Basics of Ship design 

Overview

Merchant Ship design involves the creation of a floating vessel that can not navigates on water bodies carrying cargo, passengers, or performing other specific functions.  The starting point of any ship design effort is in arriving the requirements, such as its size, speed, range, and cargo or passenger capacity or it function. The ship design process is called a design spiral – a cyclical process of iteration and refinement, each iteration building on the previous one to gradually converge on a final design.

The preliminary concept design is based on requirements that include considerations of trade, stability, seaworthiness, and performance. A general arrangement (GA) drawing is an important aspect of ship design. It is a detailed plan that evolves over time giving the layout of all major systems and components of a ship, including the hull, superstructure, machinery, propulsion, electrical systems, and other key features. The GA drawing is typically created by naval architects and marine engineers during the ship design process, and it serves as a blueprint for shipbuilders and shipyard workers to follow during construction.

The approved specification is a document that details the initial design output which is the base document for a ship building contract. The ship building contract contains in addition, details of construction materials specifying the equipment and systems that will be installed on the ship, including propulsion systems, electrical systems, and communication systems. The contract in addition outlines the performance requirements including speed, endurance, and fuel consumption. Testing and acceptance criteria to ensure that the ship meets the requirements are also outlined in the contract. Typical shipbuilding contracts include the delivery and payment terms for the shipbuilding contract, including the delivery date, payment schedule, and any penalties or bonuses for early or late delivery.

In recent times, design expectation for ships with respect to fuel efficiency ,emissions reduction and to reduce operating costs have increased. Many design elements are factored to streamline the hull to reduce power requirement or use coatings or other composite materials (for smaller vessels).

The selection of the propulsion system is also a point of high interest due to the emission requirements. In general, engines with high efficiency and low emissions are preferred, the power of the engine is determined by the required speed of the ship (this is changing and becoming a carbon intensity Index)

Alternatives such as electric, batteries, alternate fuels, hybrid systems and the much talked about fuel cells are emerging possibilities.   Fuel cells use hydrogen and oxygen to produce electricity, to power electric motors to drive the ship’s propellers. Fuel cells are highly efficient and emit only water as a by-product, making them a promising low-emission propulsion system. This is a disruptive technology since it may cause the phase out of combustion engines, rotating machinery, and heavy fuels.

For larger ships, use of emissions reduction technologies such as exhaust gas scrubbers or selective catalytic reduction (SCR) systems can significantly reduce emissions, particularly of nitrogen oxides (NOx) and sulphur oxides (SOx).

Ships are typically designed by naval architects, with expertise in ship design and engineering. Naval architects typically work in teams that include multi discipline engineers, designers, and other technical experts.

Using of advanced computer software and modelling techniques factor aspects such as hydrodynamics, stability, structural design, and materials selection. Ship must withstand the harsh marine environment and perform its intended functions; hence ship design is a complex activity.

Hull and cargo carrying capacity.

Based on requirements of different vessel types, consideration of weight distribution, ventilation, temperature control, securing the cargo area, the designers must provide for the volumes of cargo to carry, all these have an impact of ship dimensions.

The types and volumes of cargoes designed to carry impacts the ship’s size and shape of the vessel. With respect to cargo the handling equipment required for loading and unloading the cargo be it cranes, conveyor belts, and other specialized equipment are to be decided.

Determining hull loads and strength are an important aspect of ship design. The hull loads on ships arise from a variety of sources, including waves, wind, currents, and the ship’s own motion and loading pattern. Ship designers use computer simulations and mathematical models to predict the loads that acst on the hull. Suitable structural elements including materials are determined based on expected wave and wind conditions, as well as the speed and direction of the vessel.

The rules of ship classification specify the strength and hull response standard.

Ship stability is another a critical factor in ship design, and it must be considered during the initial design phase to ensure the safety and stability of the vessel. Stability is the ability of a ship to maintain its upright position and resist capsize when subjected to external forces, such as waves and wind.

Stability is determined by a range of factors, including the ship’s center of gravity (CG), center of buoyancy (CB), and metacentric height (GM). During the initial design phase, ship designers must ensure that the CG and CB are in the correct positions relative to each other and that the GM or righting level (GZ) is large enough to provide adequate stability. This can be assessed under different operating conditions. The position and weight of the cargo can significantly affect the ship’s CG and CB, and designers must ensure that the ship can maintain stability in various loading conditions.

Ship resistance, powering, and emission in ship design

In this era of green shipping, ship resistance and powering are emerging important subjects.  A ship’s resistance is the force that acts against the motion of the ship through the water, while powering is the energy required to overcome this resistance and propel the ship forward. A range of factors, including the ship’s size and shape, propulsion system, and operating conditions are considered.

Hydrodynamics play an important role in improving emission reduction in the shipping industry. By optimizing the design of a ship’s hull and propeller, it is possible to reduce the amount of fuel required to propel the ship, thereby reducing emissions.

Hull form optimization involves designing the hull shape to minimize drag and improve hydrodynamic efficiency. By reducing drag and turbulence, less energy is required to propel the ship through the water, leading to lower fuel consumption and emissions. Nowadays many energy saving devices (ESD) are being incorporated into the ships after part.

Another way to improve emission reduction is the use of advanced propeller design. Propellers convert the power from the ship’s engines into thrust. The more efficient propeller designs is they reduce fuel consumption and emissions.

Advanced propeller designs, such as those with larger diameters, skew and higher blade counts, can improve efficiency by reducing drag and increasing the amount of thrust generated. The flow to the propeller is also being optimised.

It is important to match the propeller to the engine to ensure that the engine operates at its optimal speed and load. This can improve fuel efficiency and reduce emissions. Propeller pitch and diameter are also important factors in determining propeller efficiency and should be chosen based on the ship’s operating conditions and speed requirements.

Regular maintenance of the propeller is important to ensure that it is operating at peak efficiency. Fouling, corrosion, and damage to the blades can all reduce efficiency, so regular cleaning and repair are essential.

Summary

Ship design in a low emission world is focused on reducing the environmental impact of shipping by improving energy efficiency, using alternative fuels, and incorporating emissions control systems. These design considerations are increasingly important as the shipping industry continues to face pressure to reduce its emissions and environmental footprint.

Over all, with the phase out of rotating equipment, combustion engines, comparable to what is happening in the automotive sector, could drive innovation in the development of new low-emission technologies for ships. This is expected to create new business opportunities and help position the shipping industry as a leader in sustainable transportation.

However, In the short and medium term, the phase out of rotating equipment in ships could have both positive and negative impacts on the shipping industry and global economy since it is by nature disruptive. However, the IMO and the world has committed for this trajectory.

Hence we may be entering a period of phase out of older ship designs and opportunities for designers, builders and operators to take ship design, building and operation to another level. The digital juggernaut will accelerate this transition.

Marex Media