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Design for resilience: Using latent capabilities to handle disruptions facing marine systems
Published in Pentti Kujala, Liangliang Lu, Marine Design XIII, 2018
S.S. Pettersen, B.E. Asbjørnslett, S.O. Erikstad, P.O. Brett
Towing operations is the most common deflection method for icebergs. This is commonly done using anchor handling vessels that normally are equipped with sizeable winches, and sufficient bollard pull. McClintock et al. (2007) suggest that the minimum bollard pull of offshore vessels involved with iceberg towing are in the range 70–140 tons. The efficiency of the towing operation will naturally be dependent on the size of the iceberg. Borch & Batalden (2015) investigate the management of offshore support vessels in high-turbulence, volatile environments. They point to this iceberg towing as a challenge to crews that operate offshore vessels in ice-infested areas. Doing fieldwork and interviewing crew on offshore vessels, they found that iceberg towing operations put significant strain on quality management systems. New operational procedures had to be invented to cope with the change in operations due to utilization of latent capabilities.
Ships, their cargoes, trades and future trends
Published in Alan E. Branch, Michael Robarts, Branch's Elements of Shipping, 2014
Alan E. Branch, Michael Robarts
An example of an advanced multi-purpose offshore support vessel is shown in Figure 4.10, featuring the MS Maersk Pacer. It was built in 1991 and has a speed of 16.6 knots. The overall length is 73.6 m, beam 16.4 m and draught 6.85 m. The vessel has extensive versatile equipment, including a continuous bollard pull of 180 tons, and towage and very extensive anchor-handling equipment, including stoppers, shackles, chaser, grapnel, hydraulic guide pins of triangular type, winch, triplex shark jaws and rig chain lockers. The bridge equipment/manoeuvring facilities include joystick control, autopilot, gyro compass, repeators, radars, speed log, Decca and Satnav Shipmates, echo sounder, rapid direction finder facsimile, Navtex and VHF direction finder. Cabin accommodation is provided for six officers and six ratings and there are 12 berths for passengers. A hospital is provided and is equipped to British and Norwegian stand-by rules. The vessel is also equipped for safety/standby duties for 200 survivors, in accordance with Norwegian rules.
Operations with tugs
Published in D.J. House, Ship Handling, 2007
Charter rates for tugs are based on the ‘Bollard pull’ that the vessel can exert. This is a measure that is determined from trials when the vessel and equipment are new. The towline being secured to a land based anchor point and a load cell measures the strain exerted by the tug when pulling against the fixed point – the higher the bollard pull, the greater the charter rate. Generally speaking, the more powerful the tug, the more the hirer will have to pay. Tugs tend to be hired out for a minimum time period, e.g. 3 hours. The bollard pull is defined by the amount of force expressed in tonnes that a tug could exert under given conditions. A static bollard pull test would be affected by the depth of water, the tugs propulsion rating and the type of propellers fitted.
Experimental investigation of the effects of blade geometry on pressure fluctuation and noise of tunnel thrusters
Published in Ships and Offshore Structures, 2019
Cheng Yu, Xiao-Qian Dong, Chen-Jun Yang, Wei Li, Francis Noblesse
A further comparison is made for the total amplitude of fluctuating pressures, , which is obtained by summing up the amplitudes of the first five blade frequency harmonics,Figure 22 shows the comparison of at the six transducer locations among the three impellers. The result is clear that the fluctuating pressure amplitudes of impeller P1 are higher than those of P2 and P3 in both the cavitating and non-cavitating conditions and at all the measuring locations, with only one exception at S4 for which the reason is not clear. In terms of the total amplitudes, P2 and P3 are very close to each other. The comparisons shown in Figures 18–21 suggest that unloading the impeller blade towards the tip is an effective way to reduce the fluctuating pressures on the tunnel wall. However, further study is necessary to find out if the rake distribution close to the tip can be further improved. This conclusion is just opposite to the open propeller (Yamasaki and Okazaki 2007), and a possible reason is that the tunnel thruster has much heavier tip load due to the small tip clearance and bollard pull condition. As a result, the tip-unloaded design of the tunnel thruster is more effective to suppress the tip vortex cavitation which induced larger fluctuating pressures than the sheet cavitation.
A framework for rapid virtual prototyping: a case study with the Gunnerus research vessel
Published in Ship Technology Research, 2023
Pierre Major, Rami Zghyer, Houxiang Zhang, Hans Petter Hildre
The thrust delivered by each propulsor is described in Equation (7), where β is the hydrodynamic pitch angle calculated in Equation (8), and is the thrust coefficient of Equation (9), which depends on a series of precalculated trigonometric coefficients ,, such that the thrust curve can match the requirements (Roddy et al. 2007). For DP operations, the propulsors must keep the position and orientation of the ship at low speed, and it is necessary to calculate the thrust in the four quadrants of the propulsor’s operative mode: positive/negative mean velocity of water into the propulsor and clockwise/counterclockwise rotation of the propeller, as summarized in Table 2. When the hydrodynamic pitch angle β, is zero, the thrust is the bollard pull. Note that for the tunnel thrusters, the velocity of the water stream into the propellers tends to drop as the vessel sails at higher speeds than 5 knots, thus decreasing their contribution. also decreases dramatically when the thruster ventilates, i.e. is only partially immersed. The thrust coefficients are derived from similar propellers from the Wageningen Series, with a scaling factor, wake fraction, and thrust reduction. The main propulsion of Gunnerus is based on azipods, but a similar approach is taken to calculate the drag and lift of the rudders and the torque delivered to the shaft by the engine (where applicable).
The use of computational fluid dynamic technique in ship control design
Published in Ships and Offshore Structures, 2021
M. Martelli, D. Villa, M. Viviani, S. Donnarumma, M. Figari
Figure 36 reports the actuated rudder angle, and also, in this case, the dynamics of the rudder is well caught. In Figures 37 and 38 both the propeller pitch command and feedback, respectively, are shown. In the sea trial, the commanded and the actuated values have a mean value higher than the simulated ones; this could be due to the problematic representation of the complex phenomena in the stern region during this manoeuvre. In particular, when the propellers work in bollard pull condition, strong hull-propeller-rudder interaction is present, affecting the developed forces from the rudder/propeller.