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59-697: SS Gopher State (T-ACS-4) is a crane ship in ready reserve for the United States Navy . The ship was named for the state of Minnesota , which is also known as the Gopher State . Currently at anchor in Weymouth Bay, England receiving bunkers. Gopher State was laid down on 26 July 1971, as the container ship Export Leader , ON 545126, IMO 7226689, a Maritime Administration type C5-S-73b hull under MARAD contract (MA 257). Built by Bath Iron Works , Bath, Maine, hull no. 358, she

118-452: 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

177-495: A Norwegian tanker, Sunnaas , into a crane vessel with a capacity of 300 tons, the first one in the offshore industry that was ship-shaped. It was renamed Global Adventurer . This type of crane vessel was better adapted to the harsh environment of the North Sea . In 1978, Heerema had two semi-submersible crane vessels built, Hermod and Balder , each with one 2,000 ton and one 3,000 ton crane. Later both were upgraded to

236-408: 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

295-416: A tugboat . In 1920, the 1898-built battleship USS  Kearsarge was converted to a crane ship when a crane with a capacity of 250 tons was installed. Later it was renamed Crane Ship No. 1 . It was used, amongst other things, to place guns and other heavy items on other battleships under construction. Another remarkable feat was the raising of the submarine USS  Squalus in 1939. In 1942,

354-471: A barge that was outfitted with a revolving crane capable of lifting 150 tons. The arrival of this type of vessel changed the direction of the offshore construction industry. Instead of constructing oil platforms in parts, jackets and decks could be built onshore as modules. For use in the shallow part of the Gulf of Mexico , the cradle of the offshore industry, these barges sufficed. In 1963, Heerema converted

413-467: A catamaran barge which allows it to straddle a bridge pier to lower a prefabricated section into place. Catamaran heavy lift barges that consist of two barges connected by gantry cranes across the top have been used in sheltered water like harbours and rivers. To reduce listing moments on the barges, the gantries may be attached to the hulls by pinned joints at the ends, allowing some independent roll. The gantry trusses are usually fitted at both ends of

472-421: A fixed position, and use the slewing and luffing capabilities of the derrick to position the crane tip for picking and setting the load The arrangement is a compromise of structural and stability requirements balanced against reach versatility, load capacity, and cost. One of the advantages of the slewing derrick is the ability to reach loads carried on the deck of the vessel itself. Compared to land-based cranes,

531-420: 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

590-489: A higher capacity. This type of crane vessel was much less sensitive to sea swell, so that it was possible to operate on the North Sea during the winter months. The high stability also allowed for heavier lifts than was possible with a monohull. The larger capacity of the cranes reduced the installation time of a platform from a whole season to a few weeks. Inspired by this success similar vessels were built. In 1985 DB-102

649-404: A jacking system that can grip the leg and move it up or down relative to the hull, lock it in place and move back along the leg to grip it again for a further jacking operation. The hull is lifted clear of the wave tops in the working position, and the mass of the barge and any additional load is supported by the bases of the legs, which should preferably spread the load as evenly as possible. During

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708-487: 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 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

767-477: A radius of 31.2 m (102 ft); in comparison, Saipem 7000 can use both cranes to lift a smaller load of 14,000 t (14,000 long tons; 15,000 short tons) at a wider radius of 41 m (135 ft). A heaviest single lift record was set in 2000 by Thialf for lifting the 11,883 t (11,695-long-ton; 13,099-short-ton) Shearwater topsides for Shell. Saipem 7000 set a new record in October 2004 for

826-452: 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

885-553: 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 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

944-464: 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 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

1003-420: Is a barge with sheer-legs mounted at one end, which can lift loads and luff the sheer-legs to adjust the reach, but cannot swing the load independently of the hull orientation. A typical arrangement has a substantial A-frame hinged at the stern, supported by stays to the bow. When the load has been lifted, the barge is maneuvered to the position where the load is to be lowered by onboard thrusters or tugs, and

1062-402: 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

1121-490: 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 , 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

1180-408: 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

1239-422: 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

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1298-489: 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

1357-418: 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 the system in the form of pumps, hydraulic pistons , or electric actuators . They include stabilizer fins attached to

1416-399: Is usual to luff the sheer-legs before lifting to a position suitable for both lifting and setting the load, as luffing under load is generally slow, and there is seldom any need. A heavy lift hammerhead crane barge has a fixed hammerhead crane, which neither slews nor luffs, but has a constant reach. They are operated in a similar way to sheer-legs barges. This arrangement may be mounted on

1475-612: 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

1534-488: 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

1593-560: The six degrees of freedom of the vessel, the response to the sea state and wind, and the position and motion of the upper block due to crane geometry and operational motion, can make the upper block describe a complex three-dimensional path in space. The load path is even more complex, and there may be various resonances of vessel, crane and load which must be managed, generally by passing through those conditions as soon as reasonably practicable, but motion compensation systems may help at times. Accelerations, jerk loads and impacts between

1652-614: The 12,150 t (11,960-long-ton; 13,390-short-ton) lift of Sabratha Deck. Under dynamic positioning, Saipem 7000 set another record in 2010 by lifting the 11,600 t (11,400-long-ton; 12,800-short-ton) BP Valhall Production topsides. Shortly after it was completed, Sleipnir completed a record lift of 15,300 t (15,100 long tons; 16,900 short tons) for the topsides of the Leviathan project for Noble Energy , in September 2019. Ship stability Ship stability

1711-402: The 14th century. During the age of sail , the sheer hulk was used extensively as a floating crane for tasks that required heavy lift. At the time, the heaviest single components of ships were the main masts, and sheer hulks were essential for removing and replacing them, but they were also used for other purposes. Some crane vessels had engines for propulsion, others needed to be towed with

1770-473: 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 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

1829-458: 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

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1888-418: The additional dynamic loads and motion in a seaway complicate the operation and safety. Position and movement of the boom tip are affected by all six degrees of freedom, magnified by distance from the centres of motion of the vessel, and varying during a lifting operation as the position of the tip is moved relative to the vessel. A Jack-up construction barge is a barge fitted with four to eight legs, each with

1947-459: The barges, allowing lifts of long loads. Semi-submersible crane platforms have advantages where the water is too deep or the bottom composition unsuitable for a jack-up, and the water conditions are frequently too rough for efficient use of conventional hulls. The semi-submersible hull form has a lesser and slower response to waves and swell, due to reduced waterplane area , and stability and righting moment are adjustable by ballasting to suit

2006-477: The base of the leg may be used to release firmly embedded legs. These rigs are free from motion response to sea conditions, but need occasional calm conditions to move. Performance is strongly dependent on seabed characteristics. The three main measures of capacity are load, reach, and lift height. Other factors of importance are hull draught, depth to which the hook can be lowered (for offshore work), and sea state limits for transit and lifting. The interaction of

2065-510: The beginning of the 1970s a large heavy lift contractor, but only a small player in this field at the end of the 1980s – acquired M7000 from Micoperi in 1995, later renaming it Saipem 7000 . In 1997 Heerema took over DB-102 from McDermott after discontinuation of their joint venture. The ship was renamed Thialf and subsequently was upgraded in 2000 to a lifting capacity of twice 7,100 tons. Thialf can use both cranes in tandem to lift 14,200 t (14,000 long tons; 15,700 short tons) at

2124-421: 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

2183-511: 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

2242-614: The crane ships a.k.a. "Heavy Lift Ships" SS Empire Elgar ( PQ 16 ), SS Empire Bard ( PQ 15 ), and SS Empire Purcell (PQ 16) were sent to the Russian Arctic ports of Archangelsk , Murmansk and Molotovsk (since renamed Sererodvinsk). Their role was to enable the unloading of the Arctic convoys where port installations were either destroyed by German bombers or were non existent (as at Bakaritsa quay Archangel). In 1949, J. Ray McDermott had Derrick Barge Four built,

2301-498: 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

2360-423: The force required to submerge buoyant floats or by hydrodynamic foils. In some cases, these outriggers are of sufficient size to classify 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

2419-414: 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

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2478-489: 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

2537-496: The jack-up operation the barge is secured in place by a taut mooring spread of anchors. Once at working height the legs can be released one at a time and driven deeper with pile driving hammers for greater stability. Removal is basically a similar procedure in reverse, with the legs being pulled out of the bottom ground one at a time after the hull is afloat, while the anchor spread limits side forces imposed by waves. Water jetting, sustained tension, and/or low pressure water injection at

2596-580: The largest crane vessels use fixed sheerlegs instead; in these designs, the crane cannot rotate relative to the ship, and the vessel must be manoeuvered to place loads. Other vessels use large gantry cranes and straddle the load. There are several major configurations of crane vessel, usually with overlapping ranges of functionality, but each has at least one major advantage over the others in some circumstances, and consequently all these arrangements coexist. Conventional seagoing self propelled monohulls with heavy lift crane equipment. A Sheer-legs barge

2655-496: 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

2714-410: The load and surroundings must be minimised and limited to levels which do not cause unacceptable damage. Some of these responses are inherent to the combination of vessel, crane and load, and others depend on sea state and wind forces. Pick up and set down are the critical stages for impact loads. During pickup there may be relative movement between the support on which the load stands and the hook, and if

2773-405: The load cannot be lifted clear before the gap closes, there will be impact. Similarly when setting the load down, it should be done as smoothly as possible, and once in contact should be allowed to settle as soon as possible to avoid re-lifting and pounding on the base structure. In medieval Europe, crane vessels which could be flexibly deployed in the whole port basin were introduced as early as

2832-411: The load is lowered. A sheer-legs barge always keeps the load in the line of maximum static stability, and may use ballasting at the bow to increase longitudinal righting moment to compensate for the load. The sheer-legs arrangement is more economical to manufacture and maintain than a slewing crane, but may be less convenient as the whole vessel must be moved to precise position for lifting and lowering. It

2891-421: The load. The gaps between the columns also allow waves to pass between then with little impact on the vessel. Disadvantages are lower inherent stability, and much greater cost and complexity. The low waterplane area causes a low heave response, and this can be utilised to function as a tension leg platform by using vertical mooring lines to anchor piles or clump weights on the seabed sufficient to prevent heave in

2950-439: 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 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

3009-432: The prevailing sea state. In this configuration heave sensitive operations can be done with precision and control. A revolving derrick barge is a slewing crane mounted on a barge, which can be rotated independently of the hull when carrying a load. These are highly versatile, but also expensive, complex, and have some limitations, particularly in the sea states in which they can safely operate. They are usually operated from

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3068-428: 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

3127-510: 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,

3186-544: 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 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

3245-477: 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,

3304-408: 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

3363-422: Was launched for McDermott, with two cranes with a capacity of 6,000 tons each. Micoperi ordered M7000 in 1986, designed with two cranes of 7,000 tons each. However, due to an oil glut in the mid 1980s , the boom in the offshore industry was over, resulting in collaborations. In 1988, a joint venture between Heerema and McDermott was formed, HeereMac. In 1990 Micoperi had to apply for bankruptcy. Saipem – in

3422-569: Was launched on 8 July 1972, and delivered to MARAD 22 January 1973, entering service for American Export-Isbrandtsen Lines (renamed American Export Lines in the same year). She was sold to Farrell Lines in 1978 without name change. The ship was returned to MARAD in 1986 and laid up in the National Defense Reserve Fleet (NDRF). In 1987 she was converted to a type C5-S-MA73c crane ship by Norfolk Shipbuilding & Drydock, Norfolk, Virginia. Completed on 12 October 1987, she

3481-853: Was placed in service as Gopher State (T-ACS-4) and assigned to the Ready Reserve Force (RRF), under operation control of the Military Sealift Command (MSC). Gopher State is in ready reserve, laid up at Newport News, Virginia. As of December 2016, she is in Drydock No. 3 in Boston . Crane ship The cranes are fitted to conventional monohulls and barges , but the largest crane vessels are often catamaran or semi-submersible types which provide enhanced stability and reduced platform motion. Many crane vessels are fitted with one or more rotating cranes. Some of

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