Naval architecture

The word "vessel" includes every description of watercraft, mainly ships and boats, but also including non-displacement craft, WIG craft and seaplanes, used or capable of being used as a means of transportation on water. The principal elements of naval architecture are detailed in the following sections. Hydrostatics Hydrostatics concerns the conditions to which the vessel is subjected while at rest in water and to its ability to remain afloat. This involves computing buoyancy, displacement, and other hydrostatic properties such as trim (the measure of the longitudinal inclination of the vessel) and stability (the ability of a vessel to restore itself to an upright position after being inclined by wind, sea, or loading conditions). Hydrodynamics • Hydrodynamics concerns the flow of water around the ship's hull, bow, and stern, and over bodies such as propeller blades or rudder, or through thruster tunnels. • Ship resistance and propulsion concern resistance towards motion in water primarily caused due to flow of water around the hull. Powering calculation is done based on this. • Propulsion is used to move the vessel through water using propellers, thrusters, water jets, sails etc. Engine types are mainly internal combustion. Some vessels are electrically powered using nuclear or solar energy. • Ship motions involves motions of the vessel in seaway and its responses in waves and wind. • Controllability (maneuvering) involves controlling and maintaining position and direction of the vessel. Flotation and stability While atop a liquid surface a floating body has 6 degrees of freedom in its movements, these are categorized in either translation or rotation. • Translation • Sway: transverse • Surge: fore and aft • Heave: vertical • Rotation • Yaw: about a vertical axis • Pitch or trim: about a transverse axis • Roll or heel: about a fore and aft axis Longitudinal stability for longitudinal inclinations, the stability depends upon the distance between the center of gravity and the longitudinal meta-center. In other words, the basis in which the ship maintains its center of gravity is its distance set equally apart from both the aft and forward section of the ship. While a body floats on a liquid surface it still encounters the force of gravity pushing down on it. In order to stay afloat and avoid sinking there is an opposed force acting against the body known as the hydrostatic pressures. The forces acting on the body must be of the same magnitude and same line of motion in order to maintain the body at equilibrium. This description of equilibrium is only present when a freely floating body is in still water, when other conditions are present the magnitude of which these forces shifts drastically creating the swaying motion of the body. The buoyancy force is equal to the weight of the body, in other words, the mass of the body is equal to the mass of the water displaced by the body. This adds an upward force to the body by the amount of surface area times the area displaced in order to create an equilibrium between the surface of the body and the surface of the water. The stability of a ship under most conditions is able to overcome any form or restriction or resistance encountered in rough seas; however, ships have undesirable roll characteristics when the balance of oscillations in roll is two times that of oscillations in heave, thus causing the ship to capsize. Structures drawing of the various shell plating on a convention hull. Structures involves selection of material of construction, structural analysis of global and local strength of the vessel, vibration of the structural components and structural responses of the vessel during motions in seaway. Depending on type of ship, the structure and design will vary in what material to use as well as how much of it. Some ships are made from glass reinforced plastics but the vast majority are steel with possibly some aluminium in the superstructure. ==Science and craft==

Traditionally, naval architecture has been more craft than science. The suitability of a vessel's shape was judged by looking at a half-model of a vessel or a prototype. Ungainly shapes or abrupt transitions were frowned on as being flawed. This included rigging, deck arrangements, and even fixtures. Subjective descriptors such as ungainly, full, and fine were used as a substitute for the more accurate terms used today. A vessel was, and still is described as having a ‘fair’ shape. The term ‘fair’ is meant to denote not only a smooth transition from fore to aft but also a shape that was ‘right.’ Determining what is ‘right’ in a particular situation in the absence of definitive supporting analysis encompasses the art of naval architecture to this day. Modern low-cost digital computers and dedicated software, combined with extensive research to correlate full-scale, towing tank and computational data, have enabled naval architects to more accurately predict the performance of a marine vehicle. These tools are used for static stability (intact and damaged), dynamic stability, resistance, powering, hull development, structural analysis, green water modelling, and slamming analysis. Data are regularly shared in international conferences sponsored by RINA, Society of Naval Architects and Marine Engineers (SNAME) and others. Computational Fluid Dynamics is being applied to predict the response of a floating body in a random sea. ==The naval architect==

Due to the complexity associated with operating in a marine environment, naval architecture is a co-operative effort between groups of technically skilled individuals who are specialists in particular fields, often coordinated by a lead naval architect. This inherent complexity also means that the analytical tools available are much less evolved than those for designing aircraft, cars and even spacecraft. This is due primarily to the paucity of data on the environment the marine vehicle is required to work in and the complexity of the interaction of waves and wind on a marine structure. A naval architect is an engineer who is responsible for the design, classification, survey, construction, and/or repair of ships, boats, other marine vessels, and offshore structures, both commercial and military, including: :* Merchant ships – oil tankers, gas tankers, cargo ships, bulk carriers, container ships :* Passenger/vehicle ferries, cruise ships :* Warships – frigates, destroyers, aircraft carriers, amphibious ships :* Submarines and underwater vehicles :* Icebreakers :* High speed craft – hovercraft, multi-hull ships, hydrofoil craft :* Workboats – barges, fishing boats, anchor handling tug supply vessels, platform supply vessels, tug boats, pilot vessels, rescue craft :* Yachts, power boats, and other recreational watercraft :* Offshore platforms and subsea developments Some of these vessels are amongst the largest (such as supertankers), most complex (such as aircraft carriers), and highly valued movable structures produced by mankind. They are typically the most efficient method of transporting the world's raw materials and products. Modern engineering on this scale is essentially a team activity conducted by specialists in their respective fields and disciplines. Naval architects integrate these activities. This demanding leadership role requires managerial qualities and the ability to bring together the often-conflicting demands of the various design constraints to produce a product which is fit for the purpose. In addition to this leadership role, a naval architect also has a specialist function in ensuring that a safe, economic, environmentally sound and seaworthy design is produced. To undertake all these tasks, a naval architect must have an understanding of many branches of engineering and must be in the forefront of high technology areas. They must be able to effectively utilize the services provided by scientists, lawyers, accountants, and business people of many kinds. Naval architects typically work for shipyards, ship owners, design firms and consultancies, equipment manufacturers, Classification societies, regulatory bodies (Admiralty law), navies, and governments. ==List of naval architecture software==

• Autodesk Inventor including Nastran FEM • Autodesk Revit Accommodation design, MEP design, general arrangement • Aveva - Tribon • FORAN System • NAPA • Orca3D - plugin for Rhinoceros 3D • Safehull • Sesam ==See also==