SHIP-MOORINGS

For harbours, marine terminals, floating terminals and offshore structures, optimising the mooring system is important for improving safety and minimising downtime. Moored objects are subject to external forces in the form of wind, waves, current and interaction effects from passing ships.
These forces may have various impacts, including:

• Hampering the cargo handling operations due to large motions (downtime);
• Damaging the moorings due to large loads;
• Endangering ship’s crew and terminal personnel;
• Causing discomfort for passengers of cruise-vessels and pleasure craft.

Optimising the mooring system is a cost-effective measure to reduce these negative impacts. In order to do this a thorough knowledge and efficient tools in the field of moored ship dynamics are required. Our experts have much experience in designing and testing of mooring systems. They have been involved in many mooring system designs, including more than 25 projects since 1990.

For the assessment of the downtime and the optimisation of mooring systems Alkyon has available the moored ship computer simulation program SHIP-MOORINGS. This is a tool capable of simulating the behaviour of a ship moored to fixed structures (quays, jetties) as well as floating structures (single point or spread mooring systems).

SHIP-MOORINGS models the ship response as a function of:

• Irregular waves from multiple directions, modelling includes long waves, seiches and wave drift forces;
• Wind, including gusts;
• Time-dependent current flow (including dynamic effects) and water-level fluctuations (tide);
• Water motions induced by passing ships (surface, flow, waves and propeller wash);
• Hydrostatic and hydrodynamic (added mass, damping) reaction forces;
• Non-linear characteristics of mooring lines, fenders and anchors.

The results are presented as time-plots of motions and mooring-line and fender forces. They are also analysed spectrally and statistically. The motions of the vessel may also be monitored visually on screen. The results are used to evaluate accurately, cost-effectively and in a short period of time the downtime and safe mooring conditions for a large number of design alternatives and thus facilitate the choice of an optimal design.

Special features

SHIP-MOORINGS has been designed such that it is also possible to be used for the design of a safe berth at mooring locations where the environmental conditions are harsh. Special features allowing this are:

• The forces on the ship are dependent on the actual ship’s location and orientation (commonly moored ship models assume the motions of the ship to be small and keep the relative direction of external forces constant);
• Fender forces are applied at the correct point-of-contact in the three-dimensional space (commonly this is not the case, see above);
• Forces also depend on the slowly varying ship motions themselves;
• The program produces an animation of the ship motion, which is especially important for analysing the behaviour of vessels moored to SPM-like terminals;
• The program allows for the application of special fender constructions and winch layouts

For more information on SHIP-MOORINGS please download the brochure or validation document.

© 2001Alkyon Hydraulic Consultancy & Research, The Netherlands.