In ship design there are many domain-specific models of the design process, but Evans’ design spiral is probably the most well-known. This model emphasizes that many design issues interact and must be considered in sequence, in increased detail in each pass around the spiral, until a single design that satisfies all constraints and balances all considerations is reached.

The conceptual design process includes the following phases: needs identification, requirements definition; design criteria selection and solutions framework development. Conceptual design influences the largest portion of the lifecycle cost of the product, and thus the use of a set-based design approach is more appropriate to meet an optimal global solution.
The next phase after the contract is basic design and coordination engineering together with procurement handling, master scheduling and build procedure planning. A lot of new parties are introduced into the process and the problem seems to be the coordination. Even within the design phase there are several parties involved and everybody is working within the same ship.

Coordination becomes the major issue not only technically but it is also time consuming. On the other hand procurement requires good definitions of systems, areas, etc. to be purchased and design work cannot proceed without information of these systems. Efficient coordination and timing is required.

The next phase is detail engineering, work planning and preparation including not only the İstanbul shipyard’s own work but also the work of different subcontractors and suppliers.

Case Study: Romanian Border Police Boat Project (major aspects of Ship Design)

Estimation of weight and center of gravity for vessels in an early design phase can be a challenging task, especially if the new ship to be estimated partially or completely differs from previously built ships. The lack of systematic empirical data can also make the job difficult and create considerable uncertainty around the results. Often there are few people who are involved in efforts to estimate the weight and their experience and understanding of the project are critical to the accuracy of the final results. The estimation results may be the deciding factor for success in winning a contract for design or construction of the vessel. In the case of a contract, the quality of the estimates will affect the as-built vessel when it comes to fulfillment of the requirements for load capacity, speed, stability, seaworthiness, delivery and financial gain on the building contract.

Hull form optimization

Today the most commonly method used for checking combined hull propeller flows is towing tank/cavitation tunnel testing. However, due to the cost of model testing, the combined hull and propeller designs are checked relatively late in the design process. The idea is to investigate if CFD can be used for evaluation of hull and propeller geometries in conditions where the propeller is working behind the ship.

• No requirement to physical model means a tool that can be used to improve the propeller-hull designs in the early design
• Calculation of forces and moments will give a picture of the performance of the system in the early design stage
• Calculation of the flow field will give insight in the physics of the of the system in the early design stage

Stability

Ship’s transverse stability depends upon the metacentric height, which is calculated based on the vertical position of the center of mass and of the center of buoyancy, as well as the metacentric radius. An analytical model, based on a simplified geometric representation of the ship hull, possibly as a polyedric surface, could be built for the estimation of the position of the buoyancy center and of the metacentric radius. Specifically, the metacentric height is calculated based on the first moment of area of the ship design waterplane. As for the center of mass calculation, the vertical position of the main weight items must be estimated beforehand.

Maneuverability

Some maneuverability models are based on fundamental principles, but they have some parts or parameters not completely developed or identified, estimated in a way that fit some set of empirical and/or experimental data according to some approximation criteria. These models are usually specific for certain types of ships and maneuvers. Other models rely more extensively on fundamental principles, though with some limitations such as the representation, for instance, linearity. All these models are quite convenient for application in the early stages of ship design, since the involved parameters are generally some overall dimensions, as well as some shape and functional coefficients of the hull and appendices, which could easily be taken as conceptual design parameters in an optimization search process. Attributes like those that are considered as interim maneuver criteria by the International Maritime Organization can be evaluated through these methods, for instance:

• Turning ability
• Yaw checking and course keeping ability
• Stopping ability

Seakeeping

All three ship design, ship approval and ship operation determine the safety of a vessel in rough conditions. Now while designing as much seaworthiness as economically possible into a ship from the start provides the best basis for safe operation, it alone is not enough. Experience from ship operation shows that the safety of a vessel and its crew relies strongly on the ability of the crew to judge the vessels performance and its limits. Seakeeping is here restricted to a one degree-of-freedom model of the ship rolling motion. The problem is subdivided in three cases:

• hull free to roll in previous undisturbed waters;
• roll motion in regular waves;
• roll motion in irregular waves.

• Structural design

Structural design is the oldest and most fundamental of the technical disciplines which together comprise the art of naval architecture. Over the past decades, structural design as it is applied to naval ships has diverged from and converged with that for commercial ships for a variety of reasons. In recent times, resource constraints have made it necessary for governments around the world to seek out alternatives to established practices in many areas including naval vessel acquisition. Fortunately, the convergence of commercial and naval design practices has made it possible to look at commercial processes. One development arising from these conditions is that navies have increasingly turned to the application of classification society processes and resources to help them in establishing and applying technical criteria for naval ship design and construction including those related to the ship’s structure.

• Outfitting design

3-dimensional computer models are still mainly prepared to compensate the actual plastic design models, i.e. the 3D model is prepared to produce only workshop drawings. Most of the models, modeling techniques, are specific for structural design or piping design. Models of complete vessels with all disciplines included are still rare. 3D computer modeling technique is not used at the project design stage. 3D computer modeling technique should be applied in accordance with the actual design procedure, i.e. starting from the Project design phase before the shipbuilding contract is even signed. The same model should then be extended into a real product when design and engineering are proceeding.

• Detailed design

Detailed documentation includes drawings and other documents indispensable for prefabricating and assembling the vessel (lifting documentation of hull, isometric drawings of piping installations, etc.). Usually at the detailed design stage the 3D model of the vessel is prepared including a coordination model of the engine room and cargo installations (tankers). The 3D models are prepared with the use of dedicated computer systems (CAD) such as ‘AVEVA’. From such models the documentation of specific regions and groups are then generated.