-
船
舶
专
英
< br>语
翻
译
)
课
文
+
业
(
Chapter 1 Ship
Design
（船舶设计）
Lesson 2 Ships
Categorized
（船舶分类）
2.1
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.
< br>——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
p
urposes.
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。
2.2 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
。
< br>
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
ha.s
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
。
< br>
This is called an air cushion
vehicle (ACV) ,and in a limited sense it is
amphibious.
它被称为气垫船（
< br>ACV
）
，
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
< br>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.
< br>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较平，
横剖面呈浅
V
形
（<
/p>
尤其是船的前半部分
）
。
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. <
/p>
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
< br>?
深
V
型剖面
< br>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）
3.1 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
的后侧，
而艏柱是通过船艏与夏季载重水线的交点的竖直线。
如
果船上没有舵柱，那么艉柱就取通过舵销中心线的直线。
The length between perpendiculars
(L.B.P.) is used for calculation purposes as will
be seen
later,but it will be obvious
from Figure 3.1 that this does not represent the
greatest length of
the
ship.
两柱间长
（
L.B.P.
）
是用于后面的计算之用的，
然而从图
3.1
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 3.1.
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（
L.O.A.
）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(L.W.L.).
第三种长度是水线长（
L.W.L
）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
?
am
idships
?
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
onl
y.
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
还大，
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. <
/p>
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，<
/p>
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
?
stand
ard
?
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：
< br>首舷弧
（
in
）
=
0.2L
ft
+
20
尾舷弧
（
in
）
=
0.1L<
/p>
ft
+10
这些公式用英制单位表示
为：
首舷弧
（
c
m
）
=
1
.6
66L
m
+
50.8
尾舷弧
（
c
m
）
=
0.833L
< br>m
+
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”）<
/p>
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.
< br>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。
< br>
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<
/p>
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
< br>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 sp
acing.
若用十进制单位表示，那么这些数字就可能是
10
cm
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
d
a
、
dx
和
d
f
那么
中拱或中垂
< br>=-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。<
/p>
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. <
/p>
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。
< br>
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<
/p>
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
referenc
e.
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，<
/p>
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.<
/p>
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 pla
nes.
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，<
/p>
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
?
=g
V
?
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，
< br>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
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
<
/p>
=V/
（
L
×<
/p>
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
coefficient.
当船舶设
计师已经决定需要何种体
积时，
那么他就要考虑四个因素：
船长，
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。
< br>
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
×<
/p>
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/(Mid
ship 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, i.e. 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）
7.1
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
equilib
rium.
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 7.1(a).
若此物体受外力作用而当外力移除时又
回到初始位置，
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
7.1
（
a
< br>）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 7.1(b) illustrates the condition
of neutral equilibrium.
图
7.1
（
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 7.1(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
7.1
（
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。
7.2 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 dir
ection.
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
,<
/p>
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
< br>（即，排水量）和两个力作用线的间距的乘积。
In
Figure 7.2(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
7.2<
/p>
（
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 of gravity
.
假如将船舶
重心向上移到能使发生船舶小角度横倾的位置，<
/p>
浮力作用线通过重心。
In the
new position, there are no unbalanced forces, or
in other words, the 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
7.2(c), the separation between
the
lines of action of the two forces as the ship is
inclined slightly is in the opposite direction
from
that
of
Figure
7.2(a)
.
若将重心再往上移高点，如图
7.2
（
c
）
，随着船舶小角度倾斜，
两个力的作用线的分离方向与图
7.2
（
a
）不同。
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）
< br>
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。
7.3
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 7.2(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中看出，稳心位置比重心高时，如图
7.2
（
a
）
，
船舶倾
斜时将产生正扶正力矩，使
船处于稳定平衡状态。
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，如图
7.2
（<
/p>
b
）
，将没有力矩产生，船舶处于中性平
衡状态。
When
the
metacenter
is
below
the
center
of
gravity,as
in
Figure
7.2(c),a
negative
or
capsizing moment is formed,and the ship
is in unstable equilibrium.
若稳心位置比重心低，如图
7.2
（
c
）
，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
1
0
°
。
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，
< br>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.(
?
<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。
7.4
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
7.3
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 forces.A 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<
/p>
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
7.4),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
（图
7.4
）
，
可以这样
说，
通常情
况下纵
< br>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）
8.
1Introduction
（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,
i.e.
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
于没入水中的船体表面的静水压力作用。
当处
理浮力和
稳定性问题时，
已经陈述过
< br>由这些压力产生的力有一个竖直向上的合力，
该合力等
于作用
于主船体上的重力，
即等于船舶重量。
< br>如果将这些由静水压力产
生的力沿着船舶纵向和横
向分解，
那么将会发现两个方向上的合力都为零。
< br>船以
某一速度
V
经水面向前移动，
考虑
会发生什么情况。
船舶前移效应产生了作用于
船体的动水压力，
该压力改变了原始
主要静
压力
，
而且若由这些变化的压力产生
的力在纵向上分解，
那么现在就会发现存在一个阻止
船舶水面移动的合力。
如果
这些力在
横向上分解，那么合力就为零，这是由于船型两侧对
称。
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
?
< br>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<
/p>
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
中同时移动。
船体较高的部分在空气中
移动，而
船体较低的部分在水中移动。如同水一样，空气也有粘性，因此船体水
上部分同水下部分
一样也受到两种力作用。
但是由于空气密度远远小于水的密度，由此在静止空气中产生的
阻力也非常小。
但是，
假如船舶逆风前行，
那么空气阻
力就远远大于船在静止空气中的阻
力。
因此，
这种阻力在某种程度上取决于船舶
航速，且很大程度上由风速决定。
8.2 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，
< br>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 on the surface
of the water and
spread
away
from
the
ship.
Waves
possess
energy
so
that
the
waves
made
by
the
ship
represent a loss of energy from the
system. Looked at in another way the ship must do
work
upon the water to maintain the
waves. For this reason the resistance opposing the
motion of
the ship due to this cause is
called
?
wave-making
resistance
?
.With deeply
submerged bodies
the changes in the
normal pressure
around
the
hull
due
to
ahead
motion
have only
a
small
effect on the free surface so that the
wave resistance tends to be small or negligible in
such
cases.
由于前行运
动引起的船体周围主压力的重新分布，
导致
自由面上升或下降直
到它是恒
压面
。
结果是水面上产生了波
，
波并随船传播。波具有能量，
因此由船产生的波表示船舶
系统损失的能量。
用另一种方式来看，
船必
须对水做功来维持
这些波。
针对这种
原因，
由
于船舶前移运动产生的阻碍船舶运动的阻力称为
“
兴
波
阻
力
”
。
由于船体没入水中
较深
，船
舶运动引起的分布在船体表面的主压力的
变化对自由面的影响非常小，
因此这样的情况
下，
兴波阻力将很小或者可以忽略不计。
The
resistance
arising
due to
the viscosity
of the water
is
appropriately
called
?
viscous
resistance
?
or
often
?
frictional
resistance
?
. The thin layer
of fluid actually in contact with the
immersed surface is carried along with
it but because of viscosity a shear force is
generated
which
communicates
some
velocity
to
the
adjacent
layer.
This
layer
tn
turn
communicates
velocity to the
next layer further out from the hull and so on. It
is clear then that there is a
mass
of
fluid
which
is
being
dragged
along
with
the
ship
due
to
viscosity
and
as
this
mass
requires a force to set it in motion
there is a drug on the ship which is the
frictional resistance.
The
velocity
of
the
forward
moving
water
declines
in
going
outwards
from
the
hull
and
although theoretically
there would still be velocity at infinite distance
the velocity gradient is
greatest
near
the
hull
and
at
a
short
distance
outwards
the
forward
velocity
is
practically
negligible. Forward velocity is
therefore confined to a relatively narrow layer
adjacent to the
layer is called the
?
boundary
layer
?
. The width of the
layer is comparatively small at
the bow
of the ship but thickens in going aft,as will be
seen from Figure 8.1,which shows the
fall off in velocity at various
positions in the length.
由于水
粘性产生的阻力适宜称为“粘性力”或常称为“摩擦阻力”。
与船体没入
水中部分的表面相接触的一层很薄的流体，
随船一起移动，
由于水的粘性作用产生了一个
剪切力，
该剪切力将向相邻的
流体层传递一些速度。
这层流体又依次向离船体更远的下一
层流
体传递速度，
等等。
这样就很清楚了，
有大量的流体由于粘性作用将被拖着与船一起
运动，
而且由于这
些液体一个力来运动，
所以船体上将产生一个拉力，
即摩擦阻力
。
从船
侧向外，水前行的速度逐渐衰减。虽然理论上无限远处的
水仍然有速度，
但是船体附近的
水的速度梯度最大，
离船很近
的一段距离处水的前行速度事实上可以
忽略不计。
因此水的
前行速度仅限于临近船体相对较窄的流体层
。
这流体层称为“边界层”
。
流体层的
宽度在
船首处较窄，但是向船尾逐渐变厚，
就像图
8.1
所示的那样，
沿着船长方向的不同位置处
速度逐渐减小。
The
actual
thickness
of
the
boundary
layer
is
indeterminate
but
the
point
where
the
forward velocity has
fallen to about 1% of what it would be if the
water were frictionless is
considered
to
be
the
outer
extremity
of
the
boundary
layer.
Thus,
in
Figure
8.
1
where
the
velocity V1 of the water relative to
the body is 0.99 of what it would be at the same
point if the
water was frictionless
would be the outer edge of the boundary
layer.
边界层的真实厚度是不确定的，
但如果水没有摩擦力，
那么前行速度减小至
原来的
1%
的点被认为是边界层的最外层。所以，若水无摩擦，那么图
8.1
中水
相对于船体的速度
V1
是
原来速度
的
0.99
倍的地方就是边界层的外缘。
Theoretical
investigations
on
flow
around
immersed
bodies
show
that
the
flow
follows
the
type of streamline pattern shown in Figure r,
where there are sharp changes of
curvature
on
the
surface
of
the
body,
and
party
due
to
the
viscosity
of
the
fluid,
the
flow
separates
from,
the
surface
and
eddies
are
formed.
This
separation
means
that
the
normal
pressure of the fluid is not recovered
as it would be according to theory and in
consequence a
resistance
is
generated
which
is
often
referred
to
as
?
eddy-making
resistance
?
.This
type
of
resistance, like wave-making
resistance, arises from a redistribution of the
normal pressures
around
the
hull
in
contrast
to
the
frictional
resistance
which
arises
because
of
tangential
viscous
forces.
对浸没船体周围流体的研究表明，
流体遵循流线型
，如图
8.2
所示。然而，船体表面
曲率变化非常的大的地方，
部分
是由于流体粘性的作用，
流体与船体表面发生分离，
形成漩
涡。这种分离意味着流体主压力没有恢复到原来的状态，由理论结果产生了一个称之为
“
漩涡阻力”
的阻力。
对比与由粘性力产生的摩擦阻力，这种阻力像兴波阻力一样是有船
体周围
主压力
的重新分布造成的。
The fourth type of resistance! is that
due to the motion of the above-water form through
the air, as has already been mentioned,
and could consist of a combination of frictional
and
eddy resistance.
这四种已经提到过的阻力是由通过空气的船体水上部分运动造成的，
而且由摩擦
阻力和
漩涡阻力组成的。
The
shape
of
a
ship
hull
is
determined
by
many
competing
influences.
For
ease
of
construction, it should be a
rectangular box; for adequate transverse
stability, it must be wide;
for
adequate strength as a beam being bent in a
longitudinal plane, it must be deep. All these
factors influence the shape of a hull,
but often the primary factor is the dynamic
interaction of
the
hull
with
the
water.
The
interactions
that
govern
the
resistance
of
the
hull
to
steady
forward motion
?
a
resistance that determines the choice of
propulsive power
?
usually
demand
the greatest attention from the
naval architect.
船体形状是由
很多相互矛盾的影响因素
造成的。
为了便于建造，
船体应当为矩形盒型；
为了保持一定的横向稳定性，
船必须宽；
为了维持纵向平面上梁的弯曲强度，
船
必须深。
所
有这些因素都影响船体形状，
但是通常最主要的因素就是
船体与水间的动态交互作用。<
/p>
这
种交互作用决定船体稳定前行阻力——这阻力决定推进功率的选
择，通常要求造船师的极
大关注。
Resistance to steady forward motion has
four components:(1)friction between the water
and
the
hull
surfaces,(2)energy
expended
m
creating
the
wave
system
caused
by
the
hull,
(3)energy
put
into
eddies
shed
by
the
hull
and
its
appendages(e.g.,the
ruddier),
and(4)resistance
by the air to above-water, parts of the
ship.
影响稳定前行的阻力由四个部分组成：
（
1
）
水与船体表面的摩
擦力，
（
2
）
船
体产生波
系时耗散的能量，
（
3
）
注入漩涡导致其与船体及其附体脱离的能
量，
（
例如舵）
和
（
4
）空气
对船体水上部分的阻力
。
Frictional resistance is
proportional to the product of water density, area
of contact with
the water,square of
water speed relative to the ship, and a friction
coefficient. This resistance
can be
minimized by reducing the area of a
hull
?
s wetted surface,but
usually very little can be
accomplished
in the face of many other demands on hull size and
shape. A smooth surface is
an
obvious
factor
in
reducing
fricition,but
a
surface
that
is
smoother
than
ordinary
painted
steel
has
a
benefit
that
is
trivial
compared
to
its
cost.
The
friction
coefficient
is
largely
a
function
of
the
Reynolds
number(the
product
of
water
density
times
ship
speed
times
ship
length,divided by water
viscosity);it is not controllable by a designer
since water density and
viscosity are
beyond control and ship length and speed are
almost inevitably dictated by other
considerations. The friction
coefficient was the subject of intense research,
especially during
the
first
half
of
the
20th
century,
but
since
that
time
most
ship
designers
have
employed
values standardized
by the International Towing Tank
Conference.
摩擦阻力与，
水的密度、
船体与水的接触面积、
水相对于船的速度的平方和
摩擦系数，
的乘积成正比。
能够通过减小船体湿表面积来使摩擦
阻力最小化，
但是通常在为了维持船
体尺寸和形状的要求下，<
/p>
这种情况是不可能实现的。
使接触面光滑是减小摩擦力的最明显<
/p>
的因素，
但是相对于造价而言，
将原始油
漆钢表面处理的更光滑所需的代价就很小了。
摩擦
系数主要是雷
诺数
（水的密度，
乘船速，
乘船长，除水的粘性）的函数；由于水的密度和粘
性是不可改变的，船长
和船速几乎是由其他一些因素决定的，
因此设计师也无法改变什么
。
摩擦系数大量研究的主要课题，特别是在
20
世纪上半叶，但是从那以后船舶设计师们就
采用了国际拖曳水池会议设定
的标准值。
Wave
making
and
eddy-making
resistance
components
are
often
lumped
into
a
single
?
residuary
resistance,
?
especially
when
resistance
measurements
are
extrapolated
from
model testing. Wave
making is usually by far the larger component of
residuary resistance;it is
therefore
given more attention in research and in the
designing of a hull. Indeed,wave making
increases
so
rapidly
as
ship
speed
increases
that
it
eventually
requires
more
power
to
overcome than is practicable to build
into a ship. For a ship of conventional type,it is
virtually
impossible to operate at a
speed-to length ratio (speed in nautical miles per
hour, divided by
the
square
root
of
the
waterline
length
in
feet)
higher
than
approximately
that
realm even
a trivial increase in speed requires a virtually
infinite increase in power in order to
fulfill the energy demand of the wave
system. Small craft can escape this limitation by
planing,
but the amount of power
required for the transition to a planing mode is
beyond practicality