Cavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, called "bubbles" or "voids", collapse and can generate shock waves that may damage machinery. These shock waves are strong when they are very close to the imploded bubble, but rapidly weaken as they propagate away from the implosion.
A hydrofoil is a lifting surface, or foil, that operates in water. They are similar in appearance and purpose to aerofoils used by aeroplanes. Boats that use hydrofoil technology are also simply termed hydrofoils. As a hydrofoil craft gains speed, the hydrofoils lift the boat's hull out of the water, decreasing drag and allowing greater speeds.
A propeller is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral, that, when rotated, exerts linear thrust upon a working fluid, such as water or air. Propellers are used to pump fluid through a pipe or duct, or to create thrust to propel a boat through water or an aircraft through air. The blades are specially shaped so that their rotational motion through the fluid causes a pressure difference between the two surfaces of the blade by Bernoulli's principle which exerts force on the fluid. Most marine propellers are screw propellers with helical blades rotating on a propeller shaft with an approximately horizontal axis.
An outboard motor is a propulsion system for boats, consisting of a self-contained unit that includes engine, gearbox and propeller or jet drive, designed to be affixed to the outside of the transom. They are the most common motorised method of propelling small watercraft. As well as providing propulsion, outboards provide steering control, as they are designed to pivot over their mountings and thus control the direction of thrust. The skeg also acts as a rudder when the engine is not running. Unlike inboard motors, outboard motors can be easily removed for storage or repairs.
Supercavitation is the use of a cavitation bubble to reduce skin friction drag on a submerged object and enable high speeds. Applications include torpedoes and propellers, but in theory, the technique could be extended to an entire underwater vessel.
A jetboat is a boat propelled by a jet of water ejected from the back of the craft. Unlike a powerboat or motorboat that uses an external propeller in the water below or behind the boat, a jetboat draws the water from under the boat through an intake and into a pump-jet inside the boat, before expelling it through a nozzle at the stern.
Whitewater kayaking is a recreational outdoor activity which uses a kayak to navigate a river or other body of whitewater or rough water.
An icebreaker is a special-purpose ship or boat designed to move and navigate through ice-covered waters, and provide safe waterways for other boats and ships. Although the term usually refers to ice-breaking ships, it may also refer to smaller vessels, such as the icebreaking boats that were once used on the canals of the United Kingdom.
A motorboat, speedboat or powerboat is a boat that is exclusively powered by an engine.
The Kaplan turbine is a propeller-type water turbine which has adjustable blades. It was developed in 1913 by Austrian professor Viktor Kaplan, who combined automatically adjusted propeller blades with automatically adjusted wicket gates to achieve efficiency over a wide range of flow and water level.
Rowing is the act of propelling a boat using the motion of oars in the water by displacing water to propel the boat forward. Rowing and paddling are similar. However, rowing requires oars to have a mechanical connection with the boat, while paddles are hand-held and have no mechanical connection.
A wedge is a triangular shaped tool, and is a portable inclined plane, and one of the six simple machines. It can be used to separate two objects or portions of an object, lift up an object, or hold an object in place. It functions by converting a force applied to its blunt end into forces perpendicular (normal) to its inclined surfaces. The mechanical advantage of a wedge is given by the ratio of the length of its slope to its width. Although a short wedge with a wide angle may do a job faster, it requires more force than a long wedge with a narrow angle.
Marine engineering includes the engineering of boats, ships, oil rigs and any other marine vessel or structure, as well as oceanographic engineering, oceanic engineering or nautical engineering. Specifically, marine engineering is the discipline of applying engineering sciences, including mechanical engineering, electrical engineering, electronic engineering, and computer science, to the development, design, operation and maintenance of watercraft propulsion and on-board systems and oceanographic technology. It includes but is not limited to power and propulsion plants, machinery, piping, automation and control systems for marine vehicles of any kind, such as surface ships and submarines.
A radio-controlled boat is a boat controlled remotely with radio control equipment.
The Hickman Sea Sled is an inverted vee planing hull invented by Albert Hickman. The Sea Sled is a direct forerunner of the modern high speed catamaran or tunnel hull. The reduced friction is due to a "Trapped" gas film between the hull surface and water. A similar effect is seen in super-cavitating torpedoes where a gas generator creates a film separation to water friction.
"A new type of vessel, which promises to revolutionize water craft and which takes the same place on the water that the automobile does on land" - Scientific American 26 September 1914
Wind-powered vehicles derive their power from sails, kites or rotors and ride on wheels—which may be linked to a wind-powered rotor—or runners. Whether powered by sail, kite or rotor, these vehicles share a common trait: As the vehicle increases in speed, the advancing airfoil encounters an increasing apparent wind at an angle of attack that is increasingly smaller. At the same time, such vehicles are subject to relatively low forward resistance, compared with traditional sailing craft. As a result, such vehicles are often capable of speeds exceeding that of the wind.
A ducted propeller, also known as a Kort nozzle, is a marine propeller fitted with a non-rotating nozzle. It is used to improve the efficiency of the propeller and is especially used on heavily loaded propellers or propellers with limited diameter. It was developed first by Luigi Stipa (1931) and later by Ludwig Kort (1934). The Kort nozzle is a shrouded propeller assembly for marine propulsion. The cross-section of the shroud has the form of a foil, and the shroud can offer hydrodynamic advantages over bare propellers, under certain conditions.
In aeronautics and marine hydrodynamics, the advance ratio is the ratio of the freestream fluid speed to the propeller, rotor, or cyclorotor tip speed. When a propeller-driven vehicle is moving at high speed relative to the fluid, or the propeller is rotating slowly, the advance ratio of its propeller(s) is a high number; and when it is moving at low speed, or the propeller is rotating at high speed, the advance ratio is a low number. The advance ratio is a useful non-dimensional velocity in helicopter and propeller theory, since propellers and rotors will experience the same angle of attack on every blade airfoil section at the same advance ratio regardless of actual forward speed. It is the inverse of the tip speed ratio used for wind turbines.
The Superkavitierender Unterwasserlaufkörper was a development project of the German armaments company Diehl BGT Defense in cooperation with the German Navy. The supercavitating torpedo for close-range defense of underwater targets was presented to the public in 2005 as a prototype, but it never went into development and procurement.
Propeller theory is the science governing the design of efficient propellers. A propeller is the most common propulsor on ships, and on small aircraft.
