Fig.13. A modern diesel engine aboard a cargo ship

About 99% of modern ships use diesel reciprocating engines. The rotating crankshaft can power the propeller directly for slow speed engines, via a gearbox for medium and high speed engines, or via an alternator and electric motor in diesel-electric vessels.

The reciprocating marine diesel engine first came into use in 1903 when the diesel electric river tanker Vandal was put in service by Branobel. Diesel engines soon offered greater efficiency than the steam turbine, but for many years had an inferior power-to-space ratio.

Diesel engines today are broadly classified according to

· Their operating cycle: two-stroke or four-stroke

· Their construction: Crosshead, trunk, or opposed piston

· Their speed

· Slow speed: any engine with a maximum operating speed up to 300 revs/minute, although most large 2-stroke slow speed diesel engines operate below 120 revs/minute. Some very long stroke engines have a maximum speed of around 80 revs/minute. The largest, most powerful engines in the world are slow speed, two stroke, crosshead diesels.

· Medium speed: any engine with a maximum operating speed in the range 300-900 revs/minute. Many modern 4-stroke medium speed diesel engines have a maximum operating speed of around 500 rpm.

· High speed: any engine with a maximum operating speed above 900 revs/minute.

Most modern larger ships use either slow speed, two stroke, crosshead engines, or medium speed, four stroke, trunk engines. Some smaller vessels may use high speed diesel engines.

The size of the different types of engines is an important factor in selecting what will be installed in a new ship. Slow speed two-stroke engines are much taller, but the area needed, length and width, is smaller than that needed for four-stroke medium speed diesel engines. As space higher up in passenger ships and ferries is at a premium, these ships tend to use multiple medium speed engines resulting in a longer, lower engine room than that needed for two-stroke diesel engines. Multiple engine installations also give redundancy in the event of mechanical failure of one or more engines and greater efficiency over a wider range of operating conditions.

As modern ships' propellers are at their most efficient at the operating speed of most slow speed diesel engines, ships with these engines do not generally need gearboxes. Usually such propulsion systems consist of either one or two propeller shafts each with its own direct drive engine. Ships propelled by medium or high speed diesel engines may have one or two (sometimes more) propellers, commonly with one or more engines driving each propeller shaft through a gearbox. Where more than one engine is geared to a single shaft, each engine will most likely drive through a clutch, allowing engines not being used to be disconnected from the gearbox while others keep running. This arrangement lets maintenance be carried out while under way, even far from port.

III. Answer the following questions:

1. What engines do modern ships use?

2. How can the rotating crankshaft power?

3. When did the reciprocating marine diesel engine first come into use?

4. Diesel engines offer greater efficiency than the steam turbine, don’t they?

5. How are diesel engines classified?

6. What do most modern larger ships use?

7. Is the size of the different types of engines an important factor in selecting what will be installed in a new ship?

8. What is the difference between two-stroke and four-stroke engines?

9. What do propulsion systems consist of?

IV. Ask as many questions as possible to the following sentences:

1. Many warships built since the 1960s have used gas turbines for propulsion.

2. Ship propelled by medium or high speed diesel engines may have one or two propellers.

3. Hull materials and vessel size play a large part in determing the method of construction.

4. Larger boats and ships generally have multiple decks and compartments.

5. On modern cargo ships, superstructures are almost always located near the ship’s stern.

6. The size of the different types of engines is an important factor in selecting what will be installed in a new ship.

V. Complete the following sentences, using the text:

1. The rotating crankshaft can power …

2. The reciprocating marine diesel engine first came …

3. Most modern larger ships use …

4. The size of the different types of engines …

5. As space higher up in passenger ships …

6. Multiple engine installations also give …

7. Ships propelled by medium or …

8. Slow speed two-stroke engines …

VI. Use the following words and word combinations in sentences of your own:

To power the propeller directly, via a gearbox, to come into use, to put in service, to offer greater efficiency, to be classified according to, to have a maximum speed, to install in a new ship, at a premium, in the event of mechanical failure

VII. Translate the text “Propulsion systems.”

Propulsion systems for ships and boats vary from the simple paddle to the largest diesel engines in the world. These systems fall into three categories: human propulsion, sailing, and mechanical propulsion. Human propulsion includes the pole, still widely used in marshy areas, rowing which was used even on large galleys, and the pedals. In modern times, human propulsion is found mainly on small boats or as auxiliary propulsion on sailboats.

Propulsion by sail generally consists of a sail hoisted on an erect mast, supported by stays and spars and controlled by ropes. Sail systems were the dominant form of propulsion until the nineteenth century. They are now generally used for recreation and racing, although experimental sail systems, such as the kites/royals, turbo sails, rotor sails, wing sails and SkySails's own kite buoy-system have been used on larger modern vessels for fuel savings.

Mechanical propulsion systems generally consist of a motor or engine turning a propeller. Steam engines were first used for this purpose, but have mostly been replaced by two-stroke or four-stroke diesel engines, outboard motors, and gas turbine engines on faster ships. Electric motors have sometimes been used, such as on submarines. Nuclear reactors are sometimes employed to propel warships and icebreakers.

VIII. Retell the text “Reciprocating diesel engines.”

UNIT 14. THE KEEL

I. Master the active vocabulary:

a hydrodynamic element – гидродинамический элемент

a beam – балка, брус

a bow – нос (судна)

spine of the structure – основа конструкции

cradle – кильблок

longitudinal strength – продольная прочность

stability – стабильность, устойчивость

foil – фольга, пленка

to stabilize the boat – стабилизировать лодку

winch – лебедка

bilge keel – скуловый киль

II. Read and translate the following text:

The word "keel" comes from Anglo-Saxon cēol= "ship" or "keel".

In boats and ships, keel can refer to either of two parts: a structural element, or a hydrodynamic element. These parts overlap.

A structural keel is a large beam around which the hull of a ship is built. The keel runs in the middle of the ship, from the bow to the stern, and serves as the foundation or spine of the structure, providing the major source of structural strength of the hull. The keel is generally the first part of a ship's hull to be constructed, and laying the keel, or placing the keel in the cradle in which the ship will be built, is often a momentous event in a ship's construction--so much so that the event is often marked with a ceremony, and the term lay the keel has entered the language as a phrase meaning the beginning of any significant undertaking.

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