Ship Propulsion and Ship Maneuverability - Assignment Example

Ship propulsion and Ship Maneuverability Name Tutor Institution Course Date Task 1 Range of conventional rudder configurations Spade rudder This type of rudder is usually fixed to the stock only at the top of the rudder. The spade rudder unlike some of the rudders does not run along the span of the rudder. About 40% of the rudder area is comprised of the forward stock and the remaining is an aft (Guifeng, et al, 2011). The positioning of this rudder is mainly for the purposes of ensuring that the center of gravity lies to 40% of its cord. The main advantage of this rudder is the less torque required to rotate it. This is also useful in ensuring that the fuel consumption is lowered. It limitations may however be in terms of its expenses. Source, Marine insight Unbalanced Rudders This type of rudder is has stocks which are attached at the forward most point of their span. It also runs along the chord length of the rudder. However, this creates a limitation in terms of the torque. A torque which is much higher than required is usually produced as compared to the spade rudder (Daoyi, 2010). Another limitation for this type of rudder is that it continues to remain in its angle of attack in the event of failure of the steering gear mechanism. Source, Marine insight Semi-balanced Rudder In the modern industry, this type of rudder is commonly used. Its main advantage is the ability to counter the disadvantages of the unbalanced rudders as well as the spade rudder (Yinghui, 2010). This type of rudder is partly balanced and partly unbalanced. The top part is unbalanced and it provided structural support to the rudder from vertical displacement. It has the ability of automatically returning to the centerline orientation incase the steering gear equipment fails. Source, Marine insight Pleuger Rudder This is one of the most innovative types of rudder that is commonly used in ships. It main application is in the large ships which may have difficulties in maneuvering in a small basin (Hongyu, et al, 2012). The main advantage is its ability to enable large ships to operate in areas with space constraints. This is enabled through the use of a housing that generates thrust along the rudder and hence enabling effective maneuver at a low speed. Source, Marine insight Effects on a ship motion when turning a ship In ships turning movement by steering a rudder angle and maintaining it when the ship is sailing straight is referred to as turning maneuverability. The process has effects on the motion of the ship and it can be described in three phases. The first stage is commonly referred to as side ways and introversion section. At this stage, the ship still maintains its forward speed with the sterns moving outwards. The acting point of rudder force at this point is lower than the center of gravity which causes the ship to introvert (Jaswar, et al, 2012). The second stage is referred to as the transition state which the side way speed of the ship as well as the drift angle starts to increase gradually. This in turn leads to a large angular acceleration of the ship for some times. However, as it continues to take the new path, the angular velocity continues to improve. An improvement in the angular speed leads to the gradual reduction of the angular acceleration. The gradual reduction in the angular acceleration usually leads to the disappearance of the introversion (Cheng, et al, 2010). This in turn leads to the gradual increase in the camber angle. The process is before the steadily enters a steady turning movement. The third stage is the steady turning section. At this stage, the angular acceleration of the ship turns to zero. The line speed of the ships also becomes steady alongside with the camber angle, sideways speed and drift angle. Stalling of a rudder The maximum angle that may be generated by a rudder is dependant on various factors including the angle of attack. A series of events is also known to contribute to the stalling of the ruder in a ship. Stalling of the rudder usually leads to the sudden fall of the lift to null values. Stalling of the rudder in most occurs when the flow separates from the low pressure area to envelope an area that is of vertical flow. It is due to the separation that an abrupt decrease in lift is generated. Reynolds number is involved in the changes of the flow from laminar to turbulent. This is also a function of speed and angle of attack. The critical angle of marine rudders is usually 35 degrees and it is also the stall angle (Guifeng, et al, 2011). At the stall angle, the ship does not change directions but it instead causes undesirable effects which are slowing down. The stall is also related to three different events which include separation of laminar flow, ventilation and cavitations. However, the separation of the laminar flow is considered the most detrimental as it may generate a stall by itself. Cavitations have the ability of reducing the rudder thrust and hence contributing to the stall (Guifeng, et al, 2011). Ventilation is associated with the occurrence of the low pressure valves at flows adjacent to the passive surface of the rudder and hence contributing to the stall. Source, Nautica Task 2: Standard procedures to determine maneuverability characteristics Turning circles This test is usually carried out in order to determine the turning characteristics of the ship. The information that is obtained from the test includes steady turning diameter, turning rate in steady state, tactical diameter and final ship speed. A trial agenda has to be established before the ship steady speed is established. Steering with the prescribed minimum rudder is then carried out before concluding the test when the change of heading reaches an angle of 540 degrees to 720 degrees (Daoyi, 2010). During the test, the normal rudder angle is usually 35 degrees with a supplementation of 15 degrees to the right and left. The right and the left turning are usually conducted at the same headings. The test can be represented using the diagram below. Zig-zag test This test is mainly used for the purposes of expressing course changing as well as course keeping qualities. The information obtained through the use of this test includes the angle of overshoot, initial turning time, time to second executes as well as the time to check yaw. The steady ship speed indicated during the trial agenda has to be established. A 10 degrees right rudder has to be ordered and maintained. Reversing the rudder at the same degrees to the right and left has to be carried out. This should also continue for the heading and stopped only when the approach heading has been obtained. According to the international standards, this test should be performed at plus or minus 10 to 20 degrees (Yinghui, 2010). However for the large full ships, it should be performed at plus or minus 5 to 15 rudder angles. It can be represented through the use of the following diagram. Spiral test The spiral test is mainly used for the purposes of determining the directional stability of the ship. The width and height of the ship are some of the most important parameters that are used in the test. This type of test is usually conducted in a sea state below 2 or 3 as reliable measurements cannot be obtained in a sea state above 4.This test requires intense procedures including maintaining the rudder at between 1 and 2 degrees. The test is also intense with several processes requiring repetition in order to obtain the required results. This can be represented using the diagram below. Man overboard test This type is test is used for the simulation of a rescue process where a man has fallen overboard. During the test, the rudder angle as well as the ship trajectory is checked throughout the process. A steady ship speed has to be established during the test with adjustments being made to achieve a steady course. An order of 35 degrees rudder angle to the right and the left is also utilized during the process (Hongyu, et al, 2012). A gradual reduction of the speed is usually made up to the point where the ship has achieved an angle of 180 degrees. Thruster test This type of test is mainly used for the purposes of determining the turning qualities through the use of thrusters when the ship is dead in water or running at a specific speed. The procedure involves setting the engine to stop so as to obtain the data. The bow thruster is then ordered to full thrust. The thruster has to operate for a period of over ten minutes under 30 degrees (Guifeng, et al, 2011). After the test has been completed, the ship is brought back to the dead water condition. Task 3: Propulsion types and configurations Configuration/Propulsion Technical details Advantages and disadvantages L-drive Pod mounted and driven mechanically as opposed to electrically. It can be rotated at 360 degrees. The rotary motion has to take a right angle turn. Allows for rapid changes of thrust direction (Hongyu, et al, 2012). Eliminates the need for conventional rudder. Prone to technical and mechanical problems. Z-drive Used to connect mechanically supplied driving energy. The rotary motion has to make two right angle turns (Hongyu, et al, 2012). It utilizes a shrouded conventional screw that rotates the propeller. It has the ability of allowing for rapid changes of thrust and vessel directions. It can be used on a wide range of ships. Prone to technical and mechanical problems. Pod bow Mainly used for the purposes of propulsion and maneuvering of the ships. It has a torpedo shape at the bottom. It requires electricity which is transmitted through the use of cables. It has the ability of increasing the ship maneuverability. It has the ability of turning to 360 degrees (Hongyu, et al, 2012). It frees up more space within the hull of the ship. The power consumption may be high. Centrifugal pumps The impeller is mainly used for the purposes of driving the energy into the fluid (Yinghui, 2010). Enables the transfer of mechanical energy into fluid as pressure energy. It has shafts which connect it to the power sources. Effective in terms of transferring the energy to create fluids. The impeller requires frequent replacement. May consume a high amount of energy. Ducted propeller It is fitted with non rotating nozzle. Used for ships with propellers that has limited diameters. It is shaped like foil in order deal with different conditions. Increased efficiency at lower speed with better course stability and les vulnerabilities to debris (Yinghui, 2010). Has the ability of reducing the paddlewheel effect. Reduces the bottom suction while operating in shallow waters. It has the ability of causing fatal injuries to seals and other marine animals. Task 4: Operational requirements for dynamic positioning system International maritime organization The standards that have been developed by IMO are mainly for the purposes of promoting performance quality and handling capacity of the ships. These are useful aspects that ensure safety during the maneuvering of the ships. Resolution A 751 was adopted in 1994 by IMO in order to govern the maneuverability of the ships (Yinghui, 2010). It involves principles, application, definitions and application of standards. The organization also has conditions as well as additional considerations. This is for the purposes of ensuring that the positioning system is considered under different conditions. Currently, the standards that have been set by IMO are used all over the world for promoting safety during the processes. DP classification The dynamic positioning classification illustrates different classes and it is based on the IMO standards. According to the classification, equipment class 1 does not have redundancy. The loss of position is may also occur in the event of a single fault (Daoyi, 2010). However, equipment class 2 has redundancy which enables it to experience system failure in case of fault. Loss of position cannot occur from a single fault of an active component. However, with this class of equipment, failure may occur incase static components experience problems. The positioning may be affected by the failure of the static components which includes cables, pipes and manual valves. Equipment class 3 has to withstand fire ort flood in any compartment without causing the system to fail. At this class, the loss of position should not occur from any single failure including watertight compartment. According to the IMO principles, the automatic and manual position under a specified environmental condition is under class 1 (Daoyi, 2010). At least two independent computer systems are required for class 2 and 3. The computer program used has a mathematical model that provides information about the drag, wind and thrusters. Block diagram Taught wire application This system is mainly used for the purposes of dynamically positioning a system. It plays an important role in terms of measuring the position of the vessel relative to the weight clump on the sea floor. This is however applicable to water depths that is up to 500 meters (Daoyi, 2010). This is achieved through the lowering of a weight clump through a wire to the sea floor. An inclinometer is used for measuring the angle of the wire. In most cases, the stream is usually assembled with its own power pack as well as electronics cabinet. The system is considered as a well proven and reliable offshore technology. It is also considered cost efficient and an additional positioning reference system. The level of accuracy when using this system is high which has played an essential role in improving its reliability. It is can also be developed to meet the specific needs of the clients. Use of GP Data The GP data involves the use of the satellite navigation to find their position in the ocean. It is also considered as a satellite based radio navigation. The use of the systems ensures that the dimensional position as well as the velocity is obtained. These are useful parameters during the navigation process. To fix the position of a ship, four or more satellites are usually used. However the distance between the satellite and the ship is an important factor that determines the ease of obtaining the data. The triangulation which involves obtaining data from at least three satellites is commonly used by the ships. The computers are also used alongside the systems to calculate the distances. This plays an important role in terms of ensuring that accuracy is improved with the use of the system. The satellites have the ability of obtaining data in six circular orbits of 10,900 nautical miles (Guifeng, et al, 2011). Bibliography Guifeng L., et al., 2011, Simulation and Characteristics Analysis on the Coupling Motion of Heave and Pitch with Maneuvering for a Ship in Regular Waves, Science Technology and Engineering, 11(24), 5863-5869. Daoyi, L., 2010, DesignandImplementationofDMS-2010CPP Main Engine Remote Control System, Dalian Maritime University. Yinghui W., 2010, Simulation of Ship Maneuvering Motion in Waves, Shanghai Jiaotong University. Hongyu, Z. et al., 2012, Modeling and simulation of air cushion vehicle 6-DOF maneuverability, JDCTA, 6(12), 214 -222, 2012 Jaswar, A., et al., 2012, Integrated Ship Maneuverability Simulation Tool for Very Large Crude Oil Carrier, JDCTA, 6(13), 542-548 Cheng, L. et al., 2010, Application-oriented Design of Ship’s Autopilot with Rudder Dynamics, Journal of Dalian Maritime University, (3):1-6. Read More

This in turn leads to the gradual increase in the camber angle. The process is before the steadily enters a steady turning movement. The third stage is the steady turning section. At this stage, the angular acceleration of the ship turns to zero. The line speed of the ships also becomes steady alongside with the camber angle, sideways speed and drift angle. Stalling of a rudder The maximum angle that may be generated by a rudder is dependant on various factors including the angle of attack. A series of events is also known to contribute to the stalling of the ruder in a ship.

Stalling of the rudder usually leads to the sudden fall of the lift to null values. Stalling of the rudder in most occurs when the flow separates from the low pressure area to envelope an area that is of vertical flow. It is due to the separation that an abrupt decrease in lift is generated. Reynolds number is involved in the changes of the flow from laminar to turbulent. This is also a function of speed and angle of attack. The critical angle of marine rudders is usually 35 degrees and it is also the stall angle (Guifeng, et al, 2011).

At the stall angle, the ship does not change directions but it instead causes undesirable effects which are slowing down. The stall is also related to three different events which include separation of laminar flow, ventilation and cavitations. However, the separation of the laminar flow is considered the most detrimental as it may generate a stall by itself. Cavitations have the ability of reducing the rudder thrust and hence contributing to the stall (Guifeng, et al, 2011). Ventilation is associated with the occurrence of the low pressure valves at flows adjacent to the passive surface of the rudder and hence contributing to the stall.

Source, Nautica Task 2: Standard procedures to determine maneuverability characteristics Turning circles This test is usually carried out in order to determine the turning characteristics of the ship. The information that is obtained from the test includes steady turning diameter, turning rate in steady state, tactical diameter and final ship speed. A trial agenda has to be established before the ship steady speed is established. Steering with the prescribed minimum rudder is then carried out before concluding the test when the change of heading reaches an angle of 540 degrees to 720 degrees (Daoyi, 2010).

During the test, the normal rudder angle is usually 35 degrees with a supplementation of 15 degrees to the right and left. The right and the left turning are usually conducted at the same headings. The test can be represented using the diagram below. Zig-zag test This test is mainly used for the purposes of expressing course changing as well as course keeping qualities. The information obtained through the use of this test includes the angle of overshoot, initial turning time, time to second executes as well as the time to check yaw.

The steady ship speed indicated during the trial agenda has to be established. A 10 degrees right rudder has to be ordered and maintained. Reversing the rudder at the same degrees to the right and left has to be carried out. This should also continue for the heading and stopped only when the approach heading has been obtained. According to the international standards, this test should be performed at plus or minus 10 to 20 degrees (Yinghui, 2010). However for the large full ships, it should be performed at plus or minus 5 to 15 rudder angles.

It can be represented through the use of the following diagram. Spiral test The spiral test is mainly used for the purposes of determining the directional stability of the ship. The width and height of the ship are some of the most important parameters that are used in the test. This type of test is usually conducted in a sea state below 2 or 3 as reliable measurements cannot be obtained in a sea state above 4.This test requires intense procedures including maintaining the rudder at between 1 and 2 degrees.

The test is also intense with several processes requiring repetition in order to obtain the required results.

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