Estimating the impact of new-generation antifoulings on ship performance: the presence of slime

Due to the phase-out of TBT-SPCs imposed by the International Maritime Organization, new-generation antifoulings are set to replace 80% of the existing antifouling market. Two types of coatings are claimed to offer satisfactory performance over five years: tin-free SPCs and foul-release coatings, which were both commercially introduced in the mid 1990s. This paper gives an overview of the research at the University of Newcastle upon Tyne which compares the drag, boundary-layer and roughness characteristics of both coatings when newly applied. It was found that foul-release coatings offer less drag than tin-free SPC, by an amount which depends on the quality of application and which has been related to the respective differences in roughness characteristics. Assessments have shown that foul-release surfaces are very effective against macrofouling organisms, but that the surface is covered by slime films when the vessel returns to dry-dock. A literature review on the effect of slime films on ship resistance shows that slime films have a significant effect on drag, but in turbulent flows the effect is likely to remain limited because of detachment processes. Further research is underway to investigate this

Numerical study on hydrodynamics of ships with forward speed based on nonlinear steady wave

In this paper, an improved potential flow model is proposed for the hydrodynamic analysis of ships advancing in waves. A desingularized Rankine panel method, which has been improved with the added effect of nonlinear steady wave-making (NSWM) flow in frequency domain, is employed for 3D diffraction and radiation problems. Non-uniform rational B-splines (NURBS) are used to describe the body and free surfaces. The NSWM potential is computed by linear superposition of the first-order and second-order steady wave-making potentials which are determined by solving the corresponding boundary value problems (BVPs). The so-called mj terms in the body boundary condition of the radiation problem are evaluated with nonlinear steady flow. The free surface boundary conditions in the diffraction and radiation problems are also derived by considering nonlinear steady flow. To verify the improved model and the numerical method adopted in the present study, the nonlinear wave-making problem of a submerged moving sphere is first studied, and the computed results are compared with the analytical results of linear steady flow. Subsequently, the diffraction and radiation problems of a submerged moving sphere and a modified Wigley hull are solved. The numerical results of the wave exciting forces, added masses, and damping coefficients are compared with those obtained by using Neumann–Kelvin (NK) flow and double-body (DB) flow. A comparison of the results indicates that the improved model using the NSWM flow can generally give results in better agreement with the test data and other published results than those by using NK and DB flows, especially for the hydrodynamic coefficients in relatively low frequency ranges

The effect of a foul release coating on propeller performance

With the imminent ban on the application of coatings of TBT self-polishing co-polymers in January 2003 and their eventual prohibition in 2008 a great deal of research is being conducted into the performance of the possible alternatives. As part of the ongoing work investigating the hydrodynamic performance of foul release systems, being carried out at the University of Newcastle upon Tyne, a study into the possible benefits of their use on propellers has been conducted. The benefits that this method of propeller protection offers are potential fuel savings from increased propulsive efficiency as well as lower maintenance costs and a cleaner environment. Initially a literature review exploring the effect of propeller surface conditions on ship performance and previous work on propeller coatings for merchant ships was conducted. Theoretical calculations on the possible gains were then explored for a merchant ship propeller type using a propeller lifting surface analysis program. These showed that the significant losses in efficiency caused by blade roughening can be avoided by the application of a foul release coating with a surface finish equivalent to a new or well polished propeller

A comparison of experimental and numerical behaviour characteristics of a ship entering a lock using benchmark test data

This paper discusses several papers that were presented at the 3rd International Conference on Ship Manoeuvring in Shallow and Confined Water, which had a non-exclusive focus on Ship Behaviour in Locks. For this conference, experimental model test data obtained at Flanders Hydraulics Research had been made public and researchers were encouraged to compare numerical with experimental results [1]. Data of benchmark tests carried out both with self-propelled and captive models were used by researchers for comparison with various numerical tools. The objective of this paper is to give a selected overview of how accurately numerical tools are presently able to predict the hydrodynamic forces that occur on ships approaching locks. Based on this, the paper concludes that experiments and numerical tools complement each other