Chapter 1 Ship Design（船舶设计）
Lesson 2 Ships Categorized（船舶分类）
Introduction（介绍）
The forms a ship can take are innumerable. 一艘船能采用的外形是不可胜数的
A vessel might appear to be a sleek seagoing hotel carrying passengers along to some exotic destination; a floating fortress bristling with missile launchers; 。or an elongated box transporting tanks of crude oil and topped with complex pipe connections. 一艘船可以看做是将乘客一直运送到外国目的地的优美的远航宾馆。竖立有导弹发射架的水面堡垒及甲板上铺盖有复杂管系的加长罐装原油运输轮
None of these descriptions of external appearance, however, does justice to the ship system as a whole and integrated unit所有这些外部特点的描述都不能说明船舶系统是一个总的集合体
—self-sufficient,seaworthy, and adequately stable in its function as a secure habitat for crew and cargo. ——船员和货物的安全性功能：自给自足，适航，足够稳定。
This is the concept that the naval architect keeps in mind when designing the ship and that provides the basis for subsequent discussions, not only in this chapter but throughout the entire book.这是一个造船工程师设计船舶使必须记住的、能为以后讨论提供根据的观念，不仅涉及本章也贯穿全书。
In order to discuss naval architecture,it is helpful to place ships in certain categories. For purposes of this text, ships are classified according to their means of physical support and their designed purposes.将船舶分成一些特定的种类来讨论造船工程是有好处的。本文的目的就是根据船舶物理支撑方式和设计目的来将它们分类。
Ships Typed According to Means of Physical Support（根据物理支撑方式来分类）The mode of physical support by which vessels can be categorized assumes that the vessel is operating under designed conditions- Ships are designed to operate above, on, or below the surface of the sea, so the air-sea interface will be used as the reference datum.
船舶按物理支撑的分类方式假设，船舶是在设计工况的条件下航行。船舶预定在海面上，海面中或海面以下航行，因此使用空气与水的接触面作为基准面。
Because the nature of the physical environment is quite different for the three regions just mentioned, the physical characteristics of ships designed to operate in those regions can be diverse.由于上面提到的三个区域中物理环境的本质相差很大，所以那些区域中的船的物理特性也不同。
Aerostatic Support（空气静力支撑）
There are two categories of vessels that are supported above the surface of
the sea on a self-induced cushion of air. These relatively lightweight vehicles are capable of high speeds,since air resistance is considerably less than water resistance, and the absence of contact with small waves combined with flexible seals reduces the effects of wave impact at high speed. 有两种靠自身诱导的气垫浮于海面上的船。这些重量相对轻的船能够高速航行，这是因为空气阻力比水阻力小得多，而且船舶高速航行时，弹性密封圈没有与小波浪接触，因而降低了了波浪冲击的影响。
Such vessels depend on lift fans to create a cushion of low-pressure air in an underbody chamber. 这种船依靠升力风扇在船体水下部分产生了低压气垫。
This cushion of air must be sufficient to support the weight of the vehicle above the water surface.这种空气气垫必须足够支撑水面上方船的重量。
The first type of vessel flexible “skirts ” that entirely surround the air cushion and enable the ship to rise completely above the sea surface.
第一种船有完全围绕在气垫周围并且能够使船完全漂浮在水面以上的弹性围裙。
This is called an air cushion vehicle (ACV) ,and in a limited sense it is amphibious.
它
被称
为
气
垫船（
A ，某种有限的程度上适用于两栖。
The other type of air-cushion craft has rigid side walls or thin hulls that extend below the surface of the water to reduce the amount of air flow required to maintain the cushion pressure. 另一种气垫船带有刚性侧壁，且有延伸到水下能够减小空气流量的瘦船体，该气流用来维持气垫压力。 This type is called a captured-air-bubble vehicle (CAB).这种类型船称为束缚气泡减阻船
It requires less lift-fan power than an ACV, is more directionally stable and can be propelled by water jets or supercavitating propellers. 相对于 ACV 来说，它需要较低的升力风扇动力,航向稳定性更好，并且能使用喷水推进器和超空泡螺旋桨。
It is not amphibious, however, and has not yet achieved the popularity of the ACVs, which include passenger ferries, cross-channel automobile ferries, polar-exploration craft, landing craft, and riverine warfare vessels.但是，它不是两栖用途的，也还没有 ACVs 那么广的适用范围， 适用范围包括游客渡轮，横越海峡车客渡轮，极地考察船，登陆舰及内河舰艇。
Hydrodynam ic Support （水动力支撑）
There are also two types of vessels that depend on dynamic support generated by relatively rapid forward motion of specially designed hydrodynamic shapes either on or beneath the surface of the water. 也有两种类型船，它们依赖通过船的相对高速前进运动来产生动力支持，这 种船型的水上和水下部分的形状都经过特殊设计。
A principle of physics states that any moving object that can produce an unsymmetrical flow pattern generates a lift force perpendicular to the direction
of motion. 一个物理定理这样陈述：任何运动的物体都能造成不均匀的流态，产生一个垂直于运动方向的升力。
Just as an airplane with (airfoil) produces lift when moving through the air, a hydrofoil located beneath the surface and attached by means of a surface piercing strut, can dynamically support a vessel ’s hull above the water.
正如装有空气翼的飞机在空气中移动时气翼上能产生一个升力一样，位于水面以下且其上固定有穿透水面的柱体的水翼，能够动态支撑水面以上的船体。
Planing hulls are hull forms characterised by relatively flat bottoms and shallow V-sections (especially forward of amidships) that produce partial to nearly full dynamic support for light displacement vessels and small craft at higher speeds.
滑
行船体的特
征是底部相
对
横剖
面呈浅（尤
其是
船的前半。 这种形状特点能够使船产生偏近满动力支持，适用于使小排水量船和高速小艇。
Planing craft are generally restricted in size and displacement because of the required power-to-weight ratio and the structural stresses associated with traveling at high speed in waves. 一般说来，滑行船体的尺寸和排水量有限制。这是因为需要满足动力和重量的比率要求，以及在波浪中高速航行时的结构应力要求。 Most planing craft are also restricted to operations in reasonably calm water, although some “deep V” hull forms are capable of operation in rough water. 虽然有一些?深V 型剖面船能够在恶劣的海况中航行，但大多数滑行船体也都限制在相当平静的水面上航行。
Lesson 3 Principal Dimensions （主尺度） Principal Dimensions （主尺度） Before studying in detail the various technical branches of naval architecture it is important to define various terms which will be made use of in later chapters. The purpose of this chapter is to explain these terms and to familiarise the reader with them.
在系统的学习船舶工程不同的技术分支之前，
应该定义一些术语以便于后面章节使用，这很重要。本章旨在于解释这些术语，并且让读者熟悉它们。 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. 首先，考虑用来测量船舶尺寸的尺度；它们即是“主尺度”像任何其他固体一样，船舶需要三个尺度来定义其尺寸，它们是长度，宽度和高度。
Each of these will be considered in turn.
我们将依次来讨论它们。
Length（船长）
There are various ways of defining the length of a ship, but first the length between perpendiculars will be considered.
有多种定义船舶长度的方法，但是首先应该考虑艏艉两柱间长。
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.
柱间长指的是平行于基底夏季载重水线，从艉柱到艏柱间的距离。
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 the 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 pintles.
艉
柱指的就是船舶舵柱
的而艏柱是通过船艏与夏季载重水线的交点的The length between perpendiculars is used for calculation purposes as will
be seen later,but it will be obvious from Figure that this does not represent the greatest length of the ship.两柱间长（）是用于后面的计算之用的，然而从图中可以看出两柱间长不是船舶的最大长度。
For many purposes, such as the docking of a ship, it is necessary to know what the greatest length of the ship is.
明白船舶的最大长度是必要的，很多地方都能用到最大船长，比如船舶入坞。
This length is known as the ‘length overall’ and is defined simply as the distance from the extreme point at the after end to a similar point at the forward end.
这个长度称为“总长”，是以从船艉端点到船艏端点间的距离来定义的。
This can be clearly seen by referring again to Figure . In most ships the length overall wilt exceed by a considerable amount the length between perpendiculars.
大多数船的总长都比两柱间长超出很多。
The excess will include the overhang of the stem and also that of the stem where the stem is raked forward. 超出的长度包括船艉悬挂物和前倾型船艏悬挂物。
In modem ships having large bulbous bows the length overall (L. O. A. ) may have to be measured to the extreme point of the bulb.
现代大型球鼻艏船舶的总长（）应该以球鼻为端点测量。
A third length which is often used t particularly when dealing with ship resistance, is the length on the waterline第三种长度是水线长（）常用于计算船舶阻力。
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.
水线长指的就是在船舶所漂浮的水线上从船艏与水线的交点到船艉与水线的交点间的距离
This 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. 一艘特定的船上的水线长不是一个固定值,它是取决于船舶所漂浮的水线的位置及船舶的纵倾程度
Breadth（型宽）
The mid point of the length between perpendiculars is called ‘amidships’ and the ship is usually broadest at this point. 两柱间长的中点称为“船舯”且船舶在该处的宽度是最大的。
The breadth is measured at this position and the breadth most commonly used is called the ‘breadth moulded’. 我们所说的宽度就是在船舯位置测得的，该宽度一半称为“型宽”。
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.
我们谨定义它为船舶最宽处一侧船壳板的内侧到另一侧船壳板内侧的距离。
As is the case in the length between perpendiculars, the breadth moulded does not represent the greatest breadth of the ship, so that to define this greatest breadth the breadth extreme is required.
就像两柱间长那种情况一样，型宽不是船舶最大宽度，以至于有必要定义船舶的最大宽度为计算宽度。
In many ships the breadth extreme is the breadth moulded plus the thickness of the shell plating on each side of the ship.
对于很多船，计算宽度等于型宽交上船舶两侧船体外板的厚度。
In the days of riveted ships, 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 modem welded ships the extra breadth consists of two thicknesses of shell plating only.在铆接船的年代中，由于船舶外板列板相重叠，所以计算宽度就等于型宽加上四倍的船壳板厚度，然而现代焊接船仅加上两倍船壳板厚度。
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.
有
些船的计
算宽度可能
比
上述所
说的
这是因为它指的就是船舶一舷侧 突出物极限点至相对称的另一舷侧突出物极限点间的距离。 This distance would include the overhang of decks,a feature which is sometimes found in passenger ships in order to provide additional deck area. 这种距离可能包括甲板突出物宽度，我们能从客船中发现这种特性，这是为了扩大甲板面积。 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.
我们将这些突出物称为护舷材，护舷材只用在某些船上，例如海峡渡轮，它们依靠自身的动力来进出港口，并且停靠港口时护舷能够保护船体舷侧免受损害。
Depth （型深）
The third principal dimensions is depth, which varies along the length of the ship but is usually measured at amidships. 第
三个主
尺度
是它沿船长方向会发生变化但通常以船舯处的值为标准。
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. 这种深度称为“型深”。指的就是船舯舷侧甲板板下部至基线间的距离。
It Is sometimes quoted as a ‘depth moulded to upper deck ’ or ‘depth moulded to second deck ’,etc.有时引用为“顶部甲板型深”或“次甲板型深”等等。 Where no deck is specified it can be taken the depth is measured to the uppermost c
o n
t i n u o
u s d e c
k .
如
果
没
In some modem ships there is a rounded gunwale.一些现代船舶有修圆的舷边。 In such cases the depth moulded is measured from the intersection of the deck line continued with the breadth moulded line.这种情况下，型深就取自甲板线与型宽线的交点。 Other Features （其他特征参数） The three principal dimensions give a general idea of the size of a ship but there are several ether features which have to be considered and which could be different in two ships having the same length,breadth and depth. 这三个主尺度能够总体的描述船舶的尺寸，然而，也得考虑其他的几个特征参数且同样长、宽、高的两艘船的这些特征参数可能是不同的。
The more important of these will now be defined.
现在来定义这些重要的特征参数。
Sheer （舷弧）
Sheer is the height of the deck at side above a line drawn parallel to the base and tangent to the deck line at amidships.
舷弧是甲板边板离平行于基线且相切于船舯甲板线的直线的突出高度
The sheer can vary along the length of the ship and is usually greatest at the ends.
舷
弧沿船长方向会发
生而且首尾端最明显 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; an 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.现代船舶甲板边线的形状多种多样：一方面，船舯两侧的某些长度方向可能是平的，没有舷弧，但接着以向上的斜直线的形式向首尾两端延伸；另一方面，甲板上面可能完全没有舷弧，整个船长方向上甲板都平行于基底。 In older ships the deck at side line was parabolic in profile and the sheer was quoted as its
value on the forward and alter perpendiculars as shown in Figure . So called ‘standard ’ sheer was given by the formulae ：老式船舶纵剖面上的甲板边线呈抛物线状，舷弧取自首尾两柱方向上的值，如图 所示。所谓的舷弧“标准值”用公式给出：
首舷弧（in ）=+20
尾舷弧（in ）=?+10
这些公式用英制单位表示为：
首舷弧（cm ）=?+
尾舷弧（cm ）=?+
It will be seen that the sheer forward is twice as much as the sheer aft in these standard formulae. 通过上面的标准公式可以看出，首舷弧值是尾舷弧值的两倍。
It was often the case,however, that considerable variation was made from these standard values.然而，这些标准值也会发生相当大的变化，
这种情况时常发生。 Sometimes the sheer forward was increased while the sheer after was reduced. 有时首舷弧会变大而尾舷弧会减小。
Occasionally the lowest point of the upper deck was some distance aft of amidships and sometimes departures were made from the parabolic sheer profile. 顶部
甲板的
最
低
点
离
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) 尤其是首舷
弧增加了甲板离水面的高度（称为“平台高度”）
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 modem ships is that their depths are so great that additional height of the deck above water at the fore end is unnecessary from a sea keeping point of view.这有助于防止船舶在汹涌的海况中航行时甲板上浪。某些现代船舶废除舷弧的原因是它们的型深如此之大，以至于首部额外的甲板高度就耐波性观点而言是不必要的。
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.
舷弧的取消也使得船舶的建造容易得多，但是就另一方面而言结果是船的外表变得难看了。
Draught and Trim（吃水和纵倾）
The draught at which a ship floats is simply the distance from the bottom of the ship to the waterline. 船舶漂浮时的吃水指的就是船底离吃水线的距离。
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. 如果水线平行于龙骨，那么就说船舶平浮；但是若不平行，那么就说船舶发生了纵倾。
If the draught at the after end is greater than that at the fore end the ship is trimmed by the stem and if the converse is the case it is trimmed by the bow or by the head.
如果船尾吃水比船艏大，那么就发生了艉倾；若船艏吃水比船尾大，那么就发生了艏倾。
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.
吃水可以分为两种：型吃水，即基线离水线的距离；计算吃水，即船底与水线间的距离。
In the modem 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 by 15~23cm (6~9in). 对于现代焊接形式的商船，这两种吃水仅是相差一块壳板厚度的区别，但是对于有些装有棒龙骨的船，计算吃水的测量至龙骨下表面，因此计算吃水可能比型吃水大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 stem.了解船舶的吃水或者说船舶“吃”水量，这很重要，因此一艘船的吃水能够直接获取，船艏和船艉都刻有吃水标志。
These are figures giving the distance from the bottom of the ship.
吃水标志也就是一些离船底有一定距离的一些数字。
In imperial units the figures are 6in high with a space of 6in between the top of one figure and the bottom of the next one.
这是数字用英制单位表示，6in 高，而且上下相邻的两个数字的间距也是 6in。
When the water level is up to the bottom of a particular figure the draught in feet has the value of that figure.当水位到达船底的某一个数字时，吃水就是那个数字的英尺值了。
If metric units are used then the figures would probably be 10cm high with a 10cm spacing.若用十进制单位表示，那么这些数字就可能是10cm 高，间隔10cm。
In many large vessels the structure bends in the longitudinal vertical plane even in still water t with the result that the base line or the keel does not remain a straight line.
就许多大型船舶而言，即使是在平静的海况下，它们的纵向垂直面都发生了弯曲，结果是基线或龙骨都不能保持为一条直线。
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.
这就意味着船舶漂浮时吃水不能仅仅用艏艉吃水和的一半来表示。
To ascertain how much the vessel is hogging or sagging a set of draught marks is placed amidships so that if da，dx and df are the draughts at the after end,amidships and the forward end respectively then为了确定船舶中拱或中垂程度，在船舯做了一套吃水标志，因此如果船尾、船舯和船艏吃水分别为da、dx和df那么
中拱或中垂=-dx+（da+df）/2
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 to one side or the other.使用船舯吃水时，测量船舶两侧吃水，使用两个数据是必要的，以防船舶向一侧或另一侧倾斜。
The difference between the forward and after draughts of a ship is called the ‘trim’, so that trim T = da - df, and as previously stated the ship will be said to be trimming by the stern or the bow according as the draught aft or the draught forward is in excess.
船舶首尾吃水的不同称为“纵倾”因而纵倾T= d a-d f，正如前面所说的那样，船舶艉吃水或艏吃水过多时，将发生艏倾或艉倾。
For a given total load on the ship the draught will have its least value when
the ship is on an even keel. 对于稳定航行的船，在已知的总载荷作用下，船舶吃水将有一个最小值。
This is an important point when a ship is navigating in restricted depth of water or when entering a dry dock. 这一点对于在限制水深的区域航行的船或船舶进入干船坞时很重要
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 stem is aimed at. 船舶的设计通常应满足在满载荷作用下船能够平浮的要求，如果船达不到这种状况，那么就设计成小角度艉倾。
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.艏倾这种情况是不期望发生的，应该避免,这是因为艏倾会降低艏部“平台高度”，增加在恶劣海况中甲板上浪的可能性。
Freeboard（干舷）
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.
干舷被定义为船舶离水面的距离，或甲板与下部水线的间距。
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.
例
如，由于受到甲板舷弧的影响，干舷与露天甲板Freeboard has an important influence on the seaworthiness of a ship.
干舷对船舶的适航性有重要的影响。
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.
干舷值越大，船舶水上部分的体积也就越大，而且这部分体积用来提供储备浮力，促使船舶在波浪中航行时能够上浮。
The above water volume can also help the ship to remain afloat in the event of damage.
水上部分的体积也能帮助船舶破损时保持漂浮状态。
It will be seen later that freeboard has an important influence on the range of stability.
干舷对船舶稳定性的变化有重要影响，这种情况后面将会介绍到
Minimum freeboards are laid down for ships under International Law in the form of Load Line Regulations.国际法载重公约中设定了船舶干舷最小值。
Lesson 4 Basic Geometric Concepts（基本几何概念）
The main parts of a typical ship together with the terms applied to the principal parts are illustrated in 示例船舶的主要部分以及相关的名字都在图中画出来了。
Because,at first,they are of little interest or influence,superstructures and deckhouses are ignored and the hull of the ship is considered as a hollow body curved in all directions,surmounted by a watertight deck. 首先，由于没有利害关系或影响，船舶上层建筑和甲板室都被忽略了，船体看成所有方向上都是曲线、上部用水密甲板覆盖的中空壳体。
Most ships have only one plane of symmetry, called the middle line plane which becomes the principal plane of reference.大多数船舶只有一个对称面，称为中线面，这是主要谈论的面。
The shape of the ship cut by this plane is known as the sheer plan or profile.
被该面截得的船型称为舷弧面或纵剖面。
The design waterplane is a plane perpendicular to the middle line plane, chosen as a plane of reference at or near the horizontal; it may or may not be parallel to the keel.
设计水线面垂直于中线面，取作水平或接近水平的面；它可能不与龙骨平行。
Planes perpendicular to both the middle line plane and the design waterplane are called transverse planes and a transverse section of the ship does, normally, exhibit symmetry about the middle line.
与中线面和设计水线面都垂直的面称为横剖面，船舶横剖面通常关于船体中线面对称。
Planes at right angles to the middle line plane, and parallel to the design waterplane are called waterplanes,whether they are in the water or not,and they are usually symmetrical about the middle line.与中线面成一定交角且平行于设计水线面的平面称为水线面，无论在水中与否，它们都成立，而且它们通常关于中线面对称。
Waterplanes are not necessarily parallel to the keel. Thus, the curved shape of a ship is best conveyed to our minds by its sections cut by orthogonal planes.水线面不一定平行于龙骨。因此，通过被正交面截得的面，能够向我们最清楚地表达船舶的曲线形状。
Lesson 5 Ship Form and Form Coefficients（船型系数）
Requirements of Ship Form（船型需求）
The hull form of a ship must be designed to fulfil certain requirements, and the first to be considered is the provision of sufficient buoyancy to carry the v
a
r
i
o
u
s l o a
d s
s
u c
h a
s t
h e w
e i g h t o f
t h e
s h
i
p
i
t
In other words the ship form must provide a certain displacement up to the load waterline. Calling this displacement △ it follows that 换句话说，船舶必须提供一定的排水量，直至载重水线处。称这个排水量为△，表示如下
△=g Vρ were ρ is the density of the water in which the ship is floating, g is the acceleration due to gravity,and V is the underwater volume. 其中ρ是船舶所在水域的密度，g 是重力加速度，V 是水下部分的体积。
It may be said, therefore, that the designer must so design the form that some underwater volume V is obtained. 因此可以说设计师应该有目的地设计船型，以便能够获得一些水下部分体积V 。 Another important requirement of the underwater form is that the centroid of the volume must be in a particular position in the fore and aft direction. 水下部分的船型的另一个重要的要求就是，
体积中心必须在首尾方向的特定位置处 Form coefficients （船型系数） If the ship form consisted simply of rectangular block of length equal to the length between perpendiculars, breadth equal to the breadth moulded,and depth equal to the draught,then the underwater volume would be given simply by
如果船型仅由长、
宽、深分别等于两柱间长、型宽、吃水的长方体组成，那么水下部分体积将仅由如下给出
V=L ×B ×d It will, however, be clear that the actual volume is less than the volume of this block, or in other words the ship form can be imagined to have been cut out of this block.而，真实的体积很明显小于这个长方体体积，或者换句话说，船型假想为是从这个长方体中切出来的。 What is called the ‘block coefficient’ is the ratio of the actual volume of the underwater form to the volume LBd. In other words 所谓的“方形系数”就是真实船型水下部分体积与L Bd 体积的比值。用另一种方式表示为 Block coefficient CB=V/(L×B×d)
方形系数CB =V/（L ×B ×d ）
When the ship designer has decided what volume is required he then has four factors to consider: the length, breadth and draught of the ship,and also the block c
o e f f
i c i
e
n t .
当
船舶
设
计师
已经决定
需要何种体那么他
就要
考虑四个
船宽，船舶吃水，和方形系数。
There is an infinite number of combinations of these factors which will give the required result and the problem is to decide what are the best values of the four parameters. In the meantime,however, the block coefficient only will be considered. 这些因数有无数种组合，能够给出最理想的结果，并且问题就是如何决定这四个系数的最佳值。同时，但唯独将只考虑方形系数。
Generally it is governed by resistance considerations.这一般是由阻力因素决定的。 At this stage it may be said that fast ships require low values of block coefficient while in slow ships high values of the block coefficient are permissible. 在此阶段，可以说高速船舶要求方形系数值低，而低速船只允许方形系数值高。
In slow speed ships, say of the bulk carrier type, a high value of block coefficient means a large displacement on given principal dimensions, which means that there is a large amount of displacement available for the carriage of cargo.对于低速船，例如散货船，
高的方形系数值意味着在主尺度一定的情况下排水量大，这就意味着有很大排水量来维持货物运输。 In fast ships it is essential to keep down the value of the block coefficient, so they normally have lower block coefficients than slow ships.对于高速船，降低方形系数值是必要的，因此相比于低速船它们有更低的方形系数值。 The influence of block coefficient on the shape of the hull form is that in ships with high values of this coefficient considerable parallel middle is likely to be found and the slopes of the waterlines at the ends are steep, whereas with low block coefficients parallel middle is often quite short or may not exist at all and the slopes of the waterlines at the ends will be small also.方形系数对船型的影响表现为，对于方形系数值高的船，会发现平行中体程度相 当大而且船舶两端水线范围陡，而对于方形系数值低的船，平行中体通常很小或可能完全不存在，而且船舶两端水线范围也很陡。 Another coefficient which is useful is what is known as the ‘prismatic coefficient’.另外一个有用的系数就是所谓的“棱形系数”。 The ship form could be imagined to have been cut from a prism of length equal to the length of the ship and of constant cross section of area equal to The immersed midship area. Thus 船型可以想象为是从棱柱体中切割出来的，棱柱体长度等于船长且截面积等于船舯浸没部分的面积的。因此 Prismatic coefficient Cp=V/(Midship area×L)
棱形系数Cp=V/（舯面积×L）
This particular coefficient has its use in dealing with resistance.
处理船舶阻力时能用到这个特殊的系数。
A coefficient which is used to express the fullness of the midship section is the midship area coefficient. If the midship section is imagined to be out out of a rtx:tangle of dimensions breadth ×draught then一个用来表示船舯剖面丰满
度的系数是中站面系数。若将船舯剖面想象为是从尺度等于船宽吃水的矩形中切割出来的，那么
Midship area coefficient Cm=Midship area/(B×d)
中站面系数Cm=舯面积/（B×d）
The three coefficients so far discussed are related to one another since
CB=V/(L×B×d)=[V/(Midship area×L) ]×[Midship area/(B×d)]
CB=Cp×Cm
目前为止讨论的这三种系数是相互关联的，因为
CB=V/（L×B×d）=[V/（舯面积×L）]×[舯面积/（B×d）]
CB=Cp×Cm
Generally speaking, as the block coefficient becomes finer the midship area coefficient becomes finei, as does the prismatic coefficient.
一般认为,方形系数越小，中站面系数也越小，棱形系数也一样。
The waterplane area of a ship, . the area enclosed by any particular waterline, can also be expressed in terms of a coefficient and the area of the circumsecting rectangle. Hence waterplane area coefficient
Cw=Waterplane area/(L×B)
船舶水线面面积，即被特殊水线包围的面积，也能够用一个系数和该面的外切矩形来表示。因此，水线面系数
Cw=水线面面积/（L×B）
Chapter 2 Ship Rudiments（船舶基本原理）
Lesson 7 Equilibrium and Stability（平衡性和稳定性）
Introduction（引言）
In chapter 2 the condition for static equilibrium was defined in terms of the balance of forces and moments. 第二章中的静力平衡状态是以力和力矩的平衡来定义的
From Newton’s laws of motion, it is seen that a body can be at rest or moving at constant speed only if the sum of all forces and moments acting on the body is equal to zero.
从牛顿运动定律中可以知道，若作用于物体上的合外力和和外力矩等于零，那么物体将
处于静止或以恒定不变速度运动。
The concept of stability is somewhat more complex. 稳定性的概念某种程度上更复杂些。
Here,one is concerned with whether or not a body will return to an initial state of static equilibrium when disturbed by an unbalanced force or moment. 其中一种情况与物体受到不平衡的力或力矩的干扰时是否能够回复到初始静力平衡状态有关。
While in the broader sense equilibrium refers to an overall balance of forces, which involves no acceleration or deceleration, static equilibrium is defined as follows:A body at rest is said to be in static equilibrium.静力平衡如下定义：处于静止状态的物体就出于静力平衡。但广义上的平衡指的是合力的平衡，与加速和减速无关。
If this body is disturbed by an outside force and returns to its original position when the force is removed, it is said to be in stable equilibrium. An example of this condition is a round ball lying in an upward facing bowl,as in Figure (a). 若
此
物体受
外力
作用而
当外力移除
时又
回
到
初始那么就说物体处于稳定平衡状态。一个这种状态的例子是，一个处于开口朝上的碗中的圆球，如图（a ）所示。
The ball will always return to its rest position when disturbed by an outside force. 当受到外力作用时，圆球将总能回到静止位置。
Figure (b) illustrates the condition of neutral equilibrium.
图 （b ）用 图说明了中性平衡状态。 The ball lying on a flat horizontal plane will come to rest at any point on the plane if motion is started and then stopped by an outside force (including friction). 若球在水平面上运动，然后受到外力（包括摩擦力）作 用而静止，那么球将停在水平面上的任意位置。
Unstable equilibrium is illustrated in Figure (c) ,where a round ball is balanced on top of an inverted bowl. Any slight disturbance of the balanced position will result in the ball rolling off the bowl.图 （c ）用图说明了非稳定平衡，图中圆球在倒置的碗的顶部处于平衡状态。平衡位置的任意细微的扰动将导致圆球从碗上滚落下来。
The Basis for Ship Equilibrium （船舶平衡原理） Consider a ship floating upright on the surface of motionless water. 假如一艘船平浮于静止的水面上。
In order to be at rest or tn equilibrium, there must be no unbalanced forces or moments acting on it. 为了使船静止或出于平衡状态，那么就一定没有不平衡的力和力矩作用于船上。
There are two forces that maintain this equilibrium：the force of gravity and the force of buoyancy. 有两个维持这种平衡的力：重力和浮力。
When the ship is at rest, these two forces are acting in the same vertical line,and in order for the ship to float m equilibrium, they must be exactly equal numberically as well as opposite in direction.船舶静止时，这两个力作用在同一条
竖直线上，而且，为了使船平浮于水面上，那么力就一定是大小相等方向相反。
The force of gravity acts at a point or center of gravity where all of the weights of the ship may be said to be concentrated. 重力作用于一点，或者这样说，重心是船舶全部重量集中的点。
Gravity always acts vertically downward.重力作用方向总是竖直向下。
The force of buoyancy acts through the center of forces is considered to be acting.
通过力的中心的浮力被认为作用于力的中心
This forces always acts vertically upward. 这个力的作用方向总是竖直向上。
When the ship is heeled, the shape of the underwater body is changed, thus moving the position of the center of buoyancy.
船舶横倾时,水下部分的形状发生变化，因此浮力中心的位置发生变化。
Now, when the ship is heeled by an external inclining force and the center of buoyancy has been moved from the centerline plane of the ship, there will usually be a separation between the lines of action of the force of gravity and the force of buoyancy. 如果，船舶受到外界倾斜力作用发生横倾，浮心偏离了船舶中线面时，重力与浮力作用线将发生了分离。
This separation of lines of action of the two equal forces, which act in opposite directions, forms a couple whose magnitude is equal to the product of one of these forces(that is,displacement) and the distance separating them.
两个作用于相反方向上的力的作用线的分离，形成了一个力偶，其大小等于其中任意一个力（即，排水量）和两个力作用线的间距的乘积。
In Figure (a) , where this moment tends to restore the ship to the upright position, the moment is called a positive righting moment，and the perpendicular distance between the two lines of action is the righting arm (GZ).图（a）中，这个力矩试图去使船回复至平浮位置，这种力矩称为正扶正力矩，而且，两个力的作用线间的距离称为正扶力臂（GZ上横线）。
Suppose now that the center or gravity is moved upward to such a position that when the ship is heeled slightly,the buoyant force acts in a line through the center o
f
In the new position, there are no unbalanced forces, or in other words, the g
r
a
v
ship has a zero moment arm and a zero moment.
在这个新位置，没有不平衡力，或者说，船舶力臂和力矩都为零。
the ship is in neutral equilibrium,with both the righting moment and the righting arm equal to zero.船舶处于中性平衡状态，其中正扶力矩和正扶力臂都等于零。
If one moves the center of gravity still higher,as in Figure (c), the separation between the lines of action of the two forces as the ship is inclined slightly is i
n
t h e
o p p o s i t e
d i r
e c t i o n
f r o m
t h a t
o f
F i In this case,the moment does not act in the direction that will restore the
ship to the upright，but rather will cause it to incline further In such a situation, the ship has a negative righting moment, or capsizing moment, and a negative righting arm(GZ).
这种情况下，力矩不是作用于使船回复平浮的方向，而是使船倾斜程度更大。这种状态下，船舶产生反向正力矩或者说是倾覆力矩，和反向正力臂（GZ上横线）
These three cases illustrate the forces and relative position of their lines of action in the three fundamental states of equilibrium.
绘图说明了这三种情况下的力和在三种基本平衡状态下它们作用线建的相对位置。
The Position of the Metacenter and Equilibrium（稳心和平衡位置）
The metacenter M,discussed in chapter 3,is defined as the intersection of the vertical through the center of buoyancy of an inclined body or ship with the upright vertical when the angle of inclination approaches zero as a limit. 稳心M，已经在第三章谈论过了，定义为通过倾斜物体或船舶的浮心的竖直线与船舶的横倾角度限制为零时通过浮心的垂直线的交点。
This intersection then lies on both the line of action of the center of gravity when the ship is upright and the line of action of the buoyant force.
而，这个交点的位置取决于船舶平浮时重心作用线和浮力作用线。
Consequently, it can be readily seen from the previous section that when the metacenter is above the center of gravity,as in Figure (a) ,there is a positivie righting moment formed when the ship is inclined, and the ship is tn stable equilibrium.
因
此，很容易从前面的剖面When the metacenter and the center of gravity coincide, as in Figure 7. 2(b)，
no moment is produced and the ship is in neutral equilibrium.
若
稳心与中心重合When the metacenter is below the center of gravity,as in Figure (c),a negative
or capsizing moment is formed,and the ship is in unstable equilibrium.
，将产生反向力矩或倾覆力矩，船舶处于非平衡状态。
In considering this relation between the metacenter and the ship's state of equilibrium,it is necessary to remember that the definition of the metacenter is actually valid only for angles of inclination from 0°up to the range of 7°to 10°.当讨论稳心与船舶平衡状态的关系时，有必要记住，稳心的定义仅适用于船舶倾斜角为0°至7°或10°。
Beyond this, the intersection of the lines of action of the center of buoyancy and the vertical centerplane of the ship has no significance.
除此以外，浮心作用线与船舶垂直中心面的交点没有意义了。
Therefore, the use of the relative positions of the metacenter and the center of gravity as a criterion of stability is limited to small angles of inclination.
因此，使用稳心和重心的相对位置作为评定稳定性的标准这种方法，仅限于小角度倾斜。
Obviously stability itself cannot be limited to such a restricted range.
稳定性明显不能仅限于如此限制范围。
Consequently,one must differentiate between overall stability at any angle of inclination and initial stability at small angles of inclination.(θ<10°)因此，我们应该区分任意倾斜角度的整体稳性和小角度（θ<10°）倾斜的初稳性。
Metacentric Height:A Measure of Initial Stability（稳性高：衡量初稳性）
The metacentric height,both transverse and longitudinal, is defined as the distance between the center of gravity and the transverse or longitudinal metacenter, measured vertically tn the upright equilibrium position.
稳性高度，包括横向和纵向，定义为船舶平浮时重心与横稳心或纵稳心间的竖直距离。
In Figure 7, 3, the metacentric height is GM, with the ship’s center of gravity at either G or other wise specified,the metacenter and metacentric height refer to the transverse metacentric height. If the longitudinal metacenter is being discussed, the associated metacentric height is designated GML and spoken of as the longitudinal metacentric height.
图中，G M表示稳心高度，而船舶重心用G或G1表示。除非特别说明，要不然稳心和稳心高指代的是横稳心高度。若讨论纵稳心，那么相对应的稳心高就定义为GM1，并称为纵稳心高。
If M is above G, the metacentric height is positive. If M is below G，GM is negative.
若M在G上面，那么稳心高度值就为正。若M低于G，那么GM（上横线）的值就为负。
GM is the measure of the initial stability or the ability of the ship to resist initial heel from the upright position. A ship with a positive GM will tend to float
upright and will resist initial inclining ship with a negative GM will not float upright and may be said to be initially unstable. Some ships develop a negative GM because of a condition of off-center loading and become unstable in the upright position. Because of the change in the underwater hull form with angle of inclination, such a ship will list to either port or starboard until it reaches a point of stable equilibrium.
GM （上横线）
用来衡量初稳性，或者说是衡量船舶抵抗从平衡位置开始横倾的能力。 船舶GM(上横线)值为正时，船将处于正浮状态，且能初步抵抗倾斜力作用。船舶GM(上横线)值为负时，船不能正浮，而且可能开始变得不稳定。由于偏心载荷的作用，使得一些处于平浮位置的船的GM(上横线)变为负值，船变得不稳定了。由于船体水下部分的体积因倾斜角而发生变化，这样的船将向左倾或向右倾直至到达平衡点。
Since the longitudinal metacenter ML is always located quite high above the ship ( Figure ,it is possible to state that a negative longitudinal metacentric height GML will not occur under noirmal conditions. Longitudinal stability is discussed in the next chapter.
由
于
纵稳
心M L 总是位于距离船很高的位置
（，可以这样说，通常情 况下纵稳心半径值将不会变为负值。下一章讨论纵稳性。
Lesson 8 Resistance （阻力） （引言） A ship when at rest in still water experiences hydrostatic pressures which act normally to the immersed surface. It has already been stated when dealing with buoyancy and stability problems that the forces generated by these pressures have a vertical resultant which is exactly equal to the gravitational force acting on the mass of the ship, . is equal to the weight of the ship. If the forces due to the hydrostatic pressures are resolved in the fore and aft and transverse directions it will be found that their resultants in both of these directions are zero. Consider what happens when the ship moves forward through the water with some velocity V. The effect of this forward motion is to generate dynamic pressures on the hull which modify the original normal static pressure and if the forces arising from this modified pressure system are resolved in the fore and aft direction it will be found that there is now a resultant which opposes the motion of the ship through the water. If the forces are resolved in the transverse direction the resultant is zero because of the symmetry of the ship form.
停
在静
水
中
的
船
受到
一
般
作
用
Another set of forces has to be considered when the ship has ahead motion. All
fluids possess to a greater or less extent the property known as viscosity and therefore when a surface such as the immersed surface of a ship moves through water, tangential forces are generated which when summed up produce a resultant opposing the motion of the ship. The two sets of forces both normal and tangential produce resultants which act in a direction opposite to the direction in which the ship is moving. This total force is the resistance of the ship or what' is sometimes called the ’drag‘.It is sometimes convenient to split up the total resistance into a number of components and assign various names to them. However, whatever names they are given the resistance components concerned must arise from one of the two types of force discussed t i. forces normal to the hull surface or forces tangential to that surface.
船前移时，还得考虑另一组力。所有流体多多少少都有所谓的粘性，因此当 像没入水中船体表面那样的表面在水中移动时，就会产生一些次要的力，将这些 次要的力相加就会产生一个阻止船前移的合力。这两组力，包括主要的和次要的 力，产生作用于与船舶移动方向相反的方向上的合力。这种合力是船舶阻力，或 者有时称为?拖曳力?。有时将总阻力分解成一些分力是很方便的，并且赋予它 们不同的名字。但是，无论它们被赋予了何种名字，这些相关的阻力分力必须源 于上述讨论的两种类型力中任意一个，即作用于船体的主要力和次要力。
The ship actually moves at the same time through two fluids of widely different densities. While the lower part of the hull is moving through water the upper part is moving through air. Air ，like water, also possesses viscosity so that the above water portion of a ships hull is subjected to the same two types of forces as the underwater portion. Because, however, the density of air very much smaller than water the resistance arising from this cause is also very much less in still air conditions. However, should the ship be moving head on into a wind ，for example, then the air resistance could be very much greater than for the still air condition. This type of resistance is, therefore, only to a limited extent dependent on the ship speed and will be very much dependent on the wind speed.
实
际
上
船
在
两
种密度
相差很大的
流
体
中
同
Types of Resistance （阻力类型 ） It was stated above that it is sometimes convenient to split up the total resistance into a number of components; these will now be considered. 上面已经陈述过，
有时将总阻力分解成一些分力是很方便的；现在将讨论这些分力。 The redistribution of normal pressure around the hull of the ship caused by the ahead motion gives rise to elevations and depressions of the free surface since this must be a surface of constant pressure. The result is that waves are generated