§ 12. Seaworthiness of ships. Part 2

The degree of ensuring the unsinkability of the vessel depends on its purpose. So, on civil ships, the number of bulkheads and their placement are determined by the convenience of loading cargo, the reliability of their fastening and the ability to work with them in the hold, as well as the condition that ship machinery and mechanisms are freely placed in compartments and it would be convenient to service them. On the other hand, it is necessary to comply with the Norms of the Register of the USSR, according to which, on the basis of the International Convention for Saving Human Lives at Sea, cargo ships, when any one compartment is flooded, and passenger ships, when any two and even adjacent compartments are flooded, must remain afloat and maintain at least 75 mm of freeboard height from the effective waterline to the side line of the bulkhead deck in any position of the ship (Fig. 18).

Rice. 18. The minimum height of the freeboard of a vessel with a trim.

Bulkhead deck or buoyancy deck the deck is called, to which the transverse waterproof bulkheads are brought in height.

On ships with longitudinal impervious bulkheads (on passenger ships and naval ships), in the event of a hole in the underwater part of the side and flooding of the side compartments, trimming and heeling moments are formed simultaneously towards the damaged side. This should be taken into account when choosing the location of the longitudinal and transverse bulkheads on the ship.

The division of the ship into compartments must be such that in the event of a side hole, the buoyancy of the ship is exhausted before its stability: the ship must sink without capsizing.

To straighten the vessel, which has a roll and trim obtained by flooding the compartments, as well as to restore the stability decreasing in this case, forced counter-flooding of pre-selected compartments with the same magnitude, but with the reverse value of the moments, is carried out. For example, if a vessel has received a roll to the port side and a trim to the bow from a hole, then to straighten it, it is necessary to flood the aft compartment on the starboard side with an equal moment. A straightened ship, of course, will receive additional draft, but with restored stability it will continue to maintain its seaworthiness (and the ship's combat qualities, that is, maneuver and fire from guns, launch rockets).

This principle of counter-flooding of ship compartments was proposed for the first time in the world, back in 1875, by the outstanding Russian scientist and sailor S. O. Makarov. In 1903, this idea was used for practical application on warships by the then young scientist, officer, later an outstanding Soviet shipbuilder, Academician A.N. Krylov. They were offered special tables called tables and unsinkability, according to which, for all compartments on the ship, the heeling and trim moments that occur when one or a group of compartments are flooded were calculated in advance, and the moments were predetermined and the compartments that in this case must be flooded to straighten the ship are indicated. Using the tables, in a difficult combat situation, you can quickly level a ship that has received a hole and restore its lost combat qualities. Unsinkability tables must now be drawn up for each ship.

Later, through the work of Academician Yu. A. Shimansky, Professor V. G. Vlasov and other Soviet scientists, the science of the unsinkability of a ship was developed in such a way that the death of a ship from loss of stability in case of combat damage to the hull is practically excluded.

Pitching ship - the oscillatory movements that the ship makes about the position of its equilibrium. There are three types of ship rolling:

A) vertical- oscillations of the vessel in the vertical plane in the form of periodic translational movements;

B) onboard(or lateral) - vibrations of the vessel in the plane of the frames in the form of angular displacements;

IN) keel(or longitudinal) pitching - oscillations of the vessel in the diametrical plane, also in the form of angular displacements. When a vessel is navigating on a rough water surface, all three types of rolling often occur simultaneously or in various combinations. A significant influence on all types of the vessel's motion is exerted by the direction of its movement in relation to the wave run. The pitching of the ship adversely affects its performance and seaworthiness.

We list the harmful effects of pitching:

A) periodic rise and burrowing into the wave of the extremities of the ship, causing additional resistance to movement and exit from the water of the propeller, which leads to the loss of its stop and a decrease in speed, an increase in fuel consumption, flooding of the deck and deterioration of the habitation conditions of the vessel;

B) the creation of such conditions that can lead to the capsizing of the ship due to the loss of lateral stability;

C) deterioration in the operating conditions of machines and mechanisms, as well as additional loads on the strong hull bonds from the impact of waves and the action of inertia forces arising from rolling;

D) decrease in the effectiveness of artillery or torpedo fire on ships, difficulty in the operation of rocket launchers;

E) harmful physiological effects on people (seasickness).

It is customary to distinguish between two types of oscillations of a ship in motion: free(on calm water), which occur by inertia after the cessation of the forces that caused them, and forced, which are caused by external periodically applied forces, such as sea waves.

Rice. 19. Rolling characteristics: a - amplitude; b - span; in - pitching period.

The main reason for the ship's pitching is the simultaneous action of waves, buoyancy and stability forces on it. The main characteristics of rolling as a periodic oscillatory motion of the vessel are: amplitude, span and period of rolling (Fig. 19).

pitching amplitude called the largest deviation of the vessel from its original position, measured in degrees.

Roll span- the sum of two successive amplitudes (inclination of the ship on both sides).

Rolling period- the time between two successive inclinations, or the time during which the ship makes a complete cycle of oscillation, returning to the position at which the countdown began.

The period of the ship's roll affects the nature of the roll: with a long period, the roll is smooth, on the contrary, with a short period, the roll is jerky, causing serious consequences.

The roll period (in seconds) is calculated using the following formula:

where k is a coefficient depending on the type of vessel; its value lies within 0.74/0.80;

B - the estimated width of the vessel along the current waterline, m;

H 0 - initial transverse metacentric height, m.

From the given value it can be seen that a ship with great stability has gusty rolling, which significantly affects its operation.

The period (in seconds) of free heaving on a quiet Rone is calculated using the approximate formula

and pitching - according to the formula

where T 0 is the ship's draft, m.

When a ship is sailing on rough water, since the ship is carried away by the movement of water and to some extent is a surface particle participating in orbital motion, the resultant of the weight forces, buoyancy forces and inertia forces applied to the ship is directed along the normal to the slope of the water. A change in the wave profile is continuously reflected in the shape of the underwater volume of the vessel and its magnitude, which leads to forced oscillations of the vessel.

Consequently, the nature of the ship's forced oscillations depends on the wave profile, and their period is always equal to the wave period. To reduce the ship's roll, a number of measures are taken, conditionally divided into general and special. General measures include rational choice of the form of the theoretical drawing of the ship, and to special - installation of structures - stabilizers, creating moments that counteract the roll of the ship.

General measures aimed at reducing the flooding of the ship and immersion of its extremities in the wave are: deck sheer, expansion of the upper part of the bow frames, which forms the collapse of the sides, as well as the installation of a water-breaking canopy in the bow part of the upper deck, which destroys the wave covering the ship and diverts it to sides.

To calm the most unfavorable and dangerous rolling, special measures are used, consisting in the installation of stabilizers, which are divided into passive And active. The action of the former is based on the use of the rocking energy of the vessel itself, the action of the latter is based on the use of external energy sources, they are artificially controlled. Consider the simplest and most effective pitch dampers.

1) Lateral (zygomatic) keels(Fig. 20) are the simplest passive dampers, having the form of attachments in the form of plates with an area of ​​​​up to 4% of the waterline area. These plates are installed normal to the chin in the middle part of the hull along the water flow line, up to 40% of the length of the vessel. The principle of operation of these keels is to create a moment inverse to the moment of rocking the ship. Under the action of such side keels, the roll amplitude is reduced to 50%.

2) Onboard passive tanks(Fig. 21) are arranged according to the principle of communicating vessels in the form of side tanks connected by water and air channels with a valve that regulates the overflow of water between the tanks. The valve regulates the water in such a way that it does not keep up with the roll of the vessel, but, lagging behind, would overflow by inertia towards the rising side, when the moment of water in the tank, counteracting the inclination of the vessel, calms its pitching.

Rice. 20. Side keels and their design.

These tanks give good results as stabilizers only when the pitching regimes are close to resonance. In all other cases, they almost do not moderate the roll, and even increase its amplitude.

Rice. 21. Onboard passive tanks and the position of the liquid in them when the ship is rolling in resonance with the wave.

3) Onboard active tanks are the same onboard tanks connected by channels, but the water flows into them under the influence of automatically controlled pumps. These tanks operate effectively in all modes of motion of the vessel. The weight of water in active tanks (usually used for fresh water or fuel) should be approximately 4% of the vessel's displacement.

4) Controlled side rudders(Fig. 22) are active stabilizers and are installed in the underwater part of the hull in the area where the width of the vessel is greatest.

Figure 22 Scheme of operation of the controlled side rudders of the left side, 1 - control equipment; 2 - control system; 3 - rudder drives; 4 - niches for rudders; 5 - left side rudder feather; 6 - starboard rudder feather. V-speed and direction of the oncoming flow; P - lifting force; F - frontal resistance.

The rudder shift is carried out automatically: for ascent - on the submerging board, for diving - on the pop-up board of the vessel. The lifting forces arising on the rudders form a moment opposite to the ship's inclination, which moderates the pitching amplitude to four times its size. Since the lift of the rudders depends on the speed of the boat, side rudders are only effective on fast boats.

In the absence of pitching, to eliminate additional resistance to the movement of the vessel and prevent breakage of the rudders when mooring sideboard, the side rudders are removed into special niches inside the hull of the vessel.

Rice. 23. Scheme of the device of the gyroscopic stabilizer. 1 - gyroscope; 2 - gyroscope frame; 3 - trunnions structurally connecting the frame with the body; 4 - a device that rotates or slows down the frame of the gyroscope.

5) Gyroscopic damper(Fig. 23) is based on the use of the gyroscopic effect - the property of the gyroscope to keep its axis of rotation unchanged. The gyroscopic moment largely compensates for the heeling moment, reducing the pitching amplitude. The damper is a flywheel rotating in a frame hinged to the ship's hull.

When the vessel rolls, the gyroscope frame spontaneously swings in the DP. If these swings of the frame are braked or forced to turn the frame with the help of a special electric motor, then it will exert additional pressure on the trunnions, forming a pair that counteracts the rocking of the vessel. For example, such a stabilizer (with a flywheel weighing 20 tons) is installed on the American submarine "George Washington".

Manageability the vessel is called its ability to maintain a given direction of movement or change it in accordance with the shifting of the rudder. Controllability is characterized, on the one hand, by the ability of the vessel to withstand the action of external forces on the move, which make it difficult to maintain a given direction of movement, - course stability and, on the other hand, the ability of the ship to change direction and move along a curved path - this ability is called agile.

Thus, the ship's controllability refers to both of these qualities, which are contradictory. So, if you create a ship with such a ratio of the main dimensions that will provide it with solid stability on the course, then the ship will have poor agility. On the contrary, if the ship has good agility, then it will be unstable and frisky on the course. When creating a ship, it is necessary to take this into account and choose the optimal value for each of these qualities so that the ship has normal controllability.

Yaw called the ability of the vessel to spontaneously deviate from the course under the influence of external forces. It is considered that the ship is stable on the course if, to keep it, the number of rudder shifts does not exceed 4-6 per minute and the ship manages to deviate from the course by no more than 2-3 °.

To ensure the stability of the vessel on the course and its agility, rudders are installed in the stern of the vessel. When the rudder is shifted on board, a moment of a pair of forces arises, turning the vessel around a vertical axis passing through its center of gravity, in the direction in which the rudder is shifted (Fig. 24).

Rice. 24. Scheme of the forces acting on the ship when the rudder is shifted. N is the resultant of the forces of water pressure on the rudder blade; l is the arm of a pair of forces rotating the vessel; Q - drift force; F - frontal resistance to the movement of the vessel.

Let's transfer the resultant N to the ship's center of gravity - point G, without changing its direction and magnitude, and apply the second force N in the opposite direction. The resulting pair of forces creates a moment Mp = Nl, which deflects the ship from a straight direction towards the rudder shift.

We decompose the force N of the reverse direction into two components: F - force directed along - to the side, opposite to the movement of the ship, and creating drag, which reduces the speed of the ship by about 25-50%; Q is the drift force acting perpendicular to the DP and causing the vessel to move with a lag, which is quickly extinguished by the water resistance.

If the rudder of a ship moving at a certain speed is left on board, then the center of gravity of the ship (around which it turns) will begin to change its trajectory from a straight line to a curvilinear one, gradually turning into a circle of constant diameter D c, which is called circulation diameter, and the movement of the ship along such a trajectory - vessel circulation(Fig. 25).

The circulation diameter, expressed in ship lengths, determines the ship's agility. The vessel is considered to be well agile if D c = (3/5) L. The smaller the circulation diameter, the better the agility of the vessel. The distance l traveled by the vessel between its CG at the time of the rudder shift and before the vessel turns 90 °, measured along the straight line of its movement, is called advancing.

Rice. 25. Vessel circulation. D c - diameter of the steady circulation; D t - tactical circulation diameter; ,c - drift angle.

The distance between the position of the diametrical plane at the beginning of the turn and after the ship's course has changed by 180 °, measured perpendicular to the original direction of movement, is called tactical circulation diameter, which is usually D t \u003d (0.9 / 1.2) D c. The angle formed by the position of the DP and the tangent to the trajectory of the ship during circulation, drawn through point G, is called drift angle V.

When the vessel moves in circulation, it has a roll on board, opposite to the rudder shift. The heeling moment is formed from a pair of forces: the centrifugal inertia force applied in the ship's CG, and the hydrodynamic pressure force applied approximately in the middle of the draft. The heeling angle reaches its maximum value at a circulation diameter of 5L, and becomes larger, the greater the speed of the vessel and the smaller the circulation diameter, and an increase in these parameters can lead to capsizing of the vessel.

Walkability The vessel is called its ability to move at a given speed while consuming a certain power of the main engines.

When the ship moves, the forces of water and air resistance immediately begin to act on it, directed in the direction opposite to its movement, overcome by the persistent pressure of the propulsor.

The study of issues related to the regularity of these resistances makes it possible to choose the most rational contours of the vessel, ensuring the achievement of speed with a minimum expenditure of engine power.

The resistance to the movement of the vessel increases with an increase in its speed and is equal to the sum of the individual resistances. Water resistance is made up of:

A) shape resistance or vortex resistance Rf, depending on the shape of the submerged part of the hull and the vortex formations of water created behind the stern, which, breaking away from the vessel, carry away with them the manpower of rotational motion acquired by them. The fuller the hull of the vessel and the worse its streamlining, the more vortices and the greater the resistance;

Rice. 26. The system of waves arising from the movement of the vessel. 1, 2 - divergent stern and bow, respectively; 3, 4 - transverse bow and stern, respectively.

b) friction resistance R t, which depends on the speed of the vessel and the size of the surface of the part of the hull submerged in water. Frictional resistance arises from the fact that water particles in contact with the submerged surface of the hull stick to it and acquire the speed of the vessel. Neighboring layers of water also begin to move, but as they move away from the surface of the hull, their speed gradually decreases and disappears altogether. Thus, a so-called boundary layer is formed on the surface of the submerged part of the body, in the cross section of which the water velocity is not the same. Experimentally, formulas were obtained by which the friction of the ship's surface is determined.

The surface roughness increases the frictional resistance, which is taken into account additionally.

Friction resistance is greatly affected by the fouling of the underwater part of the hull with algae, shells and other organisms that live in the water, which increases the friction between the hull and water. Cases are known when, 4-5 months after cleaning the underwater surface, the ship's speed decreased by 4-5 knots due to fouling.

C) wave resistance R B, depending on the shape of the underwater part of the hull and representing the cost of part of the power of the main engine for the formation of a wave system that accompanies the vessel on the move (Fig. 26).

At low speeds, predominantly divergent waves are formed. With an increase in travel speed, the magnitude of transverse waves increases, the formation of which requires large powers; w.h

D) resistance of protruding parts R, depending on the resistance of individual protruding parts located in the underwater part of the hull: rudders, brackets, side keels, protruding parts of instruments, etc.

To determine the value of these resistances (with the exception of friction resistance, which is determined by calculation and experiment), ship models are tested in special experimental pools, the dimensions of which reach 1500x20 m at a depth of up to 7 m. The length of the models is 2-8 m.

Towing of these models is carried out with the help of special carts moving along the rails laid on both sides of the pool. The model is connected to the trolley through a dynamometer, which measures the resistance force of the model when the trolley moves uniformly at a certain speed along the pool. Ship models are made of a wooden frame (skelton) covered with canvas and covered with a layer of paraffin. Paraffin is well processed and easily gives in to alterations and restoration. Sometimes models are made entirely of wood.

The results obtained when testing models are recalculated for a full-scale vessel according to the laws of dynamic similarity. Air resistance R B3 depends on the magnitude of the projection of the surface of the ship on the midship plane; speed, direction of movement; wind speed. It is determined in a wind tunnel by blowing a model through it and reaches impressive dimensions at high speeds, reaching up to 10% of the total resistance. After determining all the individual resistances, the total resistance to the movement of the vessel is determined as their sum, equal to

The impedance is the basis for determining the required power of the ship's main propulsion system, which is converted by the propellers into the forward motion of the ship at a given speed.

There are three types of required power

1) towing, or effective, power (EPS), necessary to overcome the total resistance to the movement of the vessel at a certain speed, expressed in horsepower (1 hp = 75 kgm / s); it is equal to

where R is the total resistance, kg

V - vessel speed, m/s;

2) motor shaft power (BPS), it is greater than the previous one and is determined on the basis of towing, taking into account the efficiency of the propulsion unit itself, transmission mechanisms (gearboxes, couplings, etc.), shafting (support and bearings, etc.), it is equal to

where n - efficiency: n d - propulsion; n n - shafting; n P - transmission mechanism and others;

3) indicated power (JPS), which in turn is greater than the power on the shaft and is equal to the required power of the power plant, taking into account the efficiency of the engine itself, i.e.

where C M is the mechanical efficiency of the machine. The product of all efficiency factors is called total propulsion ratio, which for modern ships is within m) = 0.2-0.64. All the above calculations refer to still water resistances. Excitement, pitching, yaw of the vessel and other phenomena also affect the speed of the vessel, reducing it by an average of 7-9%, and in a strong storm and waves - up to 50-60%. The power of the main ship power plant is converted into the forward motion of the ship by ship propulsion.

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Zygomatic keels.

Zygomatic keels are long plates installed in the cheekbone area along the streamline (Fig. 5.6). Representing a very simple design that does not occupy useful volumes inside the ship, and at the same time creating a noticeable calming effect, bilge keels are the most widely used and are currently used in all fleets of the world.

The effect of bilge keels is to artificially increase the rolling resistance, so it manifests itself most effectively at large pitching amplitudes in the resonance zone.

Rice. 5.6. zygomatic keels

Usually the total area of ​​the zygomatic keels is taken from 2 to 4% of LIN, keel height from 0.3 to 1.2 m depending on the type of ship, on average 3-5% of the width of the ship. Their length usually ranges from 25 to 75% of the length of the ship. The installation site is the zygomatic rounding, and so that the keels do not protrude beyond the midship dimensions. The keel line must be consistent with the streamline of the jets determined by model testing.

Structurally, the keels are made in the form of a sheet mounted on an edge. With a keel height exceeding 400 mm, a strip or semicircular iron is placed on the free edge of the sheet. With a keel height of more than 600 mm the keel is made in the form of a dihedron, inside of which ribs are welded for rigidity.

The influence of side keels on the speed of the vessel is small. For high-speed ships, the decrease in speed in calm water does not exceed 2-3%. In waves, this decrease in speed is even less.

Side steering wheels.

Side controlled rudders represent wings of small elongation, which protrude from both sides of the ship's skin and can be rotated on stocks (Fig. 5.7). The stocks pass through waterproof glands inside the ship's hull and rotate with the help of a special automatically controlled drive.

Fig.5.7. Side steering wheels

Let the ship go at speed v. When the right steering wheel is deflected at an angle ψ from the middle position, it develops a lifting force R. If the rudder is symmetrically located on the port side of the ship, deflected by the same angle ψ , but in the opposite direction, then a lifting force should also develop on it R, however directed downwards (Fig. 5.8). In this case, a moment arises that can be made opposite in direction to the perturbing one (in antiphase). The rudder shift frequency is made equal to the frequency of the disturbing moment, i.e. damper can be adjusted. Transfer control is performed automatically.

The effectiveness of such dampers is good, but they take up a lot of space and are very expensive, so they are usually used on large passenger liners sailing across the ocean.

A major drawback of these dampers is their low efficiency at low speeds and the inability to work in the parking lot.

Rice. 5.8. Forces on the side rudders

Sedation tanks.

The first liquid-type dampers were flat tanks, in which there was a liquid with a free surface (Fig. 5.9). Due to the free surface, the stability of the ship decreased, the period of its free oscillations increased, and for a ship located lag to the wave, the resonance shifted towards longer, and consequently, less steep waves. In addition, since long waves on irregular waves have a lower repeatability than short ones, the probability of the onset of a resonant regime decreased.

Fig.5.9. Flat sedation tanks

A further development of liquid dampers are passive tanks. They represent a kind of hydraulic pendulum, consisting of interconnected tanks located at the sides of the ship.

There are tanks of the first and second kind. Tanks of the first kind (closed) are connected from below by liquid channels, and from above by air channels (Fig. 5.10). Tanks of the second kind (open) also have an air channel, and instead of a water channel, holes are made in the sides, and liquid communication is carried out through the outboard water (Fig. 5.11). Thus, tanks of the first kind, if necessary, can be used as fuel, and for tanks of the second kind, this possibility is not available.

Rice. 5.10. Passive tanks of the first kind Fig.5.11. Passive tanks of the second kind

The stabilizing effect of passive tanks is based on the principle of the so-called secondary (or double) resonance. The essence of this principle is as follows. At roll resonance, the forced oscillations of the ship are out of phase with the disturbing force by 90°. If the period of the natural oscillations of the liquid in the tanks is equal to the period of the natural oscillations of the ship, then there is also a resonance (secondary) and the oscillations of the liquid, in turn, lag behind the oscillations of the ship by 90°. Thus, in the case under consideration, the phase shift between the oscillations of the liquid in the tanks and the perturbing action of the wave is 180°, as a result of which a stabilizing moment is created.

Currently, passive tanks are rarely used due to low efficiency in irregular waves, an increase in pitching amplitudes in non-resonant conditions, a decrease in carrying capacity and cargo capacity, and other shortcomings. In addition, open tanks significantly reduce the speed of the ship, since part of the power of the power plant is spent on imparting kinetic energy to the incoming water, which is irretrievably lost when flowing out.

Activation of tanks can be achieved by installing a compressor in the air channel or a variable displacement pump in the liquid channel. The compressor can be installed both in open and closed tanks, and the pump that pumps liquid from tank to tank can only be installed in closed tanks.

Active tanks are much more efficient than passive ones. They create a stabilizing moment not only at resonance, but also at any ratio of frequencies, which plays a significant role in conditions of irregular waves. They can be used to stabilize a ship that has a static list, to build on calm water, etc. However, due to their complexity, high cost, the need to expend power to set the stabilizing fluid in motion, high requirements for the automatic control system, active tanks on ships are rarely installed.

More often than passive tanks, another type of gravity-type dampers is used - tanks of the "Flum" type (Fig. 5.12).

Rice. 5.12. Flum-type tanks

"Flum" - the system consists of two side tanks connected by a channel, the height of which is the same as the height of the tanks. In the middle part of the channel has a broadened compartment. The tanks and the channel are filled with liquid so that they always have a free surface. The system is designed in such a way that the period of free oscillations of the stabilizing fluid is equal to the period of free oscillations of the ship under some load condition characteristic of its operating conditions. The change in the filling level of the liquid on the period of its free oscillations is reflected weakly. Thus, "Flum" tanks combine the properties inherent in flat tanks, which reduce stability, and passive tanks of a closed type, the stabilizing effect of which is based on the principle of secondary resonance. The fluid flow in these tanks at least twice abruptly changes its cross-sectional area, experiencing a sudden contraction and expansion. In this case, the flow loses part of its kinetic energy, i.e., damping of the oscillations of the stabilizing fluid takes place. This, on the one hand, weakens unwanted impacts of the liquid on the tank covers, and on the other hand, reduces their swinging effect in non-resonant modes.

Roll stabilizers It is customary to call devices that are used to reduce the amplitude of the ship's pitching.
The action of the motion stabilizers installed on the ship is that they create a variable stabilizing moment, opposite in sign to the disturbing moment of the wave. At present, only roll stabilizers are used. It is practically difficult to reduce the pitching and heaving amplitudes with the help of dampers, because stabilizing moments have not yet been created that are capable of developing much greater stabilizing moments than with onboard rolling.
Roll dampers are divided into passive and active. The action of the working bodies of passive dampers is based on the creation of a stabilizing moment due to the oscillatory movements of the vessel during pitching, i.e. when using them, there is no need for special energy sources. In active dampers, a variable stabilizing moment is forcibly created using special mechanisms controlled by a special control device, which, in turn, responds to vessel vibrations. Active dampers are more efficient, but they require additional power to operate.
Passive dampeners. Passive stabilizers include bilge keels and passive stabilizer tanks.

Zygomatic keels are the simplest and most effective means of reducing roll and therefore find the widest application.
Passive soothing tanks can be of two types: closed, not communicating with sea water (I kind) and open, communicating with sea water (II kind). The tanks are half filled with water (sometimes fuel) and connected by channels. Passive sedation tanks are most effective in resonant pitching. Under certain conditions and regimes of irregular waves, such dampers can lead to an increase in the pitch amplitudes. The presence of a free liquid surface in tanks also adversely affects the ship's stability. Due to these reasons, passive tanks are practically not used at present.
Active sedatives. Active roll dampers include onboard steerable rudders, active damper tanks and gyroscopic stabilizers.
Onboard steerable rudders are a very effective means of reducing roll and are widely used on transport and especially on passenger ships. They are placed on special drives that provide a change in the angle of attack according to a certain law, their extension from the hull and cleaning inside the hull.
Practice shows that it is advisable to use onboard rudders at speeds exceeding 10-15 knots. In this case, the side rudders lead to a significant (several times) decrease in the roll amplitudes.
Active sedative tanks are usually made in the form of tanks of the first kind. To regulate the movement of water, either pumps installed in the water channel or blowers located in the air channel are used. The pump or blower is controlled by special automation in such a way that it is possible to regulate the water supply from one tank to another and provide the required change in the stabilizing moment. The effectiveness of the installation does not depend on the speed of the vessel: the tanks equally moderate the pitching on the move and in the parking lot. Disadvantages of active tanks: design complexity, high cost, the use of complex control equipment, a decrease in the carrying capacity of the vessel, the need for additional energy costs.
Gyroscopic damper pitching is a powerful gyroscope rotating on an axis in the frame. The gyroscope is installed vertically. The roll of the ship during rolling causes the axis of the gyroscope to rotate - the so-called precession of the gyroscope. As a result, a gyroscopic moment arises, which is the stabilizing moment of the damper. Gyroscopic dampers can be either passive or active. In a passive damper, precession occurs as a reaction to the pitching of the ship. In active dampers, precession is forcibly created by transferring external energy to an electric motor controlled by an automatic regulator that responds to the vessel's motion. Disadvantages: significant weight, high cost, complexity of device and operation.

Topic 2.1 Rolling.

Roll stabilizers.

Passive sedatives. Passive stabilizers include zygomatic keels And passive still tanks.

zygomatic keels are the simplest and most effective means of reducing roll and therefore find the widest application. the stabilizing effect of the bilge keels is due to the increase in the damping moment created by the additional rolling resistance forces, which are most noticeable at resonance. In addition, when rolling on the keels of the starboard and port sides, as on wings, lift forces of the opposite direction arise, creating an additional stabilizing moment.

In terms of design, bilge keels (Fig. 51) are plates installed along the vessel in the bilge area. Keels are positioned so that they do not go beyond the dimensions of the vessel. The total area of ​​the keels on both sides is from 3% to 6% of the LB product. The effectiveness of side keels to a large extent depends on the well-chosen ratio of their width to length. Width Fig.51 Zygomatic keels. the keel ranges from 200 to 1200 mm. Average

the ratio of the width of the keels to the width of the vessel is 0.03 - 0.05, and their length to the length of the vessel - 0.25 - 0.60. The installation of keels of a larger area leads to a decrease in the amplitude of the resonant roll by 45 - 50%. In conditions of irregular waves, side keels of normal area reduce the amplitude of rolling by an average of 20 - 30%.

Passive sedative tanks. Passive sedation tanks can be of two types: closed, not communicating with sea water (tanks of the first kind) (Fig. 52a), and open, communicating with sea water (tanks of the second kind) (Fig. 52b). They are two flat side tanks located across the vessel. The tanks are half filled with water (for tanks of the 1st kind - sometimes with fuel) and are connected by channels. Tanks of the 1st kind have two channels - water (below) and air (above). equipped with a valve. Tanks of the second kind do not have a water connecting channel, because there are holes in the side walls that communicate with the sea water.

The principle of operation of such tanks is based on the creation of a stabilizing moment by moving a mass of liquid from one onboard compartment to another. Fluid displacement is caused by the ship's motion and does not require additional energy. 52 Passive sedation tanks: costs. Selection of elements of tanks, 1 - side tanks; 2 - air channel with channel sizes and adjustment; 3 - valve; 4 - water channel. valves can be equalized

the period of liquid oscillations in tanks and the period of the ship's natural oscillations. As a result, during resonant pitching, the phenomenon of double resonance occurs: the ship is 90 0 behind the wave oscillations in phase, and the liquid in the tanks is 90 0 behind the ship’s oscillations. The total phase delay is 180 0 , the tanks operate in antiphase with water (Fig.53), and the emerging stabilizing moment turns out to be opposite in sign to the disturbing moment and counteracts the inclination of the vessel.

Passive sedation tanks are most effective for resonant rolls and less effective for non-resonant waves. Under certain conditions and regimes of irregular waves, such dampers can lead to an increase in the pitch amplitudes.

Rice. 53 Sequential position of water in still tanks with resonance

ship's pitching.

The presence of a free liquid surface in tanks also adversely affects the ship's stability. Due to these reasons, passive tanks are practically not used at present.

Active sedatives. Active stabilizers include onboard steerable rudders, active sedative tanks and gyroscopic dampers - stabilizers.

Onboard steerable rudders are a very effective means of moderating

rolling and are widely used on transport and especially on passenger ships. They are wings of small elongation, which are installed along the sides of the vessel in the area of ​​the zygomatic part. The wings are placed on special drives that provide a change in the angle of attack according to a certain law, their extension from the hull and retraction inside the hull (Fig. 54). The dimensions and area of ​​the controlled rudders are determined by appropriate calculation, depending on the lowest speed of the vessel at which they are proposed to be used.

The principle of operation of the onboard controlled rudders is based on the occurrence of a stabilizing moment that counteracts the rolling, by properly shifting the rudders. The stabilizing moment is created by the lifting forces formed on the rudders of the right and left sides when they are flowed around .

When the ship is heeling from port Fig. 54 Steerable rudders. sides to starboard, and the rudders are shifted so that

the tail part of the starboard rudder is lowered down, and the tail part of the left side is raised up, then in this position, an upward lift occurs on the starboard rudder, and a downward lift occurs on the left side rudder. Due to this, a moment is created that counteracts the swing of the roll.

The rudder drives are controlled by a complex of special automatic devices that provide continuous measurement of the ship's roll parameters (roll angle, angular velocity and angular acceleration) by gyroscopic sensors, calculation of the lift and rudder angle of attack and subsequent feed

commands to the hydraulic drive, which provides the necessary rearrangement of the rudders. The control post for the entire system is located on the ship's bridge, and the power and actuator units are located in close proximity to the rudders in the engine room.

The effectiveness of the onboard steerable rudders depends on the speed of the vessel, since the forces generated by each rudder are proportional to the square of the speed of the oncoming flow. Practice has shown that it is advisable to use onboard rudders at speeds exceeding 10 - 15 knots.

Questions for self-control:

1. Why are stabilizers installed on the ship?

2. What types of stabilizers are divided into?

3. What are zygomatic keels and their principle of operation?

4. Design and principle of operation of passive sedative tanks?

5. What agents are active stabilizers?

6. What are on-board steerable rudders and their principle of operation?

Topic 2.2. Vessel propulsion

2.2.1 types of ship propellers and the principle of their operation.

On marine vessels, fixed-pitch propellers (FPS) or variable-pitch screws (CRPs) are most often used.

The propeller (VFS) is a system of blades (from 2 to 8), each of which is a section of the helical surface. The surface of the blades facing the nose is called sucking. Aft facing surface forcing. The leading edge of the blades is called incoming, the rear - outgoing. VFSh are solid-cast and with removable blades. They are divided into left and right rotation screws. The right rotation propeller in forward motion, when viewed from the stern, rotates clockwise, the left rotation propeller - vice versa.

The stop force created by the screw when it rotates at a given frequency depends on its basic geometric characteristics,

1. D B propeller diameter - the diameter of the circle described by the most distant points of the blades (up to 5 meters);

2. H the geometric pitch of the screw is the linear distance along the axis of the screw that the hub would pass in one complete revolution when rotating in a dense medium. (H/D step ratio ranges from 0.8 to 1.8)

3. Θ disk ratio Θ= А/А d - for low-speed vessels ≈0.35

for high-speed ≈ 1.2

A is the total area of ​​the straightened surface of all propeller blades;

And d is the area of ​​the circle swept by the propeller during its rotation.

4. Z number of blades.

as well as the speed of the ship itself.

The interaction of the propeller with the ship's hull has a significant effect on the thrust force of the propeller. The stop force without taking into account such interaction is called stop of the insulated screw. Given this interaction, useful emphasis or thrust. For VFS, changing the direction of the stop is achieved by reversing the motor. The VFS has a maximum efficiency only in one driving mode (usually full forward speed).

Unlike fixed-pitch propellers, controllable-pitch propellers (CPPs) have a drive mechanism in the hub, with the help of which the blades are turned from the “PPKh” position to the “PZKh” position. Thus, without changing the direction of rotation of the main engine, not only the magnitude, but also the direction of the propeller stop is changed. PRSh can be three-blade and four-blade. In the latter case, the blades are arranged in pairs and displaced along the axis of the propeller (Tendem-type CPPs). The angle of rotation of the blades during the transition from PPH to PZH is 40 - 50 0 . The turn time of the CPP blades is 10 - 15 seconds. The use of the CPP allows you to get the full power of the main engine in modes other than the calculated ones, provides an increase in the speed of the vessel and the efficiency of its propulsion system. % reduces the time and length of the braking distance. The CPP installation allows for remote control of the vessel and use on reversible engines, which significantly increases their engine life. The disadvantages of CPPs include the complexity of the design of both the propeller itself and the shafting, their greater sensitivity to shock loads compared to CFSs.

Questions for self-control:

12. What types of propellers are used on ships?

13. What is a propeller (VFS)?

14. What determines the thrust force created by the VFS when it rotates at a given frequency?

15. What is and how is the turn of the adjustable screw (ARS) performed?

Topic 2.3. Controllability.

2.3.2 Roll of the ship on the turn.

If the rudder is suddenly shifted on a ship going in a straight course, then at the first moment after the start of the shift, the trajectory of the ship's motion will bend in the direction. reverse direction of the rudder. At this moment, the following forces act on the ship (Fig. 55a):

Rice. 55 a - diagram of the forces that roll b - diagram of the forces that roll the ship

ship after the rudder has begun. during the period of steady circulation.

RU- the transverse component of the forces acting on the steering wheel;

Ry- the transverse component of the forces acting on the submerged part of the ship's hull;

F c- the transverse component of the centrifugal forces of inertia of the vessel, the line of action of this

the force is directed towards the turn of the vessel;

Force RU applied at the center of pressure of the rudder, the elevation of which above the main plane is determined by the applique z'd; force Ry applied at height z d , and strength F c– at the ship's center of gravity, determined by the applique z g.

moment of centrifugal force F c causes a slight roll on the side on which the rudder is shifted (the moment of force Ry we neglect in view of the small action of this force in the initial stage of circulation). This roll is amplified by the moment of force RU acting on the steering wheel.

So, at the first moment after the rudder is shifted, the ship will list on the side on which the rudder is shifted, i.e. inside the circulation.

As the curvature of the trajectory changes, the centrifugal force decreases and then changes sign, i.e. changes the direction of action to the opposite (Fig. 55b). At the same time, there is an increase in the moment from the force Ry due to an increase in the drift angle and a decrease in the moment from the force RU due to a decrease in the ship's speed. As a result of a change in the nature of the action of the indicated forces and moments, the ship first straightens up, and then begins to roll in the direction opposite to the direction of the rudder shift, and the inclination of the ship is the greater, the greater the roll angle in the direction of the rudder shift. The change in roll direction is dynamic.

The maximum inclination in the direction opposite to the direction of the rudder is called dynamic bank angle ships on circulation.

With further movement of the vessel, the angle of heel decreases. The vessel makes one or two oscillations, and after the elements of motion are established, the angle of heel acquires a certain constant value on the steady circulation. This angle coincides in sign with the dynamic roll angle, but the latter, as a rule, exceeds the roll angle in steady circulation by 1.5–2.0 times.

The Marine Register in the current "Rules for the Classification and Construction of Sea-Going Ships" prescribes to determine the heeling moment on the circulation according to the formula:

m cr = 0.238 (z g ) (2.3)

Where: – the mass of the vessel, taking into account the added mass of water. participating in the movement, t;

The speed of the ship when entering the circulation, equal to 80% of the full speed;

Vessel length.

From here, after appropriate transformations, we obtain a formula for determining

bank angle on steady circulation:

θ 0 1,4 (z g ) (2.3.1)

Expression (2.3.1), representing the well-known formula of G.A. Firsov, shows that the angle of roll, which increases in proportion to the square of the speed when entering the circulation, is inversely proportional to the metacentric height h.

Calculations give good results for sea transport vessels, the circulation diameter of which usually does not exceed five vessel lengths at the maximum rudder angle.

According to the "Rules for the Classification and Construction of Sea-Going Ships" of the Maritime Register, the angle of heel of passenger ships due to the combined action of heeling moments resulting from the accumulation of passengers on one side and the action of external forces on a steady circulation, should not exceed 3 / 4 the angle of flooding or the angle at which the freeboard deck enters the water or the chine exits the water, whichever is the smaller; in any case, the angle of heel should not exceed 12 0 .

Questions for self-control:

1. What forces act on the ship when the rudder is shifted to circulation?

2. How do the forces that roll the ship act after the start of the rudder shift and during the period

established circulation?

3. How is the heeling moment on the circulation prescribed by the Register of Shipping determined?

4. How is the angle of heel in steady circulation determined?

5. Requirements of the Register of Shipping on the maximum value of the angle of heel for passenger ships?

LITERATURE:

1. F.N. Belan, A.M. Chudnovsky. Fundamentals of the theory of the ship. - L: Shipbuilding, 1978

2. I.I. Bendus. Theory and arrangement of the vessel. Part 1.2 ed. revised and additional - Kerch.: KSMTU, 2006

3. V.D. Kulagin. Theory and arrangement of fishing vessels.- L.; Shipbuilding, 19861. L.R. Aksyutkin. Stability control of sea vessels.- Odessa: Feniks, 2003

4. A.M. Goryachov, E.M. Podrugin. The device and fundamentals of the theory of sea vessels. - L .; Shipbuilding, 1981

5. Ship documents: BMRT "Nikolay Ostrovsky", RTMA "Prometheus"

6. V.L. Fukelman. Fundamentals of the theory of the ship. - L .; Shipbuilding, 1977

APPENDIX I

The concept of vessel stability

When sailing at sea, ships are constantly affected by various heeling loads, primarily wind and waves. How, then, can a relatively small ship withstand a squally wind and waves crashing onto the deck, listing now to starboard, then to port, but not capsizing? The answer to these questions is given by the doctrine of stability.

Stability is the ability of a vessel, brought out of equilibrium by the action of external heeling loads, to return to its original position again after the termination of this effect.

Stability is one of the main seaworthiness qualities, maintaining and maintaining it is the most important task of the ship's crew.

The term "stability" comes from the concept of the stability of the equilibrium of bodies, but it has a broader meaning. When considering stability, they usually mean only small deviations from the equilibrium position, and when considering the stability of a ship, both small and large ones. The deviation of the vessel from the equilibrium position in the transverse plane is called roll, in the longitudinal - trim.

There are stability at small inclinations (initial) and stability at large angles of heel. Separating the initial stability into an independent section makes it possible to introduce a number of assumptions that greatly simplify mathematical dependencies when solving various practical problems. The initial stability formulas can be applied up to the angles of heel corresponding to the entry of the edge of the deck into the water in the event that the chine does not emerge from the water. These angles for conventional ships are 8-12° or more. Initial stability formulas should be considered as a special case of dependencies related to stability at large angles of heel.

When considering stability, it is understood that the ship is tilted under the action of a couple of forces; the value of the support force does not change. At the same time, the volume of the underwater part remains constant, and only its shape changes. Such inclinations and the waterlines corresponding to them, cutting off the same volumes, are called equal volume. In problems of initial stability, waterlines of equal volume are drawn through the center of gravity of the original waterline.

Roll stabilizers are commonly referred to as devices that are used to reduce the amplitude of the ship's roll.

The action of the motion stabilizers installed on the ship is that they create a variable stabilizing moment, opposite in sign to the disturbing moment of the wave. At present, only roll stabilizers are used. It is practically difficult to reduce the pitching and heaving amplitudes with the help of dampers, because stabilizing moments have not yet been created that are capable of developing much greater stabilizing moments than with onboard rolling.

Roll dampers are divided into passive and active. The action of the working bodies of passive dampers is based on the creation of a stabilizing moment due to the oscillatory movements of the vessel during pitching, i.e. when using them, there is no need for special energy sources. In active dampers, a variable stabilizing moment is forcibly created using special mechanisms controlled by a special control device, which, in turn, responds to vessel vibrations. Active dampers are more efficient, but they require additional power to operate.

Passive sedatives. Passive stabilizers include bilge keels and passive stabilizer tanks.

Zygomatic keels are the simplest and most effective means of reducing roll and therefore find the widest application.

Passive soothing tanks can be of two types: closed, not communicating with sea water (I kind) and open, communicating with sea water (II kind). The tanks are half filled with water (sometimes fuel) and connected by channels. Passive sedation tanks are most effective in resonant pitching. Under certain conditions and regimes of irregular waves, such dampers can lead to an increase in the pitch amplitudes. The presence of a free liquid surface in tanks also adversely affects the ship's stability. Due to these reasons, passive tanks are practically not used at present.

Active sedatives. Active roll dampers include onboard steerable rudders, active damper tanks and gyroscopic stabilizers.

Onboard steerable rudders are a very effective means of reducing roll and are widely used on transport and especially on passenger ships. They are placed on special drives that provide a change in the angle of attack according to a certain law, their extension from the hull and cleaning inside the hull.

Practice shows that it is advisable to use onboard rudders at speeds exceeding 10-15 knots. In this case, the side rudders lead to a significant (several times) decrease in the roll amplitudes.

Active sedative tanks are usually made in the form of tanks of the first kind. To regulate the movement of water, either pumps installed in the water channel or blowers located in the air channel are used. The pump or blower is controlled by special automation in such a way that it is possible to regulate the water supply from one tank to another and provide the required change in the stabilizing moment. The effectiveness of the installation does not depend on the speed of the vessel: the tanks equally moderate the pitching on the move and in the parking lot. Disadvantages of active tanks: design complexity, high cost, the use of complex control equipment, a decrease in the carrying capacity of the vessel, the need for additional energy costs.

The gyroscopic stabilizer is a powerful gyroscope that rotates on an axle in a frame. The gyroscope is installed vertically. The roll of the vessel during roll causes the axis of the gyroscope to rotate - the so-called precession of the gyroscope. As a result, a gyroscopic moment arises, which is the stabilizing moment of the damper. Gyroscopic dampers can be either passive or active. In a passive damper, precession occurs as a reaction to the pitching of the ship. In active dampers, precession is forcibly created by transferring external energy to an electric motor controlled by an automatic regulator that responds to the vessel's motion. Disadvantages: significant weight, high cost, complexity of device and operation.