B. Thomas

Wear and Friction Modeling on Lifeboat Launch Systems

The Royal National Lifeboat Institution (RNLI) provides search and rescue cover along the UK and RoI coast using a variety of lifeboats and launch techniques. In locations where there is no natural harbor it is necessary to use a slipway to launch the lifeboat into the sea. Lifeboat slipway stations consist of an initial section where the boat is held on rollers followed by an inclined keelway lined with low-friction composite materials; the lifeboat is released from the top of the slipway and proceeds under its own weight into the water. The lifeboat is later recovered using a winch line. It is common to manually apply grease to the composite slipway lining before each launch and recovery in order to ensure sufficiently low friction for successful operation. With the introduction of the Tamar-class lifeboat it is necessary to upgrade existing boathouses and standardize slipway operational procedures to ensure consistent operation. The higher contact pressures associated with the new lifeboat have led to issues of high friction and wear on the composite slipway linings and the manual application of grease to reduce friction is to be restricted due to environmental impact and cost factors. This article presents a multidisciplinary approach to modeling slipway panel wear and friction using tribometer testing in conjunction with finite element analysis and slipway condition surveys to incorporate common real-world effects such as panel misalignments. Finally, it is shown that a freshwater lubrication system is effective, reducing cost and environmental impacts while maintaining good friction and wear performance.

The potential of the water hammer in pico-scale tidal power systems: An experimental investigation

The tidal energy within the seas surrounding the United Kingdom offers a vast renewable resource that is perfectly predictable over long timescales. Currently, the bulk of tidal energy research is focused on developing large devices for the most resource rich locations, which can be many miles from populated areas. The potential of small-scale tidal power from sub-optimal shallow water sites, close to populated regions, has so far been overlooked. Such generation would benefit from reduced transmission losses and contribute towards a distributed electricity grid, helping to overcome the variability of other renewables. This work presents a novel method for generating hydropower using the water hammer effect: a pressure surge that can occur in a pipeline following the abrupt closure of a valve. These pressure surges are used to produce vertical oscillations from horizontally flowing water, allowing power to be generated in a manner analogous to a wave energy convertor. A non-optimised scale model was found experimentally to have a peak available power density of 1.08 ± 0.25 kW/m2 and a mean of 0.07 ± 0.02 kW/m2. In comparison, the MCT SeaGen S (arguably the most well-developed tidal energy device) is capable of generating 3.18 kW/m2. With further development, a water hammer device may therefore be useful for generating pico-scale tidal power in slow, shallow water flows.

The depletion of ZDDP additives within marine lubricants and associated cylinder liner wear in RNLI lifeboat engines

Previous work of authors indicated the wear of cylinder liners in marine engines of RNLI lifeboats due to the intense lubricant degradation identified by inductively coupled plasma and Fourier Transform Infrared spectroscopy techniques. In this paper, further analysis carried out to evaluate the effects of lubricant degradation on the actual cylinder liners installed in the Trent Class Lifeboat engines is presented. Surface characterisation of actual cylinder liner’s bore surface showed maximum wear near the top dead centre region compared to rest of the piston stroke. Wear in this region of the cylinder liner surface is controlled primarily by the protective film forming anti-wear additives in the lubricant which limit the direct surface contact between the piston rings and cylinder liner. The condition of zinc dialkyldithiophosphates anti-wear additives was analysed using the nuclear magnetic resonance spectroscopy. Tribology analysis was conducted to evaluate the tribological and boundary film forming performance of zinc dialkyldithiophosphates additives by simulating cylinder liner–piston ring contact near the top dead centre. To further understand the wear mechanisms of the cylinder liner, wear debris analysis (Analytical Ferrography) of lubricant samples was performed. Results revealed the depletion of phosphorus containing zinc dialkyldithiophosphates anti-wear additives as a function of the lubricant’s duty cycle within the marine engines and its effect on the tribological and boundary film forming performance of lubricants. Wear debris analysis showed the generation of ferrous debris potentially from the cylinder liners as a result of reduced anti-wear protection from the depleted zinc dialkyldithiophosphates additives during the tribological contact with piston rings and piston skirt region. These findings are useful to understand the lubricant degradation mechanisms which affect the functionality of cylinder liners, therefore allowing to plan the engine maintenance strategies.