The interaction between ship propulsion machinery, propellers and the highly dynamic environment which is the sea is a complex yet highly relevant subject. During a storm, for example, waves and ship motions may cause the propeller to draw air, or ventilate, resulting in rapid changes in propeller thrust and load torque. These fluctuations propagate through the propulsion system, potentially causing excessive loads on propulsion machinery, while also reducing the ship's manoeuvrability. A profound understanding of these complex interactions still lacks. One result of this knowledge gap is the limited acceptance of new technologies for ship propulsion, especially those technologies known to have limited transient capabilities. In this paper, hardware in the loop (HIL) is proposed as a solution to this knowledge gap. Paying specific attention to propeller ventilation, HIL is used to identify new aspects of interaction between engine and propeller, thus demonstrating the added value of HIL for ventilation studies.@en

Simulation models of the ship propulsion system play an increasingly important role, for instance in controller design and condition monitoring. However, creation of such simulation models requires significant time and effort. In this paper, the application of deterministic identification techniques on a DC-electric ship drive train is explored as an alternative for data-driven identification techniques that require extensive measured data sets collected over long periods of ship operation. First, a nonlinear and a linear simulation model that represent the dynamic behavior of the propulsion plant are developed, and the main parameters to be identified are defined. Then, a set of experiments on a model scale boat in the bollard pull condition are conducted using an ad hoc experimental setup and data acquisition system. Subsequently, various types of identification techniques are applied, aiming to determine the unknown model parameters. Eventually, a comparison is made between experimental and simulated results, using the different sets of the estimated parameters. The value of the demonstrated approaches lies in the fast determination of unknown system parameters. These parameters can be used in simulation models, which in turn can be used for various purposes such as system controller development and tuning. Furthermore, periodic determination of system parameters can support condition monitoring to detect faults or degradation of the system. The latter point directly deals with the condition-based maintenance issue; in fact, monitoring the propulsion plant parameters over time could allow for better management (and timing) of maintenance. Although the developed ideas are far from ready to be used on the full-scale, the authors believe that the methodologies are promising enough to be developed further towards a full-scale application. @en

Standards for environmental impact, safety and operational performance of ships are becoming increasingly strict. In order to meet these standards, the performance of new ship designs must be predicted with an increasing level of detail and confidence. As present prediction methods lack realistic, dynamic behaviour of the ship's propulsion plant, there is a need for more advanced methods. In this paper, an open water test with Hardware in the Loop (HIL) functionality is proposed. HIL open water tests combine software and hardware components to emulate realistic behaviour of the ship's propulsion plant in the towing tank. It is known, however, that experiments in the towing tank are subject to viscous scale effects. In addition to this, shaft dynamics are distorted by a number of scale effects occurring inside the scale model propulsion system. In this paper, it is demonstrated with measurements that if corrections for these scale effects are applied, the dynamic interaction between the propeller and simulated engine system can be accurately emulated in the ship model basin.@en

The Dutch Ministry of Defence has the ambition to reduce its dependency on fossil fuels in order to improve the effectiveness of its operations and reduce its impact on the environment. At the same time, the diversity of current threats during maritime operations require ships that are more silent, that manoeuvre better and require less maintenance.@en

In de Operationele Energie Strategie en de Defensie Energie en Omgevings Strategie legt het ministerie van Defensie zijn ambitie vast de afhankelijkheid van fossiele brandstoffen te verminderen om zo de effectiviteit van zijn operaties te vergroten en hiermee het milieu minder te belasten. Tevens vereist de diversiteit van de huidige dreiging tijdens maritieme operaties vaartuigen die stiller varen, beter manoeuvreren en minder onderhoud vereisen.@en

In this paper, a vessel model for the performance of wind-assisted ships is combined with a routing tool to assess the fuel savings available from the installation of both one and two Flettner rotors when travelling along a Great Circle Route path. This is combined with an economic analysis to assess commercial viability for these hybrid concepts. The case study is performed in collaboration with DAMEN shipyards, who have provided a design for a wind-assist concept to sail in the Baltic Sea, that, since January 2015, is an Emission Control Area where a sulphur limit content of 0.1 % is enforced on the ship fuels. Results for this case study are presented in terms of fuel savings and payback period analysis, where the reference case is an identical ship sailing without wind propulsors. For the 5,150 dwt general cargo vessel travelling at a speed of 10 knots, average fuel savings of 2.99% were obtained in the Baltic Sea for the single Flettner scenario, and 6.11% for the double Flettner scenario. A discussion of key engineering and design constraints for these ships is included.

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Dramatic increases in the underwater acoustic signature of ships have been observed during full scale trials in a seaway, compared to calm water conditions. The observed behaviour can be explained by the interaction of waves, wake field and ship propulsion system dynamics in combination with rudder action and ship motions. This paper explores whether a propulsion control system can increase the cavitation free time when sailing a straight course in a seaway. While in the past non-linear simulation tools have been used to analyse propeller cavitation in a seaway, the original contribution of this paper is that it considers the problem from a systems and control point of view. It is shown that the objective of significantly increasing the cavitation free time while simultaneously preventing thermal overloading of the diesel engine cannot simply be met by adjusting engine speed governor settings. It is however concluded that the developed plant and disturbance model are promising tools for advanced controller development and tuning aiming to reduce underwater acoustic signature.@en

In this paper the concept of ship propulsion system “fingerprinting” is explored as an alternative for data driven models that require extensive measured datasets collected over long periods of ship operation. As a first exploratory step a model of a ship in bollard pull conditions is linearised and its transfer functions are determined. Subsequently limited experimental data, involving sinusoidal excitation of the system input at a wide range of frequencies, is used to determine the system parameters. The resulting parameter estimates compare well against previously determined values. Although the developed ideas are far from ready to be used on full scale, the authors believe that the approach is promising enough to be developed further towards full scale application.@en

Regulatory demands on ship designs, such as emission and manoeuvrability requirements, are becoming increasingly stringent, raising the need for advanced methods to predict and assess dynamic propulsion plant behaviour of a new design. At present, model scale experiments and numerical simulations are not able to predict this behaviour in full detail. To fill the resulting knowledge gap, this paper proposes to further develop existing scale model tests into so-called dynamic model basin tests. These tests aim to predict dynamic behaviour of the ship propulsion plant in complex, dynamic environments in more detail, leading to improved propulsion systems and controls and ultimately, lower emissions, lower fuel consumption and increased manoeuvrability.@en

Results of trade-off studies aiming to compare different ship power and propulsion configurations inherently contain uncertainty. This is true for both the technical part and for the financial part of the trade-off study. The technical part typically includes the system characteristics of the vessel as inputs, resulting in predicted fuel consumption and emissions at various ship speeds. Fuel consumption numbers subsequently feed into the financial part of the analysis which typically includes prices of equipment, fuel prices or fuel price scenarios, the discount factor and other aspects such as the operational profile which plays an important role in the trade-off study. Finally, financial KPI’s such as Net Present Value and payback period can be compared between different power and propulsion concepts, thereby supporting decision makers in the selection of a specific configuration or retrofit. In this paper, the effect of uncertain input parameters on both the intermediate technical output and on the financial KPI’s is demonstrated by means of a case study. The study shows that the uncertainty associated with relevant KPI’s is sufficiently large to warrant further investigation beyond accepting model predictions as completely accurate, particularly when conducting techno-economic trade-off analysis of ship power and propulsion configurations. In the broader context, consideration of uncertainty is a must for statutory and regulatory authorities in the formulation of policy.@en

Crew of small fast ships often experiences excessive vertical accelerations when sailing in waves, leading to discomfort and injuries. In an attempt to avoid this, experienced operators reduce speed voluntarily when they anticipate that the next vertical peak acceleration will be unacceptably large. However, at night and during excessive spray, the operator can hardly see the environment which makes it almost impossible to anticipate wave driven events. On top of that, this approach carries the risk of operator misjudgement due to loss of concentration or fatigue. The objective of this paper is to investigate the potential of using haptic assistance to support operators in preventing excessive vertical accelerations, by using haptic speed advice on the throttle based on experienced wave statistics. A stochastic based approach was used to construct a haptic algorithm, which gives a maximum advisable propeller speed setting based on an estimate of the current sea state. To test the effectiveness of this approach, a human-in-the-loop experiment was conducted. The effect of haptic assistance was compared to manual control under both good and reduced visibility conditions. No significant decrease in the number of excessive accelerations was achieved when comparing equal conditions in the current experiment, although subjects controlled the ship with reduced workload. The lack of significance indicates a difference in control strategy between the participants, for 16 out of 22 participants experienced less excessive accelerations when sailing shared control.@en

When human operators control complex machines, haptic feedback on the control interfaces can reduce operator errors and workload and increase situational awareness. Such benefits have been demonstrated during control of vehicles, drones, remote-controlled robots, but the maritime industry has so far largely ignored the potential of haptic feedback on the control interface of vessels. This paper aims to illustrate such potential. First, three vessel control schemes are provided to illustrate similarities and differences in: manual control, supervisory control of an autopilot, and manual control while assisted by haptic feedback. Second, the design of a maritime simulator with active control levers is described, that allows exploration of the potential of haptic feedback for ship propulsion and manoeuvring control. An actuated 2-DOF azimuth control lever was designed, that can not only command engine speed and thruster azimuth angle by providing a position input, but that can also provide haptic feedback by generating force feedback in both degrees of freedom. Two such levers were constructed and were programmed to communicate with a commercial ship simulation environment, in which a scenario of a harbour tug navigating towards the next waypoint was programmed. A haptics software module was designed to allow easy programming of various types of assistive haptic feedback: virtual hard stops, damping fields, vibrations and repulsive or attractive forces. A real-time visualisation of the operation and the relevant signals is presented on multiple computer screens. Third, this paper describes the implementation of three different types of haptic feedback to support navigation towards a waypoint: vibrations when heading errors exceed a certain boundary; repulsive forces that assist in steering away from certain boundaries; and assistive forces to guide towards a waypoint. It is concluded that the developed maritime haptic simulator allows for human-in-the-loop experiments to explore potential benefits of haptic feedback for maritime applications: we could stably and reliably implement various force feedback designs based on task-related information from the simulated environment. This work also paves the way for developing operator support systems for other, more complex tug operations, as well as support for remote control of (semi-)autonomous ships.@en

The understanding, modelling and analysis of the behaviour of a non-linear ship propulsion plant are of great importance for conceptual system design, component selection, selection of control strategy and for propulsion control system tuning. Conceptual propulsion system design activities, such as deciding the combinator curve, require a relatively simple steady state simulation model, while propulsion controller design and tuning requires a non-linear time domain simulation model which captures the intricacies of the propulsion plant. In this paper a linearised model of the uncontrolled ship propulsion system is derived which can be used for analysis of propulsion system behaviour in waves and for initial controller design and tuning. Furthermore a thorough analysis is made of the conditions under which local instability of the system can occur. In a follow up paper the linearised model is extended and verified by means of comparison with a non-linear model. There it is furthermore used to investigate the effect of engine governor settings on a propulsion plant when sailing in waves at different encounter frequencies. The authors believe that, due to its transparency and clear link to well known parameters and variables, the linearised core propulsion system model as derived in this paper should appeal to marine system engineers, control engineers and hydrodynamicists alike. The linearised model should however not be seen as the replacement for a non-linear model, but rather as an additional tool that can be used.@en

The understanding, modelling and analysis of the behaviour of a ship propulsion plant are of great importance for conceptual system design, component selection, selection of control strategy and for propulsion control system tuning. Some of these activities require a relatively simple steady state simulation model, while other activities require a non-linear time domain simulation model which captures the intricacies of the plant, its components and the related controllers. In this paper a linearised model from an earlier publication is taken as a basis for further development. First of all a diesel engine and a hydraulic pitch actuating system are added to the model. Secondly a shaft speed controller is added to the system. Subsequently the controlled propulsion system is verified by scrutinising Bode plots and step responses. After this the linearised model is used to investigate the relation between parameter settings in the engine governor and actual system behaviour in regular waves. This provides the basis for understanding the behaviour of the propulsion system in irregular waves.@en

Traditionally, model scale tests of ships are carried out without taking into account the dynamics of the shipboard systems that are involved in the operation under consideration. An example of this is the way that model scale free sailing tests in waves are carried out. The ship model is mounted with an electric motor, shaft and propeller and subsequently tests are carried out with constant propeller speed. In some cases constant shaft torque or constant power are employed. However, neither of these options reflects realistic behaviour of the drive system, because in waves and during manoeuvres the propeller speed, torque and power are in fact variable and their dynamic behaviour is governed by the drive train characteristics. The question arises to what extent, and in which cases, the dynamics of the shipboard systems affect the overall system behaviour. In this paper the application of Hardware-in-the-Loop (HIL) simulation in a ship model basin or towing tank is explored as a means to answering that question. The ambition is to develop an instrumented model scale ship of which the components of the drive train and its control are included by means of a correctly scaled time domain computer simulation model of the propulsion system. This simulation model is to run on a real-time processor which, via IO cards, provides electric power to an electric motor on-board the instrumented model scale ship, which in turn drives one or multiple shafts and propulsors. In this paper the role of scale effects on the test set-up is discussed. It is also shown that, in order to simulate realistic drive train dynamics in waves and during manoeuvres, it must be ensured that the combination of partial simulated drive train on the one hand and electric motor dynamics plus shaft and propeller inertia on the other hand should, as a total, represent the real dynamics of the drive train system.

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An important aspect for a new-built vessel is the contract speed. Not reaching the contract speed can lead to penalties for the shipbuilder and dissatisfaction for the customer, while an under-predicted contract speed can lead to non-competitive design and a lower income for the shipbuilder. The performance of a new-built vessel is uncertain due to the uncertainties that are involved in the design of the ship and its propulsion installation. Another type of uncertainty is introduced during the full scale trial measurements at which the contract speed is to be demonstrated. This paper aims at quantification of the uncertainties that are involved in the predicted performance of a ship in terms of predicted trial ship speed. This is done by systematic analysis of the propagation of uncertainty from input (design) variables up to the predicted trial speed. An 80m, 22 kts Offshore Patrol Vessel is used as a case study. The effect of uncertainty reduction by means of model testing is analysed and discussed.@en