Ben ThomasPhD Student

Bournemouth UniversityThomasb@Bournemouth.ac.uk

Supervisors:Mark Hadfield – Bournemouth University

Steve Austen – RNLI

Finite Element Analysis: The results from the tribology experiments are used to validate an FEA wear model. This simulates the friction and wear of the slipway linings on a computer, this will allow the experimental results to be applied across the wide range of geometries and environmental conditions present in lifeboat slipways.

Simulation of ExperimentsCorrelation between experimental and simulated results allows accurate wear and friction simulation for real life slipway geometries. Here the TE77 reciprocating friction machine test is modelled.Simulation of WearIterative techniques are used to generate a wear scar using the wear parameters obtained

experimentally. Contact pressure data is used to determine the wear scar depth combined with wear rate data from experiments.

FEA will then allow the many different slipway stations across the UK to be modelled individually without conducting separate experiments for each one. Combined with the experimental results the FEA analysis will allow guidelines for the effective lubrication of lifeboat slipways for crewmen at each distinct slipway station.

Synopsis: To achieve reliable slipway launch conditions lifeboats currently rely on low, controlled co-efficient of friction between lifeboat keel and slipway. Current solutions involve using low friction composite materials to line the keelway, and this is supplemented by manually applying grease to ensure reliable launches.

Due to the exposed nature of the slipway and the unpredictable intervals between lifeboat launches the lubricant grease can be washed away or dry out resulting in unpredictable lubrication regimes at launch. This project considers the design, tribology and wear mechanisms involved in slipway launch systems of this type. Tribology involved in sliding contact under variable lubrication regimes in a hostile sea water environment is considered.

The project examines the suitability and performance of current materials and lubrication selections under simulated launch conditions. This involves modelling the wear and friction co-efficient of both materials over a range of environmental and lubrication conditions using micro-friction and rotary tribometer bench test machines. Wear mechanisms are identified using post-test techniques such as light and scanning electron microscopes.

The bench tests allow an understanding of the basic wear mechanisms and friction of slipway linings. Lubrication is considered by measuring the potential difference changes between sliding contacts and comparison with theoretical wear regimes. This will give an understanding of the rate wear and friction as the lubrication regime changes.

Actual launch conditions are recorded using GPS sensors to determine trajectory and 3 dimensional behaviour of the lifeboat as it travels on the slipway.

These results are used to determine the contact forces and likely areas of wear involved as the lifeboat leaves the slipway.

The project will thus provide a model for the performance and wear of slipway launch systems. The project will encompass product design and use of materials and will therefore be beneficial to the RNLI and the marine industry in general, particularly with regards to marine sliding friction, slipway and marine railway applications and modelling.

Objectives:•To identify appropriate test procedures for

modelling slipway wear•To develop a model for the wear of

slipway linings •To develop a model for the friction of

slipway linings•To evaluate the environmental impact of

slipway lubrication•To evaluate the durability of Feroform as a

slipway lining•To identify the lubrication regimes in place

throughout the slipway launch•To identify likely areas of wear along the

slipway

Launch Data:Materials:Slipway Lining Feroform 19mm

Keel (Tyne Class Lifeboat) ‘Corten’ corrosion resistant steel – shotblastedMinimum yield strength: 345N/mm2Minimum tensile strength: 480N/mm2Painted (initially)

Keel (Tamar Class Lifeboat) Steel S275 J2G3 – hot dip galvanised to BS2729Flat to ± 1.5mm

Slipway Angle: 4.7 – 11.4° (Depending on location)

Typical Entry Data: (Data from Selsey Slipway Trial 2002, Slipway angle 11.4°, 53m long, Tyne class lifeboat, Neox DT grease)

Launch time: 8.3sLaunch Velocity: 12.8m/s

46kphLifeboat mass: 25.5 tonnesFriction Coefficient: Static - 0.09

Dynamic – 0.07

Slipway is typically greased after recovery with Neox DT and not re-greased until the next launch. Launches occur every 3-4 days.

State of the art - tribology

Real life performance

Environmental considerations

Environmental conditions

FEA wear tests

Ship launching

friction tests

Design of experiments

FEALCAExperiments

TE92TE77

Real life slipway

simulation

Material recommendations

Wear prediction

Code of practice

Sustainable design of lifeboat slipways

Problem outline

Research objectives

Research

Project Outline

Abstract: This project considers the design, tribology and wear mechanisms involved in lifeboat slipway launch systems.

In rough conditions it is sometimes impossible to launch lifeboats to a rescue without the aid of an inclined slipway. To achieve reliable slipway launch conditions lifeboats currently rely on low, controlled co-efficient of friction between lifeboat keel and the slipway channel. Current solutions involve using a range of low friction materials to line the keelway, and this is often supplemented by manually applying grease to ensure reliable launches. Due to the exposed nature of the slipway and the unpredictable intervals between lifeboat launches the lubricant grease can be washed away, dry out or become contaminated with wind blown sand e.t.c. resulting in unpredictable lubrication regimes at launch. Currently this is apparent only as problems of high friction or even seizure occur during the launch and recovery of the lifeboat.

The project examines the suitability and performance of current materials and lubrication selections under simulated launch conditions and environment. This involves modelling the wear and friction co-efficient of both keel and slipway materials over a range of environmental and lubrication conditions using micro-friction and rotary tribometer bench test machines. Tribology factors involved in sliding contact under variable lubrication regimes in a hostile sea water environment are considered. Wear mechanisms are identified using post-test techniques such as light and scanning electron microscopes.

The bench tests allow an understanding of the basic wear mechanisms and friction of slipway linings. The lubrication regime is considered by measuring the potential difference between sliding contacts to indicate their separation, and by comparison with theoretical wear regimes. Friction is also measured and recorded as the tests progress.

This will give an understanding of the rate wear and friction as the lubrication regime changes. FE analysis will also be used in conjunction with the tribology tests to model the friction and wear in the varying geometries of real world slipways.

The project will thus provide a model for the performance and wear of slipway launch systems. The project will encompass product design and use of materials and will be beneficial to the RNLI and the marine industry in general, particularly with regards to marine sliding friction, slipways and marine railway applications and modelling.

Sustainable Design of Lifeboat Launch systemsSustainable Design of Lifeboat Launch systems

Life Cycle Analysis: Life Cycle Analysis is used to evaluate the environmental performance of a system or product across its entire life cycle. In the case of lifeboat slipway launches this means looking at the material and energy inputs and outputs for a functional unit (i.e. 100 launches). LCA is intended to provide a fuller picture of lifeboat slipway operation by taking into account the material and energy quantities, costs and environmental impact of possible solutions.

SimaPro life cycle analysis software and databases are used for this. SimaPro consists of a complicated series of databases outlining the environmental allows the environmental impacts of the range of greases used to be evaluated.

Environmental performance is measured by combining all weighted environmental emissions of a material during construction use and disposal into one environmental score, this allows different greases and slipway materials to be directly compared for environmental impact.

LCA also takes into account the quantities of lubricant used and the time taken to apply when making comparisons.

In this study LCA has been used to compare existing greases and to select two compatible bio-greases, which have a lower environmental impact as well as the use of sea water lubrication including the energy needed to raise the water above sea level. This information will provide a comprehensive picture of the overall implications of the lubricant, slipway liner and lubrication schedule used.

Experimental Methods:Friction and wear of slipway linings is investigated using reciprocating and rotary

tribometers. Initially a TE77 reciprocating tribometer is used for screening tests and to give an initial comparison of conditions and lubricants. Later a TE92 tribometer will be used to conduct more detailed tests simulating both launch and recovery as well as more complicated environmental conditions such as wind-blown sand included in the lubricant and deposits from salt water.

TE77 – Reciprocating Tribometer Used for screening testsUsed to investigate wear and friction using 3 commonly used greases, 2 bio-greases, salt water, water and dry.Provides quick screening tests to identify areas for investigation

TE92 – Rotary Tribometer

Used for more detailed friction and wear testsCan more accurately model real world conditionsUsed to investigate all lubricants used including environmental contamination such

as wind-blown sand and salt crystals

Result from both machines will be used to validate the FEA wear model to allow the wear, friction and likely service life of slipway linings to be predicted.