Chip log

A log (also Sign, . V. engl = log (initial ) wood chips) is in the seafaring navigation a measuring instrument for determining the drive, the speed of watercraft. It shows the distance in the water route (see speed through the water ).

The original measurement method consisted of a lead-filled wooden board in shape of a quarter circle sector, which is attached to a leash to throw from a moving vessel into the water: the wood remains almost at the same spot in the water. After a certain time ( which was earlier with an hourglass, the Logglas determined ) will determine the length of the last log-line, then the whole assembly pulled back on board. Substituting the distance traveled by ship track with how long this takes into consideration, can the speed of the vessel calculated in the water.

The calculated velocity was previously required together with the indicated compass heading for determining the location of vessels. The location determination based on the addition of single measured by log and time and compass path sections is 'Link', or dead reckoning, Eng. Dead Reckoning, called.

A log can usually only determine the speed relative to the surrounding water ( speed through the water ). To determine the absolute speed of the ship it was therefore used to rely on ( measurement and ) experience of the respective river or ocean currents. Current methods using radio and satellite navigation yield much more precise determinations of place, so that measurements with the log usually have only informative character, or provide information about the flow of water by difference to the values ​​from the satellite navigation.

Designs and measurement principles

Relingslog

The Relingslog is a simple way of determining the speed of the ship.

In this case, the measure of Meridiantertie is used: 1 Meridiantertie is the 3600ste part of a nautical mile = 0,514 meters. Since the second of 3600ste part is the hour, corresponds exactly Meridiantertien per second nautical miles per hour ( ie nodes).

To measure one marks the longest possible distance along the rail in Meridiantertien and stops the time it takes for a thrown overboard floating piece to go through this route. Example: the route 18 Meridiantertien go through in 6 seconds, the speed would 3,00 kn.

Patentlog ( Schlepplog )

The Patentlog has an impeller attached to a flexible shaft. Its rotation is indicated by a counter at the stern of the ship as traversed miles or ( in later versions, almost as a tachometer ) as additional speed. The way to the mid-20th century best known manufacturers of such devices, the company was Walker. [Note 1]

Sumlogs and Electronic Logs

Sumlogs use directly on the underwater hull -mounted impeller. Electric Log evaluate the speed of a paddle-wheel impeller, which is displayed as speed and next runs a mileage counter.

Hand Sign ( Logscheit, Dutchman's Log)

End of the 16th century, the Sign was probably in Holland, developed from which the name " node " for the speed of the ship is: a triangular wooden board ( the Logscheit ), which is held by a attached to a corner piece of lead vertically in the water. The attached thereto, marked by nodes log-line was allowed to run loose on a spindle, stopped by Hourglass ( Logglas ) and counted the last node. The imprecision was less than / - 10 percent.

Electronic Login

Work with ultrasound which is radiated obliquely forward and reflected from the seabed or air bubbles in the water. Another particular, utilizes the principle of electrical conductivity of the salt water. For an electromagnetic field is produced that changes the velocity analog, see Elektrolog.

Elektrolog

As Elektrolog (also Induktionslog ) refers to a device for measuring the speed and the traveled distance of a ship based on an electrodynamic principle. The Elektrolog encoder consists of a paddle wheel, which is flown by the water, turns and (usually a Hall sensor ) is generated by small magnets in the wings voltage pulses in electronics which are proportional to the speed. The voltages are supplied via an amplifier and signal converter to a display device which indicates the speed, and can also display the distance traveled over time.

Staudrucklog ( Rohrlog )

The hydrostatic Login again measure the dynamic pressure of the water against the running ship and comply with the pitot tube of the aircraft. The measuring range for ships is between 2 and about 50 knots. The back pressure is directly proportional to the speed of the ship. The revolutions of the propeller give a passable level for the ride when they are corrected for draft, waves, algae, etc.. This " quasi- calibration " on a known test track - as between two beacons of waterways - are called " mile run ".

Dopplerlog

Send Sonar Doppler Sign of underwater acoustic signals. When the sound wave reaches the seabed, it is reflected there and then reaches back to the transmitter / receiver of the Logges. The seabed is not moving, but still the self-movement of the vessel there is a Doppler effect, which can be evaluated in the unit.

As long as the sound waves still get to the seabed and back, measure the Doppler sonar Sign the speed over ground. But should it not be possible to use the seabed as a reference, the suspended device used ( plankton, minerals, dirt, etc.) in the water to measure the speed through the water on the basis of reflections and thereby resulting frequency shift.

General to Login

In any event log provide the " speed through the water " (more precisely, by the surrounding medium ). To use Speed ​​log values ​​in the nautical, they must - as described above - corrected if necessary because of external circumstances, especially the influence of a possible flow. These flows can distort the distances, but are

Nowadays, the easiest determination of flows is determined by comparing the Log other navigation method (for example, GPS).