Ship Propulsion and Ship Manoeuvrability - Assignment Example

Ship Propulsion and Maneuverability Name Date Course Task 1 Conventional rudder configurations a. Balanced rudder In a ship, the axis or rotation of a balanced rudder is behind the front edge. This type of rudder is useful in terms of ensuring that the angle of deflection is increased in order to counter the pressure that is acting on the after part. This is after the ship is turned resulting to pressure that is caused by the ship movement. The actions of the rudder also play an important role in terms of ensuring that the angle of deflection is reduced and hence affecting positively on the balance of the ship (An, Lee, Park & Jang, 2015). The main advantage of this type of rudder is its ability to have some degree of semi-balance. This is therefore makes it possible for the rudder to be moved with less effort. This is also an advantage in terms of low energy required to move the rudder. However, one of its shortcomings is its little strength on the rudder trunk and compacted steering gear. This has negative effects on the maneuverability of the ship. b. Semi balanced rudder This is one of the most commonly used rudders in the ships. This type of rudder is partly balanced and party unbalanced. Because of this configuration, it has the ability of returning to the centerline on its own incase of failure of the steering gear equipment. This quality is also one of its main advantages that have seen it develop a large-scale use in the industry. The semi-balanced rudder is also advantageous when dealing with a large rudder and a small steering gear (Lee, An, Park & Jang, 2015). It also has the ability of providing a high maneuverability, which is required in the industry. However, it may have some limitations in terms of the frequent technical maintenance. The technology used in this type of rudder has also plated an essential role in promoting its acceptance in the industry. Balanced rudder, Source, . c. Unbalanced rudder In an unbalanced rudder, the stock is usually attached at the forward part of the span, which makes its unique as compared to the other types of rudders. This type of rudder is currently not widely used due to the advancements that have been made in the industry. It limitation ha also impacted negatively on it uses. The unbalanced rudder is not having an automatic mechanism of changing the angle of attack in case of steering gear failure (Cai, Cai & Li, 2015). However, this type of rudder is mainly utilized for ship that cannot utilize the balanced rudder. The unbalanced rudder in most cases is applied to the small ships of deep draft. Its main advantage is the ability to endure large stresses, which is an important aspect of maneuverability. Unbalanced rudder, Source, . d. Flap rudder This type of rudder utilizes the same principles as the wings of the airplane. It has the ability of dealing with changes of the angle of attack due to its flexibility. However, it is also important to note that this type of rudder is not retractable (Jin, et al, 2013). This type of rudder is mainly configured for ships that have high maneuverability needs. Although this type of rudder is effective in providing high maneuverability, it has limitations in terms of the technical aspects. The linkage system for this type of rudder is complicated and it requires a lot of expertise. This complicated technical nature of the flap rudder has limited its use in the industry despite the advantages that it has in terms of the high maneuverability. Flap rudder, Source, . Effects of ship motion when turning a ship In the process of turning a ship that is in motion, the rudder plays a vital role. The rudder is usually at about the center of gravity of the ship which leading to the changes in its orientation and hence giving it a drift angle. A ship that is in motion is assumed rigid body that has a constant mass. When the ship is in motion, various forces usually act on it. The forces that an act on a ship that is in motion includes the thrust and traverse forces that are generated because of propulsion (Wang, Liu & Cai, 2015). The wave resistance is also a force that acts on the ship and it plays an important role during the turning process of a ship. Other force that affects the ship in motion also includes the moment caused by wind and currents. The pivot point influences the turning effects of a ship in motion. When the ship turns while in motion, the forces on the ship takes effect on the pivot point. This results to a couple effects, which contribute to the changing in direction. The turning of a ship produces different actions, which can be described in four different phases. During the first phase, the stern starts to move outwards while the ship is still maintaining the same speed and direction. In the second phase, there is a gradual increase in the drift angle s well as the speed of the ship (Kim, Rhee & Kim, 2014). The process may also lead to a large angular acceleration, which may however star to improve when the ship continues taking a new path. An increase in angular acceleration leads to the increase in the camber angle. At this phase, the ship begins to enter the turning moment and move into the new direction. The turning section is the last phase of the ship and at this point, the angular acceleration of the ship turns to zero with the line speed and camber angle gradually becoming steady. Rudder stalling Stalling of a rudder takes place when the critical angle is reached. This cause of the effect of the rudder acting like a plate and perpendicular to the flow of water and with a tendency to stop the flow of fluids across it. The action causes it to act as a break leading to a decrease in the speed of the ship and hence stalling. It is also important to note that a critical angle, which is the same as the stall angle, is reached at this point and it affects the maneuverability of the ship. In most cases, the critical angle in which the stall takes place is 35 degrees (Park, et al, 2015). At this point, the vessel fails to change direction but the speed instead slows down. In most of the modern ships, the steering gear of the ships is designed to move the rider up to 35 degrees. Above this angle, there is a safe system for responding to the emergencies, which is at 38 degrees. It is however notable that the calibration is given up to 40 degrees (Park, et al, 2015). The failure of the rudder to guide the flow of the fluids is common in most of the rudders and this is responsible for the stalling. The factors that are mainly associated with the rudder stalling include cavitations, lamination and separation of laminar flow. All the factors are known for causing undesirable effects on the rudder leading to the stall. Task 2: standard procedures employed to determine ship maneuverability characteristics a. Turning circle This test is usually performed to the starboard as well as the port. During the process, the rudder angle should not be more than 35 degrees. A steady approach is usually with the yaw being at zero rates. A circle of at least 720 degrees has to be completes for both the port as well as the starboard (Yasukawa &Yoshimura, 2013). The information that is targeted during the procedure includes the tactical diameter, advance, loss of speed in steady turn, transfer, Time taken to change heading by 90 degrees and 180 degrees and the final yaw rate. Turning circle, Source, American Bureau of Shipping b. Maneuver zig zag This test is usually performed by applying a specific rudder angle to an initially straight approach. The rudder is then deflected immediately to the opposite with the same angle after the change of heading has reached its specified value. The entire trajectory is then recorded as the processes take place. The information that needs to be recorded during the test includes initial turning time, reverse rudder heading angle, overshoot angle, time to check yaw, reach and time for complete cycle (Yasukawa & Yoshimura, 2014). Maneuver zig zag, Source, American Bureau of Shipping c. Spiral test The spiral test in most cases is conducted when the ship is found to be directionally unstable during the pull test. This type of test usually takes a significant amount of time to carry out due to the nature of the activities. This test is performed by steering the ship at a constant rate of return. During the test, the vessel has to be equipped with rate-gyro which is mainly used for differentiating the course reading from the gyro-compass (Okazaki, Ochiai, Kashima & Iwakiri, 2014). Several consecutive deflections also need to be carried out in order to obtain the given turning rate. A moderate turning angle should also be applied with the entire trajectory being recorded. Spiral test, source, American Bureau of Shipping d. Pull out test This test is usually carried out after the turning test in most of the instances. It is usually performed to both the starboard as well as the port. The rudder has to be returned to the mid-ship position and maintained at the position until when a steady rate is obtained (Qu, Bi & Xiao, 2012). The dynamic stability of the vessel on a straight course can be obtained through the use of the test. When a vessel is stable, the rate of turn delays to zero for both the starboard and port. However, in case of instability, the rate of turn usually reduces to residual rate of turn. During the test, it is usually recommended that the entire trajectory should be recorded. Pull out test, Source, American Bureau of Shipping e. Stopping test This test is usually conducted with a starting speed of not less than 90% of the speed that corresponds with 85% of MCR (Yasukawa &Yoshimura, 2013). Once the required speed has been attained, a full astern command is given. This is mainly done from the engine control position which is located on the bridge. The entire trajectory has to be recorded with the test being completed when the vessel speed is zero. The information that must be recorded includes head reach, track reach and lateral deviation. Stopping test, source, American Bureau of Shipping Task 3: Propulsion system for low speed ship maneuvering Configuration Marine application L-drive The rotary motion has the ability of taking a right angle with a 360 degrees rotation (Yasukawa &Yoshimura, 2013). The pod in this configuration is mounted mechanically. It is commonly used due to its advantages which includes the ability of rapidly changing the thrust direction. The technical system is however complicated and it requires a lot of expertise. Z-drive Unlike the L-drive it has the ability to make two right angle turns in terms of rotary motion. The conventional screws are also used for the purposes of rotating the propeller (Yasukawa &Yoshimura, 2013). Its advantage is similar to the L-drive in terms of the rapidly changing the thrust direction. It can be used for ships of diverse sizes although its limitation is in terms of energy consumption. Ducted propeller This configuration is commonly used in ships that have propellers with limited diameters. It has the ability to work under different conditions and it has a non-rotating nozzle fitted on it. Its main advantage involves increased speed as well as reduced paddlewheel effect. However, due to its high rotating speed, it has the ability of injuring or killing the marine animals. Centrifugal pumps The pump has rotating impellers, which is used for driving energy into a fluid. The centrifugal pumps require a source of energy which may be generated mechanically. The main limitation is that the impellers usually wear out easily through cavitations and hence creating the needs for frequent replacement (Park, et al, 2015). Depending on the amount of fluid being pumped, its energy consumption may be quite high. Pod bow Its main application is in terms of propulsion and maneuvering of ships. It has electric cables that are mainly used for the transmission of energy. It main advantage is the ability to reduce the space within the hull of a ship. The consumption of energy is however high. Task 4: Operational requirements for dynamic positioning system The International Maritime organization (IMO) approved standards for ship maneuverability under the IMO 2002a and 2002b (Park, et al, 2015). The operational requirements encourage the application of the standards in order to promote safety and efficiency of maneuverability. ISO standards have also been developed and they are in accordance with IMO standards and principles. IMO also has a guide that is used for the purposes of judging the maneuvering performance of the ship. The compliance with the standards plays an important role in ensuring that the industry is safe. IMO encourages the sea trials for the purposes of ensuring that the ships are in a good condition. Most of the standards that have been developed by IMO are universally adopted due to the ability to their maneuverability benefits. The IMO has also developed the standards for Dynamic Positioning (DP) which has different classifications. The classification includes equipment class 1, 2 and 3 (Cai, Cai & Li, 2015). The class 1 equipment lacks redundancy which exposes it to lack of direction. Class 2 equipment is more sophisticated and it has redundancy which enables it withstands failure in case of fault. It has the ability to operating in the presence of a single fault without losing direction. DP block diagram, Source, Brazilian Society of Mechanical Sciences and Engineering The class 3 equipment is more advanced and its can withstand a number of failures without losing direction. This includes flooding or fire at the watertight compartment. Currently, a computer program that has the ability of generating mathematical models that are used for providing useful information about dynamic positioning. The taught wire application is useful in terms of dynamic positioning. This tool is mainly applied in water that has a depth that is below 500 meters in depth (Cai, Cai & Li, 2015). Through the application, the position of the ship in relation to its weight clump can be obtained. The use of this system is widespread in the industry due to the crucial information that it provides. The Geographical Positioning data (GP) is also used for the purposes of obtaining information about the positioning. This is usually achieved through obtaining information from the satellites, which are located in different positions across the globe. The system has the ability of providing automatic information although the levels of accuracy may vary due to the high number of satellites, which are in different locations. References An, Y.S., Lee, H.G., Park, B.S. and Jang, C.S., 2015. Maneuverability of a DWT 8,000-ton oil/chemical tanker by real sea trials-A comparison between the semi-balanced rudder and the flap rudder. Journal of the Korean society of Fisheries Technology, 51(2), pp.257-264. Lee, H.G., An, Y.S., Park, B.S. and Jang, C.S., 2015. A study on the turning ability of a DWT 8,000-ton oil/chemical tanker by real sea trials-A comparison between the semi-balanced rudder and the flap rudder. Journal of the Korean society of Fisheries Technology, 51(2), pp.245-256. Cai, C., Cai, X. and Li, Y., 2015. Model Tests for Shallow-Water Ship Maneuverability in Three Gorges Reservoir. Polish Maritime Research, 22(s1), pp.136-140. Jin, L.A., et al. 2013. Influence of underwater towed system on ship maneuverability. Jiaotong Yunshu Gongcheng Xuebao, 13(1), pp.47-54. Wang, X., Liu, Z. and Cai, Y., 2015. A rating based fuzzy analytic network process (F-ANP) model for evaluation of ship maneuverability. Ocean Engineering, 106, pp.39-46. Kim, D.H., Rhee, K.P. and Kim, N., 2014. The Effect of Hull Appendages on Maneuverability of Naval Ship by Sensitivity Analysis. Journal of the Society of Naval Architects of Korea, 51(2), pp.154-161. Park, B.S., et al. 2015. The Analysis of the Ship's Maneuverability According to the Ship's Trim and Draft. Journal of Fisheries and Marine Sciences Education, 27(6), pp.1865-1871. Yasukawa, H. and Yoshimura, Y., 2013. Investigation of roll-coupling effect on ship maneuverability. Journal of the Japan Society of Naval Architects and Ocean Engineers, 17. Yasukawa, H. and Yoshimura, Y., 2014. Roll-Coupling Effect on Ship Maneuverability. Ship Technology Research, 61(1), pp.16-32. Okazaki, T., Ochiai, H., Kashima, H. and Iwakiri, T., 2014, Development of override ship maneuvering simulator using AR toolkit. In 2014 World Automation Congress (WAC). Qu, J.F., Bi, Y. and Xiao, W.B., 2012, Integrated Evaluation of Ship Maneuverability Based on the Method of Maximizing Deviation. In Advanced Materials Research (Vol. 524, pp. 3888-3895). Read More

This type of rudder is currently not widely used due to the advancements that have been made in the industry. It limitation ha also impacted negatively on it uses. The unbalanced rudder is not having an automatic mechanism of changing the angle of attack in case of steering gear failure (Cai, Cai & Li, 2015). However, this type of rudder is mainly utilized for ship that cannot utilize the balanced rudder. The unbalanced rudder in most cases is applied to the small ships of deep draft. Its main advantage is the ability to endure large stresses, which is an important aspect of maneuverability.

Unbalanced rudder, Source, . d. Flap rudder This type of rudder utilizes the same principles as the wings of the airplane. It has the ability of dealing with changes of the angle of attack due to its flexibility. However, it is also important to note that this type of rudder is not retractable (Jin, et al, 2013). This type of rudder is mainly configured for ships that have high maneuverability needs. Although this type of rudder is effective in providing high maneuverability, it has limitations in terms of the technical aspects.

The linkage system for this type of rudder is complicated and it requires a lot of expertise. This complicated technical nature of the flap rudder has limited its use in the industry despite the advantages that it has in terms of the high maneuverability. Flap rudder, Source, . Effects of ship motion when turning a ship In the process of turning a ship that is in motion, the rudder plays a vital role. The rudder is usually at about the center of gravity of the ship which leading to the changes in its orientation and hence giving it a drift angle.

A ship that is in motion is assumed rigid body that has a constant mass. When the ship is in motion, various forces usually act on it. The forces that an act on a ship that is in motion includes the thrust and traverse forces that are generated because of propulsion (Wang, Liu & Cai, 2015). The wave resistance is also a force that acts on the ship and it plays an important role during the turning process of a ship. Other force that affects the ship in motion also includes the moment caused by wind and currents.

The pivot point influences the turning effects of a ship in motion. When the ship turns while in motion, the forces on the ship takes effect on the pivot point. This results to a couple effects, which contribute to the changing in direction. The turning of a ship produces different actions, which can be described in four different phases. During the first phase, the stern starts to move outwards while the ship is still maintaining the same speed and direction. In the second phase, there is a gradual increase in the drift angle s well as the speed of the ship (Kim, Rhee & Kim, 2014).

The process may also lead to a large angular acceleration, which may however star to improve when the ship continues taking a new path. An increase in angular acceleration leads to the increase in the camber angle. At this phase, the ship begins to enter the turning moment and move into the new direction. The turning section is the last phase of the ship and at this point, the angular acceleration of the ship turns to zero with the line speed and camber angle gradually becoming steady. Rudder stalling Stalling of a rudder takes place when the critical angle is reached.

This cause of the effect of the rudder acting like a plate and perpendicular to the flow of water and with a tendency to stop the flow of fluids across it. The action causes it to act as a break leading to a decrease in the speed of the ship and hence stalling. It is also important to note that a critical angle, which is the same as the stall angle, is reached at this point and it affects the maneuverability of the ship. In most cases, the critical angle in which the stall takes place is 35 degrees (Park, et al, 2015).

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