Among the many challenges in reference to the development of today’s ports, the accurate prediction of ship’s squat for current and future vessel types is of major significance in terms of operability and safety. Due to constantly increasing vessel dimensions, the under keel clearance has become a limiting factor for traffic on the waterway of the Elbe estuary in northern Germany in recent years. Thus, the approach to the port of Hamburg is tide dependent for many modern vessels and regulated according to a tidal transit-schedule managed by the German Federal Waterways and Shipping Administration. To ensure an optimized, economical utilisation of the Elbe waterway, a reliable and estuary-specific assessment of the ship’s dynamic response in restricted waters is crucial.
In order of the Waterways and Shipping Board Hamburg and in cooperation with the German Federal Waterways Engineering and Research Institute as well as the Hamburg University of Technology, Consulting Engineers von Lieberman implemented an extensive campaign to measure the ship’s dynamic behaviour in various boundary conditions. Between 2013 and 2016, the estuary-specific correlations between the vessels’ squat and hydrological, hydrodynamic, nautical and operational parameters (e.g. propeller revolutions) were investigated for container vessels with lengths up to 400 m and for capesize class bulker carriers. Measurements were carried out on board of the design vessel itself as well as on a research vessel, which escorted the design vessel along the pilotage area of the Elbe (approximately 120 km). The survey comprised of 21 measurement runs on seven different vessel classes characterizing the current fleet on the Elbe. For most of these classes two outbound voyages and one inbound voyage were surveyed.
Aboard the design vessel, six high-precision differential GNSS receivers were installed to record the vessels’ motions, positions, speed etc. with a frequency of 2 Hz. The devices were installed at the bow, on the wings and at the stern of the design vessel at portside and starboard side. The convoying research vessel was used to measure the local salinity (using a CTD-probe) as well as the local current velocity and direction (using a Doppler Velocity Log DVL). AIS signals were recorded to collect data on encountering and overtaking vessels. Additional information about operational parameters of the design vessel was obtained from the VDR data. Mathematical models were applied for spatial and temporal interpolation of recorded water levels from existing gauges along the Elbe to the exact position of the design vessel. The bathymetry along the vessel’s track was generated from official data sets and updated regularly with routine sounding data provided by the Federal Waterways and Shipping Administration and Hamburg Port Authority. Applying this holistic setup, an overall accuracy of the measured squat of ± 0.10 m or even better could be ensured.
The extent of the measurements, the number of considered parameters and the achieved accuracy form a unique squat data set. Based on its high resolution and its completeness it allows an unrivalled comparison between real sinkage and theoretical squat, for example calculated based on the ICORELS formula.
The recorded and processed data were subsequently used to analyse the following parameters in detail:
• Comparison of measured squat to theoretical squat according to ICORELS
• Correlation of speed through water and squat
• Correlation of under keel clearance and squat
• Correlation of river width and squat
• Effect of ship-to-ship interaction on squat
• Correlation of drift and squat.
• Correlation of change of water density and change of trim
• Effect of heel on draught
• Effect of meteorological influences on the vessel’s dynamics
Based on the results of the survey the measured squat was compared to computed squat values using the ICORELS formula that is implemented in the tidal transit schedule for the Elbe. The general applicability of this approach, which had been verified for the Elbe for smaller design vessels in an earlier field study, was confirmed to be adequate for the investigated larger vessels as well. Under certain conditions, the ICORELS formula underestimated the measured squat for container vessels with a length over all of 347 m and larger. Here, a dependency on the trim of the vessel could be observed. Additionally, new insights into locally increased squat due to encountering vessels and correlations with the bathymetry could be derived from the analysis.
The paper and the presentation describe the measurement campaign and the methodology of the data analysis including an assessment of the accuracy of the measured and computed parameters. Exemplary squat time series under various boundary conditions and single events such as increased squat due to encountering vessels will be presented. The paper and presentation will focus on the analysis of the correlation of the measured squat to the aforementioned parameters and the applicability of the ICORELS formula.