Fig. 22. The bulbous bow of the U.S. Navy carrier USS Ronald Reagan

 

Long waves are faster, so a ship that wants to go fast has to excite long waves and not short ones. In a conventionally shaped bow, a bow wave forms immediately before the bow. When a bulb is placed below the water ahead of this wave, water is forced to flow up over the bulb. If the trough formed by water flowing off of the bulb coincides with the bow wave, the two partially cancel out and reduce the vessel's wake.     While inducing another wave stream saps energy from the ship, canceling out the second wave stream at the bow changes the pressure distribution along the hull, thereby reducing wave resistance. The effect that pressure distribution has on a surface is known as the form effect.

Some explanations note that water flowing over the bulb depresses the ship's bow and keeps it trimmed better. Since many of the bulbous bows are symmetrical or even angled upwards which would tend to raise the bow further, the improved trim is likely a by product of the reduced wave action as the vessel approaches hull speed, rather than direct action of waterflow over the bulb.

A sharp bow on a conventional hull form would produce waves and low drag like a bulbous bow, but waves coming from the side would strike it harder. Also, in heavy seas, water flowing around the bulb dampens pitching movements like a squiggle keel. The blunt bulbous bow also produces higher pressure in a large region in front, making the bow wave start earlier.

III. Answer the following questions:

1. What does the bulb modify?

2. Where do bulbous bows achieve maximum effect?

3. Where do bulbous bows have the greatest effect?

4. Does water flowing over the bulb depresses the ship’s bow and keep it trimmed better?

5. When did the first bulbous bows appear?

6. Who created the first bulbous bow?

IV. Translate the following text: “Coaming”

Coaming is any vertical surface on a ship designed to deflect or prevent entry of water. It usually refers to raised section of deck plating around an opening, such as a hatch. Coamings also provide a frame onto which to fit a hatch cover.

The protective metal sheeting or plating protecting against water entry into ventilator shafts in large ships is called a coaming as it suits this purpose. In these cases the coaming is usually fitted with a gooseneck as required by Title 46 of the Code of Federal Regulations (CFR). Further regulations for required coamings are available in 46 CFR. In addition, coaming is the vertical surface rising from a hatch, as in hatch coaming, which forestalls the ingress of water and provides a sealing surface for the hatch cover.

V. Translate the following sentences from Russian into English:

1. Бульбообразный нос можно увидеть только когда судно находится в сухом доке.

2. Суда с бульбообразным носом имеют большую экономичность топлива.

3. Бульбообразный нос используется на таких судах, как грузовые корабли, военно-морские суда и различные пассажирские суда.

4. Большое количество бульбообразных носов – симметричны.

5. Первое судно с бульбообразным носом появилось в США.

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

A protruding bulb, below the waterline, to be in drydock, to reduce drag, to have better fuel efficiency, to achieve maximum effect, freighter, to plan over the water, to excite long waves, to be placed below the water, to reduce the vessel’s wake. Form effect, to raise the bow, to produce higher pressure.

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

1. In 1935 the French super liner Normandie coupled a bulbous bow with a radically redesigned hull shape and was able to achieve speeds in excess of 30 knots.

2. A sharp bow on a conventional hull form would produce waves and low drag like a bulbous bow.

3. Bulbous bows achieve maximum effect at a narrow range of speeds over 6 knots.

4. Ships with bulbous bows generally have 12 to 15 percent better fuel efficiency than similar vessels without them.

5. In the 1920s some nations experimented with bulbous bows with the introduction of the Bremen and Europa, two German North Atlantic Ocean liners.

6. Water flowing over the bulb depresses the ship’s bow and keeps it trimmed better.

7. The effect that pressure distribution has on a surface is known as the form effect.

VIII. Insert the missing word, using the text:

1. A bulbous bow, a feature of many modern … …, is a protruding bulb at … below the waterline.

2. Bulbous bows have … … on large ships such as …, … …, and various passenger ships.

3. … … are faster, so a ship that wants to go fast has to excite … … and not short ones.

4. In heavy seas, … … around the bulb dampens … … like a squiggle keel.

5. The first bulbous bow appeared in … being fitted to the … … which entered service in 1910.

6. The blunt … … also produces higher pressure in a large region in front, making … … start earlier.

IX. Retell the text: “Bulbous bow.”

 

 

UNIT 20. DECK

I. Try to remember the following words and word combinations:

permanent – постоянный

compartment – отделение, отсек

to strengthen – усиливать, укреплять

primary deck – главная палуба

weather – tightness – защищенный от погодных условий

compression – давление

to reinforce – упрочнять

bollard – швартовая тумба

sole – подошва, пятка

downward – нисходящий, опускающийся

I I. Read and translate the following text:

A deck is a permanent covering over a compartment or a hull of a ship. On a boat or ship, the primary deck is the horizontal structure which forms the 'roof' for the hull, which both strengthens the hull and serves as the primary working surface. Vessels often have more than one level both within the hull and in the superstructure above the primary deck which are similar to the floors of a multi-story building, and which are also referred to as decks, as are specific compartments and decks built over specific areas of the superstructure.