Determination of the ship's speed on the GDP. Methods for determining ship speed and distance traveled
The speed of a vessel during speed tests is found in various ways.
It is widespread to determine the speed of a vessel on special measuring lines equipped with coastal secant (transverse) sections, the distance between which is precisely known. On the measuring line, the speed of the vessel is determined by the time it takes the vessel to travel a known distance between the targets. This method is one of the most accurate ways to measure the speed of a ship.
Cable measuring lines, which are some kind of the mentioned measuring lines with transverse sections, are also known to be used. On the cable measuring line, the vessel passes over electrical cables laid at the bottom of the fairway across the direction of the vessel's movement. An electric current is passed through the cables, the distance between which must be precisely known. Special electronic equipment installed on the ship records the moment the ship passes over the cable.
IN Lately Various radio navigation systems, in particular phase ones, began to be widely used to measure ship speed.
The ship's speed, with relatively less accuracy, can also be measured using the ship's own radar station, which successively, at short intervals, measures the distance to a specific object that reflects radio waves well.
Measuring the speed of a ship using the fan of bearings of two objects or using other navigational methods, for example, using lighthouses, the distance between which is known, is not sufficiently accurate.
All of the above and many other methods, including the main method of determining the speed of a ship on a measuring line, have one common drawback, which is that the speed of the ship is found relative to the shore, not the water. In this case, the measurements are affected by the influence of wind or tidal currents, which is difficult to accurately assess. Meanwhile, when conducting speed tests and for further use of the obtained data, it is necessary to know the speed of the vessel relative to the surrounding water, i.e. in the absence of a current. Therefore, the conditions and location of the tests are chosen in such a way that the influence of the flow is minimal or is directed, if possible, along the measuring section. In these cases, the vessel's runs on the measuring sections are carried out in mutually opposite directions and in a certain sequence.
Despite some difficulty, determining the speed of a ship on a measuring line or using radio navigation aids should always be preferred to measuring speed using standard ship and special logs or hydrometric meters due to the low accuracy of the latter, although they measure the speed of the ship directly relative to the water.
For speed tests, measuring lines should be used that are located close to the place where the vessel is built or based, which will save time and fuel required to approach the measuring line. In addition, due to fuel consumption when moving to a distant measuring line, it is difficult to ensure the specified value of the vessel's displacement.
The depth of water in the area of the measuring line, i.e. its measuring section and on the approach to it (on both sides), as well as in the area where the vessel turns on the reverse course, must be sufficient to eliminate the influence of shallow water on the resistance of water to the movement of the vessel , and therefore on its speed.
It is known that the wave system created by a ship when it moves in shallow water differs from the wave system in deep water and depends on the regime characterized by the so-called Froude number in shallow water
Where σ is the speed of the vessel, m/s; g-acceleration free fall, m/s2; H - fairway depth, m.
A change in the nature of wave formation leads to an increase or decrease in the resistance to the movement of the vessel and, therefore, affects its speed.
At the same time, a counter-current of water develops, increasing the speed of flow around the hull and, consequently, the frictional resistance of the vessel. Complete exclusion of the influence of shallow water requires large depths of the measuring line, which are not always possible to provide (Table 1).
Table 1. Values of the minimum depth of the measuring line, m 
As a result, when determining the minimum required depths, it is usually assumed that the speed loss due to the influence of shallow water is 0.1% of the measured value. To comply with these conditions, the value Frh≥0.5 must be taken for wave resistance, and for friction resistance 
It is based on this approach that the test rules developed by the 12th International Conference of Experimental Pools recommend taking the minimum permissible depth on the measuring line greater than that calculated using the formulas 
where B and T are the width and draft of the vessel, respectively. A similar method is recommended by the domestic standard OH-792-68, however, the formulas are written in the form
If possible, the measuring line should be located in an area protected from prevailing winds and sea waves. Finally, a prerequisite is the presence of sufficient space at both ends of the measuring line, necessary for the free maneuvering of the vessel at the end of the run on the measuring section, turning back and accelerating after the turn.
Permissible deviations in water depth at the approaches to the measuring section of the measuring line should not exceed ±5%.
The vessel's course on the survey line must be at least two to three miles from coastal hazards. Failure to comply with this condition creates the risk that the ship at high speeds, even if maneuvered correctly, may run aground if the rudder jams.
It is not always possible to satisfy all the above requirements, therefore the number of full-fledged measuring lines is very limited.
In table 2 shows some data characterizing the measuring lines of a number of foreign countries. As can be seen from the table, the length of the measuring sections of these lines is different, and the depths of many of them are insufficient for testing relatively high-speed vessels.
| Measuring lines | Length of measuring section, mile | True course of the vessel, degrees | Depth of the measuring line during the strongest low tides, m |
| England | |||
| Skelmorlie Gao Loh Abs-Hid Polperro Portland Mouth of the river Tyne Plymouth |
1 1 1 1,15 1,43 1 1 |
0 and 180 156 and 335 111 and 191 86 and 226 134 and 314 161 and 341 93 and 273 |
65-75 30-40 44-52 31-37 31 20 20-28 |
| Denmark | |||
| O. Bornholm | 1 | - | 70-80 |
| France | |||
| Porquerolles-Taya: 1st section 2nd 3rd Croix Trevignon |
3,50 2,36 4,70 5,6 |
48 and 228 48 and 228 48 and 228 120 and 300 |
70-80 70-80 70-80 40 |
| USA | |||
| Rockland | 1 | 0 and 180 | - |
In Fig. Figure 3 shows a diagram of the measuring line near Rockland (USA), on which the a large number of high-speed testing of vessels, including research vessels. This line satisfies most of the above requirements, but it is not protected from the westerly winds and the waves they cause. The length of the measuring section is one nautical mile (1852 m), the length of each acceleration section is three nautical miles. The measuring line is equipped with two coastal transverse (secant) sections perpendicular to the measuring section. One of the transverse sections is equipped with three signs (shields), the other with two.
Rice. 3. Scheme of the measuring line in Rockland (USA). Δ - leading sign.
In addition, along the line of travel, to guide the navigator, milestones are placed indicating the boundaries of the acceleration and measuring sections.
Many measuring lines are equipped with so-called leading sections, on the line of which the measuring section is located. Currently, the presence of a leading gauge is not considered mandatory, although there is still an opinion that it is necessary in cases where there is a current in the area of the measuring line that does not coincide with the direction of the measuring line. However, this opinion is incorrect: simple geometric constructions show that in this case, when steering the ship along the leading line in the same way as with a compass, the ship travels a distance greater than the distance between the lines of the lines. That is why the requirement is put forward that the direction of the flow coincides with the direction of the measuring line or, in any case, makes an angle with it that does not exceed 15-20°.
Leading marks (Fig. 4) of measuring lines are shields that are installed at such a height that they are clearly visible from the sea. Typically, the front shield, i.e., the shield located closer to the measuring section of the measuring line, is installed slightly lower than the rear shield in such a way that when the vessel passes the target, the shields overlap each other, making up almost one whole in the vertical direction. In the middle of the shields, vertical brightly colored stripes are applied, which should also be clearly visible from the sea.
Rice. 4. Leading marks of the measuring line.
Rice. 5. Linear sensitivity of the targets.
1 - front target sign; 2 - rear target sign.
However, an observer on a ship crossing the transverse sections of the measuring line at right angles can practically not absolutely accurately determine the moment of passage of the target line, that is, the moment when the middle strips of the shields are on the same vertical straight line, as if forming a continuation of each other friend.
The magnitude of the error in determining the moment of complete coverage of the middle strips of the target shields depends on the so-called linear sensitivity of the target (Fig. 5).
The resolving power of a normal eye is equal to one arc minute. Let us plot on the ship's line of travel along the measuring line (Fig. 5) the segment A1A2, corresponding to one minute of arc. In the interval A1A2, the angle between the two signs is less than one minute, and, therefore, any point in this interval can serve as the mark for the start of speed measurement. The value OA1=OA2 is called the linear sensitivity of the target and is further denoted by the letter W.
To find an expression for W, we use the relation
tgα=tg(β-γ). (1.2)
converted to the form
After substituting the values of tan β and tan γ into expression (1.3) and simple transformations, we will have
The first term on the right side of expression (1.4) can be neglected, since it will be of a higher order of smallness compared to the two subsequent ones. Then equation (1.4) will take the form
dW = tan αDc (Dc + d), (1.5)
where
By replacing the tangent of the angle with an arc and the angle with the value of the resolution of the eye, and also introducing the coefficient of illumination of the target a" (for daylight α" = 2 and for night light α "= 3.5), we obtain the value of the linear sensitivity of the target (in meters)
Where
Dс - distance from the front cross section mark to the running gear of the measuring line, m; ao is the angle of resolution of the eye; d - distance between leading signs, m.
Let us present the sensitivity values of secant sections of one of the foreign measuring lines:
If we take the sensitivity of a pair of alignments equal to half the possible absolute error, then the relative error in the length of the measuring section of the line (ranges 2-3) will be equal to 0.4%.
As can be seen from formula (1.6), in order to reduce the error in determining the distance between the targets and, consequently, increase the sensitivity of the targets, it is necessary that the ratio Dc: d be as small as possible. However, in practice this ratio is usually never less than three.
To assess the influence of an error in timing, as well as the influence of the sensitivity of the targets and the length of the line of travel on the speed measurement results, it is necessary to consider the dependence of the vessel speed on the path and time
ν=s/t (1.9)
where v is the arithmetic mean of several speed measurements, m/s; s - arithmetic mean value of the path, m; t - arithmetic mean value of travel time, s.
As is known, the error in the result of indirect measurements (speed is calculated from the measured path and time) is composed of the errors in the results of each direct measurement included in the indirect one. In indirect measurements, the relative error (root mean square, probable or limiting) of each direct measurement is found and the total relative error of the indirect measurement is calculated. Yes, in this case
where εν is the relative error of speed measurement, .%; εs - relative error of path measurement; εt is the relative error in measuring travel time.
Expressing relative errors in terms of probable ones, we obtain
or, after substitution t = s/v.
Where ρs is the probable error in measuring the path, m; ρt is the probable error in measuring travel time, s (according to ρt = 0.5 s). Probable path measurement error
if the sensitivity of both settings is assumed to be the same and equal to half the sum of their sensitivities, and the number of runs in the mode is equal to three.
Substituting these values into formula (1.12) and transforming it, we obtain
Thus, the magnitude of the error will depend on three components: the sensitivity of the secant sections, the length of the run along the measuring line and the speed of the vessel.
As an example in table. Figure 3 shows data on the accuracy of measuring the speed of a vessel on one of the measuring lines. Based on these data, we can conclude that the measured speeds, regardless of the speed of the vessel, are determined with a high degree of accuracy. Thus, in the section of the measuring line between the second and third alignments, the errors in measuring speed are 0.35-0.40%. As the length of the measuring line increases (the section between the first and second gauges is one mile, between the second and third gauges - two miles, and between the first and third - three miles), the error in speed measurement decreases sharply.
| Vessel speed, knots | Average sensitivity of targets, m | ||
| 12.8 (section between the first and second sections) | 14.9 (section between the second and third sections) | 13.0 (section between the first and third sections) | |
| 8 12 16 20 24 28 32 36 30 |
0,58 0,59 0,61 0,63 0,66 0,69 0,72 0,75 0,79 |
0,33 0,34 0,35 0,36 0,37 0,38 0,40 0,42 0,43 |
0,20 0,20 0,21 0,22 0,22 0,23 0,24 0,25 0,26 |
However, this does not mean that it is more expedient to make runs on long measuring lines, since this increases the errors caused by the possible uneven operation of the main mechanisms over a long distance and the influence of disturbing external influences leading to deviation of the course from a straight line.
When assigning the length of the measuring section of the measuring line, it should also be taken into account that during high-speed tests (in the absence of automatic equipment for recording instrument readings), it is sometimes necessary to measure the torque on the propeller shaft at least eight to ten times or take indicator diagrams once or twice, and also measure the speed of rotation of the propeller shafts several times and determine some parameters of the operation of the power plant. All this takes at least four minutes. Thus, the minimum run length s on the measuring line, which is a function of the time required to perform these measurements and determine the speed of the vessel, can be calculated using the formula
s = 0.067νs (1.15)
where νs is the speed of the vessel, knots, s is the mileage of the vessel, miles.
A dimensional coefficient of 0.067 corresponds to approximately 4 minutes, i.e. the time required to perform measurements.
05/12/2016
In order to become navigator professional, you need to read a lot of navigation, authored by scientists. In this article, using a simple language not loaded with complex terminology, we will try to find out - what speeds do the navigator take into account?.
When we talk about the speed of a ship, we consider two quantities. One of them - this is the movement of a ship on water. Direct connection between the propulsion unit, the hull of the vessel and the aquatic environment. The second is movement of a ship in relation to world space. This is the path, the segment that we have covered in a certain time. The fact is that the world Ocean and the entire water shell of the Earth are not static. She is free in her movement, although she is subject to physical laws. The system of world waters, their interaction, creates the movement of water masses, and a sea vessel, along with any straw, participates in this movement on a colossal scale. Also, do not forget about in the wind, which also affects the speed of the ship. More details about everything.
STW— Speed Through the Water — Vessel speed relative to water
SOG— Speed Over Ground — Vessel speed relative to ground
Knot—Knot— a unit of measurement for ship speed. Nautical miles per hour.
So, we are on watch, going from point A to point B. At full speed, the propeller is thrashing the water, our ship, swaying on the waves, cuts the water with its stem. - this is the water in which our ship, its hull and propeller are immersed. With positive operation of this system, the vessel, like a physical body, moves in the aquatic environment, receiving support. Let's compare this to a swimmer who methodically rows from one wall to another in a pool. His body moves through the water, which is limited by the walls of the pool and has no current that would affect the swimmer. Using only his physical strength, he overcomes the distance, walking along the water.
Let's return to our ship. Since it is located in the system of world currents, then this entire mass of water moves in a certain direction, carrying the ship with it. If we stop our ship, STW will be 0. But we will move around the globe along with the water, moving from one point to another. Let's get the ship moving again. Added to the navigation map location. Spotted time. New applied location. Measured distance traveled, divided by time, what we detected. We obtained the speed of the ship relative to the ground - SOG. Abstractly, consider our ship as a physical point that moves around the planet at a certain speed. 
Let's remember our swimmer. After the pool we invited him to swim in the river. At first he tried not to row, and he was carried downstream. The speed of movement relative to coastal objects became equal to the speed of the current. He began to row upstream. To return to the place where he started, he had to swim faster than the current. He swam quickly relative to the water ( STW), like in a swimming pool. But relative to coastal objects, his body did not move so quickly. The river current “ate” him SOG. And on the contrary, if he swam downstream, it would help him move.
Lag- a device for measuring the speed of a ship on water (there are different types, more details). These are the simplest and most primitive examples. To fully understand the picture, the navigator should learn the basics vector geometry, namely, addition and subtraction of vectors.
In modern navigation we have at our disposal a device satellite observation — GPS, which continuously gives location vessel, respectively, calculating SOG, which undoubtedly helps the navigator during work.
Next, on SOG can have a significant impact by creating wind drift. Especially, it affects ships with great windage yu, such as container ships, RO-RO, passenger ships, large tankers in ballast displacement and others. For example, in a strong headwind SOG will decrease, and vice versa, with a favorable direction the wind will “help” the ship overcome the resistance of the water.
We hope this introductory article will become “ Navigation. First steps. Vessel speed." will help you in understanding science Navigation .
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Navigation. First steps. Vessel speed. (c) NavLib
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 called absolute, 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 (attributebodyspeed) 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.
Knowing the speed makes it possible to determine the distance traveled by the ship S about in miles:
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 loss in speed 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 aft 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 agents.
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 vessel, m;
V- vessel speed, m/s;
g- gravity acceleration, 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 cross-section, 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 using 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 ship.
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.
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 operation is very high.
Logs of all systems, like any other devices, cannot give absolutely accurate readings; they require periodic verification 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 |
Rice . 5. 3 . 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
