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Ship handling in challenging conditions
Published in Alexander Arnfinn Olsen, Core Principles of Maritime Navigation, 2023
You might be asking why the bow and stern swing when the ship comes astern? This is because of transverse thrust and screw race effect. The bow thrusters are driven by motors. The power of the bow thruster generally depends upon the power of the motor. An 800 to 1,000 bhp bow thruster is effective enough for a vessel with a LOA of 150–160 metres (492–524 ft) and a beam of 22–25 metres (72–82 ft) with a gross tonnage of about 10,000 to 12,000 tonnes. It can easily counter offshore winds of 3–4 Beaufort (11 knots) whilst berthing. In areas of higher wind speeds and ships having higher LOA and GRT, a more powerful bow thruster is required. Bow thrusters are generally installed to replace the use of tugboats, which are hired by vessels coming into port. This reduces the operating costs of the vessel. In some ports, however, tugboat assistance is mandatory. In this case, the bow thrusters work in additional to the tugs. When anchoring, the bow thrusters also play an important role as they help keep the bow away from the anchor chain. When turning a vessel, such as at a congested dock, the bow thrusters help the vessel to spin on its axis. In these situations, the vessel is stopped and with the help of the bow thrusters the bow is swung to port or starboard, pivoting the stern. Occasionally, the stern is also rotated with the rudder and engines. But what is generally considered to happen in this instance is the vessel’s natural tendency to cant whilst coming astern. If the vessel has a right-handed propeller, the vessel’s bow will swing to starboard, while the engine is run astern. Therefore, it is always advisable to turn on the starboard wheel whilst coming astern as this enables the vessel to keep turning in the desired direction. When backing down, it is advisable to take a towing tug at the stern and use the bow thruster only as and when needed. The tug straightens the stern as it pulls, and any effects of transverse thrust are thus neutralised. The bow thruster thus plays an important role in the manoeuvring of ships.
Sailing status recognition to enhance safety awareness and path routing for a commuter ferry
Published in Ships and Offshore Structures, 2021
Baiheng Wu, Guoyuan Li, Tongtong Wang, Hans Petter Hildre, Houxiang Zhang
Besides t-SNE, pair plots can be used to reflect the independency of each class. Here, two pair plots are selected and shown in Figure 3. From the self-correlation of port thruster RPM, heading and speed, it shows that there is independency between different scenarios. And bow thruster RPM also gives useful information to tell scenarios apart, e.g. docking data points are explicitly away from other scenarios when the bow thruster is in correlation with port thruster RPM. It should be noted that the power density function (PDF) value of the bow thruster self-correlation at 0 is dominant over the scale. This results from that the bow thruster is strictly kept turned off in almost whole period over scenarios including cruising, turning and converging. While in departing and docking scenarios, the bow thruster is not kept at a fixed running rate, the scattering makes the PDF at each value to be trivial against the counterpart at 0.
Integrated maintenance and spare part optimization for moving assets
Published in IISE Transactions, 2018
Ayse Sena Eruguz, Tarkan Tan, Geert-Jan van Houtum
The degradationTable 6, Table 7, Table 8, Table 9Figure 1process was modeled based on our service life estimation in Equation (5) and considering how the cooling fan is used in different operating modes. We note that the cooling fan is in use only when the bow thruster is operating. This is required to make the vessel more maneuverable in the mission, harbor, and weather states. Using expert knowledge, we have assessed the operating time of the cooling fan in different operating modes. Assuming that the degradation is linearly correlated with the operating time, the cooling fan is expected to degrade 17 times faster during missions than during harbor or weather states. In transit states, the degradation of the cooling fan is assumed to be negligible, as it is never utilized. Based on this information, we built an Erlangian degradation process for each operating mode where F = 10 and the rates out of each state to the next degradation state are 0.41, 0.00, 7.13, and 0.41 for harbor, transit, mission, and weather states, respectively. By doing this, we divided the lifetime of the component in 10 equal parts (see Table 7). There is a small amount of data to statistically support the degradation process that we propose. Nevertheless, this degradation process is found to reflect actual operation based on the observations of FMS.
Challenges when creating a cohesive digital twin ship: a data modelling perspective
Published in Ship Technology Research, 2021
Ícaro Aragão Fonseca, Henrique Murilo Gaspar
Asset representation comprises three elements – one bow thruster and two azimuth assemblies with casing and propellers. When linked to operational data, they can be used to visualise the operating propulsion with rotations per minute and azimuth direction. The GL transmission format (glTF) is being assessed as an alternative to serialization and exchange of visualization models of this type. The format allows storage of entire 3D scenes as binary or JSON files, which can be used to transmit geometric models as articulated assemblies that would simplify inclusion on a digital twin visualization.