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Polar Plot Capability of a Tug in Indirect and Direct Mode of Escort Towing
Published in Adam Weintrit, Tomasz Neumann, Advances in Marine Navigation and Safety of Sea Transportation, 2019
The quoted former study (Artyszuk, 2014) was significantly dealing with the indirect towing as being exactly in the equilibrium (or steady-state) condition. The feature of it is that a tug, see Figure 1, sets her starboard side against the inflow (β < 0). If a tug is getting parallel with the assisted ship (β = 0) and starting next to expose her port side (β > 0), whatever the hawser angle, the direct towing is involved. However, the naming of the latter mode is more conventional than physical, since in some cases the hull hydrodynamic force has also some contribution to the effective hawser pull. The math model of Artyszuk (2014) is also fully ready to cover this interesting case. In the example of Figure 1 (a tug on port quarter of assisted ship), the indirect mode is thus encompassed by the drift β∈(−90°, 0°), while the direct mode covers β∈(0°, +90°).
Special Maritime Operations
Published in D. J. House, The Command Companion of Seamanship Techniques, 2007
Where a towing bridle is to be used a suitable size of chain to accommodate the weight and stress factors should be established together with appropriate anchor holding points. The ideal example is, of course, the strong point, used in conjunction with the tankers’ Smit bracket (see Figure 5.17). Specific ship types may be more suitably fitted to engage in towing with a chafing chain coupled to a smaller hawser chain. Such an arrangement employs the principle of a bridle system, but care must be taken to ensure that the chafing chain extends beyond the lead and the joining arrangement is as strong or stronger than the chain elements, so as not to present a weak link in the towline.
Search and Rescue Operations
Published in David House, Seamanship Techniques, 2019
Extreme caution should be used with this method after first establishing good communications. A rocket should not be propelled towards a tanker, but a tanker may project one to the rescuing vessel. Further caution with use of the rocket line should be exercised if survivors are in the water or the surface contains floating oil patches. Do not attempt any transfer until a messenger line has been passed. Once established a strong towing hawser can be passed between the two stations.
Hydrodynamic performances of FPSO and shuttle tanker during side-by-side offloading operation
Published in Ships and Offshore Structures, 2019
Xiaosen Xu, Prasanta Sahoo, Johanna Evans, Yanwu Tao
Ten hawsers (H1 … H10) are arranged for the SBS offloading system. Hawsers are made of Nylon ropes with the diameter of 110 mm. The minimum breaking load and wet weight of the hawser is 3548 kN and 0.85 kg/m, respectively. The hawser is connected to the fairlead on the bulwark. Six Yokohama pneumatic fenders (F1 … F6) are deployed between the FPSO and the shuttle tanker. When the relative distance between the FPSO and the shuttle tank is larger than the diameter of the fender, there is no reaction force. When the relative distance is smaller than the diameter of the fender, reaction force exists on both vessels. It is recommended that the deformation of the fender should not exceed 60% of its diameter. The fenders are 4.5 m in diameter and 9.0 m long, wrapped in a tire net. The rated compression is 2.70 m and the buckling load and energy absorption are 7328 and 9154 kN/m respectively. It is recommended that low friction materials are used to face fender panels which will reduce shear forces applied to the berth structure. The fender friction force on the contacting surface is given by, where is the friction coefficient, and is the normal compression reaction force. The Pneumatic Fenders is made up of UHMW-PE and the typical coefficient of friction against steel is 0.15∼0.2. Therefore, friction coefficient of 0.2 is chosen in this paper. Figure 4 shows the relationship between the reaction force and the deformation of the fender.