Filling operation of LNG bunkering ship usually refers to the operation that the LNG bunkering ship alongside the receiving ship and transmits LNG to the receiving ship. This operation can be carried out when the receiving vessel is berthing at the wharf, anchorage, or both vessels are sailing.
Inflation during filling operation fender It usually floats on the water surface, absorbs the collision energy when berthing, and maintains an appropriate balance distance between the two ships. Inflatable fenders are better than foam fenders because they are easy to operate, lighter than other types of fenders, have a good ability to absorb the energy of berthing collision, and can always maintain a safe balance distance between two ships. The secondary inflatable fenders are usually suspended at the head and tail of the hull to prevent collision and contact between two ships during mooring and unberthing.
1. Determination of fender performance parameters
For the filling operation of LNG bunkering ship, the main parameters used in calculating the energy to be absorbed by the fender system are adjusting the displacement and berthing speed. Among them, the adjustment of displacement mainly considers the influence of additional force generated by the ship berthing.
In addition, in addition to calculating the performance parameters of the energy absorbed by the fender itself, the fender selection table can also be used. For example, OCIMF Ship to Ship Transmission Guide provides a quick fender selection table based on equivalent displacement coefficient, which varies from 1000 tons to 500000 tons.
2. Fender selection of LNG bunkering ship during bunkering operation
When selecting fenders for LNG filling operation, first consider the ship size, berthing conditions, environmental conditions and berthing speed. Based on the weather conditions, the fender configuration can be selected according to the specific weather conditions and the calculated equivalent displacement coefficient in the quick selection table. At the same time, the energy absorption performance of the selected fenders should be checked to see if they can withstand the calculated berthing collision energy, so as to confirm that the fenders have sufficient energy absorption performance. The selection process of fenders is shown in Figure 1.
In moderate and severe weather conditions, the contact speed and ship motion (especially roll and sway) are larger than those in calm weather conditions due to the influence of greater hydrodynamic force and dynamic motion between the two ships.
If the tonnage of the LNG bunkering ship is similar to that of the receiving ship, when the fully loaded LNG bunkering ship is filling LNG to the nearly fully loaded receiving ship, the impact of misjudgment of the ship and berthing is minimal, and the berthing safety depends on the operating position, ship conditions, the risk of emergencies, and the experience of the captain and mooring personnel.
The calculation of berthing energy takes into account the weather conditions, which can be divided into three cases: calm, moderate and severe. These three cases can be defined according to sea conditions and wave heights. The berthing speed when calculating the berthing energy is determined and set according to different operations and standards. See Table 2 for details. See Table 1 for the quick reference guide for the selection of OCIMF fenders during ship to ship liquefied gas transmission, which is also applicable to LNG filling operations. The equivalent displacement coefficient shall be calculated before the fender is selected according to the fender quick selection table.
3. Increase size consideration
When the fender size needs to be strengthened, it is appropriate to increase the fender diameter. It is not recommended to increase the length or increase the internal pressure from 50kPa to 80kPa. If the length or internal pressure is increased, the reaction force and the energy to be absorbed will increase, however, if the allowable compression capacity is not increased, the increase rate of the reaction force will increase. On the other hand, only by increasing the diameter of fender, the allowable compression capacity and balance distance will increase, while the increase of reaction force gradient can be ignored. Therefore, in the process of berthing and mooring, when additional energy performance or balance distance between two ships is required, it is more appropriate to increase the fender diameter.
4. Fender Selection Table Safety Factor
The fender selection table in OCIMF's Ship to Ship Transmission Guide shows that the equivalent displacement coefficient is calculated according to the berthing collision energy under different berthing conditions and weather conditions, and the corresponding fender system is recommended. Among them, the safety factor in Table 1 is 1. Due to the high risk of emergencies, the safety factor should be increased, the berthing collision energy will also be multiplied by the corresponding safety factor, and the fenders will be selected according to the corrected energy value.
