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船舶與海洋工程英語閱讀：主要尺度界定
Definitions, Principal Dimensions 主要尺度界定
Before studying in detail the various technical branches of naval architecture it is important to define chapters. The purpose of this chapter is to explain these terms and to familiarise the reader with them. In the first place the dimensions by which the size of a ship is measured will be considered; they are referred to as ‘principal dimensions’. The ship, like any solid body, requires three dimensions to define its size, and these are a length, a breadth and a depth. Each of these will be considered in turn.
Principal dimensions 主要尺度(尺寸)
Length
There are various ways of defining the length of a ship, but first the length between perpendiculars will be considered. The length between perpendiculars is the distance measured parallel to the base at the level of the summer load waterline from the after perpendicular to the forward perpendicular. The after perpendicular is taken as the after side of the rudder post where there is such a post, and the forward perpendicular is the vertical line drawn through the intersection of the stem with summer load waterline. In ships where there is no rudder post the after perpendicular is taken as the line passing through the centre line of the rudder pintals. The perpendiculars and the length between perpendiculars are shown in Figure 1.
The length between perpendiculars (LBP) is used for calculation purposes as will be seen later, but it will be obvious from Figure 1 that this does not represent the greatest length of the ship. For many purposes, such as the docking of a ship, it is necessary to know what the greatest length of the ship is. This length is known as the length of the extreme point at the after end to a similar point at the forward end. This can be clearly seen by referring again to Figure 1. In most ships the length overall will exceed by a considerable amount the length between perpendiculars. The excess will include the overhang of the stern and also that of the stem where the stem is raked forward. In modern ships having large bulbous bows the length overall LOA may have to be measured to the extreme point of the bulb.
A third length which is often used, particularly when dealing with ship resistance, is the length on the waterline LWL. This is the distance measured on the waterline at which the ship is floating from the intersection of the stern with the waterline to the length is not a fixed quantity for a particular ship, as it will depend upon the waterline at which the ship is floating and upon the trim of the ship. This length is also shown in Figure 1 .
Breadth
The mid point of the length between perpendiculars is called ‘amidships’and the ship is usually broadest at this point. The breadth is measured at this position and the breadth most commonly used is called the ‘breadth moulded’. It may be defined simply as the distance from the inside of plating on one side to a similar point on the other side measured at the broadest part of the ship.
As is the case in the length between perpendiculars, the breadth moulded dose not represent the greatest breadth the breadth extreme is required (see Figure 2 ). In many ships the breadth extreme is the breadth moulded plus the thickness of the shell plating where the strakes of shell plating were overlapped the breadth extreme was equal to the breadth moulded plus four thicknesses of shell plating, but in the case of modern welded ships the extra breadth consists of two thicknesses of shell plating only.
The breadth extreme may be much greater than this in some ships, since it is the distance from the extreme overhang on one side of the ship to a similar point on the other side. This distance would include the overhang of decks, a feature which is sometimes found in passenger ships in order to provide additional deck area. It would be measured over fenders, which are sometimes fitted to ships such as cross channel vessels which have to operate in and out of port under their own power and have fenders provided to protect the sides of the ships when coming alongside quays.
Depth
The third principal dimension is depth, which varies along the length of the ship but is usually measured ant amidships. This depth is known as the ‘depth moulded and is measured from the underside of the plating of the deck at side amidships to the base line. It is shown in Figure 2(a). It is sometimes quoted as a ‘depth moulded to upper deck’ or ‘depth moulded to second deck’, etc. Where no deck is specified it can be taken the depth is measured to the uppermost continuous deck. In some modern ships there is a rounded gunwale as shown in Figure 2(b). In such cases the depth moulded is measured from the intersection of the deck line continued with the breadth moulded line.
Sheer
Sheer is the height of the deck at side above a line drawn parallel to the base and tangent to the length of the ship and is usually greatest at the ends. In modern ships the deck line at side often has a variety of shapes: it may be flat with zero sheer over some distance on either side of amidships and then rise as a straight line towards the ends; on the other hand there may be no sheer at all on the deck, which will then be parallel to the base over the entire length. In older ships the deck at side line was parabolic in profile and the sheer was quoted as its value on the forward and after perpendiculars as shown in Figure 1. So called ‘standard’ sheer was given by the formulae:
Sheer forward (in) =0.2Lft+20
Sheer aft (in) =0.1Lft+10
These two formulae in terms of metric units would give:
Sheer forward (cm) =1.666Lm+50.8
Sheer aft (cm) =0.833Lm+25.4
It will be seen that the sheer forward is twice as much as the sheer aft in these standard formulae. It was often the case, however, that considerable variation was made from these standard values. Sometimes the sheer forward was increased while the sheer after was reduced. Occasionally the lowest point of the upper deck was some distance aft of amidships and sometimes departures were made from the parabolic sheer profile. The value of sheer and particularly the sheer forward was to increase the height of the deck above water (the ‘height of platform’ as it was called ) and this helped to prevent water being shipped when the vessel was moving through rough sea. The reason for the abolition of sheer in some modern ships is that their depths are so great that additional height of the deck above water at the fore end is unnecessary from a seakeeping point of view.
Deletion of sheer also tends to make the ship easier to construct, but on the other hand it could be said that the appearance of the ship suffers in consequence.
Camber
Camber or round of beam is beam is defined as the rise of the deck of the ship in going from the side to the centre as shown in Figure 3(a). The camber curve used to be parabolic but here again often nowadays straight line camber curves are used or there may be no camber at all on decks. Camber is useful on the weather deck of a ship from a drainage point of view, but this may not be very important since the ship is very rarely upright and at rest. Often, if the weather deck of a ship is cambered, the lower decks particularly in passenger ships may have no camber at all, as this makes for horizontal decks in accommodation which is an advantage.
Camber is usually stated as its value on the moulded breadth of the ship and standard camber was taken as one-fiftieth of the breadth. The camber on the deck diminishes towards the ends of the ship as the deck breadths become smaller.
Bilge radius
An outline of the midship section of a ship is shown in Figure 3(a). In many ‘full’ cargo ships the section is virtually a rectangle with the lower corners rounded off. This part of the section is referred to as the ‘bilge’ and the shape is often circular at this position. The radius of the circular arc forming the bilge is called the ‘bilge radius’. Some designers prefer to make the section some curve other than a circle in way of the bilge. The curve would have a radius of curvature which increases as it approaches the straight parts of the section with which it has to link up.
Rise of floor
The bottom of a ship at amidships is usually flat but is not necessarily horizontal. If the line of the flat bottom is continued outwards it will intersect the breadth moulded line as shown in Figure 3(a). The height of this intersection above base is called the ‘rise of floor ’. The rise of floor is very much dependent on the ship form. In ships of full form such as cargo ships the rise of floor may only be a few centimeters or may be eliminated altogether. In fine form ships much bigger rise of floor would be adopted in association with a larger bilge radius.
Flat of keel
A feature which was common in the days of riveted ships what was known as ‘flat of keel ’ or ‘flat of bottom ’. Where there is no rise of floor, of course, the bottom is flat from the centre line to the point where the curve of the bilge starts. If there was a rise of floor it was customary for the line of the bottom to intersect the base line some distance from the centre line so that on either side of the centre line there was a small portion of the bottom which was horizontal, as shown in Figure 3(a). this was known as the ‘flat of bottom’ and its value lay in the fact that a rightangle connection could be made between the flat plate keel and the vertical centre girder and this connection could be accomplished without having to bevel the connecting angle bars.
Tumble home
Another feature of the midship section of a ship which was at one time quite common but has now almost completely disappeared is what was called ‘tumble home’. This is the amount which the side of the ship falls in from the breadth moulded line, as shown in Figure 3(b). Tumble home was a usual feature in sailing ships and often appeared in steel merchant ships before World War II. Ships of the present day rarely employ this feature since its elimination makes for ease of production and it is of doubtful value.
Rake of stem
In ships which have straight stems formed by a stem bar or a plate the inclination of the stem to the vertical is called the ‘rake’. It may be defined either by the angle to the vertical or the distance between the intersection of the stem produced with the base line and the forward perpendicular. When ships have curved stems in profile, and especially where they also have bulbous bows, stem rake cannot be simply defined and it would be necessary to define the stem profile by a number of ordinates at different waterlines.
In the case of a simple straight stem the stem line is usually joined up with the base line by a circular are, but sometimes a curve of some other form is used, in which case several ordinates are required to define its shape.
Draught and trim
The draught at which a ship floats is simply the distance from the bottom of the ship to the waterline. If the waterline is parallel to the keel the ship is said to be floating on an even keel, but if the waterline is not parallel then the ship is said to be trimmed. If the draught at the after end is greater than that at the fore end the ship is trimmed by the stern and if the converse is the case it is trimmed by the bow or by the head. The draught can be measured in two ways, either as a moulded draught which is the distance from the base line to the waterline, or as an extreme draught which is the distance from the bottom of the ship to the waterline. In the modern welded merchant ship to the waterline. In the modern welded merchant ship these two draughts differ only by one thickness of plating, but in certain types of ships where, say, a bar keel is fitted the extreme draught would be measured to the underside of the keel and may exceed the moulded draught of by 15-23cm (6-9in). It is important to know the draught of a ship, or how much water the ship is ‘drawing’, and so that the draught may be readily obtained draught marks are cut in the stem and the stern. These are 6 in high with a space of 6in between the top of one figure and the bottom of the next one. When the water level is up to the bottom of a particular figure the draught in feet has the value of that figure. If metric units are used then the figures would probably be 10 cm high with a 10 cm spacing.
In many large vessels the structure bends in the longitudinal vertical plane even in still water, with the result that the base line or the keel does not remain a straight line. The mean draught at which the vessel is floating is not then simply obtained by taking half the sum of the forward and after draughts. To ascertain how much the vessel is hogging or sagging a set of draught marks is placed amidships so that if da, d and df are the draughts at the after end amidships and the forward end respectively then
Hog or sag= - d
When use is made of amidship draughts it is necessary to measure the draught on both sides of the ship and take the mean of the two readings in case the ship should be heeled one side or the other.
The difference between the forward and after draughts of s ship is called the ‘trim’, so that trim T=da- df, and as previously stated the ship will the said to be trimming by the stern or the bow according as the draught aft or the draught forward is in excess. For a given total load on the ship the draught will have its least value when the ship is on an even keel. This is an important point when a ship is navigating in restricted depth of water or when entering a dry dock. Usually a ship should be designed to float on an even keel in the fully loaded condition, and if this is not attainable a small trim by the stern is aimed at. Trim by the bow is not considered desirable and should be avoided as it reduces the ‘height of platform’ forward and increases the liability to take water on board in rough seas.
Freeboard
Freeboard may be defined as the distance which the ship projects above the surface of the water or the distance measured downwards from the deck to the waterline. The freeboard to the weather deck, for example, will vary along the length of the ship because of the sheer of the deck and will also be affected by the trim, if any. Usually the freeboard will be a minimum at amidships and will increase towards the ends.
Freeboard has an important influence on the seaworthiness of a ship. The greater the freeboard the greater is the above water volume, and this volume provides reserve buoyancy, assisting the ship to rise when it goes through waves. The above water volume can also help the ship to remain afloat in the event of damage. It will be seen later that freeboard has an important influence on the range of stability. Minimum freeboards are laid down for ships under International Law in the form of Load Line Regulations.
(from “Naval Architecture for Marine Engineers” by W.Muckle, 1975)
Technical Terms 詞匯術(shù)語
1. principal dimension 主要尺度
2. naval architecture 造船(工程)學(xué)
3. naval architect造船工程(設(shè)計)師
4. length between perpendiculars (LBP) 垂線間長
5. summer load waterline 夏季載重水線
6. forward/after perpendicular 首/尾垂線
7. rudder post 尾柱
8. stem 首柱
9. rudder pintle 舵銷
10. length over all (LOA) 總長
11. overhang (水線以上)懸伸部分
12. bulbous bow 球鼻艏
13. length on the waterline (LWL)水線長
14. amidship 船中
15. breath moulded 型寬
16. breath extreme 最大船寬
17. shell plating 船殼板
18. rivet 鉚接
19. weld 焊接
20. strake (船殼板)列板
21. fender 護舷木
22. deck area 甲板面積(區(qū)域)
23. cross channel vessel 海峽船
24. port 港口，船的左舷
25. side 舷側(cè)(邊)
26. quay 碼頭
27. depth moulded 型深
28. plating of deck 甲板板
29. base line 基線
30. upper deck 上甲板
31. second deck 第二甲板
32. the uppermost continuous deck 最上層連續(xù)甲板
33. rounded gunwale 圓弧舷邊頂部
34. moulded line 型線
35. sheer 舷弧
36. ends 船端
37. deck line at side 甲板邊線
eck at side line 甲板邊線
deck at side 甲板邊線
38. profile 縱剖面(圖)，輪廓
39. sheer forward/aft 首/尾舷
40. platform 平臺
41. rough sea 強浪，洶濤海面
42. seakeeping 耐波性
43. appearance 外形(觀)，出現(xiàn)
44. camber 梁拱
round of beam 梁拱
45. weather deck 露天甲板
46. drainage 排水
47. upright 正浮，直立
48. at rest 在靜水中
49. accommodation 居住艙，適應(yīng)
50. bilge radius 舭(部)半徑
51. midship section 船中剖面
52. bilge 舭(部)
53. rise of floor 船底升高
54. flat of keel 龍骨寬
55. flat plate keel 平板龍骨
56. vertical center girder 中桁材
57. bevel 折射角，將直角鋼改為斜角
58. connecting angle 聯(lián)接角鋼
59. tumble home 內(nèi)傾
60. sailing ship 帆船
61 .steel merchant ship 鋼質(zhì)商船
62 .bar 棒，巴(氣壓單位)
63. rake 傾斜
64 .draught 吃水，草圖，通風(fēng)
65. even keel 等吃水，正浮
66 .trimmed by the stern/bow 尾/首傾
67 .moulded draught 型吃水
68 .extreme draught 最大吃水
69. bar keel 棒龍骨
70. ”drawing” “吃水”
71. draught marks 吃水標(biāo)志
72. imperial unit 英制單位
73. metric unit 公制單位
74. spacing 間距
75. hogging 中拱
76. sagging 中垂
77. heel 橫傾
78. dry dock 干船塢
79. fully loaded condition 滿載標(biāo)志
80. freeboard 干舷
81. seaworthiness 適航性
82. reserve buoyancy 儲備浮力
83. range of stability 穩(wěn)性范圍
84. Load Line Regulations 載重線規(guī)范
Additional Terms and Expressions 增補術(shù)語表達
1. form coefficients 船型系數(shù)
2. block coefficient 方型系數(shù)
3. prismatic coefficient 棱型系數(shù)
4. midship area coefficient 船中橫剖面面積系數(shù)
5. waterplane area coefficient 水線面面積系數(shù)
6. vertical prismatic coefficient 豎向棱型系數(shù)
7. body section of U-form U形橫剖面
8. V-shaped section V形橫剖面
9. geometrically similar ships 幾何相似船
10. base plane 基平面
11. center plane 中線面
12. midstation plane 中站面
13. moulded base line 基線
14. length breadth ratio 長度比
15. cruiser stern 巡洋艦型尾
16. principal coordinate planes 主坐標(biāo)面
17. transom 方尾
18. soft chine 圓舭
19. hard chine 尖舭
20. counter 尾伸部
21. forefoot 首踵
22. aftfoot 尾踵
23. deadwood 尾鰭(呆木)
Notes to the Text 課文注釋
1. as will be seen later 和as is the case in the length between perpendiculars 中as 引出的從句為非限制性定語從句。關(guān)系代詞as代替整個主句，并在從主語中作主語。as 也可在從句中作賓語，表語用。
2. A third length 序數(shù)字前面，一般用定冠詞“the”，但當(dāng)作者心目中對事物總數(shù)還不明確，或還不足以形成一個明確的序列時，序數(shù)字前面用不定冠詞“a”。例：
Will they have to modify the design a fourth time? (它們的設(shè)計究竟要修改多少次，心中無數(shù)，但依次下來已是第四次，所以用不定冠詞“a”。)
3. This is the distance measured on the waterline at which the ship is floating from the intersection of the stern with the waterline to the intersection of the stem with the waterline.
這是一個符合據(jù)。其中at which the ship is floating 為定語從句，修飾the waterline. from the intersection of the stern (with the waterline為intersection 所要求的介詞短語)to the intersection of the stern(with the waterline 為第二個intersection 所要求的介詞短語)都屬于介詞短語，作狀語用，說明測量的范圍。
5. quay 一般指與海岸平行的碼頭
pier 系指與海岸或呈直角面突出的碼頭
wharf 一般用于的碼頭
6. the deck line continued 和the stern produced 為過去分詞作后置定語，分別修飾“the deck line 和the stern .都可譯成“延長時”。
considerable variation was made from these standard values 和departures were made from the parabolic sheer profile 和(when)use is made of amidship draughts 這三句都屬于主語的成分被位于動詞隔離成兩部分。這是英語句子結(jié)構(gòu)平衡的需要中帶有這種情況，閱讀和翻譯時需加以注意。
7. considerable variation was made from these standard values 和departures were made from the parabolic sheer profile 和(when)use is made of amidship draughts 這三句都屬于主語的成分被位于動詞隔離成兩部分。這是英語句子結(jié)構(gòu)平衡的需要中帶有這種情況，閱讀和翻譯時需加以注意。
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