When the vessel moves in shallow water, an increase in the draft of the hull is observed. This phenomenon is called drawdown.

The main reason for the occurrence of subsidence is a decrease in the hydrodynamic forces supporting the ship's hull due to an increase in the flow rate between the bottom of the ship and the ground. The smaller the distance from the bottom of the vessel to the bottom and the greater the speed of the vessel, the greater will be the amount of drawdown (Fig. 8.3). In addition, the speed of the flow around the bottom increases due to the operation of the propellers.

With a small supply of water under the bottom (when< 1,2 ÷ 1,5) и движении судна с критической скоростью (V) it is possible not only to touch the ground, but also for a short-term suction of small vessels to the bottom.

Let us assume that when the vessel moves through deep water (position 1 in Fig. 8.3), the flow of oncoming water flows under the bottom of the hull at a speed V about. In this case, the hydrodynamic force of supporting the vessel R o acts evenly over the entire area of ​​the bottom and ensures the buoyancy of the vessel with the same draft of the bow and stern ( T ko \u003d T but). When the ship starts to enter

Fig. 8.3 Scheme of the formation of a ship's drawdown.

in shallow water (position P), the water resistance in the bow increases, and the speed of the oncoming flow under the bottom V 1 increases ( V 1 > V about). As a result, the hydrodynamic force of supporting the hull R 1 decreases and causes the ship to trim aft ( T k1 > T n1). With a further decrease in the water supply under the hull, the movement of the ship (position W) is accompanied by an increase in the rate of water flow under the bottom ( V2 > V1) and a decrease in the support forces ( R 2< Р 1 ). In this case, the trim of the vessel to the stern increases ( T k2 > T k1) and the ship receives some total draft increment.

Further movement of the vessel in conditions of minimum depths (position 1V) and at high speed is characterized by an increase in the total resistance of water to the movement of the vessel R, the formation of a large bottom wave at its stern and the maximum total drawdown of the vessel. In this case, the total draft of the ship amidships T cf3 significantly exceeds the ship's draft when moving through deep water T cf0.

Drawdown ΔT depends on the speed ratio V, precipitation T ship and the depth of the ship's course H, as well as from the contours of the ship's hull. It can be determined by field tests or calculations.

Total Draft Increment ΔT (in m) when moving in shallow water, it is recommended to determine for single vessels according to the formula of A.M. Polunin

ΔT =(0,08 + 0,34 ) . (8.3)

V- speed of the vessel (composition), m/s;

T– draft, m;

h- depth of the ship's passage, m;

g– free fall acceleration of the body, m/s 2 .

With a ratio of 1.4, it is convenient to determine the increment of precipitation by the formula of G.I. Suchomela and V.M. Zass

ΔT \u003d mV 2, (8.4)

where m- numerical coefficient depending on the ratio of the length of the vessel L to the width of the ship's hull AT(see table 8.1);

When a ship moves from a deep-water fairway to shallow water, wave formation increases, resistance increases and speed decreases. In shallow water, at a sufficiently high speed, the ship will receive a trim to the stern, and near the middle of the ship the water level will noticeably decrease - a large depression is formed, where the support force will decrease. Therefore, the vessel can increase the draft compared to the draft in deep water. The greater the draft of the vessel, the smaller the gap between the hull and the bottom, and, consequently, the relatively greater the speed of the water flow under the hull. Therefore, the vessel, while moving in shallow water, will be sucked to the bottom (usually by the stern). This phenomenon is especially characteristic of vessels with flat bottoms. The additional draft of the vessel increases with increasing speed and may cause damage to the hull or propellers when passing through an area with shallow depths. The increase in draft during movement in shallow water for some types of ships reaches 0.5 m.

In the event of an unexpected approach to a shallow place, the bow of the vessel may abruptly “push off” from it due to a sudden increase in water resistance, and also because the water in front of the bow will be displaced into a shallow place, pushing the vessel to a greater depth.

If the vessel is sailing in shallow water with variable depth, then the correct direction of the vessel's movement must be maintained by frequent rotation of the steering wheel. The narrower and shallower the fairway and the faster the ship moves, the faster and more disorderly the stern waves will overtake the ship, acting unevenly on its stern, now from one side, then from the other. At the same time, the water pressure on the rudder blade changes all the time. The described phenomena cause the vessel to yaw, especially when approaching from a deep place to a shallow one. This is most dangerous when passing from oncoming vessels, as it can cause the vessel to be stranded, damage to the hull, and collision of vessels.

Therefore, in a shallow fairway, the speed should be reduced in order to reduce the additional draft and yaw of the vessel and thereby ensure greater traffic safety and improve controllability.

Chapter XII. WAVE FORMATION AND SUCTION OF MOVING VESSELS

WAVE GENERATION

The vessel, when moving, displaces the water, pushing it in front of it. After the passage of the vessel, the water fills the volume released behind the stern. Overcoming the resistance of water, the ship sets its particles into oscillatory motion, which, due to the elastic properties of the water surface, propagates in the form of waves. Wave formation is different and depends mainly on the size of the vessel, the contours of its hull, draft, width and depth of the fairway. With an increase in the speed of the vessel, the size of the will grows according to the law of the square of the speed. Wave formation, as already mentioned, consumes the energy of motion.

With an increase in the speed of a displacement vessel, the water level at the bow rises noticeably, forming a system of bow waves. A diagram of the formation of waves during the movement of a displacement non-fast vessel on calm water is shown in fig. 105. Along the sides in the middle part of the vessel following in the navigation mode, the water level decreases, forming a depression. In the stern of the vessel, the water level rises again, forming a system of stern waves.

Rice. 105. Scheme of wave formation when the ship is moving on calm water BUT- nasal diverging waves; B - stern diverging waves; AT- stern transverse waves

Bow waves are subdivided into diverging bow waves and bow transverse waves.

Bow diverging waves, like whiskers, extend from the stem of the ship on both sides. Their front is located at an angle of about 40 ° to the direction of movement, and the middles are on straight lines, making an angle of about 20 ° with the diametral plane. The waves are short in length.

Bow shear waves, perpendicular to the direction of motion of the vessel, originate together with divergent bow waves and propagate between them. Transverse bow waves move in the direction of the vessel's motion, gradually increase in length from bow to stern, and decrease in height.

Stern diverging waves begin somewhat ahead of the sternpost from both sides of the ship. They are smaller than the bow waves and have the same angles with the direction of the vessel as the bow diverging waves.

Stern transverse or so-called "satellite" waves begin in the same place as stern divergent ones, but they are more intense, as they are located behind the propellers. As they move away from the stern, where they are equal to the width of the vessel, the waves decrease in height, but increase in length.

With an increase in the speed of movement, the wave formation increases. In shallow water, the length of the diverging waves and the angle between them increases and can make an angle of 90 ° with the diametrical plane of the vessel. Depending on the depth of the fairway, with the achievement of a certain high speed by the vessel, divergent waves, together with transverse waves, form a powerful wave system. The wave moving together with the vessel in the area of ​​the zygomatic formation or in the area of ​​the stern of small high-speed vessels and boats is called a single wave or a displacement wave. The wave of movement is typical for ships with blunt zygomatic formations, as well as tugboats moving without caravans.

Wave formation depends not only on the speed, but also on the relationship between the speed and the length of the ship. Short ship calls big waves at low speed, and a long ship would need a very high speed to generate the same waves. Between the places of formation of the bow and stern wave systems at the ends of the hull, in the middle part of the sides of the vessel, lowered water horizons (depression) are formed. Compared to the normal water level in the depression, it decreases with an increase in wave formation and a decrease in the depth of the fairway. Thus, when the vessel is moving at full speed along the entire length of the hull, there are three main zones of influence of hydrodynamic fields: two zones of increased pressure, where repulsive forces act in the bow and immediately near the stern, and a zone of reduced pressure along the side of the vessel. The center of the low pressure zone in wheeled vessels is the hollows of the vessel's wheels. In screw steam ships, the low pressure zone is somewhat shifted aft. This pattern is especially well seen when the ship moves along the fairway with low current velocities.

When the ship passes over the shallows, the stern wave system changes sharply, and the first transverse wave increases in height. This transverse wave in shallow water is called a bottom wave. The appearance of a bottom wave behind the stern of the vessel indicates that the depth under the keel of the vessel is decreasing. This is used to control the correct movement of the vessel.

SUCTION OF VESSELS

In maritime and especially in river practice, there are many cases of collisions of ships when they diverge at a meeting or overtaking when moving in parallel courses at a short distance from each other due to the increased speed and movement of water between their hulls. According to the Bernoulli equation, this increase in water velocity between the ships leads to a decrease in pressure between them compared to the pressure from the outer sides. There is a hydrodynamic attraction of ships on parallel courses, which increases with an increase in the relative speed of their movement. This phenomenon is called ship suction.

The suction of vessels increases with the difference in hull dimensions and acts more strongly on a vessel of smaller mass.

The probability of suction increases with decreasing distance between diverging vessels and with increasing their speed. Suction depends on the shape of the vessels. On fig. 106 shows the interaction between two identical ships diverging on a collision course at close range from each other. Both vessels are single-rotor, with right-hand pitch propellers. The arrows show the direction of deviation of the extremities of the vessel in different positions of the vessels in relation to one another. In position III, on parallel courses, the hydrodynamic fields with a minus sign coincide, i.e., depressions, and the ships can stick to each other's sides. In this case, each of the vessels appears to roll towards the other vessel.

Rice. 106. Interaction between ships diverging at a close distance from each other. The arrows show the direction of the ends of the vessel

The list is explained by the lowering of the water level between the sides due to the increase in current velocities in the gap between the two vessels compared to the current velocities relative to the outer sides of the vessels, where the level is higher.

In addition, suction depends on the interaction of wave systems formed by vessels. The interaction of wave systems is also the cause of the emergence of attractive forces between ships diverging at a considerable distance from each other.

The suction of a smaller vessel to a larger one increases if the smaller vessel enters the wave zone of the larger vessel. As the distance decreases, the interaction between ships increases. Therefore, in order to prevent collision of vessels during overtaking, the overtaking vessel should go as far as possible from the overtaken vessel, if possible, outside the zone of wave formation of the overtaken vessel, which, in turn, must reduce its speed to reduce wave formation.

Suction has a sharp effect when a single vessel overtaking towed trains, the barges of which suddenly acquire yaw (Fig. 107). Small vessels are especially susceptible to the suction action of ships when passing, when overtaking and when meeting with ships of larger displacement (Fig. 108). A collision from suction is observed due to the recklessness of navigators of small boats, their violation of the elementary rules of overtaking and divergence.

The basic rules for overtaking and passing are as follows:

1) when overtaking and passing by, ships should pass as far as possible from each other;

2) on narrow fairways, on rivers, in canals, divergent ships must reduce their speed to the lowest possible;

Figure 107. Action of an overtaking single vessel on tugboats: I - the vessel is approaching non-self-propelled vessels being overtaken; II - the vessel passes by non-self-propelled vessels being overtaken

Rice. 108. Suction of a small vessel to a large one

3) at the first sign of suction between two ships of approximately the same size, the course should be stopped.

It must be remembered that when sucking, the ship does not obey the rudder well, even if the rudder is put on board.

In the event of a collision of boats with the sides, there can be not only damage to the hull, but also people falling overboard due to a sudden shock, injuries to those holding their hands on the gunwale, standing on the run-out, etc.;

4) overtaking by a small vessel of a vessel of a larger displacement should take place in such a way that the overtaking smaller vessel goes to overtake, i.e., the traverse of the sternpost of the vessel being overtaken is outside the zone of its stern wave formation. It is strictly forbidden for small vessels to overtake large vessels from under their stern. This leads not only to a loss of control, but also to capsizing a small vessel by the stern wave system, sucking it in when the overtaken vessel leaves the stern wave system into its cavity, etc.

A ship moored near the shore is affected by waves from ships moving in close proximity along a roadstead, river or canal. Under the influence of suction and oncoming waves moving in close proximity along a raid, river or canal. Under the action of suction and oncoming waves of moving vessels, the moored vessel experiences oscillations, due to which the mooring ends may burst, ladders, various cargoes and mechanisms may fall. Therefore, ships passing by should slow down.

It is advisable for a smaller vessel to overtake a larger one, having previously left the wave formation zone of the overtaken vessel at a distance not less than one length of the hull of the overtaken vessel with a sufficient fairway width.

It is recommended to overtake and diverge when meeting motor boats and hydrofoils in the displacement mode.

It should be remembered that when ending overtaking, you need to stay as far as possible from the bow of the vessel being overtaken; Failure to comply with this recommendation will result in the overtaking vessel falling under the stem of the larger vessel being overtaken. This can cause the death of not only a small vessel on inland waterways, but also the cause of the death of large sea vessels overtaking even larger ships.

The estimated draft of the vessel can be determined from sediment chart . The arguments for entering the chart are the deadweight/displacement of the ship and the total moment M x. As a result, we get drafts fore and aft and the trim of the vessel.

You can determine the ship's draft from a diagram called cargo size . In the cargo size, the dependence (in the form of a curve) of the vessel's displacement on the average draft is given. If this dependence is presented in the form of a table, then it turns out load scale . In addition to this, the load scale gives:

Deadweight;

Freeboard;

Number of tons per 1 cm of precipitation

The weight scale is ship's main cargo document. The load gauge and load scale are built for the ship's draft on an even keel with no hull bend. When trimming and bending, corrections must be made.

(a) Determination of average draft forward Tn av, stern Tk av, T Ä av.

Tn avg = (Tn l / b + Tn p / b) / 2(11.6)

Tk cf = (Tk l / b + Tk p / b) / 2(11.7)

T Ä av = (T Ä l/b + T Ä p/b)/2(11.8)

(b) Calculation of the average draft of the vessel.

There are several ways to calculate the average draft of a ship. In fact, it is very important to calculate the ship's draft as close as possible to the actual one, since it is extremely rare for a ship to be loaded on an even keel without heeling (only then the average draft corresponds to the calculated average draft and each of the drafts in particular). If the vessel is loaded with a certain trim and/or heel, then all drafts of the vessel have to be reduced to the average draft in order to calculate the amount of loaded cargo. In fact, this is not entirely correct, because the same average draft from the “trim to the bow” and “trim to the stern” positions will give the same amount of loaded cargo, in fact it is different due to the different contours of the vessel in the bow and stern, different weight bow and stern superstructures, different volumes of rooms submerged under water and displacing different amounts of water.

In addition, the ship is usually not completely inflexible. Depending on how the cargo is distributed in cargo spaces and ballast tanks, the ship may have deflection arrow in one direction or another, with an uneven and asymmetric arrangement of the load and ballast, more complex bending moments can be obtained, which are extremely difficult to fully calculate.

However, at the moment there is no simple methodology that allows to determine the ship's displacement from the actual draft of the vessel, therefore, the method of determining the average draft of the vessel is used to obtain further displacement. For these calculations, we also need to know the value trim vessel.

(c) Calculation of the average draft of the vessel from the bow and stern drafts.

This is a simplified version of the average draft calculation:

Тср = (Тн ср + Тк ср)/2(11.9)

It is used in approximate calculations, or on ships, the bending moment of which can be neglected.

(d) Calculation of the average draft of the vessel from eight drafts.

The most commonly used calculation option:

Тav = (Тн av + Тк av + 6Т Ä av)/8(11.10)

This calculation option quite accurately reflects the average draft, taking into account the deflection arrow.

(e) Calculation of the average draft of the ship in a composite way

Determine the average draft:

T 1 \u003d (Tn + Tk) / 2(11.11)

Let's define the average draft:

T 2 \u003d (T 1 + T Ä) / 2(11.12)

Tav = (T2+ T Ä) /2(11.13)

(e) Calculation of the average draft of the vessel by the "half" method

Determine the average draft of the bow half of the vessel:

T 1 \u003d (Tn + T Ä) / 2(11.14)

Let us determine the average draft of the stern half of the ship:

T 2 \u003d (Tk + T Ä) / 2(11.15)

Determine the average of the average sediment:

Тav = (Т1 + Т2)/2 (11.16)

(g) Trim calculation

d \u003d Tn avg - Tk avg(11.17)

The trim is calculated in meters, it can be both positive and negative.

(g.1.) Calculation of the correction for trim. The need to calculate the correction for precipitation for trim.

Each vessel has its own dimensions necessary for the best solution of the tasks assigned to the vessel. All calculations use length between perpendiculars (LBP). This is one of the main characteristics of the ship. Draft at the bow or stern perpendicular corresponds to the draft of the vessel fore or aft. However, the sediment scales are not opposite the perpendiculars. Since they are shifted, they do not show the exact draft of the bow or stern, but the local draft of the vessel and require the introduction of an amendment. Also, the draft along the midsection should be taken from the scale located at a distance of not more than 0.5 m from the midship frame. Otherwise, correction and drafts amidships are required.

(g.2) Calculation of the nose draft correction for trim

∆Н = (f x d)/LBP(11.18)

where f is the distance from the stem to the forward perpendicular

d - trim

The sign of ∆Н is positive when trimmed to the bow and negative when trimmed to the stern. The corrected draft by the nose is equal to:

Тн = Тн sr + ∆Н(11.19)

If the aft scale of the recesses does not pass along the aft perpendicular line, then the same correction is introduced for the aft draft. Its sign is opposite to the sign of the correction ∆Н.

(g.3) Calculation of correction of stern draft for trim

∆K \u003d (a x d) / LBP(11.20)

where a is the distance from the aft scale to the aft perpendicular

d - trim

LBP - ship length between perpendiculars

The corrected stern draft is:

Tk = Tk cf + ∆Н(11.21)

(h) Define the corrected mean draft:

T’sr = (Tn + Tk) / 2(11.22)

The values ​​“a” and “f” are taken from the scale drawing of the vessel or the drawing of the longitudinal section of the vessel to scale.

Fig.11.1- Drawing of a longitudinal section of the vessel on a scale.

(h.1) Calculation of corrections for trim to the ship's displacement.

Since the true displacement of a ship trimmed to the stern or bow differs from the displacement given in the cargo scale (where the displacement is calculated on an even keel), it is necessary to introduce corrections to the displacement to trim. There are two of them:

∆1 = (TPC x LCF x d x 100)/LBP(11.23)

where TPC is the number of tons per 1 cm of precipitation. Removed from the load scale;

LCF - CG ordinate relative to the midship frame (m);

d - ship trim (m);

LBP is the length of the vessel between perpendiculars (m).

∆2 = /LBP (11.24)

where d is the ship's trim (m);

d m /d z is the difference in the moment that changes the trim by 50 cm above and 50 cm below the average calculated draft. Usually given in the ship's stability information.

LBP - ship's length between perpendiculars (in meters)

An example of finding d m /d z for draft Tav = 3.40:

We find the trimming moments for draft 3.90 and 2.90, the difference between them is the desired value.

LCF from amidships to the stern is negative, from midships to the bow is positive.

Correction sign ∆1:

Trim	LCF aft(-)	LCF in the nose (+)
Aft (-)	+	-
In the nose (+)	-	+

Correction sign ∆2 is always positive

General correction for trim:

∆ = ∆1 + ∆2

Find the displacement corrected for the trim

D1 = D + ∆

(h.2) Calculation of the correction to displacement for water density

If the actual water density γ differs from the accepted one (γ \u003d 1.025 t / m 3), then it is necessary to correct D 1 for the actual water density measured with a densimeter

Correction for water density

∆D \u003d D 1 (γ fact - γ 1.025) / 1.025

Find the displacement corrected for the density of water:

D2 = D1 + ∆D

(i) Quantity determination

The mass of the cargo is defined as the difference between the weight of the ship loaded and empty without stores

Рgr \u003d Dgr - D 0 - Z

Where Z - reserves (fuel, oil, water, ballast, dead ballast)

Dgr - ship displacement in cargo

D 0 is the displacement of the vessel as light.

But a simpler way to determine by the example of a container ship if there is a cargo program on board (MAX3):

1. Ensure that information is available on the ship's ballast, fuel, and stores.

2. Measure the ship's draft fore and aft before loading and calculate the ship's displacement using the cargo program.

3. Measure the vessel's bow and stern drafts after loading and calculate the vessel's displacement using the cargo program.

4. Subtract from the displacement after loading the displacement before loading and determine the loaded cargo.

5. The program can be used to calculate bulk cargo.

Determination of the weight of the loaded or unloaded cargo according to the ship's draft (Draught survey)

General provisions.

Determining the weight of the loaded or unloaded cargo according to the draft of the vessel consists of two main stages: the production of measurements and the production of calculations.

Measurements are the main source of errors and therefore must be carried out with great care and with all possible accuracy under the given conditions. When making any measurements, it is useful to remember some provisions of the theory of measurements and errors.

On the scale of the problem being solved, it is necessary to measure:

• draft on at least 6 scales: bow, stern, midships, all measurements must be taken from both sides;
• tanks: ballast, drinking water, sometimes fuel, settling, etc.;
• water density: outboard, and sometimes ballast;
• effective freeboard to control ship's draft calculations.

It should be said that on this path there are a number of serious obstacles that the surveyor has to overcome, sometimes even at the risk to health. Among the circumstances that can give rise to problems for the successful solution of the problem of determining the weight of the cargo from the ship's draft include:

• instability environment: wind, waves, precipitation, low temperatures, ice, diurnal temperature fluctuations, ebbs and flows, currents;
• design features of the vessel: freeboard height, bilge gaps arrangement, presence, condition and places of drawing draft marks, as well as the system of units in which this is done (metric or imperial), the presence and condition of measuring tubes of tanks, the value of the constructive trim and the possibility of its regulation ;
• the age of the vessel: knowledge of Vessel's Experience Factor and Constant, the availability of documentation necessary for calculations and the language in which it is presented;
• qualification of ship personnel involved in the task being solved, overcoming the language barrier and readiness of ship personnel to cooperate;
• technical equipment of the surveyor: availability of means of transport, communication, computer with peripherals, measuring accessories (hydrometer, large and small tape measure, remote electronic thermometer, hand-held electronic probe-thermometer, remote electronic density meter, adjustable sampler, powerful flashlight), availability of floating equipment for sediment control vessel from the sea side.

The theoretical substantiation of the method is the law of Archimedes and the theory of the ship. Ultimately, the amount of loaded or unloaded cargo is determined as the difference between the displacement in the loaded and unloaded state of the vessel, taking into account changes in stocks. However, the definition of displacement has features that not all specialists are familiar with, since a number of concepts and patterns in domestic literature and textbooks are either completely absent or presented in a very complicated way. These are, for example, issues of definition, average draft, compensation for deflection or kink of the hull, corrections for trim and the effect of the roll of the vessel.

Due to the fact that the surveyor has to deal with a wide variety of types, sizes and nationality of ships, it is necessary to know and understand the notation system and the principles for presenting information in the documents of various technical schools. Basically, you have to deal with two types of designations and calculation principles: the former Soviet (Russian) and Western.

In the Western system of notation and calculation principles, a system of signs is adopted in which the position of the center of gravity of the waterline area forward of the midships is considered negative (-Fwd), and the trim aft is considered positive (+Aft), in contrast to the domestic one, in which the opposite is true. This does not affect the results of the final calculations, but you need to know this in order not to make mistakes when choosing data from the ship's hydrostatic tables.

Calculation of the average draft.

Draft measurement is carried out at 6 points from both sides according to the bow, stern and midship draft scales. In the metric system of measures, the sediment scale has a decimeter breakdown: the height of the numbers is 10 cm and the gap between the numbers is also 10 cm. Next to the numbers there may be a scale of horizontal scratches applied after 10, and sometimes after 5 cm. The thickness of the scratches is usually 2 cm , but on ships of the "river - sea" type it can be 1 cm. In this case, the risk scale can be located in relation to the digital one at the level of either the upper or lower edge (Fig. 3.1).

At the horizontal line of the Plimsol disk, deck line and load marks, the reference point is always the upper edge. It may turn out that there is no draft scale on the midships. In this case, the draft amidships is obtained by measuring the active freeboard with a special long-length steel tape measure. From official ship documents, a freeboard is selected relative to the summer mark and draft according to the summer mark. Adding these two values, get the height of the side amidships. Subtracting from it the measured effective freeboard, the draft amidships is obtained. This operation is performed from both sides and then averaged. A similar method of measuring the draft at the stern can also be used in the presence of a draft scale, for example, when a high berth prevents accurate measurement of draft from a small angle of view or in the case of a steep stern gap. In the latter case, the official drawing of the vessel is used, on which the side height is measured in the frame area on which the aft draft scale is located, it is converted through the scale into the actual side height, and then measurements are made with a tape measure from both sides, and by analogy with the operation amidships, a determination is made feed sediment.

After removing the sediment, they must be corrected by corrections for the distance of the sediment scales from the perpendiculars, since the sediments on the perpendiculars differ from the sediments on the scales (Fig. 3.2, Fig. 3.3).

It can be seen from the drawing that the values ​​of the correction values ​​are obtained from the solution of triangles A=Tim 1 ;

Amendment A=Tim 1 /(LPB –A-B)

Nasal Correction = A x Tim 1 /(LPB –A-B)

Stern Correction = B x Tim 1 /(LPB –A-B)

Midel Correction = C x Tim 1 /(LPB)

A - distance of the nasal draft scale from the nasal perpendicular (-aft);

B - distance of the aft draft scale from the aft perpendicular (-aft);

C - distance of the midship sediment scale from the center of the Plimsol Disk (-aft);

Tim 1 - trim for uncorrected drafts (+aft);

LBP - length between perpendiculars (length between perpendiculars).

Rule of signs

If the draft scale is located aft of the perpendicular, then the values ​​of A, B and C will be negative (principle - aft). In the Western system of signs, the trim to the stern is considered positive (in the domestic system of signs, on the contrary, it is negative). The correction sign is obtained algebraically.

If the ship is considered to be an unevenly loaded beam, then, since it is not absolutely rigid, bending in the form of deflection (hogging) or bending (sagging) will take place.

A form of deflection or inflection is considered to be a hyperbola. In this case, the difference between the draft amidships and the average draft fore and aft can sometimes reach significant values ​​- several tens of centimeters. In addition, torsion bending can also take place - around the X axis. In order to obtain the value of the average draft under these circumstances, according to which calculations are made, it is customary all over the world to use the following formula:

Mean of Means Draft (M/M) = (Mean Draft(M)) = 3 Middle Draft)/4

M/M = (F + A + 6Mid)/8 which is the same,

Mean Draft(M) = (F + A)/2;

F - nose draft;

A - draft astern;

Middle Draft (Mid) - draft at the midsection.

After that, according to the M / M draft, the displacement corresponding to this draft is selected from the ship's hydrostatic tables, and corrections for trim and water density are calculated. A special case is the determination of M / M in the presence of a roll. The fact is that when heeling only in the area of ​​​​the cylindrical part of the hull, the wedge that entered the water is equal to the wedge that came out of the water. In the area of ​​the extremities of the vessel, the wedge that entered the water will be larger than the wedge that came out of the water, and, consequently, the volume of the underwater part will increase. But, since the weight of the vessel remained unchanged, the vessel floats somewhat, i.e., M / M decreases and the more, the greater the roll. In order to take into account this error, an empirical formula is applied:

Amendment = 4.6 - 6.0 (T 1 - T 2) x (D 1 - D 2)

T 1 ;T 2 - draft of low and high bottoms, respectively, in cm;

D 1 ;D 2 - TPC (correction for trim) for the draft of the lowered and increased bots, respectively.

The value of the numerical coefficient within the specified values ​​will be the greater, the sharper the contours of the hull. This formula was obtained by computer calculations of various ships and is used for any significant roll (for example, emergency) on large ships. With an arbitrary choice of a numerical coefficient, a certain error will occur, but it will be much less than that which occurs if this formula is not applied.

Calculation of corrections for trim (1st correction for trim).

The physical meaning of the 1st trim correction (1 st Trim Correction).

According to Euler's theorem, any floating body rotates around an axis passing through the center of gravity of the watershed area. In the case of a ship, this is the center of gravity of the current waterline. In Western literature, the center of gravity of the current waterline is called the Longitudinal Center of Flotation (LCF), fig. Z.3.

1. The position of the vessel on the GVL (even keel),

Average draft amidships = ½ (A + F) = ½ (2a) = a

1. Vessel position on VL 1 (LCF = 0),

Average draft amidships = ½((a + t) + (a - t)) = a

1. Vessel position on VL 2 (LCF /= 0),

Average draft amidships = ½((a + t + b) + (a - t + b)) = a + b

1. b/ LCF = 2t / LCF; b = 2t x LCF / LCP,

where 2t is the ship's trim (Trim)

1. 1 st Trim Correction = b x TPC = Trim x LCF x TPC x 100 / LBP.

From fig. 3.3 it can be seen that the 1st correction for trim can have both a plus and a minus sign. It depends on where the LCF is in relation to midships. If the LCF is in the stern of the midships, it has a plus sign, if in the bow - a minus sign. In domestic literature, the system of signs is the opposite. Given the fact that our trim sign is also opposite to the Western system of signs, this does not affect the result of the calculations.

It is very important to remember the principle: when loading (increasing draft), the LCF always shifts aft.

Calculation of corrections for trim

1st trim correction (adjustment for offset of the center of gravity of the effective waterline LCF

Longitudinal Center of Floating) (I ST Trim Correction for Layer)

I ST Trim Correction (tons) = (Trim x LCF x TPC x 100) / LBP,

Trim - ship trim;

LCF - displacement of the center of gravity of the current waterline from the midship;

TPC is the number of tons per cm of precipitation;

LBP is the distance between perpendiculars.

The sign of the correction is determined by the rule: the first correction for trim is positive if the LCF and the largest of the bow and stern drafts are on the same side of the midships, which can be illustrated by the following table:

Trim	LCF nose	LCF feed
Stern	-	+
Nose	+	-

2 nd Trim Correction is ALWAYS POSITIVE. It compensates for the error resulting from the displacement of the LCF position when changing the trim.

2 ND Trim Correction = (50 x Trim x Trim x (D M / D Z)) / LBP

where (D M / D Z) is the difference in the moment that changes the ship's trim by 1 cm at two draft values: - one 50 cm above the average recorded draft value, the other 50 cm below the registered draft value.

PS. If the ship has hydrostatic tables in the IMPERIAL system, the formulas take the following form:

I ST Trim Correction (tons) = (Trim x LCF x TPC x 12) / LBP,

2 ND Trim Correction = (Trim x Trim x 6 x (D M / D Z)) / LBP.

Correction for sea water density.

Ship hydrostatic tables are compiled for a certain fixed density of outboard water - for sea ​​vessels usually by 1.025, on river-sea vessels either by 1.025 or by 1.00 or by both. It happens that tables are compiled for some intermediate density value - for example, 1.20. In this case, it becomes necessary to bring the data selected from the tables for calculation into line with the actual density of outboard water. This is done by introducing a correction for the difference between the tabular and actual water densities.

Correction \u003d Displacement (table) x (Density (meas) - Density (table)) / Density (table)

It is possible, without correction, to immediately obtain the value of the displacement corrected for the actual density of sea water:

Displacement (actual) \u003d Displacement (table) x (Density (meas) / Density (table))

A problem for surveyors and a subject of discussion is often the question: should the density correction be determined by the value of only the tabular displacement, or by the value of the tabular displacement corrected by trim corrections? Generally speaking, in both cases, the same result is obtained if the TPC value is brought into line with its density, since it is clear that this value changes with density according to the law:

TRS (actual) \u003d TRS (table) x (Density (meas) / Density (table))

In the production of Draft Survey, a special place is occupied by the determination of the actual density of outboard water. Measurements are made on the open deck, so it is necessary that the densimeter take the ambient temperature, and not interior, otherwise its readings will have an error.

Water sampling should be carried out at three points: in the bow, middle and stern parts of the vessel at three depth levels, then a composite sample is compiled, the temperature of which is measured, or the density of each sample is measured separately and then averaged, which is preferable, since the preparation of a composite sampling takes time, which may change the initial temperature of the sample taken in case of high or low outdoor temperatures. The need for such a complex sampling procedure is dictated by the fact that water densities often have a significant difference in depth under conditions of the same high or low outdoor temperatures, floating ice, or tidal currents near river mouths or on rivers. For this purpose, special equipment is needed that allows taking an autonomous water sample at a given depth and a special densimeter for the purposes of a draft survey, which should be indicated on the back of the densimeter scale. Such densimeters are manufactured by the English company Zeal. Never use densimeters designed to measure the density of other liquids: petroleum products, alcohols, liquid chemicals, milk, etc., even if their scales cover the range of possible seawater densities. This cannot be done because different liquids have different surface tension, which is taken into account when applying the densimeter scale, otherwise the readings of the densimeter lowered into a liquid not intended for measurement will be erroneous Despite this well-known fact, in practice this is often not taken into account . In particular, Draft Survey Densimeters, tested and certified, measure the density of fresh water. The values ​​of these measurements are underestimated. For example, measurements of water density at the mouth of the Neva River in St. Petersburg That is, in February, at an outside air temperature of minus 15-20 ° C in conditions of floating ice, branded densimeters for a draft survey give values ​​of 0.9985 instead of 1.0000. But this means that the temperature of the measured water must be plus 20 °C, which, of course, cannot be in these circumstances.

The source of the error is the stereotype of the idea that water is water, whether fresh or sea (salty). However, this is a delusion. The fact is that salt water is a solution that has a surface tension that is different from the surface tension of fresh water. The Draft Survey Densimeter is a salt water or solution densimeter. It makes no sense to measure the density of fresh water, since it is a constant value and as such is included in all reference books, including Nautical Tables. The density of fresh water (or simply water) only changes with temperature. And in the third decimal place, it begins to change, starting from a temperature of +7 °C (see table).

Table of changes in the density of fresh water depending on temperature:

Temperature, 0 C	Density	Temperature, 0 C	Density
0 1 2 3 4 5 6 7 8 9 10 11 12	0,9999 0,9999 1,0000 1,0000 1,0000 1,0000 1,0000 0,9999 0,9999 0,9998 0,9997 0,9996 0,9995	13 14 15 16 17 18 19 20 21 22 23 24 25	0,9994 0,9993 0,9991 0,9990 0,9988 0,9986 0,9984 0,9982 0,9980 0,9978 0,9976 0,9973 0,9971

Therefore, if you measure, then either the temperature of fresh water and then convert according to the tables into density values, or use a fresh water densimeter, the scale of which is calibrated only for fresh water. On a small vessel with a small consignment of cargo, the error that has arisen due to this will not be very significant. However, on a large ship in the port of loading with a steady flow of cargo, this will cost the shipper a very large amount.

So, for example, about 3,000,000 tons of granular fertilizers are currently shipped for export through St. Petersburg. Due to the erroneous concept of measuring the density of fresh water, this figure is reduced by 4,500 tons. With a cargo value of about 100 USD / t, a surveyor's mistake will cost the sender 450,000 USD per year.

Separately, there is the question of the need to introduce a temperature correction. The fact is that with increasing temperature, the density of sea water decreases, while fresh water in the range from 0 ° С ^ TO +2 ° С increases, in the range from +2 ° С to +6 ° С it remains unchanged, and then steadily decreases. The ship as a physical body increases its volume with increasing temperature due to the linear expansion of the metal. Thus, with a decrease in water density, the ship must either sink or increase the volume of the underwater part due to linear expansion in order to maintain equality:

Weight = V 1 y 1 = V 2 y 2 = const;

where V 1 y 1 - the initial volume of the underwater part of the vessel and the density of outboard water; V 2 y 2 - increased volume of the underwater part of the vessel due to thermal expansion and decreased density of outboard water due to temperature increase.

The same thing happens with a densimeter when measuring the density of water, the temperature of which differs from that to which the densimeter scale is calibrated.

Generally speaking, there is a temperature error under conditions other than standard, but its magnitude is the second order of magnitude of the accuracy of the method of calculation and measurement in the production of Draft Survey.

Therefore, the water temperature is never measured and the temperature correction is never introduced due to its numerical insignificance, being limited to the usual measurement of water density with an appropriate densimeter. This, however, only applies to salt water, as discussed above.

Tank freezing.

The magnitude of the total error depends on how carefully the ballast tanks are measured and the calculations are made on these measurements. Measurements should be made with a certified steel tape using a special water-reactive paste. During measurements, all operations for the reception, delivery and pumping of fuel, fresh and ballast water must be stopped. Generally speaking, the best option is one in which all ballast tanks are rolled dry.

In this case, the amount of water not pumped out (dead stock) in double-bottom tanks is determined from the calibration tables, taking into account this trim. In the absence of calibration tables, according to established international practice, it is considered that the dead stock (not pumped out) is equal to 2-2.5% of the tank capacity. This only applies to double bottom tanks. In suspended, under-deck and deep tanks, at zero measurements, the tanks are considered to be absolutely empty.

In the case of full tanks, it should be borne in mind that even during pressing and water outlet from the air tubes, there may be air bag, especially in the presence of a roll of the vessel.

When determining the amount of ballast, it is necessary to measure the density of water in the ballast tanks, otherwise, when in large numbers ballast, a perceptible error will appear. This procedure is not easy due to the difficulty of taking water samples from the ballast tanks. Therefore, in order to avoid delaying the start of cargo operations and laboriousness when taking samples, the density of water is often determined at the place where the tanks are filled, although the correctness of the draft survey method requires scrupulousness when performing all measurements and calculations. Therefore, when filling out the table of tank measurements, one should not write “empty”, “full”, “overflow”, as can often be found in the reports of some surveyor companies, but indicate measurements in numbers, which will indicate the conscientiousness and literacy of the surveyor.

As for the rest of the tanks: fuel, waste, fresh water, then during a short stay, their filling is accepted at the request of the ship administration with a reasonable rate of fuel and water consumption for the period of cargo operations, since only the change in the initial quantity matters for calculations, and the quantity itself reserves, regardless of their size, are subtracted when determining the difference in displacement in cargo and in ballast. If the ship administration declares an incorrect amount of reserves, then this will only affect the value of the Constant.

In case of long parking, especially in the case of receiving fuel and fresh water, it is necessary to take measurements at the beginning and at the end of cargo operations.

1. On ships of the "river - sea" type, there are 5 draft scales from each side. However, to date, there is no calculation method for 5 draft measurements from one side, so calculations should be carried out using 3 measurements. It should be borne in mind that on these vessels, the aft perpendicular may not pass along the rudder post (they may not have it), but along the intersection of the GVL with the sternpost, or on some other frame. It is possible to set the position of this perpendicular, as well as the distance of the sediment scales from the perpendiculars, according to the theoretical drawing.
2. These ships often do not have calibration tables for ballast tanks, therefore, in the presence of a trim, it is not possible to determine the exact amount of ballast.
3. It should be borne in mind that the ballast tanks of these ships may contain a very significant amount of sand and silt, so the amount of ballast rolled off during loading will be less than the calculated one in this case, which, in turn, will cause an error in determining the amount of cargo.
4. In some cases, these vessels lack technical documentation, and as a rule, it is completely absent on purely river vessels. On inland navigation vessels, the qualifications of the personnel in terms of draft survey leave much to be desired. So, in a number of cases, the navigators of these vessels cannot give a qualified answer to the surveyor's questions.
5. These ships in the ballast condition have a significant trim (sometimes more than 3 meters), which under these conditions does not allow for corrections for trim.
6. Since the number of types river vessels albeit significantly, but of course, it is possible to form a data bank necessary for calculations, by types of ships. These data can be obtained from shipowners, on ships, at the LCPKB or at construction plants.
7. Calculations should not be made with a trim of more than 3 meters, it is necessary to require the ship administration to bring it to an acceptable value.
8. The most favorable option is completely empty ballast tanks before loading and trim no more than 3 meters.
9. In all other cases, which are difficult to predict in advance, decisions should be made on the spot, based on available information, own experience, understanding and market conditions.

In the world merchant fleet, it is customary to subdivide ships into types, which are determined by the properties of the cargo being transported: tankers, container ships, gas carriers, bulk carriers, dry cargo ships, and so on. But there is a classification of ships by size.

This classification takes into account the peculiarities of the navigation area, namely the depths in the straits and port waters, the dimensions of the locks, the conditions of navigation on artificial channels and inland waterways. The actual navigation situation on the ocean and sea routes is the reason why the size of ships has clear requirements.

For determining ships by size a two-word phrase is used. The first part uses the term meaning belonging to geographical feature, in the second part - the term defines the maximum size or just the size.

Vessel size Handysize

Although there is no official definition of the exact terms of tonnage, to ship types"Handysize" most often refers to bulk carriers for general cargo, less often - tankers for petroleum products with a deadweight of 15,000 to 50,000 tons. Cargo ships larger than "Handysize" are already of the "Handymax" type, and less than 15,000 tons are not defined.

Handysize bulk carrier

Vessel size"Handysize" are considered the most common and amount to almost 2000 units with a total deadweight of about 43,000,000 tons. These dimensions courts are very common because they allow them to enter small ports and in most cases they are equipped with cranes, which also allows them to load and unload goods themselves in ports that do not have loading and unloading systems. Compared to large bulk carriers, vessels of the size"Handysize" allow for a wider handling of the so-called "piece" goods. These include: steel products, grain, ore, phosphates, cement, timber, crushed stone, etc.

Vessels with sizes"Handysize" is mainly built at shipyards in Japan, Korea, China, Vietnam, Russia, Ukraine, the Philippines and India, as well as in several other countries. The most common standard in this category of ships are bulk carriers with a deadweight of about 32,000 tons and a draft of no more than 10 meters. They have five cargo holds with hydraulic tween decks, and four thirty-ton cargo handling cranes. Some Handysize ships are equipped with racks on the upper deck, between which timber is stacked, for which they are called "timber carriers".

Despite numerous orders from shipping companies, new ship types, "Handysize" remains the most sought after, and has the highest average age among bulk carriers.

boat size Handymax

Vessel size"Handymax" or "Supramax" apply to 35,000 to 60,000 DWT. Vessels of this type are 150-200 meters in length, although in some cargo terminals, such as in Japan, many court sizes"Handymax" have a hull length of not more than 190 meters. Modern vessels of this type have a deadweight of 52,000 to 58,000 tons, are equipped with five cargo holds and are equipped with four cranes with a lifting capacity of up to 30 tons.

Handymax Bulk Carrier

boat size Seawaymax

The term Seawaymax refers to ship sizes, which allow them to pass through the St. Lawrence Canal - the name of the waterway from Montreal to Lake Erie, including the Welland Canal and the Great Lakes waterway from the Atlantic Ocean to the Great Lakes in North America.

dry cargo ship «CSL LAURENTIEN» type Seawaymax

Seawaymax size ships are 226m long, 24m wide and have a draft of 7.92m. Although the channel is 235m wide, cargo and passenger ships Larger sizes cannot exit the Great Lakes into the Atlantic Ocean due to draft restrictions at some points in the waterway. In recent years, the lowering of the water level on the Great Lakes has created additional problems for shipping. The famous one was built according to the type of Seawaymax ships. He set a water crossing record on the St. Lawrence Canal, passing through it with a load of 28,502 tons of iron ore, at a time when the annual deadweight of the waterway was 72,351 tons. In 2006, at least 28 vessels of various types were decommissioned due to their size and were too large to leave the Great Lakes.

boat size Aframax

The term is derived from the words for the Average Freight Rate Assessment (AFRA) tanker level system. Vessel size Aframax are usually oil tankers with deadweight from 80,000 tons to 120,000 tons. Tankers of this type are widely used in the Black Sea, North Sea, caribbean, East China Sea and mediterranean sea, since the channels, straits and ports through which exporting countries that are not members of the OPEC organization transport oil and are not capable of receiving VLCC and ULCC type supertankers.

tanker "Torben Spirit" type Aframax

Vessel size Suezmax

"Suezmax" is a nautical term for a large vessel size, capable of passing through with a full load, and is exclusively associated with oil tankers. Since the Suez Canal has no locks, the only major limiting factor is draft ( maximum depth vessel below the waterline). At present, the depth of the waterway is 16 m. Max Height vessels is limited by the height of the bridge in the channel, which is 68 m. A small part of the vessels is also limited by the width of the channel - the maximum allowable width of the vessel is 70.1 m.

tanker "CAP GUILLAUME" type Suezmax

Most large-capacity tankers, given these conditions, can pass through the channel, but some supertankers with a full load do not allow draft. To meet these parameters, supertankers ship part of their cargo to another vessel or transport it through a pipeline to the other end of the canal, where it is loaded back onto a supertanker.

Vessels with a displacement of more than 150,000 tons and a width of 46 m cannot pass through the Suez Canal, therefore they are forced to continue their journey around the cape Good Hope in the south of the African continent.

The head of the Suez Canal, Admiral Ahmed Ali Fadel, plans to increase the depth of the waterway to 22 meters in 2010, which will allow supertankers to move along it.

vessel size Panamax

ships classified as "Panamax" have a maximum dimensions, which strictly correspond to the parameters , and is determined by the size of the lock chambers, and not by the depth of the water barrier. The term "Panamax" is an important factor in the construction of cargo ships, and requires the most accurate exposure of the specified dimensions.

Panamax type container ship

As mentioned above ship sizes"Panamax" is determined mainly by the parameters of the lock chambers: width - 33.53 m, length - 320 m, height - 25.9 m. The useful length of each chamber for setting the ship is 304.8 m.

To date, the following limits have been set ship sizes for passage through the channel: length - 294.1 m, width - 32.3 m, draft - 12 m, height from the waterline to the very high point vessel is 57.91 m. Panamax types typically have a displacement of around 65,000 tons. The rules for passing through the Panama Canal are set out on 60 pages of the Vessel Requirements N-1-2005 magazine.

The construction of a large number of this type of vessels creates some problems waterway. Vessel sizes Panamax require high accuracy of setting in airlocks, which takes more time. In addition, the pilotage of ships is carried out only during the daytime.

battleship Missouri in the Panama Canal

In 1945, a unique operation was carried out to escort a huge " USS Missouri».

vessel size Post-Panamax

AT recent times from the term "Panamax" new definitions were formed - "Post-Panamax", "NeoPanamax". Supertankers, modern container ships and bulk carriers of this type are longer than Panamax and cannot pass through the canal. Also, the class " Nimitz". Thus, there is an urgent need, especially for the United States, for another reconstruction of the Panama Canal. In this regard, on October 22, 2006, a referendum was held among Panamanian citizens, who were supposed to express their opinion on the occasion of the expansion of the canal. The vote received positive feedback. The planned cost of the renovation, which will be completed in 2014, is US$5.3 billion. This amount will be reimbursed over 11 years.

bulk carrier «SHIRANE» Post-Panamax type

Soon dimensions courts Panamax will have other ships. The new locks of the Panama Canal will have the following parameters: length - 427 m, width - 55 m, permissible draft of ships - 18.3 m. After the expansion, the canal will be able to receive container ships with a capacity of up to 12,000 TEUs. Container ships with such parameters have already received the name "NeoPanamax".

Vessel size Malaccamax

The term "Malaccamax" refers to oil tankers transporting crude oil from areas Persian Gulf to China through the Straits of Malacca, connecting Indian Ocean with the South China Sea. The restriction is caused by certain banks where the minimum depth is 25 meters.

Malaccamax-class tanker

Vessels of the Post-Malaccamax type, larger than those of the Malaccamax, are forced to continue on their way to China, bypassing the island of Java from the east along the deeper Lombok Strait.

Post-Malaccamax type container ship

The shortest sea route for supertankers going to China and Japan from Europe, the Persian Gulf and India will soon be the Kra Canal, which is being built through Malaysian territory on the border with Burma.

Just the majority of supertankers and dry cargo ships were built with the passage through the Strait of Malacca. Vessel sizes"Malaccamax" correspond to the type of VLCC tankers.

Also, the name "Malaccamax" will be given to future container ships, which will be 470 m long, 60 m wide, 20 m draft and 300,000 DWT to carry 18,000 twenty-foot equivalent containers. It is assumed that these will work on the above waterway.

boat size Capesize

The term "Capesize" refers to cargo ships that, due to their large size, are not able to pass through the Suez and Panama canals. On the English language the word "cape" means "cape" (the size of the vessel "Capesize" is larger than the "Panamax" and "Suezmax"). Thus, ships of this type should pass along the Cape of Good Hope in the south of the African continent or Cape Horn - the most southern point mainland South America.

ore carrier type Capesize

Capesize ships typically have a deadweight of over 150,000 tons, so VLCC and ULCC supertankers and heavy ore carriers with an average deadweight of 175,000 tons make up the majority of ships of this size. However, there are ore carriers with a deadweight of 400,000 tons. Most often, the term "Capesize" is used for bulk carriers. Naturally, vessels of this size are handled at specialized deep-water terminals. The economic growth of China, with its strong demand for raw materials, has led to an increase in demand for vessels of the size Capesize.

TANKER DIMENSIONS

Oil tankers also have a separate size classification. In 1954, Shell Oil developed a system by which tankers could be classified by size based on the ship's deadweight:

From 10,000 to 24,999 tons - a general purpose tanker;
- from 25,000 to 44,999 tons - a medium-sized tanker;
- from 45,000 to 79,999 tons - tanker type LR1;
- from 80,000 to 159,999 tons - tanker type LR2;
- from 160,000 to 319,999 tons - a very large tanker (Very Large Crude Carrier - VLCC);
- from 320000 to 549999 tons - ultra (Ultra Large Crude Carrier - ULCC);