Mooring facilities in Ports are in general planned several years or even decades ago focusing on smaller ships compared to ship sizes seen today. Ship size has increased considerably in the last and recent years. We are now facing ship length >400m. Thus, formerly planned mooring facilities were often not designed for these kind of Post Panamax ship sizes. The existing international guidelines (PIANC, OCIMF) or local guidelines (EAU, Germany) did not include the latest ship sizes and therefore lead to widely overestimated mooring facilities.
To assess the real capabilities of existing or new planned mooring facilities on piers and in harbours, dynamic mooring simulation can be made. Such methods will in general lead to more realistic loads and help determining the priority for updating the infrastructure. Such analyses can further be used to expand lifetime of existing mooring facilities.
DHI has developed a new software to calculate dynamic mooring forces (MIKE 21 Mooring Analysis (MA), DHI, 2017). Compared to other dynamic mooring analyses software, two-dimensional flow fields (incl. infra gravity seiching waves) can be incorporated, which can be of evidence in ports. It was already applied in several ports in Germany. 3 examples will be given to prove the savings and advances of dynamic mooring force calculations.
The existing coal pier “Niedersachsenbrücke” in Wilhelmshaven, Germany, is currently used on the sea side for Post Panmax Bulk Carriers. Additional, Feeder Bulk Carries should use the land side. The construction was build centuries ago and the design ship was clearly smaller than an actual Bulker. Re-assessments of the mooring forces (Albrecht, 2011) took static design loads (wind, current) into account. It turned out, that the static forces on both sides of the Pier can take values close to the maximum static load of the whole pier. Additional dynamic loads have even not been considered. This is particularly critical in the light of future requirements, for with two large Bulk Carriers are to be hosted simultaneously at the pier. To get a comprehensive and more realistic overview of mooring forces to expect, dynamic mooring force calculations combined with wind and currents (from measurements) and passing ships (from a hydrodynamic simulation) were carried out. It could be confirmed, that minor changes in the mooring arrangements would be sufficient to fulfil the future requirements without exceeding the structural maximum loads at the pier. No further reinforcements of the structure are needed.
Hamburg Port Authority (HPA) is planning to enforce mooring facilities along the Elbe at the port entrance to mainly host Ultra Large Container Vessels (ULCVs) while waiting for a suitable berth inside the port. The existing facilities are detached from the river bank and located near the fairway. They are designed for the former Panmax size ships. Using static standard guidelines, like the EAU (Germany), would lead to large groups of piles to host the mooring facilities. Since these berths are mainly used by Ultra Large Container Vessels (ULCVs) wind and currents play an important role. Additionally passing ships have an additional impact. The Hamburg Port Authority decided to use the dynamic mooring force tool from DHI to assess the operational limits of the existing mooring facilities in order to prevent any damage to the existing infrastructure. Additionally dedicated piles were set to cover some critical situations identified by the dynamic mooring simulations. A general renewal based on static load assumptions could be avoided.
A third and very demanding example for dynamic mooring force calculations to improve facilities can be found in Bremerhaven. To manifest its leading position as one of the main ports for the Offshore Wind industry, Bremerhaven decided to support this industry with an improved infrastructural connection. A new terminal located in the “Blexer Bogen” of the Weser river was planned for shipment of offshore components. At the “Blexer Bogen” large Bulker are passing this planned terminal in short distance. Therefore interplay of ship traffic and mooring forces of ships with special size and forms will occur. The main objective of this study was about to prove that drawdown generated by passing vessels does not endanger the applied mooring systems. DHI’s mooring assessment tool in combination with the hydrodynamic module were used to analyse the mooring forces for special offshore installation vessels. Different passing vessels were modelled using the standard 2D hydrodynamic model MIKE 21. The resulting ship waves were compared to in situ measurements to proof the reliability of the model result. As a second step these first order ship waves (draw down) and its corresponding current speeds were coupled to the mooring analysis software in the vicinity of the terminal area. The tool includes the ship geometry of special installation vessels affected by the induced drawdown and calculates the mooring forces due to the relative movements of the floating ship hull. Finally it could be shown, that in general the planned mooring can withstand the forces due to ship traffic (draw down). Only special cases need additional moorings using e.g. shore tension systems.
In all cases the dynamic mooring assessment tool showed good results and finally lead to savings in the design processes. Ship to ship interactions can be dynamically resolved and show more realistic results compared to static approaches.
Literature:
DHI (2017): “MIKE 21 Maritime Frequency Response Calculator and Mooring Analysis-Scientific Documentation”, http://manuals.mikepoweredbydhi.help/2017/Coast_and_Sea/M21Maritime_Scientific_Doc.pdf, Hørsholm, Denmark.Permanent International Association of Navigation Congresses (PIANC, 1995) "Criteria for Movements of Moored Ships in Harbours" PIANC, Brussels, Belgium
OCIMF publication (1992) "Mooring Equipment guidelines", Oil Companies International Marine Forum
EAU Empfehlungen des Arbeitsauschusses Ufereinfassungen Häfen und Wasserstraßen, November 2012, Verlag Ernst & Sohn, Germany