On methods for measuring ship speed. Measuring lines
In our life the speed of movement Vehicle measured in kilometers per hour (km/h). This is how the movement of a car, train, or plane is characterized. But there is one exception to this rule. In maritime navigation, the speed of a ship is indicated in knots. This unit of measurement is not included in the International SI System, but is traditionally accepted for use in navigation.
Vessel speed measurement
This order has developed historically. Once upon a time, the speed of a ship's movement was determined using a special device called sector log. It was a board, at the end of which a line was attached - a thin ship's cable. Knots were tied at regular intervals along its entire length. The sailor, touching the cable with his hand, counted the number of knots that passed through his hand in a certain time, thus determining the speed immediately in knots. It is important that this method did not require any additional calculations.
No one has been using lags of this design for a long time. Now to measure speed sea vessels they use instruments based on the latest scientific and technical achievements in the field of hydroacoustics and hydrodynamics. Meters based on the Doppler effect are popular. There are more simple ways- using special metal turntables placed in water. In this case, the speed is determined based on the number of revolutions per unit time.
Nautical mile
Translated into ordinary language, one knot means the speed at which a ship travels one nautical mile in an hour. At first its value was 1853.184 meters. This is exactly the length of the Earth's surface along the meridian in one arc minute. It was only in 1929 that the International Conference in Monaco established the length nautical miles at 1852 meters.
It must be remembered that, in addition to the nautical mile, there are others. In the past, several dozen different miles existed as units of measurement for length in different countries. After the introduction of the metric system, miles as a unit of measurement of distances began to rapidly lose popularity. Today, out of all the variety of land miles, only about ten remain. The most common of them is American mile. Its length is 1609.34 meters.
Not only the nautical mile is attached to the length of the earth's meridian. The old French unit of length, nautical league, is equal to 5555.6 meters, which corresponds to three nautical miles. It is interesting that, in addition to the sea league, in France there was also a land league, also tied to the length of the meridian, and a postal league.
Speed recalculation rules
Today, the speed of sea vessels is still measured in knots. In order to present this characteristic in a form familiar to us, it is necessary to convert them into kilometers per hour. It can be done in several ways:
- Simply multiply the number of nodes by 1.852 in any way possible, for example using a calculator.
- Make a rough calculation in your head by multiplying the number of nodes by 1.85.
- Apply special translation tables from the Internet.
Having made such a recalculation, it is easy to compare the speeds of sea vessels and other vehicles.
Record holders among ships
Speed of sea passenger ships usually higher than trading ones. The latest official record (“Blue Ribbon of the Atlantic”) belongs to the American high-speed transatlantic liner "United States". It was installed in 1952. Then the liner crossed the Atlantic with average speed 35 knots (64.7 km/h).
The infamous Titanic, on its only voyage, was sailing almost at the limit of its technical capabilities at a speed of 22 knots when it hit an iceberg on the night of April 14-15, 1912. The highest speed then passenger airliners(“Mauritania” and “Lusitania”) was 25 knots (46.3 km/h).
Here are some of the ships that were once winners of the Atlantic Blue Ribbon:
- Great Western (Great Britain) in 1838.
- "Britannia" (Great Britain) in 1840.
- "Baltic" (Great Britain) in 1873.
- "Kaiser Wilhelm der Grosse" (Germany) in 1897.
- Lusitania (Great Britain) in 1909.
- "Rex" (Italy) in 1933.
- Queen Mary (Great Britain) in 1936.
There is a separate category of ships - hydrofoils, which are used for passenger transportation and the Coast Guard. They can reach speeds of over 100 km/h (60 knots), but their range of use at sea is severely limited to the coastal zone and low economic characteristics.
Changing priorities
With the development of aviation, such active competition among ocean-going passenger ships has lost its relevance. Passengers began to prefer airplanes to cross the Atlantic, and ship-owning companies had to reorient themselves to serving tourists. For cruise ships The most important indicators were reliability, comfort and economic efficiency.
The optimal speed of modern ocean cruise ships is usually from 20 to 30 knots, and for cargo ships- approximately 15 knots. A record achievement for that time, United States remains the highest in history. For merchant ships today, the priority indicators are primarily economic. The pursuit of records is finally a thing of the past.
Video
In this video collection you will find a lot interesting information regarding the measurement of the speed of maritime transport.
“Determining the speed of a ship and the distance traveled at sea”
Distance at sea is measured in nautical miles and cables, so the distance traveled by a ship is measured in the same units. 1 mile = 10 kbt.
A boat's speed is expressed in miles per hour, or knots.
A knot is a unit of speed of a ship, equal to one mile per hour. 1 knot = 1 mile/hour.
Instruments that measure the speed of a ship and determine the distance traveled are called lags.
Depending on the principle of operation and device, logs are divided into
Relative (Hydrodynamic, induction), measuring the speed of the vessel relative to the water
Absolute (Doppler logs, inertial and geoelectromagnetic systems), measuring the speed of the vessel relative to the ground.
1. Hydrodynamic. The operation of these logs is based on measuring the difference between static and dynamic water pressure, which depends on the speed of the vessel.
2. Induction. The operating principle is based on the use of the relationship between the speed of the vessel and the emf induced in water by a magnetic field source attached to the bottom of the vessel.
3. Doppler. The operating principle is based on the use of the Doppler effect, which consists in a change in the observed frequency due to the relative movement of the source of emitted energy
The movement of a vessel is also usually divided into relative with a speed V o (V l), absolute with a speed V (V a, V i) and portable V c under the influence of wind, current or their combined influence.
Ships mainly use relative logs, which measure speed and distance traveled relative to the water, taking into account the wind, but not the current. Typically, lags have an error called a lag correction.
Lag correction is called systematic error, expressed as a percentage.
S-ROL
ΔL= ----------- 100%
Where S– actual (true) distance taken from the map;
ROL– difference in lag counts. ROL=OL 2 – OL 1.
Often the lag correction is expressed through the lag coefficient k l.
The lag correction and the speed of the vessel are determined after construction or repair at special testing grounds - measuring lines under the following conditions: waves no more than 3 points, wind up to 8 m/s, depth no less than 6 average draft.
The log correction and the ship's speed are determined at the PPH, SPH, MPH, SMPH in cargo and in ballast.
The results obtained are entered into the table of maneuverable elements.
If there is no current on the measuring line, 1 run is made.
If there is a constant current, 2 runs are made to eliminate it, because on mutually inverse courses from formula (1) on the first run, suppose V 0 = V 1 - V T , then on the second run V 0 = V 2 - V T . The joint solution of these two equations allows one to eliminate the current and determine the speed of the vessel relative to the water.
The lag correction will be determined accordingly: it is calculated using formula (2) for two runs.
If a fixed-pitch propeller is installed on the ship, then during the runs the speed of rotation of the propeller N is noted and the speed of the ship V rev depends on it. Then the distance traveled can be determined by the formula: , where a- advance, i.e. the distance traveled by the ship relative to the water during one revolution of the propulsion. It is calculated based on V about and the corresponding rotational speed of the propulsors N: . .
In the sea the speed and lag correction are determined by a free-floating reference point (to exclude the current) using radar or using high-precision observations (by satellites) with the exclusion of the current graphically or using formulas. To eliminate accumulated errors, the length of one run should be at a speed of 10 knots. – 2.3 NM; 15kt. – 3.6 NM; 18 knots – 4.3 mm or; 20 knots – 4.9 NM (N.V. Averbakh, Yu.K. Baranov Determination of maneuverable elements of a sea vessel and log corrections). Then
Problems solved when keeping numbers.
Pre-calculation of the lag count: OL i +1 =ROL+ OL i, where ROL=Sl/kl.
Calculation of the distance traveled along the log: S l =V l DT.
Calculation of swimming time: T= S l / V l; DT= S and / V and;
ship speed finder
Alternative descriptions. (English "lag") a gap in time between two events
An indicator reflecting the lag or advance in time of one phenomenon compared to others
Navigation device
A device for determining the speed of a vessel and the distance traveled
Arab Union (abbreviation)
Ship speedometer
The speedometer of a sea vessel, which has nothing to do with the disease AIDS
A ship's instrument for determining the distance traveled by a ship
Beam under the floor
Marine speedometer
Device for determining the speed of a ship
Speedometer on a yacht
Ship's side
. "speedometer" on a schooner
. speedometer on a ship
Temporary "gap"
Marine instrument
. "speedometer" on a ship
Lag
Ship's "knot meter"
Marine analogue of the speedometer
Ship's instrument
Knot meter
Speedometer
There's a speedometer in a car, but what's on a ship?
Measures ship speed
Ship's "speedometer"
Vessel speedometer
Device for determining the speed of a ship
Vessel speed measuring device
Time gap between events
. "Speedometer" on a ship
. "Speedometer" on a ship
. "Speedometer" on a schooner
. "Speedometer" on a yacht
There's a speedometer in a car, but what's on a ship?
Temporary "gap"
Ship's "speedometer"
M. Morsk. one side, the side of the ship, relative to the guns; fire with a lag, from all guns on one side. Regarding water barrels: layer, row. A projectile for measuring the speed of a ship: a wooden triangle is thrown upright into the water, on a string measured in knots
Ship's "knot meter"
. (English "lag") a gap in time between two events
5.2. Principles for measuring ship speed
The speed of the vessel is measured with special devices ® lags . Currently, the following systems (types) of logs are used on ships:
Vertical logs (produced on the lagline and bottom).
The speed of rotation of the turntable is proportional to the speed of the vessel. The proportionality coefficient is determined by testing. The number of revolutions of the turntable is recorded on a counter indicating the distance traveled by the vessel.
Hydrodynamic logs (GDL).
The receiving devices of these logs measure the high-speed water pressure that occurs when the vessel moves. Based on the measured pressure value (the difference between dynamic and static pressures), the lag's calculation and decision circuit generates the vessel's speed and the distance it has traveled. To measure the pressure difference in these logs, spring (bellows) and liquid (mercury) differential pressure gauges are used. (LG-25, LG-50, LG-4, LG-6, MLG-25, MLG-50, etc.).
Induction logs (IEL).
The operating principle of these logs is based on the phenomenon of electromagnetic induction that occurs when sea water moves between two electrodes in an alternating magnetic field. The source of the magnetic field in the log is an electromagnet powered by alternating current. It is enclosed in a fairing, on the surface of which there are two measuring electrodes in contact with sea water. Under the influence of the alternating magnetic field of a magnet, water appears variable emf. The amplitude of this emf. turns out to be proportional to the speed of movement of the electromagnet, and therefore the ship. The signal taken from the electrodes is measured using the compensation method. If hydrodynamic logs give stable readings when V>3 knots., then induction® with almost 0 knots
Hydroacoustic logs (GAL).
The principle of their operation is based using the Doppler effect. A pulse of ultrasonic vibrations sent from the ship is reflected from the ground and returns back to the ship's log receiver. When the ship is moving The frequency of the received signal will differ from the emitted one depending on the speed of travel.
GALs measure the speed of the vessel not relative to the water, like all those mentioned above, but relative to the ground and therefore are considered absolute lags ( not relative). However, stable operation of these logs is possible at relatively shallow sea depths, but the accuracy of their work is very high.
Logs of all systems, like any other devices, cannot give absolutely accurate readings; they require periodic alignment and adjustment. That part of the error in the log readings that cannot be compensated is determined on the “measuring line” and then taken into account using a log correction.
Lag correction – a value equal to the relative error, expressed as a percentage and taken with the opposite sign, i.e.
Where S L– actual distance traveled by the vessel;
ROL– the distance traveled by the vessel according to the log counter ( ROL=OL 2 -OL 1 )
(5.7)
Where V 0 – true speed of the vessel;
V L– speed of the vessel according to log readings.
5.3. Determination of ship speed. Correction and lag coefficient
Speed of the vessel or ship ( V) and corrections to their lags (D L%) are determined in various ways:
on a visual measuring line;
using ship's radar;
using high-precision RNS;
on a cable measuring line, etc.
All methods of determination V andD L% differ from each other only in the method of obtaining the true distance ( S), necessary to calculate the true speed of the vessel ( V 0)®see rice. 5.4, 5.5, 5.6.
Let's consider one of the methods ®determining the speed of a vessel ( V) and its lag corrections (D L%) on the visual measuring line.
Visual measuring line ®a specially equipped testing ground for high-speed testing of ships.
Such a training ground must meet the following requirements:
– be located away from the paths of ships and vessels;
– be free from navigational hazards (>2 miles) and sheltered from wind and waves;
– must provide freedom of maneuver ( V£36 bonds.® L= 3miles;V£24 bonds.® L= 2miles And V£12 bonds.® L= 1mile);
– be able to ensure the required accuracy of position determination and navigation safety;
– have depths that exclude the influence of shallow water on the speed of the vessel (with a draft of 5 m And V£30 knot N³ 95m).
Rice. 5.1. Visual measuring line
The visual measuring line is equipped with secants ( B, C, D) alignments (not<2-х), направление которых перпендикулярно линии пробега судна (рис. 5.1), а расстояние между створами измерено с высокой точностью.
Some measuring lines are equipped with a leading alignment along which the vessel's line of travel is directed ( A).
Method for determining travel speed ( V) and lag corrections (D L%) boils down to the following:
®vessel, at a steady state of propulsion operation, i.e. at a constant number of revolutions of the propellers (propellers), makes a run along the leading target A. (In the absence of a leading alignment, the course during the run is kept perpendicular to the direction of the secant alignments B, C, D).
When crossing the line I of the secant alignment ( B) on the command “Zero!” The observers' stopwatches are switched on and the lag count is taken ( OL 1 ) and counting from the total counter of propulsion revolutions ( n 1 ).
When crossing the line II of the secant alignment ( G or IN) on the command “Zero!” The stopwatch is stopped and the following is removed: – the lag countdown ( OL 2 ) and counting from the total counter of propulsion revolutions ( n 2 ).
®the true speed of the vessel during the run is calculated using the formula:
(5.8)
Where S– distance (from the form or description of the measuring line) between secant sections B And G(or B And IN or IN And G) (i.e. the length of the run, which is set depending on the speed of the vessel during the run: if V<12bonds. – 1mile; If V= 12¸24 bonds. – 2miles; If V>24bonds. – 3miles);
t i – average running time in seconds (average time of all stopwatches).
®the speed of the vessel during the run along the log is calculated using the formula:
(5.9)
Where ROL = OL 2 – OL 1 – difference in lag counts (lag counter readings).
®the number of propulsion revolutions per minute during the run is calculated using the formula:
(5.10)
Where 
.
®calculate the lag correction as a percentage (D L%) on mileage according to the formula:
(5.11)
®calculate the lag coefficient ( TO L) on the run according to the formula:
(5.12)
To eliminate the influence of the flow on the results in each mode of operation of the propulsors, the following is performed:
A)®2 runs each ®if the flow speed in the area of the measuring line is constant;
b)®3 runs each ®if the flow is not constant and its elements ( TO T , u T) are unreliable.
There must be at least 3 operating modes of propulsors (as a rule: I– “PH” – designated move; II– “SH” – 75% of “PH”; III– “MH” – 50% of “PH”). In each mode, (usually) 3 runs are performed and after calculations we have:
1st run:V O1 , V L1 , N 1 , D L 1 %;
2nd run:V O2 , V L2 , N 2 , D L 2 %;
3rd run:V O3 , V L3 , N 3 , D L 3 %.
®calculate the average values of the required quantities for a specific, designated operating mode of the propulsors:
A)®true (relative) speed of the vessel ( V ABOUT) in the mode according to the formula:
;
(5.13)
b)®speed of the vessel along the log ( V L) in the mode according to the formula:
;
(5.14)
V)® number of revolutions of the propellers (propellers) in the mode according to the formula:
;
(5.15)
G)®lag correction in percentage (D L%) in the mode according to the formula:
;
(5.16)
d)®lag coefficient ( TO L) in the mode according to the formula:
. (5.17)
Note:
If not 3 but 2 runs are performed in the mode, then formulas (5.13¸5.17) will take the form:
(5.13A)
(5.14A)
(5.15A)
(5.16A)
(5.17A)
IImode–V O II, V L II, N O II,D L II%, TO L II;
IIImode–V O III, V L III, N O III,D L III%, TO L III.
®based on the results of measurements on the measuring line, the following are compiled:
|
A) graph of the correspondence between the speed of the vessel and the rotational speed of the propulsors (Fig. 5.2) |
b) lag correction correspondence plot (D L%) vessel speed (Fig. 5.3) |
|
Rice. 5. 2 . Speed Compliance Chart progress |
vessel speed of rotation of its propulsors . 5. 3 . Rice Compliance schedule |
ship speed log corrections
Data is taken from these graphs to fill out the navigator's work tables (RTS).
Correspondence of travel speed to the speed of rotation of the propulsors
and correction (coefficient) of the lag
Constant knowledge by the navigator of the reliable speed of his vessel is one of the most important conditions for accident-free navigation. The movement of the vessel relative to the bottom at a speed calledab solute,
is considered in navigation as the result of the addition of the vessel’s speed vector relative to the water and the current vector acting in the navigation area. In turn, the vector of the ship’s speed relative to the water(attributebody speed)
is the result of the work of ship propulsors and the action of wind and waves on the ship.
In conditions of absence of wind and waves, it is most simply determined by the speed of rotation of the propellers.
S about = V about t, (38)
where V rev is the speed of the vessel, determined by the speed of rotation of the propellers, knots; t- vessel voyage time, hours.
However, this method is inaccurate, since it does not take into account changes in the condition of the vessel (fouling of the hull, changes in draft), the influence of wind and waves. The speed of the ship relative to the water is influenced by the following factors.
1. Degree of loading, list and trim of the vessel. The speed of the ship changes with the change in draft. Typically, in good weather conditions, a ship in ballast has a slightly higher speed than when fully loaded. However, as wind and waves increase, the speed loss of a vessel in ballast becomes much greater than that of a fully laden vessel.
Trim has a significant influence on the change in speed. As a rule, bow trim reduces speed. A significant trim to the stern leads to the same results. The optimal trim option is selected based on experimental data.
The presence of a ship's roll causes its systematic departure from a given course towards a higher side, which is a consequence of a violation of the symmetry of the contours of the part of the hull submerged in water. For this reason, you have to resort to shifting the rudder more often to keep the ship on course, and this in turn leads to a decrease in the speed of the ship.
2. Wind and waves usually act on the ship simultaneously and, as a rule, cause losses in speed. Headwinds and waves create significant resistance to the movement of the vessel and impair its controllability. The speed loss in this case can be significant.
Winds and waves in the following direction reduce the speed of the vessel mainly due to a sharp deterioration in its controllability. Only with a weak tailwind and slight waves do certain types of vessels experience a slight increase in speed.
3. Hull fouling is observed when ships are sailing in any conditions, both in fresh and salt water. Fouling occurs most intensively in warm seas. The consequence of fouling is an increase in water resistance to the movement of the vessel, i.e. reduction in speed. In mid-latitudes, after six months the decrease in speed can reach 5 - 10%. The fight against fouling is carried out by systematically cleaning the ship's hull and painting it with special non-fouling
overgrowing colors.
4. Shallow water. The effect of shallow water on reducing ship speed
begins to take effect at depths in the navigation area
H≤4Tcp + 3V 2 /g,
Where N - depth, m.
Tcp, - average draft of the vessel, m;
V- vessel speed, m/s;
g- acceleration of gravity, m/s 2.
Thus, the dependence of the ship's speed on the speed of rotation of the propellers, determined for specific sailing conditions, will be violated under the influence of the listed factors. In this case, calculations of the distance traveled by the vessel, made using formula (38), will contain significant errors.
In navigation practice, the speed of a vessel is sometimes calculated using the known relationship
V=S/ t,
Where V- speed of the vessel relative to the ground, knots;
S - distance traveled at a constant speed, miles; t - time, h.
Accounting for the speed and distance traveled by the vessel is carried out most accurately using a special device - a log.
To determine the speed of the vessel, measuring lines are equipped, the areas of which are subject to the following requirements:
lack of influence of shallow water, which is ensured at a minimum depth determined from the relation
N/T≥ 6,
Where N- depth of the measuring line area, m; T- vessel draft, m;
protection from prevailing winds and waves;
the absence of currents or the presence of weak constant currents coinciding with the directions of the runs;
possibility of free maneuver of vessels.
Rice. 23. Measuring line
The measuring line equipment (Fig. 23), as a rule, consists of several parallel cutting sections and one leading section perpendicular to them. The distances between secant sections are calculated with high accuracy. In most cases, the line of passage of ships is indicated not by the leading line, but by buoys or milestones placed along it.
Typically, measurements are taken at full load and in ballast for the main operating modes of the engines. During the period of measurements on the measuring line, the wind should not exceed 3 points, and waves - 2 points. The vessel should not have a list, and the trim should be within optimal limits.
To determine the speed, the ship must take a compass course perpendicular to the secant lines and develop a given speed of rotation of the propulsors. The duration of the run is usually measured using three stopwatches. At the moment of crossing the first transect, stopwatches are started and tachometer readings are noted every minute. The stopwatch stops when the second cross section is crossed.
Having calculated the average run time according to stopwatch readings, determine the speed using the formula
V = 3600S/t, (39)
where S is the length of the run between secant sections, miles;
t- average duration of the run between cutting sections, s; V- speed of the vessel relative to the ground, knots.
The rotational speed of the propulsors is determined as the arithmetic average of the tachometer readings during the run.
If there is no current in the area of the measuring line, then the velocities relative to the ground and water are equal. In this case, it is enough to make just one run. If there is a current in the maneuvering area that is constant in direction and speed, it is necessary to make two runs in opposite directions. Relative speed of the vessel V 0 and rotational speed of the propulsors P in this case will be determined by the formulas:
Vo=(V 1 +V 2)/2, (40)
n=(n 1 + n 2)/2, (41)
Rice. 24. Graph of the dependence of speed on the speed of rotation of the propulsors
where V 1, V 2 are the vessel’s speed relative to the bottom on the first and second runs; n 1 and n 2
- rotation speed of the propulsors during the first and second runs.
When there is a uniformly changing current in the area of the measuring line, it is recommended to make a third run in the same direction as the first, and the speed free from the influence of the current is calculated nO approximate formula
V 0 = (V 1 + 2V 2 + V 3)/4. (42)
If the nature of the change in the flow is unknown or they want to get a more accurate result, then make four runs and the speed is calculated using the formula
V 0 = (V 1 + 3V 2 + 3V 3 +V 4)/8. (43)
The average rotation speed of the propellers in these cases is calculated for three and four runs, respectively:
n = (n 1 + 2n 2 + n 3)/4; (44)
n = (n 1 + 3n 2 + 3n 3 +n 4)/8. (45)
In this way, the speed and rotation frequency of the propulsors are determined for several modes of operation of the main engines in cargo and in ballast. Based on the data obtained, graphs are drawn of the dependence of speed on the speed of rotation of the propulsors at different loads of the vessel (Fig. 24).
Based on these graphs, a table is drawn up that corresponds to the speed of the propellers and the speed of rotation of the propellers or a table that corresponds to the speed of the propellers and the speed of the vessel.
If, based on the results of passing the measuring line, any speed and the corresponding propeller rotation speed are known, then the speed value can be calculated for any intermediate value of the propeller speed using the Afanasyev formula
V AND =V 0 (n 1 /n 0) 0, 9, (46)
where V 0 - known speed at propulsion speed n 0 ; V And, - the desired speed for the speed of rotation of the propulsion n 1 .
Thus, having determined the speed of your ship from a graph of its dependence on the speed of rotation of the propellers, you can calculate the distance traveled in nautical miles using the formula
where V 0 - ship speed, knots; t- swimming time, min.
If the distance traveled is known, then the swimming time is calculated:v
Using these formulas, the tables “Distance by time and speed” and “Time by distance and speed” were compiled in MT - 75, appendices 2 and 3, respectively.
Calculations of the distance traveled using the speed determined from the screw speed V o6 are performed only in the absence of a lag or to control its operation.
