Lesson Twenty-four
Application of Engineering Economics to Ship Design
The general approach
Earlier Parts have given a broad picture of the economic environment within which marine transport operates,and the mechanics of making economic calculations,Ship design links the two,i.e.,the marine transport requirements must be developed into a series of feasible ship designs,which must then be evaluated for their technical and economic performance,covering the following:
Trading pattern and operating environment
Range of feasible technical designs
Estimation of building and operating costs,and income
Economic evaluation of alternatives.
Although a superficial glance might suggest that such a process is a matter only for shipowners,this is not so,the shipbuilder is also concerned,in two principal ways:
Specialist knowledge To design the optimal ship,extensive experience is required of the influence of different,design features on first cost,The builder is much better able than the shipowner to quantify accurately the cost of alternative hull proportions,materials,machinery arrangements,etc.
Commercial competition As shipowners have become more ready to apply the principle of income and costs,rather than minimising ship first cost,there has arisen a greater need for a shipbuilder to show not that his design is necessarily the cheapest,but that it is the most profitable,This approach has been used by the aircraft industry for some time,and is particularly applicable to standard ship designs.
Traditionally,ship design from the builder’s viewpoint has meant the receipt of an enquiry from a shipowner,accompanied either by a statement of requirements or an outline design,In the former case,a design is worked up,often using a basis ship; in the latter,the design is checked out,Time usually prevents anything but a single design being investigated,then the cost is estimated and a price submitted to the shipowner,If the tender is successful,a contract is placed,and the design worked up into a complete building design.
There are thus two principal stages of design:
Preliminary or tender design.
Detailed or contract design.
Stage (ii) will not be considered here,because the principal features have already been settled and calculations are largely in the form of analytical procedures and detailing for production,The importance of stages (i) is often overlooked,U.K,shipbuilders receive over 1000 enquiries for ships in a typical year,resulting in a very large number of outline designs,but less than 10% result in orders,Thus,tender designs outnumber contract designs by at least 10 to 1,It is at this creative stage that the approation of engineering economics has its greatest ‘pay-off’.
The traditional approach survived during the many years in which developments in ship types were slow,e.g.,1910 to 1960.It has proved inadequate for the highly competitive years since then,during which ship types have changed significantly,because
design was usually based on previous ships,yet there was no existing experience of the new ship types.
Generally only one design for one size and speed was investigated.
No economic evaluation were made either for the single design or any alternative.
Traditional cost estimating methods did not reflect the changing ship types and production methods.
A modern approach aimed at improving designs of ship requires good collaboration between potential owners and builders.
Shipbrokers can contribute to this dialogue,while it is often desirable for consultants to be used to investigate the range of possibilities (especially for the smaller ship operator) on account of their independent commercial status,and the availability of suitable staff.
A comprehensive process includes the following:
(i) Investigation of transport demand and corresponding market research
(ii) Concept formulation,range of possible technical solutions,ship types,sizes and speeds
Preliminary technical design of a number of alternative (often using specialised computer programs)
Estimates of first costs,operating costs and income of the alternatives
Economic evaluation of the alternatives
Selection of the optimal design,either by judgement,or mathematical programming techniques
Discussion of the proposed design (and any suitable alternatives ) with clients
Contract,detailed design and construction of the final selection.
the practicing ship designer should be interested in every aspect of these stages,but here we are concerned mainly with stages,but here we are concerned mainly with stages(iii),(iv) and (v),The relationship between these activities are shown in design spiral,The important feature of the design spiral concept is that each successive cycle is made with an increasing degree of complexity,but a decreasing number of possible designs,The spiral starts with known information on cargoes and routes,generating a matrix of several hundred potential designs,Before the economic evaluation is made,each combination of principal particulars has its design features evaluated in terms of capacity,deadweight,trim and stability,and cost,After the first cycle,the matrix is reduced in size by the application of technical criteria,e.g.,stowage factor too small or insufficient stability,and of economic criteria,e.g.,inadequate rate of return,The second cycle focuses on the optimal region and enlarges it,examining a few tens of designs in greater depth,using the results of the first cycle as first approximation,The results of the second cycle may be sufficient for giving price indications to a shipowner for a range of possible designs,For a more detailed estimate,a third cycle may be made in still greater depth,but for only a single design or a very small number of designs.
Such a system is ideal for computers,where each intersection of spoke and spiral can be sub-program,increasing in complexity as each spoken is traversed outwards,e.g.,steelmasses are initially estimated from principal dimensions and coefficients,and subsequently from actual scantlings,The early cycles should treat each function as continuous,as at this stage relative values are more important than absolute values,The later cycles will use the step functions that may apply in practice,e.g.,diesel engines available with integer number of cylinders,The application of step functions too early may lead to the area to be enlarged proving non-optimal when more accurate design information has been generated.
It should be noted that principal dimensions are the independent variables,Deadweight,although a convenient and simple measure of ship size is a merging of three one-dimensional measures which does not reflect the relative importance of length,breadth and draught (or depth for volume-limited ships),There is an infinite number of ships which can be designed to have equal deadweight,but one of these will prove to be more economical than all the others,given particular operating and financial circumstances,Route characteristics generally have a strong influence on the principal dimensions which,in conjunction with hull fullness,may determine displacement and,for a particular ship type,largely determine lightship also,Hence,deadweight tends to be a drop-out from the calculation and should not require to be attained exactly in a broad-based design system,What is required is the optimal ship within a general band of deadweight and speed,Allowing the individual dimensions to take up whatever values produce the most profitable ship within any given constraints,such as availability of cargoes and port facilities.
Such a design system is most easily applied to the straightforward ship types (such as bulk carriers) which dominate the number of enquiries; in practice,this frees valuable design effort for the more complex ship types,
(From,Engineering Economics and Ship Design” by 1,L,Buxton,1976)
Technical Terms
engineering economics 工程经济学
marine transport 海上运输
economic environment 经济情况
feasible technical design 可行的技术设计
building costs 建造成本，造价
operating costs 营运费
income 收入，收益
economic evaluation 经济评价
alternative 方案
commercial competition 商业竞争
present worths 现在的价值
standard ship 标准船
enquiry 探询
basis ship 母型船
tender 投标，供应船
contract design 合同设计
pay-off 效果
collaboration 合作
shipbroker 船舶经纪人（中间人）
mathematical programming techniques 数学规划技术
client 买主
design spiral 设计螺旋线
technical criterion (复数criteria) 技术横准
economic criterion 经济横准
spoke 径向辐条线
sub-program 子程序
step function 阶梯函数
integer number 整数
independent variable 独立变量
broad-based designed system 笼统的设计系统
Additional Terms and Expressions
net present value 净现值
required freight rate 需要的货运费率
the time value of money 钱的时间价值
capital recovery factor 资金回收因数
average annual cost 平均年度费用
interest rate 利率
annual return 年收益
annual cost of capital recovery 年资金回收额
present worth factor 现值因数
tax rate 税率
port days per round trip 每航次停泊时间
round trip per annum 年航次数
handling rate 装卸效率
vessel investment 船舶投资
total costs 总成本
depreciation 折旧费
maintenance and repair cost 维修费
insurance 保险费
fuel and lubricating oil costs 燃润料费
stores 物料费
port charges 港口费
cargo handling charges 装卸费
administration 企业管理费
crew expenses 船员费
freight revenue 运费收入
complex economic criteria 综合经济指标
transport cost per unit 单位运输成本
recovered years of investment 投资回收年限
profit per annum 年利润
life of ship 船舶使用年限
Notes to the Text
To design the optimal ship,extensive experience is required of the influence of different design features on first cost.这个句子中，主语成分被谓语is required隔离，见第二课注7。
.348.
2,not that…,but that… 不是……而是……
3,It is at this creative stage that the application of engineering economics has its greatest,pay off”.这是一句“it is …that …”型强调句型，可译成“正是在这个创造性的阶段，工程经济学的应用有它最大的效果。”
4,on account of their independent commercial status 考虑到他们个子独立的经营情况
5,Before the economic evaluation is made each combination of principal particulars has its design features evaluated in terms of capacity,deadweight,trim and stability,and cost.此句中has its design features evaluated 为“have+宾语+补足语（过去分词）”句型，译为“使其设计特性做出评价”。in terms of 在……方面（意义）
6,in greater depth 可译成“比较深入一些地”; in still greater depth 可译成“更深入一些地”。
7,a drop-out from the calculation… drop-out 在此为“被略去”之意。
