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n expected need for expeditionary operations in the future involving ship-shore and shore-ship connec-


tions of materiel and personnel has led to the operational concept of Sea Basing. Amphibious operations and employment of materiel is set to become more and more critical in proving the concept and assessing the overall mission effectiveness.


The ship design of a LPD and the assessment of its overall operational performance is characterised as highly complex, given the amphibious operations performed by Land- ing Craft Utilities (LCUs) and Landing Craft Vehicle and Personnel (LCVPs). These organic units embark/disembark the well dock usu- ally located in the aft of the ship when it is fully submerged and trimmed by the stern. The craft are used to bring equipment and personnel ashore and vice versa.


Sea Basing A typical major requirement for a LPD is that embarking/disembarking operations should be feasible for sea con- ditions up to and including, sea state 4 (significant wave height of up to 2.5 m). A long crested swell especially, has a limit- ing effect on the manoeuvring capability of the LPD. Moreover, the LPD and LCU often experience multiple wave systems, which can easily generate extreme water motions inside the well dock. This can happen whether the stern ramp is (partly) opened or closed. A forward speed of the LPD and a change of wave heading make the associated hydromechanics even more complex.


Since LPDs are of vital importance in the concept of Sea Basing, there is an increasing need for an accurate but efficient assessment of the ship operations. Given that operational performance requirements have changed gradually with time, the original manoeu- vring limitations needed to be adjusted accordingly. Acknowledging some of the substantial inadequacies (with respect to the associated hydromechanics) of model tests and simplified calculation models, the Dutch Defence Materiel Organisation (DMO) decided to conduct an extensive series of docking trials in order to establish a suffi- ciently accurate Safe Operating Envelope (SOE). Furthermore, the recorded data would assist DMO and MARIN in their attempt to


verify and validate contemporary calculation models and future simulation capabilities.


Extensive docking trials MARIN de- veloped the trial program in conjunction with DMO, and the crew members of the LPD2 Hr.Ms. Johan de Witt and a LCU. For all different modes of LCU operations the most critical parameters were identified. The docking trials focused, amongst other things, on the following: - Water motions inside the well dock, with special attention to sloshing and possible water build-up on the car deck.


- Water motions between the wing tanks at the entrance of the well dock.


- Lift generated by the stern ramp causing the LPD to trim by the bow, resulting in decreased water depth at the entrance of the well dock.


- Vibrations of the stern ramp and hydraulic pressures inside the closure system of the stern ramp.


Given the relatively short measurement time of one week, the measurement set-up was rather extensive. The following parameters were captured: wave condition, wind, current, ship speed, ship course, ship motions, water motions inside the well dock and accelerations of the stern ramp. Moreover, the on-board platform management system was also log- ging ship related parameters. A high-defini- tion, synchronised video system of four cameras was installed to be able to compare the visual information with the measured parameters. A qualitative assessment of the feasibility of LCU operations was made by two experienced crew-members (boats’ man and LCU driver) during the trial. MARIN decided to synchronise and analyse all data directly onboard. This approach proved to be very effective because it saved on the required analysis time afterwards.


Based on the series of docking trials, DMO and MARIN successfully established an ac- curate Safe Operating Envelope concerning the LPD2. This could only be accomplished by recording the relevant ship parameters, including the visual information and qualitative assessment of the feasibility of LCU operations. As a result, MARIN has been invited to perform similar docking trials onboard the LPD1 Hr.Ms. Rotterdam.


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