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Ships Typed According to Means of Physical Support

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. 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.

Aerostatic Support

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. Such vessels depend on lift fans to create a cushion of

low-pressure air in an underbody chamber. This cushion of air must be sufficient to support the weight of the vehicle above the water surface.

The first type of vessel has flexible “skirts” that entirely surround the air cushion and enable the ship to rise completely above the sea surface. This is called an air cushion vehicle (ACV), and in a limited sense it is amphibious.

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. This type is called a captured-air-bubble vehicle (CAB). It requires less lift-fan power than an ACV, is more directionally stable, and can be propelled by water jets or supercavitating propellers. 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 warface vessels.

Hydrodynamic Support

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. 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. 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.

Planning hulls are hull forms characterized 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. Planning 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. Most planning craft are also restricted to operations in

reasonably clam water, although some “deep V” hull forms are capable of operation in rough water.

Hydrostatic Support

Finally, there is the oldest and most reliable type of support, hydrostatic support. All ships, boats, and primitive watercraft up to the twentieth century have depended upon the easily attained buoyant force of water for their operation.

This hydrostatic support, commonly recognized as flotation, can be explained by a fundamental physical law that the ancient philosopher-mathematician Archimedes defined in the second century B.C. Archimedes’ Principle states that a body immersed in a liquid is buoyed up (or acted upon) by a force equal to the weight of the liquid displaced. This principle applies to all vessels that float (or submerge) in water---salt or fresh. And from this statement the name of the ships in the category are derived; they are generally called displacement hulls.

Although this ship type is very familiar, its subcategories warrant special discussion. For example, in some vessels reasonably high speed must be combined with the ability to carry light cargo or to move more comfortably in rough water than a

planning hull. High-speed planning-hull characteristics can be modified to produce a semidisplacement hull or semiplaning hull. These compromise craft, of course not as fast as full-planing hulls but faster than conventional displacement hull, must have more power and less weight than the latter. Such types are obviously the result of “tradeoffs.”

The example cited above lies between clear-cut physically defined categories----it is not a good example of a variation of a true displacement-type ship. The latter must be recognized primarily as a displacement vessel, and its variations depend primarily on the distribution of buoyant volume----the extent of the depth and breadth of the hull below the water.

The most ubiquitous type of displacement ship can be generally classified as the common carrier, a seagoing vessel. It may be employed for passenger service, light cargo-carrying, fishing by trawling or for hundreds of other tasks that do not require exceptional capacity, speed, submergence, or other special performance. It is the most common and easily recognizable type of ship, with moderate displacement, moderate speeds, moderate to large lengths, and moderate capacities. It usually embodies the maximum in cruising range and seaworthiness. It is the “ship for all seasons.” It is the standard to which all other ship classifications in the displacement category may be referred.

The closest relative to this standard vessel, which plays a crucial role not only in world commerce but in the survival of the industrial world as well, is the bulk, oil

carrier, the tanker, or supertanker. These terminologies are common but unspecific, and in this discussion they are inadequate, for what was called a supertanker several years ago is today not a supertanker. The industry itself has created a far more explicit nomenclature. Based upon the index of 1000000 tons oil cargo capacity, the size

categories are LCC (large crude carrier), VLCC (very large crude carrier), and ULCC (ultra large crude carrier). Any tanker greater than 100000 tons but less than 200000 is a LCC, those between 200000 and 400000 are VLCCs, and those over 400000 are ULCCs. The current necessity for these designations becomes clear when we realize that before 1956 there were no tankers larger than 50000 tons, and not until the early sixties were any ships built larger than 100000 tons. In 1968 the first ship over

300000 tons was built. With their bulk and enormous capacity (four football fields can be placed end to end on one of their decks), these ships are designed and built to be profit-makers, enormously long, wide, and deep, carrying thousands of tons of crude oil per voyage at the least cost. Few of these elephantine tankers have more than one propeller shaft of rudder. Their navigation bridges are nearly one quarter of a mile from their bows. Their top service speed is so low that a voyage from an Arabian oil port to a European destination normally takes two months.

Such vessels belong to a category of displacement ship that has a great range of

buoyant support. They have a very large and disproportionate hull volume below the surface when fully loaded. Indeed, the cargo weight far exceeds the weight of the ship itself. The draft or depth of water required for a fully loaded VLCC runs to 50 or 60 feet and the ULCC may be 80 feet. Such ships belong in the exclusive category of displacement vessels called deep displacement ships.

There exists another type of displacement hull with extreme draft. However, it is

similarity to the crude-oil carrier of the preceding discussion goes no further than that. This type of vessel is called the SWATH( small waterplane area twin hull). Briefly, this rather rare breed of ship is designed for relatively high speed and stable platform in moderately rough water. Its future is problematical, but the theory of placing the bulk of the displacement well below the surface and extending the support to the above-water platform or deck through the narrow waterline fins or struts is sound. Twin hulls connected by an upper platform provide the necessary operating stability. The most significant class of displacement hull for special application is the sub marine, a vessel for completely submerged operation. The nature of the submarine and a description of her various operational attitudes, both static and dynamic, is covered in subsequent chapters. It is only necessary here to emphasize that

submerisible vessels are specifically displacement vessels applying the theory of Archimedes’ Principle and all that it implies.

Multihull Vessels

There is one other type of hull in common use that has not yet been mentioned, primarily because it fits into none of the categories described but rather can exist comfortably in any. This craft is the so-called multihull vessel----the catamaran and the trimaran. These vessels are most frequently displacement hulls in their larger sizes, such as the SWATH mentioned above, or more conventionally, ocean research

vessels requiring stable platforms and protected areas for launching equipment. There are also the twin-hulled CAB vessels mentioned earlier and high-speed planning catamarans. Actually, the multihull ship is an adaptation of any of the basic hull

categories to a special application that requires exceptional transverse stability and/ or the interhull working area.

中文翻译：

按照物理支撑方式而划分的船舶类型

就船舶分类而言，物理支撑形式是基本于船舶在设计情况下进行的假定。船舶设计成在水上、水面或者水下工作，因此气—水交界面将用于参考数据。因为前面提到的三个区域的物理环境特性差异很大，设计成在这些区域工作的船舶的物理特性也不同。

空气静力支撑

有两种类型船舶是靠前身产生的空气垫而支撑在海面之上的。这些相对较轻的船舶具有很高的航速，因为空气阻力远小于水阻力，还有的原因是在告诉航行时不与海浪接触以及采用的柔性密封连接减少了海浪的冲击。这类船舶依靠鼓风机在船底部形成一个低压空气垫。这个空气垫必须足以支撑起水上船舶的重量。 第一种类型船的四周具有柔性的“裙”，在船底围成一个空气垫，试船能完全升离水面。这种船成为“气垫船”（ACV），再有些场合是两栖的。

另外一种是具有刚性侧壁或薄壳的气垫型船，侧壁伸到水面下，维持气垫压力所需的空气流量就降低了。这种类型的船称为束缚气泡减阻船（CAB）。这种船所需的升力风机功率要小于气垫船的，方向稳定性也更好，并可以由喷水装置或者超空泡螺旋桨推进。此类船非两栖，并且还没有达到像空气船那样推广，如旅客渡船、海峡汽车渡船、极地考察船、登陆艇及内河船等。

水动力支撑

依靠水动力支撑的船也只有两种类型。水动力是靠专门设计的水动力板在水面下具有快速相对运动而产生的。物理学原理表明任何带来不对称流体的运动物体都会在垂直于运动的方向上产生一个升力。正像具有机翼的飞机在空气中运动能产生升力一样，通过一个穿过水面的支柱而固定在水下的木翼，其水动力可以支撑一般船舶离开水面。

滑行船体的特点是具有相对平坦的底部和浅V型剖面（特别是在船中前），高速航行时在局部可以为轻排水量船和小型船艇提供足够的水动力支撑。滑行艇的尺寸与排水量一般都受限制，因为功率重量比和在波浪中航行产生的结构应力大小都有要求。大多数滑行艇都要求在静水中航行，尽管某些深V型船体具有再波浪中航行的能力。

静水力支撑

最后，是最古老的也是最可靠地支撑类型——静水力支撑。一直到20世纪，所有的船、艇和建议的水艇都依靠静水的浮力而工作在水面上。

静水力支撑通常称为浮力，可以由公元前二世纪古代哲学及数学家阿基米德发现的物理定律来解释。阿基米德定律指出，浸没在液体中的物体将受到一个等一所排开的液体重量的浮力作用。这一定律适用于浮在水面或在下潜到水中的任何船。水包括海水和淡水。依据这一定律，这类船可以统称为排水型船。

尽管这类船非常相似，其详细分类还是有必要进行特别讨论。例如，对某些船，合理的高航速必须与装载轻量货物的能力相结合，或者比滑行艇在波浪中航行更

具舒适性。高速滑行船体的特点可以通过修改而产生半排水型船体或半滑行船体。这些折中的船艇，尽管没有全滑行船那样快，但还是比常规的排水型船快。它们需要比排水型船更大的功率和更小的重量。这些类型船很明显是“折中”的结果。

上面引证的例子是用物理定义作清晰分类而定义的类型，并不是从其实的排水型船中分化出的船型的一个良好的例子。后者应当认为是排水型船，它的归类主要取决于浮体体积即水下船体长度和宽度范围的分布情况。

最常见的是排水型船一般分类为通用海洋运输船，它们可以用作客运、轻货运输、拖网捕鱼或各种不需要特殊舱容、速度、吃水、或其它特殊性能的其他业务。这类船最常见并很容易识别，具有适度的排水量、航速、长度和舱容。它们通常具有最大的航程和最好的适航性，属于“全季节船”，是所有其它排水型船分类时重要参照的标准。

在这种标准船型中，最重要的船型是散装油船，油船和其它超级油船，它们不仅在世界贸易中也在全球工业中扮演重要角色。这些术语是普通的但不具体。在该讨论中它们的称呼也是不充分的，因为多年前称为超级油船而现在并不是。工业本身已经产生了非常清晰的术语。基于10万吨级油船的指标，其尺度可定为LCC（大型油船），VLCC（非常大型油船）和ULCC（超级油船），大于10万吨但小于20万吨的油船属于LCC，再20万吨至40万吨的是VLCC，超过40万吨的是ULCC。我们知道，再1956年以前还没有超过5万吨的油船，在60年代初期也没有超过10万吨的任何船型。而现在关于这些名称的规律变得清晰了。1968年，第一艘超过30万吨的船建成。这些巨型船舶（一个甲板相当于4个足球场大）设计并建造成为利润创造者，超长、超宽、超深船型，每个航次以最小的消耗运输大量的原油。这些超大油船很少配有超过一个的螺旋桨轴和舵。它们的驾驶台距其船首将近1/4英里远（约400m）。其最高服务航速很低，以至于从阿拉伯油港到欧洲目的港的航程通常要两个月时间。

这些船属于排水型船，具有巨大的浮力支撑。当满载时其船体在水下有非常巨大的和不成比例的（？）体积。事实上，货物重量远远超过船本身的重量。一艘满载的VLCC的吃水或要求的水深在50~60英尺之间，一艘ULCC大概要80英尺。这些船舶在排水型船舶中有专用的类型称为深排水量船。

另外还有一类排水型船具有大的吃水。类似于前面讨论过的原油船，但吃水还没有 超过它们。这类船称为SWATH（小水线面双体船）。简单地讲，这类极少见的船型设计成在中等程度海况中具有高速和稳定性的上体（上部结构）。它们的未来是有疑问的，但在水面以下提供大多数排水体积，通过窄的立柱支撑水面以上的船体或甲板的理论是完善的，通过上层平台而连接在一起的双船体提供了必要的稳性。

排水型船中最值得关注的特殊应用是潜艇，完全潜入到水中工作。潜艇的特性和它的各种工作状态，包括静力的和水动力的，的描述在后面章节中有全面介绍。这里有必要强调的是潜艇是一种特殊的排水型船，应用了阿基米德定律及其所有隐含的定理。

多体船

有一种常用的船型还没有提到，主要因为不能归到已介绍的任何一种船型中，但是都在一定程度上可以归纳到它们之中。这种船即所谓的多体船——双体船和三体船。它们是常见的排水型船，例如前面提到的SWATH，或更常规的海洋考察船，要求有稳定的平台和保护区域以便于向水中投放设备。还有前面提到的双体气泡

(幕)船和高速滑行双体船。实际上，多体船是一种由任何基本船型至特殊应用之间的改造船，以满足期望的横稳性要求和大的内部工作面积要求。

图2.1绘出已经介绍过的船体轮廓图（没有比例尺）以及与其物理支撑的关联。除了多体船依据不同用途有不同的船速外，它们按速度从高向低排列。

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