Ship Design and Construction - Coursework Example

Ship Design and Construction Name Course Institution Date Ship Design and Construction The most important phase in the overall construction process of a ship is determining the main dimensions, because various characteristics of the ship such as power requirements, economic efficiency, hold capacity, as well as the stability are decided by its main dimensions. The main dimensions of a ship include width B, length L, depth D, and draught T. Other dimensions include the block coefficient CB, prismatic coefficient CP, and midship area coefficient CMA. These dimensions are usually determined first and are coordinated in such a manner that the ship meets the design requirements specified by the client (Schneekluth, 1998). The desired characteristics are achieved through various combinations of dimensions. This option allows an economic efficiency to be achieved whilst meeting the client’s desired characteristics. An iterative procedure is usually required when determining the main ratios and dimensions of the ship. According to Schneekluth (1998), the sequence below is suitable for a multi-purpose vessel. i. Determination of the weight of the loaded ship; this is carried out using a typical deadweight: displacement ratio for the ship size and type ii. Choosing the length between perpendiculars iii. Determination the block coefficient, prismatic coefficient, midship area coefficient collectively iv. Determination of the depth, draught, and width collectively The process of determining the main dimensions of the ship, which include length, depth, breadth, and form coefficients, is carried out based on the following factors: The hydrodynamic capability of the ship such as propulsion and resistance, maneuverability, and seakeeping Adequate cargo holds volume Adequate stability Sufficient structural strength Cost of construction FORM COEFFICIENTS a) Block coefficient Block coefficient of a ship at any given draft is the ratio of the volume of displacement at that draft to the volume of a rectangular block with the same overall length, depth, and breadth (Schneekluth, 1998). Assuming that the ship form simply consists of a rectangular block of breadth equal to the breadth moulded, length equal to the length between perpendiculars, and depth equal to the draught, then the underwater volume would be given by the equation below: V = L x B x d. Now if we assume that the ship form has been cut out of this block, then the ratio of the actual volume of the underwater form to the block volume (LBd) is referred to as the block coefficient, and is given by the equation below: Block coefficient CB =, where v is the actual volume of the underwater form As mentioned earlier, when the required ship volume has been decided, there are four factors to be considered, namely breadth, draught, and length of the ship, as well as the block coefficient. Slow speed vessels such as the cargo and multi-purpose vessels require high values of block coefficient, while fast speed vessels require low values of block coefficient. The high value of block coefficient in multipurpose vessel implies that there is large amount of displacement available for carriage of cargo (Schneekluth, 1998). Block coefficient influences resistance significantly such that if block coefficient is reduced, width must be increased to maintain the stability of ship. These changes have opposing significance on resistance in waves, with that of block coefficient dominating. With lower block coefficient, power reduction in heavy seas is less required. Recommendations for the choice of block coefficient usually draw on the statistics of built ships and are normally based on the form given below: CB = Where is the moulded displacement volume, LBT are the length, width B, and draught T of the rectangular block. Moulded displacement volume is obtained by multiplying the volume of the water displaced by the density of water as shown in the equation below: Displacement = Volume x density Calculation Given that the vessel to be developed is a multi-purpose vessel meant for worldwide general cargo trade, the recommended dimensions are as follows: Length L = 950 ft, breadth B = 98.4 ft, draft T = 40 ft, midship area = 1460 ft2, and Weight = 42000 tones. Using these measurements and the formula above, the block coefficient of the ship will be, CB = Where is the moulded displacement volume, LBT are the length, width B, and draught T of the ship. Given that = 42000 tones, L = 950 ft, B = 98.4 ft, and T = 40 ft, and the water in reference is the sea water and therefore we use a density of 35 which is constant for body object found in Salt Water Then CB = = = 0.393 This implies that the block coefficient of the ship in sea water will be 0.393 According to Schneekluth (1998), the “block coefficient, midship area coefficient CM, and longitudinal position of the centre of buoyancy determine the length of entrance, parallel middle body, and run of the section area curve” shown in the figure below: From the above section area curve, P represents parallel middle body, LE is the length of entrance, and LR represents the length of run. As the parallel middle body increases, the shoulders become more pronounced. b) Prismatic coefficient Prismatic coefficient of a ship at any given draft is the ratio of the displacement volume at that particular draft to the volume of a prism having the same length as the ship and the same cross-sectional area as the midship area of the ship. It is a term used to describe how displacement is distributed along a hull or how full or fine the ends of a hull are. The coefficient is a measure of distribution of volume along the length of the hull and is used to examine the volume distribution of the hull. It is calculated by dividing the underwater area by the area of the midship section time the ship’s overall length. In fact, the prismatic coefficient CP of a ship is calculated using almost the same method as that used to calculate the block coefficient CB. The coefficient is an indication of the fineness of the hull and can be simplified into aft and fore components, and its equation is expressed as follows: CP = Vu /Am x L or Cp = Where Vu or is the underwater volume, L is the length between perpendiculars, and AM is the submerged portion of the midship section. Calculation Given that the vessel to be developed is a multi-purpose vessel meant for worldwide general cargo trade, the recommended dimensions are as follows: Length L = 950 ft, breadth B = 98.4 ft, draft T = 40 ft, midship area = 1460 ft2 and Weight = 42000 tones. Using these measurements and the formula above, the prismatic coefficient of the ship will be calculated as follows: Prismactic coefficient (Cm) = , where ∇ is the moulded displacement volume, L is the length, and AM is the midship area of the ship. Since = 42000 tones, L = 950 ft, AM = 1560, and the water in reference is the sea water hence we use a density of 35 which is constant for body object found in Salt Water, then (Cp) = = = = 0.992 This implies that the prismatic coefficient of the ship in seawater will be 0.992 c) The Midships Coefficient (Cm) Midships coefficient is the ratio of transverse area of the midships section (Am) to a rectangle having the same depth and breadth. This coefficient is used to express the fullness of the midhip section of the ship. If the midship section is imagined to be cut out of a rectangle of dimensions breadth (B) x draft (T) then, Midships coefficient (Cm) = area of the midships section/ area of rectangle Cm = Am/B x T Calculation Given that the vessel to be developed is a multi-purpose vessel meant for worldwide general cargo trade, the recommended dimensions are as follows: Length L = 950 ft, breadth B = 98.4 ft, draft T = 40 ft, midship area = 1460 ft2 and Weight = 42000 tones. Using these measurements and the formula above, the midship coefficient of the ship will be calculated as follows: Cm = Am/B x T, where Am is the area of the midships section Since AM = 1560, B = 98.4 ft, and T = 40 ft, then (Cm) = = = = 0.396 This implies that the midship coefficient of the ship will be 0.396 In summary, block coefficient is the ratio of moulded displacement volume to the volume of the rectangular block with the dimensions L, B, and T, and is expressed as CB = Where is the moulded displacement volume, LBT are the length, width B, and draught T of the rectangular block. Midship coefficient is the ratio of midship cross-section area to the product of the breadth and draught, and is expressed as CM = , where AM the midship cross-section area. Finally, the prismatic coefficient is the ratio of the moulded displacement volume to the product of the midship section area and the length, and is expressed as Cp = All the three form coefficients discussed above are related to each other because, CB = Therefore, CB = CP x Cm SHIP CONSTRUCTION METHOD/PROCEDURE AND MATERIALS Lines plan Lines Plan is a scale drawing on which the hull form of the ship is outlined. It is also described as a two-dimensional scaled representation of the three-dimensional form of the ship through descriptive geometry (Kemp, Young & Eyres, 2013). The set of lines comprise three main views namely cross-sectional view or body plan, plan view or half breadth plan, and side elevation or sheer (Kemp, Young & Eyres, 2013). Modern shipyards are equipped with computerized design and manufacturing systems that simplify ship design and construction process. The figure below shows the Lines Plan of a ship. Ship Lines Plan by Kemp, Young and Eyres (2013) The basic version of the Lines Plan is created at the phase of conceptual design to present the desired requirements such as displacement and capacity and is then polished during the preliminary design phase to achieve the required sea keeping and propulsive features. The Lines Plan should be fair; the corresponding dimensions of the same point in different views must be in coordinate with each other and the curved lines should run smoothly and evenly (Kemp, Young & Eyres, 2013). With the help of computerized design and manufacturing systems found in the shipyard, the abstract creation of the hull form and the subsequent faring for the purpose of production is achieved without committing the plan to paper (Kemp, Young & Eyres, 2013). The computerized design and manufacturing system presents the hull form in 3D model, which defines the moulded lines of all structural components to allow any structural part of the ship to be created automatically from the 3D model. Preparation of plate and section The quality of the final structure of the ship and the efficiency of the construction process depend on the initial preparation of the steel. To make sure that the steel plate is perfectly flat, it is pushed through very heavy straightening rolls called mangles. The millscale and rust are then removed by shot blasting the plate and steel sections before applying priming paint by passing them through spray painting plant. This process is meant to keep off rust from the steel during the construction of the ship. Plate Cutting Most of the plates in the hull of a ship need cutting and smoothening of edges and this is done using a planing machine. However, plates that require more sophisticated trimming are cut using a profiling machine that is controlled automatically. In modern shipyards, numerical control is used for plate profilers (Kemp, Young & Eyres, 2013). “Numerical control implies control of the profiling machine by a tape on which is recorded the coordinate points of the desired plate profile. With the integrated software of computer aided design systems, the plate profile and the cutting data can be programmed and the data transferred to the tape, which is then read into a director that generates command signals to the servo-mechanism of the plate profiler” (Kemp, Young & Eyres, 2013). Frame bending Using a bending machine, frame bending is carried out on the transverse side framing material and other curved members in order to achieve the required curvature. Powered hydraulically, the bending machine bends the frame by applying a horizontal ram while the rolled section is held by gripping levers (Kemp, Young & Eyres, 2013). To achieve the required curvature, the straight length of the rolled section is marked the ‘inverse curve’ of that desired curvature. “The length of the rolled section reaches the required curvature when it is bent to the degree that the marked ‘inverse curve’ becomes a straight line”. Like the profiling machine, the cold bending machine can be controlled numerically. Prefabrication Ship construction follows an organized production process with fabrication of units under workshop conditions and the subsequent assembly on the construction dock (Kemp, Young & Eyres, 2013). The 3D block assemblies that are moved to the construction dock for assembling comprise various 2D sub-assemblies and can be outfitted with units of pipework, machinery, and other systems of the ship before leaving the workshop (Kemp, Young & Eyres, 2013). The various sub-assemblies are designed to reduce positional welding and may be turned to facilitate this and the erection of outfit items in a block assembly (Kemp, Young & Eyres, 2013). Block sizes depend on the lifting capacities available, nature of the structure, which must be accessible and self-supporting, and dimensions that can be handled (Kemp, Young & Eyres, 2013). Based on the past experiences of ship erection sequence as well as yard challenges experienced in the past, a standard procedure of erection has been outlined. This, together with the desirability to minimize positional fairing and welding, is factored in during the design stage of the construction. According to the standard erection sequence that has been established, the sequence of erecting the different blocks starts from fore and aft and bottom and upwards. The figure below shows a typical sequence of erection for a cargo ship. Launching Way Launching ways are prepared when the ship is almost ready for launching. The launching ways comprise a portion attached to the ship known as the sliding ways and a fixed portion on the ground known as the standing ways (Kemp, Young & Eyres, 2013). To allow the movement of sliding ways over the standing ways a lubricant is applied to the standing ways. Prior to launching the ship is moved to the launching ways where it is restrained temporarily before releasing it to the water for testing. Materials The decisions made regarding the materials to be used to construct the ship can account for more than 40% of the total costs of ownership over the entire life of the ship (Nguyen, 2008). Therefore, at the initial stages of ship design, it is imperative to make prudent decision regarding the kind of material to use, especially with respect to their mechanical performance. It is worth noting that, the materials used to construct ships are the same materials used to construct other related structures, and some of these materials include aluminum, plastics, and steel. However, there are a number of mechanical properties that must be considered when choosing the ship construction materials, and some of these properties include ductility, toughness, and weldability. Ductility is the ability of a material to be deformed before it fails as a result of tension. Temperature influences ductility of a material; an increases in temperature reduces ductility of a given material. Toughness is a property of a material to be bent without breaking. Ship construction materials should have the capacity to deform to a great degree and withstand flaws and cracks while retaining its structural integrity. Weldability, on the other hand, is the ability of material to be welded without being damaged. Welds play a key role in the overall strength of a ship, and therefore, the construction material must be able to be welded without creating weld defects such as cracks. Aluminum Even though aluminum is can make a good material to build a ship due to its advantages such resistance to corrosion and ease of construction, it must be alloyed with other materials such as manganese, zinc, copper, silicon and magnesium in order to come up with a material with desired characteristics (Nguyen, 2008). According to Nguyen (2008), it is imperative to weigh the advantages of aluminum against buckling strength, lower modulus, higher cost, as well as electrolytic interaction with other materials when compared to steel construction. For instance, the failure region of aluminum after the tensile limit is quite different from that of steel. In addition, strain hardening is responsible for the failure of aluminum structures, unlike steel that behaves in a manner that is more linear. Moreover, the overall strength of aluminum structures is greatly affected by the softening in the heat-affected zone from welding (Nguyen, 2008). Steel Compared to other materials, steel is the most suitable material to construct the ship as it satisfies most of the desired requirements such as durability, security, and strength. According to Grantham (2009), a ship built of steel is safer, from the fact that the material she is made up of not only have significant strength but also since the joints are joint using rivets, effect a level of security that cannot be achieved in a ship built of other material. Steel ship is also very durable and serviceable. It has, however, been suggested by some ship engineers that steel may not be a very good material for constructing ships because of the issue of oxidation. Nonetheless, these claims are not well substantiated because the past experience, as claimed by Grantham (2009), shows that steel ships, when kept is continuous operation, is completely free from oxidation. Another feature exhibited by a steel-build ship is the great strength and retention of form. According to Grantham (2009), steel ship does not only yield to pressure, but it also, by her elastic force, restores herself to her original form and shape. This is due to the nature of material used to construct her, and the combination of the parts, by which the entire, and more specifically the sides, provides a strong resisting force to rapture (Grantham, 2009). Composite materials Composite materials, according to Nguyen (2008), are the materials obtained through combination of reinforcing fibers that individually have only tensile characteristics with a binder matrix that allows the resulting mixture to behave as an engineering material. Various desirable qualities such as resistance to corrosion and light weight have made composite materials suitable to build tanks, pressure hulls and control surfaces of cargo and multipurpose ships. RULES AND REGULATIONS THAT APPLY TO THE BUILDING OF THE SHIP There is a set of regulations and standards that apply to the construction of ships. Proposed and administered by the International Maritime Organization (IMO), these regulations and standards vary with different types of ships. Before IMO was formed in 2002, the duty of determining the regulations that govern ship construction was accomplished by shipyards and classification societies (Attard, 2016). Initially, the purpose of the regulations were to allow innovations in ship designs but at the same time ensure that the construction was carried out in a way that with proper maintenance, the ship would remain safe for their economic life. Today, however, the regulations have been reviewed by various relevant authorities, such as the Maritime Safety Committee, to come up with more comprehensive regulations dubbed goal-based standards (GBS). Unlike the previous standards, GBS does not stipulate the means of attaining the acquiescence but outlines goals that allows alternative means of achieving the acquiescence. Under the GBS are the regulations called International Goal-based Ship Construction Standards Oil Tankers and Bulk Carriers that outline the ship construction requirements for commercial ships. These regulations were established based on a five-tier system (Attard, 2016). These five tires under this system include functional requirements, goals, confirmation of conformity, rules and regulations for ship design and construction, and industry standards and practices (Attard, 2016). Tires one to three consist of the goal-based standards introduced by the IMO, whose main objective is to put in place parameters of what has to be achieved, leaving the ship design experts to decide on how best to employ their skills to meet the required standards (Attard, 2016). On the other hand, the last two tires outline rules and regulations to be developed by classification societies, other relevant agencies, and organizations in the shipping industry. Currently the application of these standards and regulations is mandatory and cannot be avoided. In the meantime, however, these regulations can change anytime because there is a continuous dialogue between the ship constructors, ship owners, classification societies, and other concerned parties to discuss their mutual interest regarding various issues pertaining ship construction to ensure that the ships are fit for purpose (Attard, 2016). Tier I: Goals The tire outlines the objectives to be met. According to this tire, a ship should be designed and built for a particular design life to be environmentally friendly and safe when maintained and used properly within the outlined environmental and operating conditions, in intact and specified damage conditions, throughout their life (International Maritime Organization, 2015). Environmentally friendly and safe implies that the ship will have the recommended stability, integrity, and strength to reduce the chances of pollution and loss of the ship as a result of structural failure, including collapse, leading to flooding or loss of its watertight integrity. In addition, environmentally friendly comprises the ship being built of materials for environmentally tolerable recycling, while safety also comprise the form, fittings, and structure of ship allowing for secure access, routine inspection, safe operation, and proper maintenance (International Maritime Organization, 2015). Specified environmental and operating conditions are determined by the proposed area of operation for the ship in its operation life and include the conditions such as intermediate conditions emanating from ballast and cargo operations at the sea, in ports, and other similar situations. Specified design life, on the other hand, is the supposed duration that the ship will be subjected to environmental and operating conditions or corrosive environment and is used to choose the suitable parameters for designing the ship (International Maritime Organization, 2015). The actual operation life of the ship may however, be shorter or longer based on the real conditions of its operation and its maintenance throughout its life. Tier II – Functional requirements The second tire, which outlines the criteria to be met in order to keep to the set goals, comprises the functional requirements listed below (International Maritime Organization, 2015). These requirements are applicable to commercial ships such as the cargo carriers. Design life – at least twenty-five years Environmental conditions – designed for Mediterranean and Atlantic environment Structural strength – accomplished based on its purpose (cargo ship) Fatigue life – equal or more than the design life of the ship Residual strength – adequate for predictable casualty situations Protection against corrosion – net scantling sustained for ship’s design life Structural redundancy – damages on small area should not lead to entire damage of the ship Weather and watertight integrity – sufficient for the intended purpose and environment in which the ship will operate Human element considerations – accomplished using principles of ergonomic Design transparency – accessible design parameters are used Construction quality procedures - Quality production standards Survey during construction - Survey plan needed Survey and maintenance – easy survey is considered in design Structural accessibility - offer sufficient means of access Recycling - built using materials that are recyclable TIMELINE The table below shows the build sequence and timeframe of building the ship from start (signing of the contract) to final delivery of the vessel Event Period (months) Assigning contract 1 Basic design 4 Working drawings 15 Fabrication and assembly 18 Delivery 1 The above information can be presented in a bar graph as shown below: References: Attard, D. 2016. The Imli Manual on International Maritime Law: Shipping Law. Oxford: Oxford University Press. Muckle, W. 2013. Naval architecture for marine engineers. ‎Amsterdam: Elsevier Schneekluth, H. 1998. Ship design for efficiency and economy. ‎Amsterdam: Butterworth Heinemann. Grantham, J. 2009. Iron, as a material for ship-building: being a communication to the Polytechnic Society of Liverpool. New York: Simpkin, Marshall, and Company. International Maritime Organization, 2015. international goal-based ship construction standards for bulk carriers and oil tankers. Retrieved on June 16, 2016 from www.imo.org Kemp, J., Young, P., & Eyres, D. 2013. Ship construction sketches and notes. New York: Routledge. Nguyen, B. 2008. A multi-attribute decision process for structural material assessment and selection of light-weight, high-performance naval ships. New York: ProQuest. Read More

The high value of block coefficient in multipurpose vessel implies that there is large amount of displacement available for carriage of cargo (Schneekluth, 1998). Block coefficient influences resistance significantly such that if block coefficient is reduced, width must be increased to maintain the stability of ship. These changes have opposing significance on resistance in waves, with that of block coefficient dominating. With lower block coefficient, power reduction in heavy seas is less required.

Recommendations for the choice of block coefficient usually draw on the statistics of built ships and are normally based on the form given below: CB = Where is the moulded displacement volume, LBT are the length, width B, and draught T of the rectangular block. Moulded displacement volume is obtained by multiplying the volume of the water displaced by the density of water as shown in the equation below: Displacement = Volume x density Calculation Given that the vessel to be developed is a multi-purpose vessel meant for worldwide general cargo trade, the recommended dimensions are as follows: Length L = 950 ft, breadth B = 98.

4 ft, draft T = 40 ft, midship area = 1460 ft2, and Weight = 42000 tones. Using these measurements and the formula above, the block coefficient of the ship will be, CB = Where is the moulded displacement volume, LBT are the length, width B, and draught T of the ship. Given that = 42000 tones, L = 950 ft, B = 98.4 ft, and T = 40 ft, and the water in reference is the sea water and therefore we use a density of 35 which is constant for body object found in Salt Water Then CB = = = 0.393 This implies that the block coefficient of the ship in sea water will be 0.

393 According to Schneekluth (1998), the “block coefficient, midship area coefficient CM, and longitudinal position of the centre of buoyancy determine the length of entrance, parallel middle body, and run of the section area curve” shown in the figure below: From the above section area curve, P represents parallel middle body, LE is the length of entrance, and LR represents the length of run. As the parallel middle body increases, the shoulders become more pronounced. b) Prismatic coefficient Prismatic coefficient of a ship at any given draft is the ratio of the displacement volume at that particular draft to the volume of a prism having the same length as the ship and the same cross-sectional area as the midship area of the ship.

It is a term used to describe how displacement is distributed along a hull or how full or fine the ends of a hull are. The coefficient is a measure of distribution of volume along the length of the hull and is used to examine the volume distribution of the hull. It is calculated by dividing the underwater area by the area of the midship section time the ship’s overall length. In fact, the prismatic coefficient CP of a ship is calculated using almost the same method as that used to calculate the block coefficient CB.

The coefficient is an indication of the fineness of the hull and can be simplified into aft and fore components, and its equation is expressed as follows: CP = Vu /Am x L or Cp = Where Vu or is the underwater volume, L is the length between perpendiculars, and AM is the submerged portion of the midship section. Calculation Given that the vessel to be developed is a multi-purpose vessel meant for worldwide general cargo trade, the recommended dimensions are as follows: Length L = 950 ft, breadth B = 98.

4 ft, draft T = 40 ft, midship area = 1460 ft2 and Weight = 42000 tones. Using these measurements and the formula above, the prismatic coefficient of the ship will be calculated as follows: Prismactic coefficient (Cm) = , where ∇ is the moulded displacement volume, L is the length, and AM is the midship area of the ship. Since = 42000 tones, L = 950 ft, AM = 1560, and the water in reference is the sea water hence we use a density of 35 which is constant for body object found in Salt Water, then (Cp) = = = = 0.

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