Different Stages of Ship Design Explained

Ship design is a convoluted process that involves multiple steps before the construction and fabrication work is commenced. When we use the word convoluted, it not only means complex but also a roadmap where with each stage, the methodology becomes more specific and refined and the shipbuilding process gets closer to being commenced. 

The various stages of ship design are discussed below.

Concept Design 

Unlike a car or a commercial aircraft, a ship is designed specifically based on the exact requirements of the mission and the optimization of various parameters and resources. 

This is the preliminary stage at the outset of the entire design cycle, where the vessel’s operational requirements are identified. Operational or mission requirements essentially mean a study of the exact yardsticks specified by the clientele (owner, operator, liner, company, authority, government, etc.) regarding how the vessel is suited to its purpose. 

For instance, in cargo vessels like tankers, bulkers, or containerships, the cargo capacity in terms of deadweight tonnage or TEU is specified, along with the type of cargo that is intended to be carried. Similarly, for passenger vessels, the number of passengers required to be carried in one leg of the voyage, along with the various suitable provisions, are detailed.

In addition, the other main mission requirements in terms of the voyage, like speed, range, conditions, and routes, are also specified in all kinds of ships at this stage. All these give a clear picture of what direction the vessel needs to be designed in.  

After identifying the mission requirements, a primary design of the vessel in terms of hull form, main particulars, cargo or freight stowage layout is envisaged along with the feasible metrics in terms of the type of stability criteria, propulsion system, engine options, fuel, manoeuvring systems like rudders, basic equipment like cargo cranage, and so on. 

The concept design of the vessel, including the hull-form design, involves the generation of line drawings or line plans that are combined with the principal requirements like the parameters or dimensions, stability design, a preliminary general arrangement layout, cargo or deadweight capacities, basic powering standards, tankage, primary engine selection, etc. 

Now, the preliminary design of the vessel under discussion is subjected to a techno-economic evaluation to assess the feasibility of the aforesaid design against two critical benchmarks: 1) Technical and 2) Economic. 

While in the preliminary stage, the vessel is designed keeping in mind the technical requirements intended, the technical assessment mostly involves running checklists of the concept design against standard set benchmarks that shed light into whether the apropos vessel can cater to the requirements for safety, integrity, and expected performance. 

In a more elaborate sense, the technical perspective mostly involves the following fundamental yet critical verticals: 

• Floats without sinking (lightweight + deadweight = displacement equivalent to buoyancy): Archimedes’ Principle 
• Whether the given design can float upright and remain stable under worst-case scenarios: Stability and seakeeping 
• Is spacious enough for the desired service (that includes the ability to sustain every aspect ranging from crew to cargo, machinery to equipment, fuel to effects, etc.): volume and tonnage deadweight available within the bounds of the given design 
• Is strong enough to withstand all forms of loading ranging from global to local, internal to external: Structural safety and integrity 
• Can cater to the speed requirements in reaching from point A to B without overshooting the cost index: Resistance, propulsion, powering, fuel efficiency  
• Can manoeuvre and steer as and when required: Manoeuvring and course-keeping 
• Has a build such that it can last for the desired amount of time without compromising on the functionality: Nature of material and construction 
• Latest environmental concerns that mandate it to adhere to the requirements of pollution 
• Compliance with the basic regulations and guidelines of IMO, classification societies, flags, and other concerned authorities encompassing all the above factors within set acceptable criteria for that kind of vessel. 

The other stage of the feasibility study involves assessing the cost of the intended design against the budget constraints as defined. Along with the construction costs, the probable operating costs of the given design are also evaluated against the revenue limitations of the owner or liner as defined.

If either the building costs or operational costs of the proposed preliminary design of the vessel exceed the capped monetary limits from the client, the primary design is essentially refined without compromising on the technical standards, and the process is iterated till the techno-economic evaluation is fully satisfied within the necessary constraints. 

Hence, at the outset of the entire design cycle, vessel design mostly involves optimization, evaluation, and iteration till the best feasible design is worked out at the optimum cost. 

The concept design stage has a very high level of involvement for a naval engineer or architect as the aforementioned roles of optimisation, evaluation, and iteration presupposes a fair deal of knowledge, experience, and the sleight for application of engineering expertise to zero down to a design state that is essentially a trade-off between cost and the technical soundness.  

In today’s time, various computational resources aid in evaluation of the design metrics and optimize designs using complex algorithms based on past vessel data and numerical techniques. 

Basic Design 

Once the primary or conceptual design is finalised and given a heads-up from all stakeholders including the client party, the supervising teams of design bodies, class society and other authorities involved in the process, the vessel is now ready to be shifted into the critical basic design stage. 

While improvements, iterations, and changes constantly happen at local and larger levels in the entire ship design cycle, the basic design is that stage from which the major aspects of the vessel are virtually irreversible in a broad sense. In other words, by the end of the basic design stage, the overall design of the vessel attains a state of permanency and everyone involved in the cycle has a basic idea about the critical design characteristics of the vessel. 

These areas include the hull form design, basic parameters and proportions, weights-volumes, and tonnages (with very minimal room for variation due to minor design alterations till advanced stages), stability characteristics, tankage, principal structural design, disposition of spaces, hydrodynamics, propulsion systems, engine type, fuels, electrical distribution, steering gear, ventilation and piping, major outfit items, safety, and fire-fighting capabilities, and so on. 

Basic design essentially builds over concept design. This is the most crucial step in vessel design and along with detailed design, involves the highest level of involvement for a naval engineer or architect. However, from the basic design stage onwards, other disciplines also gain an equal level of importance like mechanical, electrical, structural, construction, material science, electronics, and so on. 

Some of most common scopes that come under the basic design stage till the end are: 

• Hull-form representation (virtual model or CAD) 
• Bill of Material listing 
• Advanced General Arrangement
• Major structure drawings like midship, decks, critical bulkheads, shell expansion, etc. 
• Global loads and basic scantling and strength calculations 
• Stability and seakeeping calculations (Generation of trim & stability booklet). 
• Resistance and powering calculations (also involving other aspects like CFD, manoeuvring, mooring, and other hydrodynamic calculations).  
• Tank arrangement and capacity 
• Cargo holds arrangement 
• Engine room and machinery space layout 
• Accommodation layout 
• Alignment of propulsion systems 
• Integration of electrical, piping, HVAC, heating, ducting, pumping, systems (along with electrical load calculations, estimates of distribution and consumption)
• Communication and navigation system design 
• Finalising basic outfitting, cranage, and other major cargo or service equipment to be used (if any) 
• Design adherence for safety and compliance with all applicable guidelines and regulations 

Basic design is mostly carried out by a design body or an in-house design office of a shipyard. Most of the deliverables post the basic design phase is subject to validation and approval from a certified classification society. 

Detailed Design 

Detailed design is mostly an extension of the basic design. At this stage, most of the outcomes from basic design are further refined and made more detailed. 

The general arrangements and tankages are now made final based on factors like tonnage calculations, stability calculations, strength calculations, and optimization of other metrics. 

All the structural drawings available are updated and made more precise including each and every structural element or entity along with details like welds, seams, and bracketing. Higher volumes of drawings are generated encompassing all structural aspects of the vessel with adequate details. The material details and specifications are further finalised and associated aspects like necessary insulation and paint types to be used are also alluded to. All drawings must be approved by classification society/societies along with a class letter without fail. 

Talking from a structural point of view, at the detailed design stage, for any new building vessel, structural analysis is carried out at an extensive level to assess the level of loads (local and global levels) and more importantly, measure the behaviour of the structure in response to such range of loads at their worst-case feasibilities.

Structural analysis works like Finite Element Analysis (FEM) are carried out either by design houses or classification authorities who also must certify the structure as being safe within acceptable limits. For any form of non-compliance, the structural drawings are further updated by incorporating necessary changes (revised and approved under class) and the analysis is performed again, iterating till meeting satisfactory strength criteria. 

Similarly, the stability and hydrodynamic analysis including manoeuvring and seakeeping is performed on a comprehensive scale and ambits about loading plans and propulsion systems are modified to obtain best results. The final reports are to the satisfaction of the concerned classification.

 One important point that is worth mentioning here is that for problems with resistance and propulsion, the propulsion systems are subject to modification or improvement along with other secondary practices (like hull paintings, coatings, external devices, etc.). The hull form itself, the major factor that contributes to the resistance and propulsive characteristics of a vessel, is essentially a constant design value at the basic design stage itself and cannot be changed.

Furthermore, all details related to machinery, electrical, systems, piping, ducting, ventilation, heating, HVAC, air-conditioning, cargo systems, pumping, sewage, water supply, and so on are finalised at the end of this stage.  Outfitting items along with deck equipment and cranage are concluded along with their disposition and design, and the list of all items is ready to be forwarded to the yard for procurement from third-party vendors.  

Modern practices demand multiple full and comprehensive 3D models of the vessel for various applications: structural, hydrodynamic, electrical/machinery/piping, etc. 

The detailed design stage also requires a great deal of optimisation and aims to: 

• Satisfy all client requirements in the best way 
• Minimise any form of errors 
• Ensure peak performance, safety, and serviceability of the vessel under feasible design limits 
• Reduce Steel Weight to a minimum 
• Optimise construction, and fabrication costs in the best manner 
• Make the vessel ready from a design point of view for transition to final production. 

Though often used interchangeably, basic and detailed design stages are combinedly known as the contract design phase. This is because from the basic stage, the vessel’s overall feasible design is finalised and the client is ready to place a contract for order with the shipbuilder or yard in question. All activities and workflow from thereon are irreversible, as mentioned above, and the client knows that the project planned is now on a set track to be executed to satisfaction.  

Production Design 

This is the last stage of the design spiral and is done at the yard level. Production design deals with planning the actual construction and fabrication process of a ship in an elemental way, ensuring that the necessary data generated can be used alike by people at the engineering as well as the working level. 

Production design involves the creation of advanced working-level drawings (production drawings) that give clear instructions for cutting and welding sequences, erection of modules or building blocks, assembly of building blocks, installation procedures of all lightweight items onboard, and so on. 

Furthermore, they include schedules of all activities at the level of the yard, and clear work instructions that facilitate all workers involved in the construction process to move ahead as per the desired timeline.

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