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MASS Design and Engineering
Published in R. Glenn Wright, Unmanned and Autonomous Ships, 2020
The uncrewed RAmora tug is the creation of naval architects Robert Allan Ltd (Vancouver, Canada) as part of their TOWBoT (tele-Operated Workboat or Tug) series of vessels designed to work in tandem with a conventional tug during ship handling [den Hertog, et al. 2016]. Featuring a hybrid propulsion system the vessel is fitted with Voith Schneider propeller drives in a fore/aft configuration. With substantial battery storage capacity, it is highly maneuverable and can provide a bollard pull of up to 55 tons in extended operations and even in hazardous conditions [RAL 2015]. The use of immersive telepresence features provides live 360-degree video and real-time electronic position-sensing to capture a continuous onboard perspective for safe and effective ship handling through remote operation from the command tug. A real-time control system provides the interface for the operator in addition to onboard maneuvering and positioning controls, equipment and workspace monitoring and safety management functionality.
Mooring and berthing
Published in Alexander Arnfinn Olsen, Core Principles of Maritime Navigation, 2023
In addition to the main three types of tugboats outlined above, there are a host of other types of tugs, many of which specialised functions and systems. For example, there is the tractor tug with cycloidal propellers. Prior to the Second World War, tugboats were designed with high power ratings to maximise potential tonnage capacities. These boats required a special type of propeller called the cycloidal propeller to provide the necessary manoeuvrability. Today, these have been replaced by the Voith Schneider propeller (VSP), which is a technological advancement on a cycloidal drive. It provides excellent manoeuvring and smooth handling, making it ideal for ferries and barges. The Carousel Tug was developed by the Dutch and emerged as an award-winning maritime innovation in 2006. It consists of interlocking inner and outer rings in which the former is connected to the boat, and the latter to the tug’s body. The ship under tow us connected via winch or hooks. The Reverse Tractor Tug has a Z-drive aft-mounted propulsion unit. These tugs do not have a skeg and work efficiently as escort tugs. With Combi-Tugs, a bow thruster and steering nozzle is fitted to a conventional screw tug to offer improved manoeuvrability. Z-PELLER tugs have two towing positions: one forward and one amidships. Main propulsion is provided from two rotating azimuth units which are placed similarly to the conventional twin-screw tug. The azimuth propulsion unit replaces the conventional shafts and propellers, which allows 360 degree rotation about the vertical axis. The Giano Tug is a highly capable class of tug that serves well as both a support and escort tug. It is a technologically advanced tug that allows remote manoeuvring through VSAT or 4G connections. Its 360° rotation and excellent side-stepping speed places it at the top in the order of tugs standard. Hybrid technology tugs or tugs that use Liquid Natural Gas (LNG) as their running fuel are categorised as eco-tugs. These tugs serve the same purpose of escort and support as conventional tugs but are considered more less polluting to the marine environment. Last of all, ice tugs are used to escort ferries and barges through ice frozen waters. Though not classified as ice breakers, the strengthened hull means they can break through ice packs that would ordinarily cause damage to standard hulled vessels.
Simulation of a marine dynamic positioning system equipped with cycloidal propellers
Published in C. Guedes Soares, T.A. Santos, Progress in Maritime Technology and Engineering, 2018
M. Altosole, S. Donnarumma, V. Spagnolo, S. Vignolo
In order to automatically maintain position and heading of a vessel, Dynamic Positioning (DP) systems employ in general waterjets or azimuth thrusters; in case, rudders and propellers (together with bow and stern thrusters) can be used too (Alessandri et al. 2014). Marine cycloidal propellers (Jürgens et al. 2002, Taniguchi 1962, Esmailian 2014), usually driven by diesel‐electric propulsion to better handle the large changes in power demand (typical during DP operations), can represent a good alternative to traditional propellers since they can generate almost the same thrust in all directions. They are classified into true cycloidal, epicycloidal (e.g. Voith Schneider Propeller) and trochoidal propellers on the basis of their eccentricity value e, namely the ratio between the distance of the steering center from the propeller axis and the radius of the circular orbit described by the blade axes (the rotor radius): a true cycloidal propeller is characterized by e = 1, while the conditions e < 1 and e > 1 distinguish epicycloidal and throcoidal propellers, respectively (Bose 2008). In the present study, the performance of an epicycloidal propeller is modelled within a DP propulsion simulator, already developed by some of the authors for a surface vessel equipped with two conventional twin‐screw propellers and a bow thruster. This kind of configuration is not very suitable for station‐keeping and DP applications (Sørensen 1996, Sørensen 2011, Fossen 1996, Fossen 2002), nevertheless, a conventional propulsion configuration could be requested for specific operations characterized by limited DP capabilities. For instance, the mentioned simulator was developed for a patrol vessel designed with a twin propeller‐rudder configuration and a single bow‐thruster, which were requested to provide a certain dynamic positioning performance at zero speed with moderate weather conditions. The main purpose of the DP simulation model was to validate the Force and Thrust Allocation Logic (FAL, TAL, Johansen 2013), specifically designed for such propulsion configuration (Donnarumma et al. 2015). In this new work, the same vessel, but supposed equipped with a single bow thruster and two epicycloidal propellers at stern, is simulated in order to analyze the main differences during DP operations, in terms of general performance and control system behavior. This kind of simulation involves a reliable representation of the epicycloidal propellers, whose manufacturers unfortunately do not publicly share their performance maps for confidential reasons. Therefore, simplified simulation approaches, as possible for traditional propellers (Altosole et al. 2012, Martelli 2015) or waterjets (Altosole et al. 2005), are quite difficult to be developed. The present numerical modelling is based on a mixture of theoretical and empirical considerations: in particular, the propeller thrust and torque evaluation is based on the kinematics of the blades, taking into account suitable correction factors in order to consider the interference phenomena among blades. The result is a simulation approach able to predict the performance of an epicycloidal propeller, avoiding demanding computations (e.g. CFD methods) that would not allow an effective simulation of the whole DP system.
Hydrodynamic analysis of cycloidal propellers
Published in Ships and Offshore Structures, 2022
Tao Li, Jian Hu, Yingzhu Wang, Weipeng Zhang, Yixuan Mao, Chunyu Guo
In 1926, Boeing introduced the Kirsten–Boeing propeller, the first cycloidal propeller across the world. In 1927, Voith manufactured another cycloidal propeller with an upgraded structure, commonly referred to as the Voith–Schneider propeller. Early studies on cycloidal propellers focused on the use of simplified analytical methods to estimate their hydrodynamic characteristics. Haberman and Harley (1961) and Taniguchi (1962) made significant contributions in this area. Meanwhile, Nakonechny (1961) and Van Manen (1966) conducted extensive experimental work on this topic. However, it is found that the simplified analytical methods were only accurate at medium load condition. At large eccentricities, the methods cannot obtain precise results. Considering these, Zhu (1982) improved the methods used by Taniguchi by taking into account the effects of the curvilinear paths and the rotation of the propeller blades atlow-Reynolds numbers on the drag and lift coefficients. Comparison between the numerical results and the experimental results show that the methods fitted quite well with most eccentricities.