Impacts of rudder configurations on inland vessel manoeuvrability

Ship manoeuvrability is fundamental for the navigation safety of ships. Furthermore, through the equipment used for manoeuvring, it also affects investment, operation, and maintenance cost of these ships. Ships are primarily designed from an economic point of view. To ensure and improve the maritime efficiency, research on inland vessel manoeuvrability deserves more attention than the present situation. Most of the research on manoeuvrability has been performed for seagoing ships. Since sailing conditions and ship particulars between seagoing ships and inland vessels are different, the impacts of these differences on manoeuvring prediction and evaluation should be carefully considered.

Inland vessels should be designed in such a way that they should always be capable of manoeuvring without significantly harming the cost-effectiveness of operations. One of the biggest differences between seagoing ships and inland vessels is the rudder configuration. Conventionally, seagoing ships have similar single-rudder configurations while inland vessels have more complex multiple-rudder configurations. Although multiple-rudder configurations can have a positive effect on manoeuvrability, they often have a negative effect on resistance and, therefore, also a negative effect on the fuel consumption.

Quantitative impacts of the rudder configuration on ship manoeuvrability have not been fully understood, especially for multiple-rudder configurations with complex rudder profiles. These differences in the rudder configuration may significantly change the ship manoeuvring behaviours and, therefore, should require further research. Moreover, to compare and evaluate the manoeuvring performance of inland vessels with different configurations, the existing manoeuvring tests and standards for inland vessels are less elaborate than those for seagoing ships. The above-mentioned considerations formulate the following main research question: What are the proper rudder configurations to achieve well manoeuvrable inland vessels without significant loss of navigation efficiency?

The main research question of this thesis can be answered through resolving four key research questions as follows:

Q1. What are the practical manoeuvres to evaluate and compare the manoeuvring performance of inland vessels?
Q2. How does the rudder configuration affect the rudder hydrodynamic characteristics?
Q3. How do changes in the rudder configuration affect the ship manoeuvrability in specific manoeuvres?
Q4. How to choose a proper rudder configuration according to the required manoeuvring performance?

An accurate estimation of rudder forces and moments is needed to quantify the impacts of the rudder configurations on ship manoeuvring performance. This thesis applied Reynolds-Averaged Navier-Stokes (RANS) simulations to obtain rudder hydrodynamic characteristics and integrated the RANS results into manoeuvring models. Additionally, new manoeuvres and criteria have been proposed for prediction and evaluation of inland vessel manoeuvrability. Simulations of ships with various rudder configurations were conducted to analyse the impacts of rudder configurations on ship manoeuvrability in different classic and proposed test manoeuvres. Accordingly, guidance on rudders for inland vessel manoeuvrability has been summarised for practical engineers to make proper design choices.

Through the research presented in this thesis, it is clear that different rudder configurations have different hydrodynamic characteristics, which are influenced by the profile, the parameters, and the type of a specific configuration. New regression formulas have been proposed for naval architects to quickly estimate the rudder induced forces and moments in manoeuvring. Furthermore, an integrated manoeuvring model has been proposed and validated for both seagoing ships and inland vessels. Using the proposed regression formulas and manoeuvring model, the impacts of rudder configurations on inland vessel manoeuvrability have been studied.

The manoeuvring performance of a typical inland vessel can be improved by 5% to 30% by changing the rudder configuration. The rudder configuration should be capable of providing sufficient manoeuvring forces and then optimised to reduce the rudder induced resistance. In general, well-streamlined profiles are good for efficiency but not as good as high-lift profiles for effectiveness. As a summary, the ship manoeuvring performance can be improved by using effective profiles, enlarging the total rudder area, accelerating the rudder inflow velocity, increasing the effective rudder aspect ratios, and enlarging the spacing among multiple rudders.