Sensitivity analysis is applied to ship manoeuvring mathematical models as a means of dealing with model uncertainties, and often leads to model simplifications. A rather standard 3DOF manoeuvring model was tuned with the available results of full-scale trials of a naval combatant and was further used as the reference model for sensitivity analysis. The present research was based on multiple perturbed simulations of the turning, zigzag and spiral manoeuvres. A salient feature of the present study is that the perturbations were applied to the total hydrodynamic forces and moments as well as separately to their characteristic parts, i.e., to the linear and nonlinear single-variable and coupled components. Another special feature is that the deviations of the perturbated responses were estimated not only considering the standard manoeuvring performance indices, but also through application of the Euclidean metric directly to the time histories and to the spiral curve. The performed analysis permitted the sensitivity of the model to be traced to various parameters and groups thereof. It was established that the highest sensitivity of the model was to linear and some nonlinear multivariable parameters, and the Euclidean metric permitted a more detailed analysis than that based only on standard discrete manoeuvring indices. The obtained results are expected to be useful in the application of system identification methods to typical inherently stable fast surface-displacement ships.

This paper explores the impact of sampling rates during sea trials on the estimation of hydrodynamic parameters in a nonlinear manoeuvring model. Sea trials were carried out using an offshore patrol vessel and test data were collected. A nonlinear manoeuvring model is introduced to characterise the ship’s manoeuvring motion, and the truncated least squares support vector machine is employed to estimate nondimensional hydrodynamic coefficients and their corresponding uncertainties using the 25°–25° zigzag test. To assess the influence of the sampling rates, the training set is resampled offline with 14 sampling rates, ranging from 0.2 Hz to 5 Hz, encompassing a rate 10 times the highest frequency component of the signal of interest. The results show that the higher sampling rate can significantly diminish the parameter uncertainty. To obtain a robust estimation of linear and nonlinear hydrodynamic coefficients, the sampling rate should be higher than 10 times the highest frequency component of the signal of interest, and 3–5 Hz is recommended for the case in this paper. The validation is also carried out, which indicates that the proposed truncated least square support vector machine can provide a robust parameter estimation.

The biggest challenge of the aerated fluid drilling technology development was overcome with the well in Albacora being drilled with the semi-submersible platform Petrobras 17 (P-17). A previous paper 1 described the stages before the drill

The reduction of response motion experienced by monohull marine structures through energy dissipation performed by passive stabilisers such as bilge keels is an inexpensive system, when compared to the active motion reduction systems such as active stabilisers or active stabilising fluid tanks. This is the main reason why, despite the obvious advances in motion reduction and control, bilge keels are still designed, produced and fitted to the most recent ships and other marine structures produced. The design philosophy of passive roll stabilisers such as bilge keels has been, and still is, often based on empirical or design codes that define a standard structural arrangement, which is then sized in accordance with the specific characteristics of the vessel. This paper discusses the main internal structural arrangement configurations which may be adopted for bilge keel design, highlights the critical details which particular attention has to be paid to, presents the main steps involved in the sizing of the structural elements, and evaluates the more advantageous configurations with respect to performance vs. production cost. In what respects internal arrangement, the widest possible range of possibilities is considered, from the simple and fairly inefficient flat bar configuration, to the highly complex high performance diaphragm based designs. The advantages, disadvantages, estimated design and production efforts are presented and discussed. This work aims at providing a comprehensive review and a systematisation of the design principles applied for these structural components, envisaging to providing a simple and effective guide for the global and detailed design of their structures. Conclusions and further research work are drawn regarding the results obtained and the best solutions proposed.