usually measured at amidships.
第三个主尺度是深度，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 continuous deck. 如果没有指出是哪处的甲板，那么深度就以连续甲板的最高处为基准。
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。
3.2 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变化，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 3.1. 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 3.1 所示。所谓的舷弧“标准值”用公式给出： 首舷弧（in）=0.2Lft+20 尾舷弧（in）=0.1Lft+10 这些公式用英制单位表示
为：
首舷弧（cm）=1.666Lm+50.8 尾舷弧（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. 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船舯尾部偶尔有一段距离，有时抛物线状的纵剖线会发生分离。舷弧值。
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= da-df，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，干舷与露天甲板的间距沿船长方向将会发生变化，而且一定条件下间距也受纵倾的影响。一般说来，船舯干舷值最小，向首尾两端逐渐增大。
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 Fig.4.1. 示例船舶的主要部分以及相关的名字都在图 4.1 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） 5.2 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 various loads such as the weight of the ship itself, plus cargo, fuel, etc. 船型设计是用来满足特定的需求，而且首先要考虑的是能够提供做够的浮力来支撑多样的载荷，例如船舶本身重量，加货物，燃料等。 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
?=gV? were ? 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 5.3 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LBd体积的比值。用另一种方式表示为
船舶专业英语(课文+翻译)教学教材
