonic waves are reflected on the sea floor and return to the receiver, measuring the time that intersects between the transmission and the reception. The depth is registered straightly by the bathymeter without further calculations.
It is the instrument that is used for the calculation of the vessels’ velocity and the distance it covers. There are both mechanical and electronic logs.