The coupling between heel and the loads in the horizontal plane is usually neglected in manoeuvrability studies. However, the heel–sway and heel–yaw coupling can play an important role in potentially unsafe conditions, such as in a following sea. In these conditions, small fast vessels experience dynamic instabilities which threaten their ability to maintain a straight course. In this study, the coupling between the static heel and the sway force and yaw moment was investigated for a high-speed craft. The objective of this work is to understand the effect of heel on the manoeuvring in following waves, and to predict this effect by means of numerical tools for different combinations of wave characteristics and vessel speeds. A dedicated captive model test campaign was conducted to evaluate the manoeuvring loads in sway and yaw when the craft has a heel angle in following regular waves. The tests were performed in the towing tank of Delft University of Technology. The heel-induced loads depend strongly on the longitudinal position of the vessel in the wave, and they significantly differ from the heel-induced loads in calm water at the respective speed. The data carried out in the model tests were used to describe empirically the heel-induced loads for several combinations of ship speeds and wave characteristics. This empirical description was meant to correct a 3D potential flow boundary element method (BEM), with the objective of being able to predict these loads on a wide range of conditions. The corrected 3D BEM was used to simulate the behaviour of the high-speed craft in following regular waves. This analysis showed that the heel-induced loads have the effect of stabilizing the ship to the inception of dynamic instabilities in the following sea.@en

What it is Broaching-to? When it can occur? What can happen if it happens? What is known about it? How it can be investigated further? Practical ways to prevent it in design and in operation@en

Broaching-to is a highly complex, non-linear dynamic instability event that several vessels might face when sailing in the same direction of the waves, for example when returning to port during a storm. This condition is referred to as following sea. Vessels such high-speed craft but also patrol and rescue boats, fishing trawlers or small frigates are the most subjected to the severity of the sea, and therefore also the most vulnerable to the broaching. A broach occurs when the ship is captured by the incoming stern waves (surf-riding), and is turned beam-to-sea by the large wave yawing moment. This yawturning motion is so sudden and the acceleration is so high that even the most skilled mariners are not able to avoid it, losing dangerously the control of the vessel. In extreme cases, a broach can cause the capsize of the vessel. The first apparitions of the term broaching-to date back to the 18th century. Sailors have always been frightened by the potentially devastating consequences of sailingwindward, but this phenomenon has been consistently studied starting from the 1950s only. Several naval architects put in evidence the main characteristics of the physical phenomenon of the broaching-to in following sea, developed useful and accurate techniques meant to predict the behaviour of the vessel sailing in those scenarios. Although the great efforts spent in the research on this subject, there is still some uncertainty about the causes of a broaching-to event, and about the characteristics of the vessel that might lead to an unsafe behaviour in following waves. This thesis aims to investigate these aspects, with the final desirable result of providing guidelines for safer vessels to designers and shipbuilders.@en

Small high-speed craft are the most vulnerable to the severity of the sea: achieving a design which pairs good performance and acceptable levels of safety is not a trivial task. The seakeeping and manoeuvrability of these vessels play a crucial role in following sea conditions: dynamic instabilities, namely broaching-to and surf-riding, are more than a rare eventuality and threaten the survivability of the vessel and the life of the mariners. This study investigates the effects of the steering qualities on the broaching-to behaviour of a high-speed craft when it is sailing in following and stern-quartering waves. The motions and loads of the vessel are simulated by means of a 3D time domain blended potential flow boundary element method (BEM), validated using captive model tests in regular waves carried out at the Seakeeping and Manoeuvring Basin (SMB) of MARIN. The hull directional stability and turning ability of the high-speed craft were artificially modified, showing that an increase in the directional stability as well as in the effectiveness of the steering can be beneficial to avoid the inception of broaching-to, but they have different consequences on the dynamics of the vessel's loss of control.

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The manoeuvring characteristics of high speed craft are greatly influenced by the hydrodynamic loads generated by the asymmetrical underwater hull shape when the vessel heels. In order to provide an insight into this aspect of the manoeuvring of high speed craft, captive model experiments were conducted in the model towing tank at the Delft University of Technology. The experiments were divided in two main phases. In the first phase, the heel-sway, heel-yaw coupled linear coefficients and hydrodynamic heel moment were measured using static heeled model measurements over a range of speeds. The second stage of the experiments examined the influence of different running trim attitudes on the values of the manoeuvring coefficients. The results from three running trim conditions were compared.@en

In order to provide an insight into the manoeuvring of high speed crafts, an experimental study was undertaken at the towing tank of Delft University of Technology, using a rescue vessel of the Royal Netherlands Sea Rescue Institution (KNRM). @en