In recent years particularly, investigations of the roll behaviour, especially the roll damping of ships, has developed into a special field of hydrodynamic research. Due to high deck loading, modern container ships have low stability reserves and, in high seas, are exposed to the risk of extreme rolling motions. The development of specialised vessels and supply ships for the offshore sector is characterised by strict specifications in terms of positioning and motion stabilisation to reduce the risks of coming along side under rough conditions.

The SVA Potsdam has advanced testing methods along with the latest associated measurement methods. The SVA has offered innovative methods for improving and optimising the rolling behaviour of ships, mainly for stabiliser fins, rudders, Voith-Schneider equipment and roll damping tanks.

The SVA has a system that causes forced rolling motions of ship models with variation of rolling amplitude and frequency, with and without forward motion. By doing this, the rolling moment can be measured.

Parameterically excited rolling can be simulated with the ROLF method (nonlinear strip method), which has been integrated into the UTHLANDE program system. For a quick estimate of the risk of a ship with respect to parameterically excited oscillations, an SVA developed method is used which provides, based on fluctuations in metacentric heights, an indicator as to whether a rollover impulse is to be expected for a combination of ship speed, wave height and wavelength.

For the selection of roll damping tanks, calculation methods are available that allow both Frahm and box tanks to be analysed.

For large yachts and cruise ships in particular, stabiliser fin systems are available with corresponding geometries which damp rolling even while the vessel is stationary. The roll damping rates of these and similar systems are determined in the towing tank by applying different wave conditions to the model.

The seakeeping of ships and offshore structures is determined by model tests and numerical simulations. Model tests in a seaway are carried out in the towing tank. For this purpose, a hydraulic wave generator is available with which various wave spectra as well as regular waves and transient wave packets can be generated. Significant wave heights are possible in model scale to 0.23 m and at modal periods up to 2.5 s. For a model scale of about 1:40, wave conditions can be simulated up to gale force with about 10 m significant wave height at 18 s modal period in ship scale. To avoid unwanted wave reflections there is a beach with a natural inclination and an additional lateral wave damper to absorb diagonal waves. Sea state testing done with free-running, self-propelled models is used for detecting movements and accelerations, the shipping of water, relative motion, propeller ventilation and slamming phenomena. The effectiveness of controlled, zero speed, fin stabilisers, regarding their roll damping is tested with models having no forward motion. The determination of force coefficients is done in experiments with a tethered model.

Seakeeping tests can be carried out in countering and following seas as well as quartering seas at an angle of up to 35° off course. The latter takes the form of zigzag driving, which is recognised by the classification societies as an experimental technique. The motion behaviour of tested objects is detected with a high resolution optical tracking system. This system allows contactless measurement of the coupled motions of two-body systems in all 6 degrees of freedom as well as speed and acceleration at defined positions.

For numerical simulations of sea keeping the UTHLANDE program system is available. Based on linear and non-linear strip method, this system allows the calculation of the motions and loads of mono hull ships and catamarans for all 6 degrees of freedom. The program provides the statistical characteristics (short and long term statistics) for long and short crested seas represented in Cartesian or polar diagrams and a video animation based on a “ship motion viewer”. The process provides valuable insights by varying different sea state specific parameters in the optimisation process and serves as a valuable support of model experiments.

The manoeuvrability and transverse stability of a ship are crucial criteria for the safe operation of a vessel. Therefore, studying the manoeuvring behavior of ships is among the core tasks of the SVA Potsdam. The focus is both on the implementation of model tests as well as simulation calculations. Manoeuvring trials are realised either with free-running models in the towing tank (an evaluation is carried out via a system identification) or on open water. Any desired manoeuvres, such as turning circles, Z manoeuvre, Williamson-turn, and spiral curves, are investigated. In open waters, model sizes up to 8 m are tested. Submersibles are tested both in free running and at a SUBPMM plant. Manoeuvre testing is performed for conventional ship types and for special vessels such as fast ships (semi-planing and planing), double-ended ferries and submersibles. Manoeuvre simulations are based on both tests and calculations. Among other things, the SVA developed software environment, UTHLANDE, can be used to simulate the manoeuvrability of ships in a seaway. This is the given approach particularly in the design stage, if different variants are to be compared.

Depending on the task, the customer receives, as a result of the criteria for the IMO standard for Ship Manoeuvrability (IMO Resolution MSC. 137 (76)), statements about the yaw stability, the loss of speed, spiral curves, etc.

Full-scale measurements are performed with our own team and recording system (DGPS). In addition to determining the manoeuvring behaviour of full-scale and measured miles trials, the SVA Potsdam executes, performance, vibration and noise measurements, and cavitation observations.

For a good propeller design it is necessary to have detailed knowledge of the nominal wake field and also the velocity distribution in the propeller plane. For experimental determination of wake fields, 5-hole ball probes, LDA or PIV (“Particle Image Velocimetry”), are used. It is standard that a 5-hole ball probe is used, offering the following options:

• Measurements in the propeller plane
• Measurements at the point of appendages, ie. the shaft struts
• With the probe, any coordinates can be approached
• 3-Dimensional wake field measurement

The standard measurement of a wake field for single screw vessels is carried out on 6 radii respectively, every 5 °. For measurements behind podded drives and shaft struts among others, the resolution is adjusted accordingly.

In addition to the experimental determination of the wake field, a calculation based on CFD simulation is possible. An advantage of a CFD simulation is the calculation of the velocity field for the Reynolds number of the full-size version.

The SVA Potsdam examines and optimises planing and semi-planing hulls with regards to their dynamic riding characteristics in displacement and planing modes. This includes, among other things, investigations concerning constructive measures which encourage early and stable “planing” and ensure a stable trim while on plane. In all considerations, low power consumption, stability and seaworthiness are the focus of investigations. Dynamic performance of speedboats can be studied both experimentally and numerically. Doing this, optimum solutions can be found through specific modifications and adjustments to the model. The range of services provided by the SVA regarding planing includes following study focuses:

• Resistance and propulsion tests
• Finding an optimal interceptor settingg
• Optimal center of gravity
• Optimal stern wedges or planing flaps
• Design and testing of the spray rails
• Manoeuvring tests in the field
• Testing of lifting strakes

The typical Offshore Support Vessel (OSV) is a twin-screw vessel. When the bollard pull is the most important operating parameter, the OSV is mostly equipped with controllable pitch propellers in nozzles. When manoeuvering and DP capabilities determine the design of the OSV, thruster and Voith Schneider Propellers (VSP) are used. The Voith Schneider Propeller can also be used for roll stabilisation and offers the optimum DP control of the vessel. Moreover OSVs are equipped in some cases with roll damping tanks. By these means, the OSV becomes a stable working platform in a stormy sea.

Within the framework of various research projects and industrial contracts [1], [2], [3] an extensive investigation of such ship propulsion, with VSPs or with thrusters, were performed. Thus the SVA Potsdam can offer options from a wealth of experience, for example regarding influence of the blade geometry or installation conditions. In addition to resistance and propulsion analysis, manoeuverability and seakeeping investigations for these vessels can be carried out at SVA Potsdam [4], [5].