The resistance of water and air to the motion of a vessel. Resistance of water and air to the movement of the ship

Power plants, in which power from the main engines is transmitted to the propellers by means of power transmission, are commonly called propeller electrical installations (PPU).

Electric transmission makes it possible to ensure the fulfillment of one of the main requirements for the power plant of an icebreaker - maintaining a constant power of the main engine with changes in the torque on the propeller.

1. GEU classification

Rowing electrical installations(GEM) can be classified according to the following

common signs:

by type of current - alternating, direct and alternating-direct current (double

different kind of current);

2. by type of prime mover - diesel-electric, turbo-electric and gas-turboelectric;

3. according to the control system - with manual control and with automatic control

4. according to the method of connecting the propulsion motor with the propeller - with a direct connection

and with a gear connection.

In propulsion electrical installations direct current as the main generators

generators with independent excitation are used, and as propulsion motors - engines with independent excitation.

In propulsion electric installations of alternating current as the main generators

Tori are used synchronous machines, and as propulsion motors - synchronous or asynchronous.

The advent of powerful controlled semiconductor rectifiers led to the creation of an AC-DC (double current) GEM.

The advantages of AC-DC GEM are:

1. high reliability and efficiency of synchronous generators;

2. smooth and economical regulation of the speed of the propeller motor

a body controlled by a rectifier;

3. the possibility of supplying electricity to all ship consumers from the main generators (single AC power plant).

2. GEU DC

2.1. Basic information

DC propulsion electrical installations, in which the propulsion motors and the generators supplying them are DC electrical machines, differ

They are characterized by simplicity, convenience and smoothness of propeller speed control in a wide range of their load torques.

DC power plants are used in low and medium power installations on ships with high maneuverability. Limiting the power of the direct current GEM is determined by

It is due to the fact that the creation of high-power electric machines on direct current is more difficult than on alternating current.

2.2. Schemes for switching on generators and propulsion engines of DC power plants

A DC power plant uses a number of options for the main circuits for switching on generators and propulsion electric motors. Some of them are shown in fig.

Rice. 14.1. Connection diagrams for generators and motors in DC power plants

Scheme with serial connection generators and armatures of the engine (Fig. 14.1, a) allows you to get an increased supply voltage to the engine, since the voltage

generators summed at the rated current of the generator.

For example, if the generator voltage is 600 V, then 1200 V will be supplied to the engine. As required by the Register Rules, this is the voltage limit that is allowed

between any two points of the GEM main current circuit.

In a power plant with a series connection of generators, a dangerous emergency situation is possible if one of the prime movers loses its fuel supply, for example, due to a diesel fuel pump jamming.

At the same time, the current of the main circuit continues to flow through the generator. A large negative moment is created on the generator shaft, which will stop the emergency primary motor.

the valve and will start to rotate it in the opposite direction, which will lead to major damage to the diesel engine. This situation should be quickly detected by appropriate sensors (often

rotation, water pressure, oil pressure), which issue an emergency stop signal and both

sinter the removal of excitation of the generator.

Scheme with parallel connection generators (Fig. 14.1, b) provides convenient

switching on and off individual generators.

If the generators are installed on the same shaft, then the uniformity of their load is ensured

reads relatively easy. If the generators have different prime movers, then a uniform distribution of loads is achieved with the help of additional measures, for example, by introducing cross-links between the series excitation windings.

On fig. 14.1, in shows an example of a single-circuit power plant with a serial connection of four generators and two engines. Such a scheme, in which a pair of generators and one engine alternate, allows you to lower the voltage between any two points in the circuit to double the voltage of one generator and thereby increase safety.

maintenance of the GEM.

A power plant of such a composition of generators and a HED can also have a two-circuit structure: each electric motor is powered by its own pair of series (or parallel) connected generators. Two GEM circuits provide greater reliability of the installation as a whole.

Power plants, in which power from the main engines is transmitted to the propellers by means of power transmission, are commonly called propeller electrical installations (PPU).

Electric transmission makes it possible to ensure the fulfillment of one of the main requirements for the power plant of an icebreaker - maintaining a constant power of the main engine with changes in the torque on the propeller.

The following schemes of power plants are most widely used:

1. With regulation of the magnetic flux of the propeller motor (PM) with a constant magnetic flux of the generator.

2. With the regulation of the magnetic flux of the main generator with a constant magnetic flux of the HEM.

3. With the regulation of magnetic fluxes of both the generator and the HEM.

An example of schemes of the first type, with automatic regulation of the magnetic flux of the PEM, is the scheme used on the Wind-type icebreakers (Fig. 118), using a high-speed regulator of the Silverstat type. The magnetic circuit of this regulator has two windings. One of them (OH) is connected to the armature terminals of the D HED, and its current is proportional to the armature voltage. The second winding (OT) is connected to the voltage drop in the additional poles of the DP HEM, and its current is proportional to the current of the main circuit. The ampere turns of the OT winding create a magnetic flux opposite to the flow created by the ampere turns of the OH winding. The total magnetic flux of both windings affects the armature of the regulator P, which, when moving, closes or opens the lamellar spring contacts connected to the sections of the rheostat Gr. At the nominal values ​​of current and voltage of the PEM, the armature of the regulator takes a position that ensures the flow of the nominal current in the excitation winding of the ATS electric motor and, consequently, the nominal value of the torque.

With a sudden increase in the moment of resistance on the propeller, in the first period, the revolutions of the propeller shaft and the voltage of the generator remain constant, and the current in the main circuit increases sharply. In proportion to the increase in the current of the main circuit, the current in the current winding of the OT regulator also increases. In this case, the magnetic flux in the magnetic circuit decreases, and, consequently, the force of attraction of the regulator armature. As a result, the armature deviates and closes some of the springy contacts, thereby shunting individual sections of the rheostat. This causes an increase in the HEM excitation current and, accordingly, a decrease in its rotation speed. The power consumed by the HEM will remain approximately constant, since

Rice. 118. Scheme of electric movement. 119. Scheme of an electric propulsion-icebreaker of the type Windnia leyaokola Kapitan Belousov

The generator voltage is almost unchanged. The regulator will increase the excitation until the main circuit current reaches the nominal value.

With a decrease in the moment of resistance applied to the screw, the current of the main circuit decreases. In this case, the demagnetizing effect of the current winding from the regulator will decrease and the armature will open some of the spring contacts. The resistance of the rheostat in the HEM excitation circuit will increase, the excitation current will decrease, and the rotation speed will increase. The power consumed by the PEM will again be equal to the nominal one. Thus, the use of the regulator makes it possible to fully use the rated power of the installation in all navigation modes without overloading the primary engines.

An example of schemes of the second type, with automatic regulation of the magnetic flux of the main generator, is the scheme used on the icebreaker Kapitan Belousov. Here, an excitation and control system was used using high-speed regulators (Fig. 119).

To power the excitation windings of the main OVG generators, two-winding VT exciters were used. One of the windings, anti-compound (PKO), is connected to the voltage drop in the additional poles of the DC and HED. The other one - the control winding of the OS receives power from the control post of the PU through the high-speed regulator Gr. The high-speed regulator and the PKO winding are designed to limit the current in the main circuit with a changing resistance moment. With an increase in the current in the main circuit above the nominal value, the effect of the PKO winding, connected towards the control winding, is enhanced. As a result, the voltage on the main generator G decreases, and consequently the speed of rotation of the PEM decreases, which protects the primary engines from overload. The high-speed regulator begins to operate at a current greater than the rated current. The regulator spring tends to turn the movable contact Gr into a position in which the excitation of the generator will be the greatest. The winding of the regulator is connected to the voltage drop in the additional poles of the HEM, and therefore it flows around with a current proportional to the current of the main circuit. In the presence of current in the main circuit, a torque acts on the armature of the Yar regulator, which is counteracted by the spring moment. When the current of the main circuit reaches the value to which the regulator is set, the moment created by the current coil will exceed the moment of the spring, as a result of which the moving contacts will begin to move, introducing additional resistance into the op-amp winding. The current in the op-amp winding will decrease; generator voltage will also decrease. This process will stop as soon as the voltage drop at the additional poles of the propulsion motor reaches a value corresponding to the rated load current.

The disadvantage of regulators is the low response speed, which does not ensure the stability of the current of the main circuit when ice floes hit the propeller blades, reverses, etc.

An example of schemes of the third type, with automatic regulation of the magnetic flux of the main generators and the propulsion motor, can be the scheme used on the icebreaker Murmansk. Consider the onboard circuit of the power plant of this icebreaker (Fig. 120), paying attention to the control and regulation system of the power plant.

The onboard circuit (Fig. 120, a) consists of two main generators G, GED-D, exciters of the VT generators and the HP engine. The excitation of the VT and HP units is provided by controlled (thyristor) and uncontrolled (diode) rectifiers, in turn, the rectifiers are powered by an auxiliary three-phase ship's network. It should be noted that the anti-compound winding of the PKO operates only in emergency mode, when the thyristor excitation of the generators fails. In this case, the OVVG ^ ^ and OVVG windings perform the functions of the control winding of the OS and shunt din, respectively.

Rice. 120. Scheme of the electrical movement of the Murmansk icebreaker: a - circuit diagram GEM; b - block diagram of regulation

The excitation of the HEM is carried out as follows: from the auxiliary AC network through the rectifier // (Fig. 120, b) the main excitation winding of the exciter of the ATS exciter ^ ^ ^ receives power. The exciter of the HP motor is excited and supplies power to the excitation winding of the HP motor.

Another HP winding - additional OVVD ^^ ^ ^ - is prepared for action and works only in dynamic modes. When shifting the handle of the control post, the PU receives power from the excitation winding of the exciters of the main generators of the OVVG. X or OVVG ^ ^ x- These windings are powered from the auxiliary AC network through thyristor rectifiers 5a and 56. The exciter of the VG generator is excited and supplies power to the excitation windings of the OVG generator.

The scheme provides for constant power and constant speed control. These modes are provided by the influence feedback(by current and voltage of the main circuit, by the speed of rotation of the PEM, by the excitation voltage of the generators and the excitation current of the engine) for the excitation of the VG and HP. For example, when reversing the control system works as follows. The handle of the control station is shifted from the "full forward" position to the "full back" position. At the same time, at the output of the rotary transformer, rigidly connected to the control station, the sign of the driving signal changes to the opposite. This signal passes through the control blocks 1a-~1v or 16-1v (the first case - for the constant speed mode, the second - for the constant power mode) to the control blocks 4a and 46 thyristor rectifiers 5a and 56. Blocks 4a and 46 act in this way, that the thyristor rectifier 5a, which feeds the forward excitation winding OVVG^.u, closes, and the rectifier 56 opens. Such switching is carried out using the sign inverter 3. The generators are excited in the opposite direction, and the HEM is reversed. In this case, the main parameters of the GEM (speed, current, voltage) change dramatically. The main circuit current changes sign and, having reached its maximum value, remains approximately at this level for a considerable time. Despite the relatively high current of the main circuit, the additional winding of the HEM does not work until the propeller stops almost completely, i.e., the reverse occurs at a constant flow of the HEM. This is explained by the fact that the circuit provides for the adjustment of the operation of the additional winding OVVDop depending on the reverse power.

At the moment of recuperation, the reverse power logic device 12 sends a signal to the control unit 1d, which, acting on the control circuit of the thyristor rectifier 5v, locks it. When the regenerative period ends, the additional winding of the OVVD ^ ^n comes into operation, the excitation current of the HEM increases, the current of the main circuit decreases, and soon the main parameters of the GEM approach normal.

More details on rowing electrical installations can be found in.

other types of power transmission from the prime mover to the propeller should include hydraulic transmissions. Two types of transmissions are used in marine power plants: hydraulic clutches and torque converters. For the power plants of icebreakers, mainly torque converters and hydraulic torque converters are of interest.

Torque converters have the ability to smoothly change the gear ratio depending on the torque on the driven shaft at a practically constant speed of rotation of the primary engine, i.e. they are self-adjusting, while ensuring satisfactory traction characteristics of the power plant.

Compared with the power plant, torque converters have the following advantages: lower weight and dimensions, lower construction cost, and a smaller staff of supper personnel.

However, torque converters also have very significant drawbacks: low flexibility of the installation scheme (since during hydraulic transmission each main engine is connected to only one propeller shaft), relatively low power in reverse (20-30% lower than in forward). In addition, at partial loads, the torque of the torque converter when ice gets under the propeller blades may be insufficient, as a result of which the propeller may stop and even break. Absence practical experience The operation of ships with torque converters in ice conditions does not allow us to give an exhaustive answer about the advisability of installing them on icebreakers.

Types and types of propulsion plants

TOPIC 1. GENERAL INFORMATION AND CONCEPTS ABOUT PROPELLER ELECTRIC INSTALLATIONS

Ship power plants consist of an energy source located on the ship, a transmission mechanism and a mechanical propulsion unit that converts the mechanical energy of rotation into the energy of the ship's translational motion.

Power sources on ships are mainly heat engines - diesel engines and steam or gas turbines. In them, the energy of the fuel or thermal energy converted to mechanical.

The transfer of energy from heat engines to ship propulsion can be mechanical, hydraulic or electrical.

Installations with electrical energy transfer to the propellers are called propulsion electric installations - GEM.

Reliable and economical propulsion units are units that include low-speed (low-speed) diesel engines 1, (Fig. 1.1) connected directly to the propeller shafts on which the propellers are located. The thrust force developed by the propeller 3 is transmitted to the ship's hull through the thrust bearing 2.

Fig.1.1. Diesel propulsion plant

On ships with high-power power plants and on high-speed passenger liners, propellers 3 are driven by steam turbines 1 with gear reducers 4 (Fig. 1.2). They are called turbo gear units (TZA).

Fig.1.2. Propulsion plant with steam turbine

On ships with nuclear power plants, thermal energy from nuclear reactors is also converted into mechanical energy with the help of heat engines - steam or gas turbines. Nuclear power plants (NPPs) are much more complicated than other plants, have a high degree of automation, and require a larger number of qualified service personnel. The use of AECS is justified for large-capacity tankers and icebreakers, because at the same time, the useful volume and autonomy of navigation are increased and the downtime required for replenishment with fuel is reduced.

Rowing electrical installations (PPU) consist of heat engines 1 (Fig. 1.3), which operate on generators 2, direct or alternating current 2, the generators' electricity is supplied to the propulsion motors 3, through the control panel 4.

Fig.1.3. Scheme of the propulsion electrical installation

Propeller motors are connected to propellers (most often propellers).

Also in the power plant circuit there is an excitation system 5. The power plant control post 6 is designed to control the power plant circuit through manual or automated control 7.

Power plants allow you to reduce noise, allow you to often change the speed and direction of movement, and the power plant can also be used to power other ship mechanisms.

1.3. Requirements for GEM. Advantages and disadvantages of GEM.

The power plant, like all ship equipment, must be highly reliable and reliable, as well as have a simple device and be safe for maintenance. Power plants should not completely fail and cause the ship to stop in case of damage to one heat engine, generator, electric motor or their control system.

Advantages of GEM compared to other types of transmission:

For power plants, heat engines are used with high frequency rotation, which reduces mass.

The absence of a direct connection between the heat engine shaft and the propeller shaft makes it possible to optimize the operation mode and dimensions of the ship propulsion unit and reduce the length of the connecting shafts.

It is possible to switch generators and propulsion motors (PM) in emergency situations to save the ship's progress.

Ease of control compared to other types of transmission;

High efficiency at low and medium speed;

In diesel - electric power plants, the aggregate repair method can be used (each node is repaired by its specialists at the same time).

The application of the power plant eliminates the transmission of propeller vibration and shock to heat engines

Along with the advantages of GEMs, they also have disadvantages:

1.- During electrical transmission in generators and PEM, additional losses appear that reduce efficiency - 5-8%

2.- The use of power plants without automatic control requires an increase in maintenance personnel.

3.- Power plants have increased operating costs, but this is often offset by an increase in payload.

The propeller electric plant is the main power plant of the vessel, which drives the propeller into rotation with the help of an electric motor powered by a current generated by a generator. Installations of this type are mainly used on icebreakers, special purpose ships, and submarines.

The largest ship using a propulsion electric installation can currently be considered the ocean liner RMS Queen Mary 2, equipped with four movable electric motors of the Azipod type with a power of 215 MW each.

The electrical transmission makes it possible to ensure that the power of the main engine remains constant with changes in the torque on the propeller.

Rowing electrical installations (PPU) can be classified according to the following criteria:

1. By the type of current - AC, DC and AC-DC (dual current);

2. By type of prime mover - diesel-electric, turbo-electric and gas-turbo-electric;

3. According to the control system - with manual and automatic control;

4. According to the method of connecting the propulsion motor with the propeller - with a direct connection and with a gear connection.

In propulsion electric DC installations, generators with independent excitation are used as main generators, and engines with independent excitation are used as propulsion electric motors.

In AC propulsion electric installations, synchronous machines are used as main generators, and synchronous or asynchronous electric motors are used as propulsion electric motors.

The use of powerful controlled semiconductor rectifiers made it possible to create a GEM of a double kind of current.

The advantages of this type of power plant are:

– high reliability and efficiency of synchronous generators;

- smooth and economical regulation of the frequency of rotation of the propulsion motor controlled by the rectifier;

– the possibility of supplying all ship consumers from the main generators, i.e. from a single ship AC power plant.

DC GEMs are used in installations of low and medium power with high maneuverability. The power limitation of this type of GEM is determined by the complexity of creating high-power electric machines at direct current compared to machines at alternating current.

Such installations are characterized by simplicity, convenience and smooth control of the propeller speed in a wide range of their moments and loads.

AC power plants are installed on ships with a relatively rare change in traffic mode.

They are characterized by the use of increased voltages: at power plants up to 10 MW - 3000 V, at high powers - up to 6000 V. The rated current frequency is usually 50 Hz.

In AC power plants at low and medium power (up to 15 MW), diesel engines are usually used as the prime mover, and turbines at high power.

Regulation of the rotational speed of propulsion electric motors in AC power plants with fixed-pitch propellers is ensured by changing the voltage frequency of the generators when the rotational speed of the primary engines changes, or by using asynchronous machines with a phase rotor as propulsion electric motors. Frequency control of the angular velocity of AC propulsion motors turns out to be energetically beneficial, since this minimizes their electrical losses. Changing the direction of rotation of the propulsion motors is achieved by switching the phases in the main circuit, the number of which, as a rule, is three.

A way to control the operating mode of an AC power plant, which makes it possible to avoid the difficulties of regulating the rotational speed of AC motors, is the use of controllable pitch propellers (CPPs).

Dual current power plants are called installations in which synchronous alternators are used as sources of electricity, and DC motors as propulsion motors.

The development of powerful rectifiers made it possible to combine the high maneuverability of DC GEMs with the advantages of AC GEMs, which consist in the use of high-speed prime movers and small weight and size indicators.

Two types of semiconductor rectifiers are used:

- uncontrollable output voltage which are not regulated;

- controlled - with adjustable output voltage;

Dual current GEM with rectifiers provide:

– high maneuverability due to a wide range of regulation of the frequency of the propulsion motor;

- the possibility of creating turbine-generator units without gearboxes and the convenience of their layout in the engine room;

- reduction of noise and vibration of power plant elements;

– increase in overall efficiency. installations;

– the greatest simplicity of execution and reliability of propulsion motors.

The use of a CPP for a dual-current power plant brings additional advantages:

- constancy of the frequency of rotation of the engines of the generators;

- constancy of the frequency of rotation of the propulsion motor and propeller.

The constancy of the frequency of rotation of the primary engines of the power plant makes it possible to take power from the tires of the electric propulsion system for general ship consumers and more rationally use the installed capacity of the ship's power plant.

Dual current GEMs are superior in their characteristics to GEMs of both direct and alternating current.

The main task in the operation of the power plant is to ensure its trouble-free and trouble-free operation, constant readiness for action.

The solution of this problem is achieved under the following conditions:

– providing qualified service;

– timely replenishment of spare parts and materials;

- correct determination of the terms and volumes of preventive and repair work performed by the ship's crew;

- carrying out extended tests and organizing the adjustment of the power plant in accordance with the intended purpose of the vessel;

- constant monitoring of the degree of contamination of insulating surfaces in electrical machines of the power plant;

– checking the condition of cables and terminating their terminations.

Thus, the complex of measures for technical operation covers the maintenance, care and repair of the power plant and its elements.

Bibliography

1. Akimov V.P. Ship automated power plants, "Transport", 1980.

2. Handbook of a ship mechanic (in two volumes). Ed. 2nd, revised. and additional Under the general editorship of Cand. tech. Sciences L.L.Gritsay. M., "Transport", 1974

3. Zavisha V.V., Dekin B.G. Ship auxiliary mechanisms., M., "Transport", 1974, 392 p.

4. Kiris O.V., Lisin V.V. Thermodynamics and heat engineering. Head helper. At 2 hours. Part 1.: Thermodynamics. - Odessa: ONMA, 2005. - 96 p.

5. Ovsyannikov M.K., Petukhov V.A. Ship automated power plants. "Transport", 1989.

6. Taylor D.A. Fundamentals of ship technology. "Transport", 1987.

7. Methodical introductions to the completion of laboratory work from the discipline "Ship power plants and electrical control of ships". Odessa: ONMA, 2012.

8. Vereskun V.I., Safonov A.S. Electrical engineering and electrical equipment of ships: Textbook. - L .: Shipbuilding, 1987. - 280 p., ill.

Automated rowing

Electrical installations

Lecture notes

for students of specialty 7.07010404

"Operation of ship's electrical equipment and automation"

full-time and part-time education

Kerch, 2011

Reviewer: Dvorak N.M., Candidate of Technical Sciences, Associate Professor of the Department of KSMTU.

Lecture notes reviewed and approved at the meeting

Department of ESiAP KSMTU, Protocol No. 2 dated 10/18/2011

at the meeting of the methodological commission of the MF KSMTU,

Protocol No. 2 dated 1.12.2011

Ó Kerch State Maritime

University of Technology, 2011

Introduction

The first rowing electric installation appeared in Russia in 1838. It was a boat with paddle wheels, cruising along the Neva. The inventor was a Russian scientist, academician B.S. Jacobi, who used a DC motor to rotate the paddle wheels.

In the 70-80s of the 19th century, the first electric ships appeared in Europe. In Russia at the beginning of the 20th century, the first diesel-electric ships were Vandal and Sarmat.

In the USSR, the construction of electric ships began in the 1930s. A large number of them were built in connection with the development of the Northern Sea Route and the development of the fishing fleet.

Electric ships can meet a wide variety of conditions and requirements from the operation, ship design and specifications, and for some types of ships are indispensable propulsion electric installations are equipped with icebreakers, ferries, fishing boats, rescue boats, tugboats, etc.

Promising directions for the development of electric propulsion systems are the introduction of alternating current units with semiconductor frequency converters and a PEM with vector control, as well as the use of main machines with superconducting windings, which make it possible to reduce weight and size characteristics and apply the best layout of electrical equipment in the ship's engine room.

Thematic plan disciplines

and distribution of study time according to the topics of classes

Rowing electrical installations (PPU)

Purpose and types of power plants

The electric propulsion of ships should be understood as their movement using electric energy by propulsion electric installations.

The GEM includes:

a) prime mover (diesel or turbine);

b) main generators supplying electric power to the propeller engine;

c) propeller engine connected to the propeller;

d) a propeller (screw) that communicates movement to the ship.

According to the type of current, GEMs are divided into direct and alternating current installations. DC power plants are used on ships where high maneuverability and frequent reversal of the propeller engine are required (icebreakers, ferries, whaling ships, etc.). AC power plants are used on ships for which the installation efficiency is of the greatest importance.

According to the type of primary engine, power plants are divided into diesel electric (DEGU) and turboelectric (TEGU). On fishing vessels, as a rule, DEGU is used.

The power of the diesel engine and its speed are regulated by changing the amount of fuel supplied to the cylinder. The dependence of and on at the limiting fuel supply is called external characteristics(Figure 1.1). Similarly, the dependencies obtained with a lower fuel supply are called partial characteristics. Both on the external and partial characteristics, the torque almost does not change when the diesel speed changes.

Permissible overloads for a diesel engine are 10-15%. The diesel engine develops its rated speed at the maximum fuel supply. At the limit regulator is activated, which stops the fuel supply by the fuel pump. Large diesels, in addition, have an all-mode regulator that can be set to any speed.

TEGU usually operate on alternating current, where the property of turbines is used to change speed over a wide range by simple change the amount of steam. They allow overload.

At present, gas turbine installations are also beginning to be used.

According to their purpose, power plants are divided into main (or autonomous), auxiliary and combined.

In the main power plants, the propeller is driven only by the propeller motor, which is powered by its main generators.

In auxiliary power plants, the main generators feed production mechanisms during operation, and propeller motors during the transition.

In combined power plants, the screw is driven by both the main engine and the electric motor, which consumes the free power of auxiliary generators. An additional propeller engine in this case is used either to help the main one, or to independent work on the propeller at low speeds of the vessel, or as a power take-off generator.

The benefits of GEM include:

a) freedom to choose a place on the ship;

b) the possibility of using high-speed, non-reversible, small-sized diesel engines;

c) good maneuverability;

d) the ability to work with an incomplete number of primary units;

e) high survivability;

f) the ability to work in difficult sailing conditions, provided by the high overload capacity of electric machines;

g) the possibility of using the main generators to power other consumers;

The disadvantages of power plants in comparison with diesel and turbine plants are:

a) low efficiency due to double conversion of energy;

b) high specific gravity and cost;

c) increased staff.

Water and air resistance to ship movement

A vessel stationary in the water is subject to pressure forces, the resultant of which is equal to the vessel's gravity and directed opposite to it (Figure 1.2). When the ship is moving, the resultant of the pressure forces R deviates from the vertical position, and the point of its application is shifted along the DP to the nose.

Figure 1.2 - Diagram of the forces acting on the ship.

The balance of the system will not be disturbed if the ship's center of gravity O apply two opposite forces R 1 and R 2 equal in size and parallel R. Received pair of forces R and R 1 will create a moment causing a defect in the stern.

Force expanded along mutually perpendicular axes R 2 forms the components Q and R.

Q is called the hydrodynamic support force.

R- water resistance; directed opposite to the direction of the ship.

The water resistance R is overcome by the stop force of the propeller, which causes pressure R. The forces of water viscosity at the boundary with the hull create tangential forces R .

, (1.2)

where is the coefficient. thorn resistance of a smooth plate = 0, 0315Re ,

Re- Reynolds number,

ship speed, m/s,

L- vessel length according to GVL, m,

Kinetic viscosity of water at t=4 ,

Hull curvature coefficient, at L/B\u003d 6 \u003d 1.04, with L/B=12 =1,01,

for welded ships, the roughness coefficient of the ship's hull,

is the density of sea water.