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Berthing Velocity

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berthing velocity
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  whereDT: displacement tonnage (amount of water, in tons, displaced by the vessel when fully loaded)GT: gross tonnageDWT: deadweight tonnage(3) The softness factor represents the ratio of the remaining amount of the berthing energy after energyabsorption due to deformation of the shell plating of the vessel to the initial berthing energy. It is generallyassumed that no energy is absorbed in this way and so the value of is often given as 1.0.(4) When a vessel berths, the mass of water between the vessel and the mooring facilities resists to move out andacts just as if a cushion is placed in this space. The energy that must be absorbed by the fenders is thus reduced.This effect is considered when determining the berth configuration factor . It is thought that the effectdepends on things like the berthing angle, the shape of the vessel  s shell plating, the under-keel clearance, andthe berthing velocity, but little research has been carried out to determine it.[2] Berthing VelocityThe berthing velocity of a vessel shall be determined based on the measurement in situ or past data ofsimilar measurements, considering the type of the target vessel, the extent to which the vessel is loaded, theposition and structure of the mooring facilities, weather and oceanographic conditions, and the availabilityor absence of tugboats and their sizes.[Technical Notes](1) Observing the way in which large cargo ships and large oil tankers make berthing, one notices that such vesselscome to a temporary standstill, lined up parallel to the quaywall at a certain distance away from it. They are thengently pushed by several tugboats until they come into contact with the quay. When there is a strong windblowing toward the quay, such vessels may berth while actually being pulled outwards by the tugboats. Whensuch a berthing method is adopted, it is common to set the berthing velocity to 10 ~ 15 cm/s based on past designexamples.(2) Special vessels such as ferries, roll-on/roll-off vessels, and small cargo ships berth under their own powerwithout assistance of tugboats. If there is a ramp at the bow or stern of such a vessel, the vessel may line upperpendicular to the quay. In these cases, a berthing method different from that for larger vessels described in (1)may be used. It is thus necessary to determine berthing velocities carefully based on actualy measured values,paying attention to the type of berthing method employed by the target vessel.(3) Figure T- 2.2.1 shows the relationship between the vessel handling conditions and berthing velocity by vesselsize 4); it has been prepared based on the data collected through experience. This figure shows that the larger thevessel, the lower the berthing velocity becomes; moreover, the berthing velocity must be set high if the mooringfacilities is not sheltered by breakwaters etc.(4) According to the results of surveys on berthing velocity 5),6), the berthing velocity is usually less than 10 cm/s forgeneral cargo ships, but there are a few cases where it is over 10 cm/s (see Fig. T- 2.2.2). The berthing velocity  only occasionally exceeds 10 cm/s for large oil tankers that use offshore terminals (see Fig. T- 2.2.3). Even forferries which berth under their own power, the majority berth at the velocity of less than 10 cm/s. Nevertheless,there are a few cases in which the berthing velocity is over 15 cm/s and so due care must be taken whendesigning ferry quays (see Fig. T- 2.2.4). It was also clear from the above-mentioned survey results that thedegree to which a vessel is loaded up has a considerable influence on the berthing velocity. In other words, if avessel is fully loaded, meaning that the under-keel clearance is small, then the berthing velocity tends to belower, whereas if it is lightly loaded, meaning that the under-keel clearance is large, then the berthing velocitytends to be higher.
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