The propulsion systems of Ro-Ro and Ro-Pax are getting closer to the soil of the docks generating erosion and stability problems to harbor’s structures due to the increase in ship and propulsion systems dimensions. Moreover, Ro-Ro and Ro-Pax vessels, which serve regular services, have high docking frequencies. The most significant effect from propeller induced current can be found during maneuvering situation in restricted waters due to the magnification caused by harbor structures. Therefore, larger vessels, more powerful propulsion systems along with higher frequencies can cause severe damages both to docking structures and basin maneuverability. The aim of this contribution is to design new maneuvers of a regular maritime service to minimize their effects on erosion and sedimentation and avoid adverse impacts resulting from ship maneuvering.
This paper describes the results of scouring processes caused by maneuvers of a particular Ro-Pax vessel without the help of a tugboat. The erosion action is studied based on Automatic Identification System (AIS) data. The AIS is an automatic tracking system for identification and location of vessels by exchanging data via VHF communication to other nearby vessels. The AIS information received contains mainly, time, latitude and longitude, ship speed and ship course (IMO, 2003). The use of AIS data permits to understand the effect of changes to the fairway and vessel maneuvering. However, AIS data alone are not enough. AIS data are combined with Acoustic Dopper Current Profiler data obtained during April 2017 at a fixed dock close to the docking area. The parameters extracted from AIS data are used as input to a real-time full mission bridge simulator to mimic the behavior of the real situation (Aarsæther, 2007). From the simulation of specific maneuvers, main parameters of the propellers are obtained (thrust power, speed propeller and pitch/diameter ratio propeller). Considering these parameters and the existing formulae in maritime engineering proposed by PIANC (2015) and R.O.M 2.1-11 (2012), the efflux velocities, the axial velocities along the propeller and the maximum bed velocities are calculated. The potential scouring effects of the particular ship’s propellers in the present conditions (weather, harbor and manoeuver) are obtained using the formulae proposed by Hamill (1988) and Hamill et al., (1999). Propeller-generated current velocity measures obtained during the campaign has been useful to consider the duration of the scouring forcing in both arrival and departure maneuvers, but not its magnitude. We can conclude that the used method, based on the study of a particular case starting from the reproduction of the maneuver, becomes adequate to establish the relation between the scouring forcing and its generator, which is the ship’s maneuver near the docking. However, field campaign data should be recorded in different positions of the docking area.
The present article further analyses maneuver patterns to understand the effects of the sedimentation of the eroded sediment using real-time full mission bridge simulator. The final acceptation of the best maneuvering behavior is chosen according to criteria of acceptable reduction of the effect in harbor basins. Authors propose alternative docking and undocking maneuvers with the same ship and in the same navigation area in order to reduce the effect of the toe scouring induced by vessel propeller. Docking and undocking maneuvers assessed are: alternative berthing without tugs (controlling the speed of the main engine), berthing with one tug assistance and finally, maneuvers with the assistance received from two tugs (without ship propulsion system). Results obtained show less sediment erosion close to toe of the docks and less stability problems to the docking platforms with the proposed tug-assistance maneuvers.
Acknowledgment
This research has been supported by MINECO (Ministerio de Economía y Competitividad) and FEDER (Unión Europea- FondoEuropeo de Desarrollo Regional "Una Manera de hacer Europa") from Spanish Government through project BIA2012-38676-C03-01 and TRA2015-70473-R.
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