Effects of a muddy bottom on the straight-line stability

In the period 2001-2004 an extensive experimental research program has been carried out which enabled the development of a mathematical model for ships manoeuvring in various muddy bottom conditions. Real-time simulation runs based on this mathematical model resulted into a redefinition of the nautical bottom concept of the harbour of Zeebrugge. This paper introduces a new mathematical ship manoeuvring model taking the characteristics of the mud layer into account. The developments for the hull related forces are discussed and applied to the calculation of the straight-line stability criterion

Development of a test program for the prediction of ship manoeuvrability in deep and shallow water

As in many coastal and estuary areas, navigation to and in the Belgian harbours takes place in environmental and operational conditions which differ from the design conditions of sea-going ships: water depth to draft ratios vary between 2.0 and 1.1 which means that the under keel clearance is often restricted to 10% of the ship’s draft. In addition, low ship velocities have to be considered as manoeuvring in harbour areas is characterised by a wide range of speed - propeller rpm combinations. Based on the results of captive model tests executed in the Towing Tank for Manoeuvres in Shallow Water (co-operation Flanders Hydraulics Research - Ghent University, Antwerp, Belgium) with a 6000 TEU containership and the tanker Esso Osaka, an optimized test program has been developed for the determination of a mathematical manoeuvring model in later-ally unrestricted water. Contrary to deep water and service speed the selected test types and test parameters will influence the measured contributions of the modules hull, propeller and rudder in shallow water: as an example, stationary oblique towing and harmonic sway tests may lead to dif-ferent results, while the reliability of the test results is much more sensitive to the selected test pa-rameters during PMM tests. Due to the reduced under keel clearance even unusual phenomena may occur

Prediction of load on mooring ropes of a container ship due to the forces induced by a passing bulk carrier

The hydrodynamic surge and sway forces and yaw moment on a moored ship induced by a anothership moving near and parallel to it are estimated. The results are compared with the values obtained byexperiments carried out in the Towing tank for manoeuvres in shallow water (co-operation Flanders Hydraulics -Ghent University) in Antwerp. Subsequently, equations of motion of the moored ship are solved to determine theloads on the mooring ropes. The effect of underwater form of the ships on the forces is also discussed

Ship-bank interaction induced by irregular bank geometries

The forces and moments induced by the vicinity of banks on a sailing vessel are known as bank effects.An extensive set of model tests have been carried out in a towing tank to investigate bank effects inducedby irregular bank geometries. Tests along sloped surface-piercing as well as submerged banks are carriedout. A mathematical model (for the longitudinal force, sway force, yaw moment and sinkage) found onthese tests is formulated. This model copes with the geometry of the banks tested and not tested bankgeometries. This paper emphasises on the mathematical model and on two parameters of thismathematical model: The distance between ship and bank d2b and the equivalent blockage meq such that the properties of an irregular bank geometry are taken into account

On sinkage and trim of vessels navigating above a mud layer

This article presents a theoretical extension of a semi-empirical method for the determination of squat of ships in shallow water, based on a one-dimensional theory in which the solid bottom is replaced by a higher density fluid layer. It can be shown that, for the evaluation of the effect of the mud layer, a distinction has to be made between three ranges of the ship's speed, separated by two critical values. The first critical value is approximately equal to the maximum velocity of propagation of internal waves at the interface, while the second critical value depends on the blockage factor and on the lower fluid density.Numerical results of theoretical calculations are compared with experimental data obtained in tests carried out at the Hydraulic Research Laboratory in Antwerp-Borgerhout with self-propelled ship models in restricted waters above a solid bottom and above a simulated mud layer

An overview of squat measurements for container ships in restricted water

Squat is an important issue for ships navigating with limited under keel clearance in restricted waterways such aschannels and canals. The admittance policy for containerships on the Western Scheldt, a tidal estuary in theNetherlands giving access to the port of Antwerp (Belgium), is based on a minimal static under keel clearance toensure safe passages on the river. A large number of captive model tests executed in the Towing Tank forManoeuvres in Shallow Water (co-operation Flanders Hydraulics Research - Ghent University) have beenevaluated to determine squat prediction formulae. Measured sinkage and trim depend on a number of parameterslike ship velocity components, ship loading condition, propeller action, blockage of the waterway, bankgeometries and characteristics of other shipping traffic. The derived mathematical models have beenimplemented in the ship manoeuvring simulators of FHR to visualize the dynamic under keel clearance duringreal-time simulations at different locations on the Western Scheldt

A novel methodology for revision of the nautical bottom

Since the 1980s, the nautical bottom in the outer harbour of Zeebrugge is determined by the 1150kg.m-3 density level, as due to siltation conventional bottom survey techniques are not adequate. As a consequence of modifications of the mud layer characteristics, a revision of this criterion was required. A research project, involving comprehensive captive model testing in a manoeuvring tank with a bottom covered with mud simulating materials, mathematical modelling and real-time full mission bridge simulator runs, resulted in new criteria, based on the ship behaviour and controllability in muddy navigation areas. The application of the results of this research project increases the efficiency of maintenance dredging works and contributes to the safety of shipping traffic, as the pilots involved in the manoeuvres obtain a more profound insight into specific aspects of ship behaviour

Validation of ship manoeuvring in shallow water through free-running tests

The shallow water effect on ship manoeuvring cannot be neglected. Most sea-going ships become more course stable when they sail from deep to (very) shallow water. International collaborations such as SIMMAN intend to grade up the knowledge on ship manoeuvring prediction through model tests and system based and numerical methods. Free-running model tests executed with the very large crude carrier KVLCC2 at two laboratories have been compared with the results of simulated turning circles and zigzag manoeuvres from two different mathematical models.It was concluded that the type of mathematical model has an important influence on the simulated behaviour. Moreover, further research is necessary as simulations result into a more course stable behaviour compared to free-running tests at model scale

Paper 99: design guidelines versus practices for the Upper Seascheldt, the inland waterway connection between Antwerp and Ghent

Design guidelines for inland waterways are so far a national matter. PIANC InCom Working Group 141 "Design Guidelines for Inland Waterways" is nevertheless working on a report with a summary of existing guidelines and a methodology for the concept and detailed design of canals and rivers. For tidal rivers the design is a difficult process and an example is given through the accessibility of the Upper-Seascheldt for CEMT class IV and Va inland vessels between the port of Antwerp and the locks in Merelbeke. A combined evaluation based on concept design guidelines for canals, practices measured during a full-scale voyage and detailed design using ship handling simulators is discussed and illustrated