Naval architecture

Naval architecture is the science of design of water borne transport, ships, boats, barges and other vessels for marine and freshwater use, in military and civilian roles. Naval Architecture bases its science on the elements it must draw from several vital criteria for a vessel to be useful.

Naval architecture is practised by skilled and qualified Naval Architects.

Customer criteria

Customer criteria are usually directly linked to the purpose of the ship. For example deadweight and hold volume are measures of the amount of cargo that can be carried and thus linked to the amount of money that the ship receives per transport, while the speed determines the number of transports that can be made in a given amount of time and so determine the amount of income per timeframe.

Commonly used criteria

The design criteria differ per ship type, commonly used criteria per ship type can be:
- General cargo vessels: Commonly used criteria are: deadweight, hold volume, speed, number of containers that can be carried.
- Bulk carrier: Commonly used criteria are: deadweight, hold volume, speed, maximum loading of the underside of the hold.
- Container ships: Commonly used criteria are: deadweight, hold volume, speed, number of containers that can be carried, different types of container that can be carried.
- Reefer (ship) (refrigerated vessel): Commonly used criteria are: deadweight, hold volume, speed, number of pallets and containers that can be carried, different types of pallet container that can be carried.
- Tankers: Commonly used criteria are: deadweight, volume of cargo tanks, speed, types of cargoes that can be carried, number of types of cargo that can be carried simultaneously.
- RO/RO ship (roll-on/roll-off vessel): Commonly used criteria are: deadweight, lane-meters of vehicle space, speed, number of containers that can be carried, number of passengers that can be carried.
- Ferry: Commonly used criteria are: Number of passengers, lane-meters of vehicle space, speed, manner of docking.
- Cruise ships: Commonly used criteria are: Gross tonnage, number of passengers, speed.
- Platform supply vessels: (mainly ships to supply and assist oil rigs), Commonly used criteria are: deadweight, cargo tank volume, speed, bollard pull, max. allowable deckload.
- Dredger: Commonly used criteria are: dredging method, deadweight, hopper volume, speed.
- Fishing boat: Commonly used criteria are: Type of fishing gear, deadweight, speed, bollard pull, hold volume.
- Tug boat: Commonly used criteria are: Bollard pull, speed, maneuverability.
- Motor yacht: Commonly used criteria are: dimension, number of beds and cabins, speed.
- Sailing yacht: Commonly used criteria are: dimension, number of beds and cabins, speed.
- Warship, general (corvette, frigate, destroyer, cruiser): Commonly used criteria are: weapons-carrying capability, speed, range, endurance.
- Aircraft carrier: commonly used criteria are: speed, range, endurance, landingway-length, number of catapults.
- Submarine: commonly used criteria are: noise generation levels, displacement, weapons carrying capability, speed, range, endurance.

More specific criteria

More specific criteria, for a particular ship can be:
- Dimension: if, for example, the ship must navigate a certain canal lock, canal or seaway then the maximum dimensions of that canal, or the maximum water depth of that seaway or canal are limiting constraints e.g. panamax, suezmax. (In the case of car, freight, or foot-passenger ferries there may be constraints due to the fixed loading/unloading arrangements at their usual ports of call).
- Seakindliness: a measure of the motion of the ship in a given sea state, mostly required for cruise vessels and ferry's to limit the amount of sea-sickness among the passengers.
- Build price: especially for yachts.
- "Through-Life" Cost: especially for commercial operators (of interest to the relevant share-holders), and in the case of Naval/Military/Government vessels (to provide the best return to relevant tax-payers).
- Type of propulsion and fuel.
- Capacity and type of loading gear.
- Ice class, the ability to sail through ice of a certain thickness and age.
- Containment system, the construction of the tanks of liquefied gas carriers.

Efficiency

Commercial

Broadly, a commercial vessel is efficient if the ship's owner can make a profit against the mortgage and running costs. A pleasure vessel's efficiency is harder to measure, but some boats, such as racing yachts, are every bit as tightly designed as any commercial vessel.

Functional

Generally, the speed of a vessel is critical to its efficiency. The basic speed of a vessel is its hull speed. For hull speed of displacement (non-planing) vessels, adding more energy to the propulsion has little effect on the speed. For this type of vessel the maximum efficient speed increases as the square root of the waterline length.

The maximum speed of a single-hull displacement boat (non planing) is calculated as follows:

}= 1.34 \times \sqrt }

^{^*}

Some vessels are capable of exceeding this theoretical maximum displacement speed. Monohulls accomplish this by transitioning from a displacement-mode where the entire weight of the vessel is supported by the force of the water displaced by the hull (see Archimedes) to a dynamic lift mode where only part of the vessel is supported by the static force of the water displaced.

If ultimate stability isn't important, as on inland lakes, a catamaran is an extremely clever compromise. A catamaran is a boat built on two widely-spaced narrow hulls. It has good instantaneous stability because the hulls are widely spaced. It has a good hull speed because the hulls are narrow, and very long for their width. It is usually comfortable, because it is wide, and can have a wider cabin or cargo area. The trade-off is loss of ultimate stability; most catamarans will capsize at less than 90 degrees of roll. Once capsized a catamaran will tend to invert, from which it may be very difficult to right the vessel. Some catamarans employ a float near the top of the mast to prevent inversion after a capsize.

Habitability

Vessels intended for cruising and "live aboard" marina use will compromise other factors, typically speed, in the interest of providing a useful and comfortable living environment.

Habitability is of prime importance for cruise vessels and comprises items such as cabin lay-out and size and the availability of restaurants, bars, theaters and sporting facilities.

Range

A vessel not provided with sailing capabilities will be limited in its range by its fuel supply and fuel consumption, with fuel consumption being highly dependent upon engine type, hull shape and operating speed. Another factor which has an impact on the range and fuel consumption of ocean-going vessels may be the operating environment (i.e. sea state(s) and weather may be adverse).

Style

Style (or fashion) will reflect attitudes of the time in which an "modern" vessel is designed or may be a homage to an earlier style of vessel design. In some cases the designs of small craft have echoed themes found in automotive design which in turn were influenced by aircraft.

Beauty

A vessel has three lines that define most of its beauty. The coaming line is the line of the top of the hull. The silhouette defines how the superstructure looks. The entry line defines how the bow looks.

In general, the lines should remind a viewer of each other. A low silhouette is pleasing, and also reduces danger from wind.

External criteria

External criteria mostly are criteria concerning safety which are imposed mostly by one or more of 3 parties:

International Maritime Organization (IMO), a sub-organization of the United Nations specifically concerned with shipping.
Flag state, the state in which the ship is registered. The flag state usually only enforces IMO-rules and regulations and demands that a ship is classified by a classification Society.
Classification Society, a commercial organization enforcing minimum technical and management standards.

Safety

Maritime safety is concerned with five major items.

The strength of hull the and its separate parts.
Buoyancy, the ability of the ship to remain above water.
The stability, the ability of the ship to remain or return to a safe position.
- Initial stability
- Dynamic stability
- Damage stability
Seakeeping and Freeboard
Fire protection.

Strength of ships

Strength is an issue because most ships can be twisted or suspended between two wave-tops under some conditions. The hull only has to fracture once to fail in service and endanger people. see also: Strength of ships.

Stability

Instantaneous stability is a measure of how the vessel's buoyancy is distributed. For example, a flat wooden board floats flat on water because its buoyancy is widely distributed. Some useful measures are the angles of roll (tilting to the side) or pitch (nose down or up) per unit of wind speed, or ton of misplaced cargo.

Ultimate stability is concerned with where the vessel's center of gravity has been located. It measures the angles of pitch or roll at which the vessel capsizes and cannot recover. Sometimes this is more than 180 degrees; for example, most lifeboats and single-hulled pleasure sailboats can recover after being dropped into a basin upside down. Most vessels can recover from rolls of 100 degrees (a knockdown), and pitches of 30 degrees. Larger ships can be overstressed by their own weight at extreme pitches or heave.

Damaged stability gives an indication of the ability of the ship to survive a collision, grounding, of explosion in which the hull is breached and water enters one or more compartments of the ship. There are two methods of calculation of damaged stability:
- Deterministic calculation, in which a limited number of important compartments or combinations of compartments are flooded after which the floating position of the ship and the remaining positive stability are assessed.
- Probabilistic calculation, in which all compartments and all combinations of two or three compartments are flooded after which the floating position of the ship and the remaining positive stability are assessed. The results of this calculation are corrected for the chance that a damage occurs and the corrected outcome is compared with a prescribed minimum.

In all designs, calculations are performed with cargo and fuel present and absent. Cargo and fuel can act as a ballast, holding the bottom of the ship down. If absent, or placed above waterline, the ship may become top heavy. Ultimate stability calculations have to plan what will happen if the cargo or fuel shifts - or specify that this must never occur. Dynamic ballasting, deliberately altering the location and amount of ballast (usually water), is important for trimming submarines for diving, cruising and surfacing and for optimising the attitude of landing ships for cruising and beaching.

Seakeeping and Freeboard

Seakeeping of ships means the way the ship reacts and copes with the wind and waves of open waters.

A vessel's hull shape, center of gravity, mass, superstructure and for sailboats its sail plan will determine its response to waves in various sea conditions and to wind. On smaller vessels designed for cruising (as opposed to racing) the ability to smoothly handle rough seas and (particularly in sailing vessels) stormy wind conditions without imposing extreme pilot skills or attention is highly desired. Such considerations are of lower importance for racing vessels.

Seakeeping is also important for a range of commercial vessels, such as ferries, cruise vessels and off-shore vessels and equipment such as semi-submersible drilling rigs and oil exploration vessels.

Fire protection

Fire is a major danger for all ships, whether they are made of wood, plastic, or metal. Wood and plastic are combustible by themselves and these ships will burn until the hull of the vessel is weakened so far that it collapses causing the boat to sink. Metal ships usually have a structure which is non-combustible. Fire on board of such vessels (often interior parts or fuel) will often cause the destruction of pipes, valves or portholes through which the sea enters causing the metal ship to sink as well.

Most measures to prevent fire are contained within the management procedures of the ship and the construction of the ship and its parts.
Most measures to contain and fight fire are prescribed by either the IMO or the classification society:
- Fire retardancy of fire bulkheads.
- Number and spacing of fire bulkheads (in particular on passenger ships).
- Position of escape routes.
- Type and size of main extinguishing installation (sprinkler, fog or foam)
- Number and position of fire hoses and portable extinguishers.
- Number and type of fire fighting equipment.
- The presence of emergency escape breathing apparatus (scba).

External links

^*Australia's national centre for maritime education, training and research.
The Royal Institution of Naval Architects professional institution involved at all levels in the design, construction, repair and operation of ships, boats and marine structures.
The Society of Naval Architects and Marine Engineers dedicated to advancing the art, science and practice of naval architecture, shipbuilding and marine engineering.
American Society of Naval Engineers to advance the knowledge and practice of naval engineering in public and private applications and operations.
Coventry University - Boat Design MDes degree Undergraduate course in industrial design for the boat industry.

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