Ben Thomas

1
Sustainable Design of Lifeboat Launch systems
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.
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.
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.
Launch Data Materials Slipway Lining Feroform
19mm Keel (Tyne Class Lifeboat) Corten
corrosion resistant steel shotblasted Minimum
yield strength 345N/mm2 Minimum tensile
strength 480N/mm2 Painted (initially) Keel
(Tamar Class Lifeboat) Steel S275 J2G3 hot dip
galvanised to BS2729 Flat 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 8.3s Launch Velocity 12.8m/s 46kph Li
feboat mass 25.5 tonnes Friction 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.
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 Experiments Correlation
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 Wear Iterative 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.
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 tests Used 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 tests Can more accurately model real world
conditions Used 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.

• 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

Ben Thomas PhD Student Bournemouth
University Thomasb_at_Bournemouth.ac.uk Supervisors
Mark Hadfield Bournemouth University Steve
Austen RNLI