Seamanship is the art , competence , and knowledge of operating a ship , boat or other craft on water. The Oxford Dictionary states that seamanship is "The skill, techniques, or practice of handling a ship or boat at sea."
70-460: A gale is a strong wind; the word is typically used as a descriptor in nautical contexts. The U.S. National Weather Service defines a gale as sustained surface wind moving at a speed between 34 and 47 knots (63.0 and 87.0 km/h ; 17.5 and 24.2 m/s ; 39.1 and 54.1 mph ). Forecasters typically issue gale warnings when winds of this strength are expected. In the United States ,
140-452: A General Electric scientist, Dr Alexanderson. He proposed a gyro to control the current to the electric motors on the stabilizer fins, with the actuating instructions being generated by thyratron vacuum tubes . When a hull is designed, stability calculations are performed for the intact and damaged states of the vessel. Ships are usually designed to slightly exceed the stability requirements (below), as they are usually tested for this by
210-408: A classification society . Intact stability calculations are relatively straightforward and involve taking all the centers of mass of objects on the vessel which are then computed/calculated to identify the center of gravity of the vessel, and the center of buoyancy of the hull. Cargo arrangements and loadings, crane operations, and the design sea states are usually taken into account. The diagram at
280-434: A maritime (or marine) pilot . Marine pilots are seafarers with extensive seafaring experience and are usually qualified master mariners who have been trained as expert ship-handlers. These pilots should be conversant with all types of vessel in their local waters and possess a good knowledge of the different propulsion systems, as well as handling ships of all sizes in all weather and tidal conditions. They are also experts in
350-502: A better overall understanding of fluid and ship motions has allowed much more analytical design. Transverse and longitudinal waterproof bulkheads were introduced in ironclad designs between 1860 and the 1880s, anti-collision bulkheads having been made compulsory in British steam merchant ships prior to 1860. Before this, a hull breach in any part of a vessel could flood its entire length. Transverse bulkheads, while expensive, increase
420-435: A boat if possible, the use of oars or sails, as well as basic sail theory, sail terminology and markings on sails. One other aspect of traditional good seamanship is housekeeping on the vessel. This involves correct stowage of stores, supplies, crew personal effects, etc. It also involves keeping the decks, engine room and accommodation clean and free of debris or spills. This reduces the chances of fire at sea and reduces
490-748: A gale warning is specifically a maritime warning; the land-based equivalent in National Weather Service warning products is a wind advisory . Other sources use minima as low as 28 knots (52 km/h; 14 m/s; 32 mph), and maxima as high as 90 knots (170 km/h; 46 m/s; 100 mph). Through 1986, the National Hurricane Center used the term “gale” to refer to winds of tropical force for coastal areas, between 33 knots (61 km/h; 17 m/s; 38 mph) and 63 knots (117 km/h; 32 m/s; 72 mph). The 90 knots (170 km/h; 46 m/s; 100 mph) definition
560-420: A generator. In specifications for gyro stabilizers, the total angular momentum ( moment of inertia multiplied by spin speed) is the key quantity. In modern designs, the output axis torque can be used to control the angle of the stabilizer fins (see above) to counteract the roll of the boat so that only a small gyroscope is needed. The idea for gyro controlling a ship's fin stabilizers was first proposed in 1932 by
630-420: A greater degree of seamanship may be necessary for some vessel types compared to others. Seamanship involves paying close attention to the stability of the vessel at all times. This involves calculation of the vessel and the effects of its cargo at various stages of the voyage (on departure, at sea and on arrival in port) to allow for safe passage and prevent capsizing (where a vessel turns on to its side or
700-452: A ship is underway, a fast rudder change will not only initiate a heading change, but it will also cause the ship to roll. For some ships such as frigates, this effect is so large that it can be used by a control algorithm to simultaneously steer the ship while reducing its roll motions. Such a system is usually referred to as " Rudder Roll Stabilisation System ". Its effectiveness can be as good as that of stabiliser fins. However, that depends on
770-531: A ship. Larger ship types usually have a crane for cargo operations and for bringing on stores, provisions and supplies for the crew. Seamanship knowledge and experience is an integral part of Dry-docking . This includes careful planning (of all jobs, tasks and repairs), adequate preparations (eg or painting), dry-docking calculations (primarily stability and upthrust), safety within the dry-dock and checks upon departure (eg plugs returned and sealed). Lifeboat, rescue boat and survival craft maintenance and operation
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#1732840461442840-529: A stage, rigging of a bosuns ladder, canvas work, use of chain blocks and pulleys, etc. Other traditional practices apply to life onboard, such as forms of address to the Captain and in use of marine flag, including courtesies and flag signalling. Specifically, these include items such as flag signalling terms, single and double letter meanings according to the International Code of Signals, flag maintenance,
910-402: Is a measure of the extent to which the flywheel will continue to rotate about its axis unless acted upon by an external torque. The higher the angular momentum, the greater the resisting force of the gyro to external torque (in this case more ability to cancel boat roll). A gyroscope has three axes: a spin axis, an input axis, and an output axis. The spin axis is the axis about which the flywheel
980-567: Is a statutory requirement and considered good seamanship to regularly practice (drill) these skills when at sea. Other emergency skills include the Man overboard rescue turn . Historic or traditional seamanship skills are less frequently used on modern commercial ships, but are usually still practiced in training colleges and used on smaller ships, fishing vessels and leisure craft. These include ropework (included tying knots, rope splicing , wire splicing, lashings and whippings ), as well as rigging of
1050-432: Is an essential part of seamanship. This involves being able to operate survival craft in emergencies, but also to be able to maintain them effectively to operate in accordance with SOLAS requirements. The STCW Convention requires that modern seafarers be familiar with emergency operations, including fire fighting. Personnel at sea are required to undertake fire fighting training at shore based training establishments. It
1120-403: Is based on the nautical mile . Navigation also includes electronics such as GPS and Loran (Long Range Navigation). Celestial navigation involves taking sights by sextant on the planets, moon, stars, sun and using the data with a nautical almanac and sight reduction tables to determine positions. Accurate time information is also needed. After nautical dusk , navigation at sea referencing
1190-523: Is being able to manoeuvre a vessel safely with accuracy and precision both at sea and also in port and during pilotage . Unlike land based vehicles, a ship afloat is subject to the forces of the water in which it floats, as well as the resistance and effects of marine weather. A complicating factor is that the mass of a ship that has to be accounted for when stopping and starting, as the inertia of large vessels may take large distances to stop and therefore ship-handlers must be aware of basic Hydrodynamics and
1260-461: Is dependent upon the nature of the work and the type of vessel employed by a seafarer . Seamanship on a commercial level involves a knowledge of all the different ship types (such as bulk carriers , container ships , oil tankers , cruise ships , platform supply vessels , and others), including a basic knowledge of ship recognition, a basic understanding of nautical terms, ship structure and naval architecture and cargo operations, specific to
1330-505: Is important because when a pilot is in command, the master can not take any action, but is limited to advising the pilot on any circumstance that creates what he considers a dangerous situation. A working knowledge of the relevant rules and regulations, including those of the International Maritime Organization is good seamanship as it ensures compliance with international, flag and port State requirements. For example,
1400-408: Is less vulnerable and it causes less drag. Even better, the required high-quality components provide excellent steering properties also for those periods when roll reduction is not required and a significant reduction of underwater noise. Known navy ships with this stabilisation solution are F124 (Germany), M-fregat and LCF (both of Dutch Navy). Gyroscopes were first used to control a ship's roll in
1470-451: Is little or no specialisation. Deck crew perform all boat handling functions. The officers of the ship are responsible for navigation, communication, and watch supervision. Ship stability Ship stability is an area of naval architecture and ship design that deals with how a ship behaves at sea, both in still water and in waves, whether intact or damaged. Stability calculations focus on centers of gravity , centers of buoyancy ,
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#17328404614421540-422: Is spinning and is vertical for a boat gyro. The input axis is the axis about which input torques are applied. For a boat, the principal input axis is the longitudinal axis of the boat since that is the axis around which the boat rolls. The principal output axis is the transverse (athwartship) axis about which the gyro rotates or precesses in reaction to an input. When the boat rolls, the rotation acts as an input to
1610-448: Is the art and science of safely and efficiently directing the movements of a vessel from one point to another. Piloting uses water depth and visible references, while dead reckoning uses courses and distances from the last known position. More than just finding a vessel's present location, safe navigation includes predicting future location, route planning and collision avoidance. Nautical navigation in western nations, like air navigation ,
1680-489: Is to be placed in the area of the ship where it would cause the most damage to vessel stability. In addition, United States Coast Guard rules apply to vessels operating in U.S. ports and in U.S. waters. Generally these Coast Guard rules concern a minimum metacentric height or a minimum righting moment. Because different countries may have different requirements for the minimum metacentric height, most ships are now fitted with stability computers that calculate this distance on
1750-770: Is upside down). This includes familiarity and application of the Load Line Convention , where a vessel can only be safely loaded to its markings to ensure residual stability for the likely weather conditions. Seafarers should regularly inspect their vessel and ensure the hull is in good condition for navigation. Seamanship skills apply to the safe use of different types of lifting gear, whether for cargo operations or for bringing on stores, supplies and provisions. These example Derricks , Union purchase arrangements, midship or aft cranes , heavy lifting gear, rigging other sheer legs etc. This should include knowledge of calculations of stresses and effects on stability. Navigation
1820-459: Is very non-standard. A common alternative definition of the maximum is 55 knots (102 km/h; 63 mph; 28 m/s). The most common way of describing wind force is with the Beaufort scale which defines a gale as wind from 50 kilometres per hour (14 m/s) to 102 kilometres per hour (28 m/s). It is an empirical measure for describing wind speed based mainly on observed sea conditions. On
1890-605: The Bureau Veritas , American Bureau of Shipping , Lloyd's Register of Ships , Korean Register of Shipping and Det Norske Veritas , the blueprints of the ship must be provided for independent review by the classification society. Calculations must also be provided which follow a structure outlined in the regulations for the country in which the ship intends to be flagged. Within this framework different countries establish requirements that must be met. For U.S.-flagged vessels, blueprints and stability calculations are checked against
1960-480: The International Code on Intact Stability . Damage stability calculations are much more complicated than intact stability. Software utilizing numerical methods are typically employed because the areas and volumes can quickly become tedious and long to compute using other methods. The loss of stability from flooding may be due in part to the free surface effect. Water accumulating in the hull usually drains to
2030-489: The International Regulations for Preventing Collisions at Sea are the principal international rules for navigation between vessels at sea. Rule 2 sets out responsibility for safe navigation by stating “Nothing in these Rules shall exonerate any vessel or the owner, master or crew thereof, from the consequences of any neglect to comply with these Rules or of the neglect of any precaution, which may be required by
2100-496: The Suez canal . Crew should be able to keep the vessel from collisions, moor the vessel during canal lockgate operations and also respond to local currents and river conditions while on passage. Two other types of operations, berthing alongside another ship (usually for Ship-to-ship cargo transfer and replenishment at sea, are occasionally included in ship-handling seamanship for some vessel types. In addition to being fully conversant with
2170-624: The United Kingdom and the United States of America ), the pilot's role is as an advisor. However, in practice, they are likely to have the conduct of the vessel, especially on larger ships using tug boats to assist. In some places, specifically in the Panama Canal , a pilot assumes command of a vessel and is not classed as "an advisor". Other instances may be crossing the sill of a drydock , or in any port in Russia (or ex-Soviet States). This distinction
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2240-418: The charted area , including the depth of water in which their ship is navigating. Ship-handling in coastal areas may involve arriving and departing a berth, anchorage or buoy , maneuvering in confined channels and harbours and in proximity to other ships, whilst at all times navigating safely. Seamanship also involves safe navigation in restricted waterways, for example in river and canal transits eg along
2310-454: The U.S. Code of Federal Regulations and International Convention for the Safety of Life at Sea conventions (SOLAS). Ships are required to be stable in the conditions to which they are designed for, in both undamaged and damaged states. The extent of damage required to design for is included in the regulations. The assumed hole is calculated as fractions of the length and breadth of the vessel, and
2380-564: The U.S., the progression begins with what is known as "the six pack", a license that allows fishing guides to operate with up to six passengers . In the United Kingdom , all seafarers, both deck officers and crew, must complete an Efficient Deck Hand (EDH Course) at an approved training provider under direction of the UK Merchant Navy Training Board . The crew of a large ship will typically be organized into "divisions" or "departments", each with its own specialty. For example,
2450-421: The bilges, lowering the center of gravity and actually increasing the metacentric height . This assumes the ship remains stationary and upright. However, once the ship is inclined to any degree (a wave strikes it for example), the fluid in the bilge moves to the lower side. This results in a list . Stability is also reduced in flooding when, for example, an empty tank is filled with seawater. The lost buoyancy of
2520-420: The center of gravity as the ship heels. A line drawn from the center of buoyancy in a slightly heeled condition vertically will intersect the centerline at a point called the metacenter. As long as the metacenter is further above the keel than the center of gravity, the ship is stable in an upright condition. Intact stability for ships at sea is governed by the International Maritime Organization (IMO) standard
2590-490: The change of injury eg due to slips, trips and falls. Officers and Masters must pass formal examinations to demonstrate their knowledge at various levels, in accordance with national laws and the STCW Convention . These examinations have a progression based on the size and complexity of the ship, including its sailing area as well as by rank. Globally, most seafarers are required to possess a basic seamanship certificate. In
2660-455: The concept of the metacenter in the 1740s ship model basin , allow much more complex analysis. Master shipbuilders of the past used a system of adaptive and variant design. Ships were often copied from one generation to the next with only minor changes; by replicating stable designs, serious problems were usually avoided. Ships today still use this process of adaptation and variation; however, computational fluid dynamics , ship model testing and
2730-498: The damage stability calculations are of a probabilistic nature. That is, instead of assessing the ship for one compartment failure, a situation where two or even up to three compartments are flooded will be assessed as well. This is a concept in which the chance that a compartment is damaged is combined with the consequences for the ship, resulting in a damage stability index number that has to comply with certain regulations. In order to be acceptable to classification societies such as
2800-462: The deck department is responsible for navigation, ship handling and general maintenance, while the engineering division are responsible for propulsion and other mechanical systems. Crew start on the most basic duties and as they gain experience and expertise advance within their area. Crew who have gained proficiency become "able seamen", "petty officers", "rated", or "mates" depending on the ship type and organisation. On smaller commercial craft, there
2870-727: The first opportunity. Training is more formal in the merchant navy and naval forces, but still covers the basics of traditional seamanship. Smaller vessel types may have traditional methods of seamanships unique to their vessel types, for example turtling on dinghies and small sailing boats. Boatwork is a traditional seamanship skill. On commercial ships, this is usually limited to rescue boats and lifeboats, however yachts and other vessels such as passenger ships may have tenders and small boats for transporting people between ship/shore. boatwork includes knowledge and operation of different types of boat, launching procedures, recovery of boats (in normal and in heavy weather conditions), how to beach
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2940-432: The geographical areas they work. In most countries, the pilot takes over the 'conduct' of the navigation from the ship master. This means that the master and crew should adhere to the pilot's orders in respect of the safe navigation of the vessel when in a compulsory pilotage area. However, the master may with good cause resume 'conduct' of the vessel's navigation but this is not done lightly. In some countries and areas (eg
3010-414: The gyro, causing the gyro to generate rotation around its output axis such that the spin axis rotates to align itself with the input axis. This output rotation is called precession and, in the boat case, the gyro will rotate fore and aft about the output or gimbal axis. Angular momentum is the measure of effectiveness for a gyro stabilizer, analogous to horsepower ratings on a diesel engine or kilowatts on
3080-400: The horizon is no longer possible, and after nautical dawn such navigation again becomes possible. Ice navigation involves navigating and operating a ship within sea ice conditions. Along with general navigation, seamanship involves being able to respond to weather at sea. For example, the onset of heavy or rough weather may require an alternative passage plan (or weather routeing) for
3150-491: The late 1920s and early 1930s for warships and then passenger liners. The most ambitious use of large gyros to control a ship's roll was on an Italian passenger liner, the SS Conte di Savoia , in which three large Sperry gyros were mounted in the forward part of the ship. While it proved successful in drastically reducing roll in the westbound trips, the system had to be disconnected on the eastbound leg for safety reasons. This
3220-480: The length of the ship at the turn of the bilge. Bilge keels are employed in pairs (one for each side of the ship). Rarely, a ship may have more than one bilge keel per side. Bilge keels increase hydrodynamic resistance when a vessel rolls, limiting the amount of roll. Outriggers may be employed on vessels to reduce rolling, either by the force required to submerge buoyant floats or by hydrodynamic foils. In some cases, these outriggers are of sufficient size to classify
3290-432: The likelihood of ship survival in the event of hull damage, by limiting flooding to the breached compartments they separate from undamaged ones. Longitudinal bulkheads have a similar purpose, but damaged stability effects must be taken into account to eliminate excessive heeling . Today, most ships have means to equalize water in sections port and starboard (cross flooding), which helps limit structural stresses and changes to
3360-499: The metacenters of vessels, and on how these interact. Ship stability, as it pertains to naval architecture, has been taken into account for hundreds of years. Historically, ship stability calculations relied on rule of thumb calculations, often tied to a specific system of measurement. Some of these very old equations continue to be used in naval architecture books today. However, the advent of calculus-based methods of determining stability, particularly Pierre Bouguer's introduction of
3430-485: The nozzle are the ship can be steered astern which a conventional rudder cannot, and the ship can be steered fully under control to a standstill switching between ahead and astern mode to give complete control over speed. Seamanship applies to general Mooring practices and anchoring (anchors are a device used to secure a vessel to the bed of a body of water to prevent the craft from drifting) and established marine procedures for anchoring (anchorwork). This also includes
3500-476: The ordinary practice of seamen, or by the special circumstances of the case.” The ordinary practice of seaman is seen as equivalent wording for seamanship. Other accepted practices of seamanship relating to the COLREGs include maintaining a proper look-out (Rule 5), proceeding at a safe speed (Rule 6) and taking correct actions to avoid collision (Rule 8). Seamanship involves the correct and adequate maintenance of
3570-1262: The original 1810 Beaufort wind force scale, there were four different "gale" designations whereas generally today there are two gale forces, 8 and 9, and a near gale 7: The word gale is derived from the Middle English gale , a general word for wind of any strength, even a breeze. This word is probably of North Germanic origin, related to Icelandic gola (breeze) and Danish gal (furious, mad), which are both from Old Norse gala (to sing), from Proto-Germanic * galaną (to roop, sing, charm), from Proto-Indo-European * gʰel - (to shout, scream, charm away). Nautical It involves topics and development of specialised skills, including navigation and international maritime law and regulatory knowledge; weather , meteorology and forecasting; watchkeeping ; ship-handling and small boat handling; operation of deck equipment, anchors and cables; ropework and line handling; communications ; sailing ; engines ; execution of evolutions such as towing; cargo handling equipment, dangerous cargoes and cargo storage; dealing with emergencies; survival at sea and search and rescue ; and fire fighting . The degree of knowledge needed within these areas
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#17328404614423640-443: The pitch and not the direction of rotation was reversed to go astern. These propellers rotate counterclockwise at all times and so the "walk" is "normal". Other variations on propulsion include what are known as bucket rudders and Kort Nozzles where instead of a conventional rudder a pair of dish-shaped rudders, one either side of the propeller can be swivelled vertically to direct the propeller thrust through 360 degrees. Thus to put
3710-446: The principles of ship-handling, a good shiphandler or pilot will have developed their sense of 'situational awareness' to a point well beyond that of an ordinary member of a ship's crew; their reactions will appear to be instinctive, positive and at all times safe. A key ability for a ship-handler with good seamanship is to possess an understanding of how wind , tide and swell influence vessel movement, along with passing vessels and
3780-410: The propeller would turn counterclockwise when going astern and the stern would walk to port. This aided in docking operations, where "port side to" was the preferred situation and the vessel would be brought to the dock with a small bow-in angle and backing would flatten the angle, slow or stop the vessel and walk it alongside. An exception to this is vessels which use a controllable-pitch propeller, where
3850-428: The right shows the center of gravity is well above the center of buoyancy, yet the ship remains stable. The ship is stable because as it begins to heel, one side of the hull begins to rise from the water and the other side begins to submerge. This causes the center of buoyancy to shift toward the side that is lower in the water. The job of the naval architect is to make sure that the center of buoyancy shifts outboard of
3920-411: The shape of the nearby seabed (the interaction effect). These must also be combined with an understanding of a specific vessel's performance, including its propulsion and stopping distance to allow safe handling. Fundamental to low-speed maneuvering of most vessel types is an understanding of the configuration and handedness of the propeller (s). An effect known as propeller walk will kick the stern of
3990-510: The ship speed (higher is better) and various ship design aspects such as position, size and quality of the rudder positioning system (behaves as fast as a stabiliser fin). Also important is how quickly the ship will respond to rudder motions with roll motions (quick is better) and rate of turn (slow is better). Despite the high costs of high-quality steering gear and strengthening of the ship's stern, this stabilisation option offers better economics than stabiliser fins. It requires fewer installations,
4060-440: The ship's heel and/or trim. Add-on stability systems are designed to reduce the effects of waves and wind gusts. They do not increase a vessel's stability in calm seas. The International Maritime Organization International Convention on Load Lines does not cite active stability systems as a method of ensuring stability. The hull must be stable without active systems. A bilge keel is a long, often V-shaped metal fin welded along
4130-770: The ship, as well as the use of an alternative heading to keep the vessel from rolling ( Heaving to ). Additionally, heavy weather precautions onboard such as lashing furniture in the accommodation or keeping crew off the deck is considered good seamanship when navigating in heavy weather. Navigation and seamanship also involves a working knowledge of correct marine communications and the Global Maritime Distress and Safety System . Seamanship also involves recognition of and navigation with Buoys including IALA maritime buoyage such as Lateral marks , Cardinal marks , Safe water marks , Special marks and Isolated danger marks . A fundamental skill of professional seamanship
4200-484: The ship’s structure and equipment to keep the vessel seaworthy . This involves knowledge of tasks such as painting, greasing, renewing ropes, wires and other equipment items. Seamanship also involves a working knowledge of the relevant wires, ropes, chains, shackles and slings onboard. This includes mooring ropes using to keep the vessel secure in port. Seamanship on some vessel types may involves being able to maintain and use marine cranes and lifting equipment if fitted on
4270-450: The system in the form of pumps, hydraulic pistons , or electric actuators . They include stabilizer fins attached to the side of the vessel or tanks in which fluid is pumped around to counteract the vessel's motion. Active fin stabilizers reduce the roll a vessel experiences while underway or, more recently, while at rest. They extend beyond the vessel's hull below the waterline and alter their angle of attack depending on heel angle and
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#17328404614424340-477: The tank results in that section of the ship lowering into the water slightly. This creates a list unless the tank is on the centerline of the vessel. In stability calculations, when a tank is filled, its contents are assumed to be lost and replaced by seawater. If these contents are lighter than seawater, (light oil for example) then buoyancy is lost and the section lowers slightly in the water accordingly. For merchant vessels, and increasingly for passenger vessels,
4410-559: The use of drogues as applicable. Anchor work includes an understanding and awareness of types of anchors, marks on anchors and cable and shackles. It includes learning established procedures for securing anchors and cable, use of windlasses, how to prepare the anchors/clearing away anchors for letting go, letting-go (dropping) the anchor, keeping an anchor watch, clearing a foul Hawse , weighing anchor and securing anchors for sea. Most commercial vessels in excess of size limits determined by local authorities are handled in confined areas by
4480-404: The use of ensigns and also Morse code procedure and practice. In the days of sailing ships , an able seaman was expected to be able to "hand, and reef, and steer" and to "know the ropes" , the basic knowledge on the identity of the many ropes with different functions. This latter knowledge was essential for both safety and efficient working - those without it would be dismissed or dis-rated at
4550-581: The vessel as a trimaran ; on other vessels, they may simply be referred to as stabilizers. Antiroll tanks are interior tanks fitted with baffles to slow the rate of water transfer from the tank's port side to its starboard side. It is designed so that a larger amount of water is trapped on the vessel's higher side. It is intended to have an effect counter to that of the free surface effect . Paravanes may be employed by slow-moving vessels, such as fishing vessels, to reduce roll. Active stability systems, found on many vessels, require energy to be applied to
4620-456: The vessel into astern mode the rudder can be rotated through 180 degrees without altering the speed and direction of the engine. Since with the conventional propeller or rudder configuration the propeller is designed to operate at maximum efficiency when going ahead, it produces far less thrust when going astern. But with the Kort Nozzle, the ahead and astern thrust is the same. Other advantages of
4690-421: The vessel the seafarer is working on. Some ship types will have specialist cargo equipment and tools; for example, a bulk carrier may have gantry cranes or grabs for cargo or a container ship may have container lashings. Cargoes should be properly stowed and secured to prevent shifting while at sea. Oil tankers and gas carriers can be somewhat complex due to the hazardous nature of their cargoes, and therefore
4760-399: The vessel to port or starboard depending on the configuration and the type of propeller, when large variations on propeller rotation speed or changes of propeller rotation direction take place. (In single-screw vessels where the rotation of the propeller is reversed on an astern bell, a standard was established that the propeller would turn clockwise when viewed from astern. This would mean that
4830-705: The vessel's rate-of-roll, operating similarly to airplane ailerons . Cruise ships and yachts frequently use this type of stabilizing system. When fins are not retractable, they constitute fixed appendages to the hull, possibly extending the beam or draft envelope and requiring attention for additional hull clearance. While the typical "active fin" stabilizer effectively counteracts roll for ships underway, some modern active fin systems can reduce roll when vessels are not underway. Referred to as zero-speed, or Stabilization at Rest, these systems work by moving specially designed fins with sufficient acceleration and impulse timing to create effective roll-cancelling energy. In case
4900-408: Was because with a following sea (and the deep slow rolls this generated) the vessel tended to 'hang' with the system turned on, and the inertia it generated made it harder for the vessel to right herself from heavy rolls. Gyro stabilizers consist of a spinning flywheel and gyroscopic precession that imposes boat-righting torque on the hull structure. The angular momentum of the gyro's flywheel
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