specialist committee on surface treatment€¦ · representation of surface roughness (continued)...
TRANSCRIPT
Specialist Committee on Surface Treatment
Committee Members
Richard Anzböck (Chairman), Vienna Model Basin
Michael Leer-Anderssen (Secretary), SSPA
(Dazheng Wang replaced by
Mehmet Atlar, University of Newcastle (Sept, 2010)
Eloy Carillo, CEHIPAR
Hishashi Kai, Yokohama National University
J.H. Jang, Samsung Heavy Industries
M. Donnelly, NSWCCD (left, 2009)
2
Specialist Committee on Surface Treatment
Committee meetings were held in:
Vienna in November 2008,
Madrid in May 2009,
Daejon in February 2010
Gothenburg in October 2010
3 Specialist Committee on Surface
Treatment
Tasks given to the Committee
TASK 1 - Review the-state-of-the-art different surface treatment methods.
TASK 2 - Review the possible impact on ship performance in the following areas in the light of the recent rapid development of coating systems:
Resistance (friction line)
Propeller characteristics
Cavitation behaviour
Comfort (propeller induced noise)
Acoustic signature
4
TASK 3 - Review the existing measurement methods for surface roughness at model scale and at full scale.
TASK 4 - Propose methods that take into account surface roughness and other relevant characteristics of coating systems in model testing.
Check the need for changes to the existing extrapolation laws.
Study the roughness allowance for high speed and conventional ships (hull, appendages and propellers).
Tasks given to the Comitte (continued)
5
STC concentrated only on coating systems for hull &
propellers,
No practical support from paint manufacturers to the
request of the committee, except, available poduct briefs:
Claims fuel consumption upto 10%
No serious scientific evidence and proof
Examples from major stake holding company product
briefs are in the Committee report
TASK 1 - Review the state-of-the-art different
surface treatment methods
6
Example advertisements by some Paint Manufacturers
7
Example Advertisments by some Paint Manufacturers
Foul Release coating compared to self polishing coating
8
Example advertisments by some Paint Manufacturers
9
Example advertisements by some paint manufacturers
10
Example advertisements by some Paint Manufacturers
11
Example advertisements by some Paint Manufacturers
12
Example advertisements by some Paint Manufacturers
13
Examples of Advertisements by Paint Manufacturers
14
Example advertisement by some Paint Manufacturers
15
Several thousands of species of marine organisms can
foul a ship
Most will release when ship is running above 4- 5 Kn,
except slime!!
Each organism can attach is affected by many factors
including, e.g.
pH
Temperature
Salinity
Dissolved salts
Oxygen concentration
Types of Fouling
16
17
Microalgae
(slime)
Animal Plant
Macroalgae
(weeds) Soft Bodied Hard Shelled
Red Brown Green Unlimited Limited Barnacles Mussels Tube Worms
Specialist Committee on Surface
Treatment
Marine fouling classification
Antifouling technology is under further scrutiny due to
environmental concerns and current financial climate
Although currently in small proportion (~ 10%) the application of
completely environmentally friendly Foul Release coatings are
increasing worldwide requiring further attention and investigation.
Credible evidence comparing the drag characteritics between
majority of coatings is non-existent. Different application, evaluation
and measuring techniques make it very difficult to come up with
reliable performance comparisons.
TASK 1 - Conclusions
18
TASK 2 - Review the possible impact on ship performance in the following areas in the light of the recent rapid development of coating systems
Task 2.1 - Resistance (friction line)
Task 2.2 - Propeller characteristics
Task 2.3 - Cavitation behavior
Task 2.4 - Comfort (propeller induced noise)
19
Task 2.1 - Resistance (Friction Line)
Committee report includes review on:
Ship resistance (Data Published)
Ship resistance (Data Not Published)
Resistance of Flat Plates (Data published)
Resistance of Circular Cylindrical surfaces
Interaction Ship – Propeller
Further Papers of Possible Interest
Paints
Marine creatures
20 Specialist Committee on
Surface Treatment
Ship resistance (data published)
Schultz, MP (2007) – Effect of coating roughness and biofouling on ship
resistance (*)
Munk, T (2006) – Effect of drydocking and propeller polishing using
performance monitoring system
Yokoi ( 2004) – Effect of fouling on trial performance
Leer-Andersen, M and Larsson, L (2003) – Full-scale skin friction
estimations using CFD and roughened pipe experiments
Lars-Erik, J(1984) – Full-scale skin friction estimation of two hulls using
measured floating element friction data and 3D BL theory
21
Ship resistance (data are not published)
Yano, Y and Wakabayashi, N. (2008) – Effect of fouling with different coatings by trials
Townsin, RL (2003) – A good review on coating penalty and economies based on vast experience (*)
Willsher, J ( 2001) – Discusses benefits of FR coatings
Doi, H. and Kikuchi, O (1984) – Five rough plates as replicates of real ship hull surfaces were tested in flow channels and speed penalties were predicted.
Yamazaki, H. et al (1983) – Experimental study with sand roughened pipes to establish roughness-drag correlations
Yamazaki, H et al (1984) – Investigated difference between sand roughened surfaces and painted surfaces using wavy roughened surfaces
Tokunaga, K. and Baba, E. (1982) – 2D turbulent BL theory and 3D potential flow for full-scale prediction of resistance increase due to roughness
Sone, M. (1981) – Power penalty estimations based on 10yrs ship abstract log-book data
Orido, H. and Kakinuma, M. (1980) – Some practical analysis of surface roughness penalties based on full scale ship in-service data 22
Drag of flat plates (Data published)
Candries, M and Atlar, M (2005) – BL, Roughness and drag
comparisons of FR and SPC coatings using LDA and drag tests (*)
Schultz, MP (2004) – Frictional drag data for different ship hull coatings
Schultz, MP (2002) – Very useful rough wall friction data with 7 different
grades
Candries, M and Atlar, M (2001) – Relative drag data on FR and SPC
coatings using a large flat plate in a large towing tank
Candries, M, Atlar, M and Anderson, M (2001) – Relative drag data on
FR and SPC data using a medium flat plate in a small tank.
Schultz, M (2000) – Investigated the effect of macro algae on skin
friction using LDV in a water channel
Schultz, M and Swain, G W(1999) – Effect of marine biofilms on flat
coated surfaces investigated using LDA 23
Resistance of circular cylindrical surfaces
Mirabedini, SM et al (2006) – Drag and roughness characteristics of
different coatings on aluminium circular cylinders by using rotor drums
Weinell CE et al, T (2003) – Comparative effects of paint roughness and
large scale irregularities of different paint systems were investigated
Tanaka, H. et al ( 2003) – Effect of surface characteristics of paints on
their drag including the influence of aging was demonstrated using a
specially built rotating drum
Candries, M et al (2003) – Effect of different coatings and application
methods (spraying and rollering) were investigated on a rotating drum (*)
24
Interaction ship and propeller
Miyamoto, M (2007) – An approximate method exploited to estimate the
effect of fouling, aging of paint and sea conditions and compared based
on abstract log-book data (*)
Matsuyama, A et al (2001) – Marine fouling effect on a ship hull and
propeller was investigated based on 8 years abstract log data
Nagamoto, K et al (1993) – Bottom and propeller fouling of a real ship
was investigated over a year data including special protection to bow
thruster
Sato K et al (1987) – Comparative performance of coatings on flat
plates and actual ships in sea water were investigated
Nishikawa, E and Uchida, M (1985) – Effect of marine fouling on hull
and two different type propulsors (CPP and FPP) were investigated
Nakai , N and Suzuki S (1984, 1983, 1983) – Effect of bottom and
propeller fouling on a full-scale ship were investigated 25
Further studies of possible interest (on Paint)
Almeida, E, Diamantino, TC and de Sousa O (2007) – An overall review of marine paints is given
Chambers LD et al (2006) – Review paper on the development of marine coatings
Casse, F and Swain, GW (2006) – Effect of microfouling on three different type of coatings under static and dynamic immersion were investigated
Tetsuya, S (2006) – Environmental risk evaluation methods of different coatings were presented
Anderson et al (2004) – A state-of-the-art review of new generation marine coatings with a good balance on their chemistry, biofouling and hydrodynamics including effect of hull and propeller performance is presented. (*)
Ogawa, K (1996, 1996) – Early generation silicon paint was investigated on FRP plane in sea water and physics of the foul release were discussed
Hirota, N (1985) – Early generation non-toxic “bioclean” coatings were investigated on large ships and propellers 26
27
TASK 2 - Review the impact of coating
systems on
Task 2.2 - Propeller characteristics
Task 2.3 - Cavitation behavior
Task 2.4 - Comfort (propeller induced noise)
There has always been an interest to propeller coatings to control biofouling growth
to reduce galvanic corrosion
to prevent cavitation erosion
Propeller coating applications are growing since the introduction of
Foul Release (FR) coatings
FR applications currently about 5% but increasing (e.g. 250 ships)
Smoother; may reduce drag; durable; non-biocidal
Promoted by paint companies
Control fouling
Further anectodal claims (fuel saving, reduced cavitation/vibration)
Reality is that frictional losses in a propeller’s efficiency can be
as high as a 15% compared to potential (axial & rotational) losses
So keeping the propeller smooth and free of fouling is saves energy
Rest needs to be proven
Introduction
Measurements of propeller surface condition Roughness comparator (e.g. Rubert roughness scale)
Portable stylus instrument
Taking replicas and measure in the laboratory
They all have their own problems
Representation of surface roughness Townsin’s approach for APR using Musker’s characteristic
roughness parameter (h’)
i Region Weight
1 0.2 - 0.5 0.07
2 0.5 - 0.7 0.22
3 0.7 - 0.8 0.21
4 0.8 - 0.9 0.27
5 0.9 - tip 0.23
35
1
31
)'(
ii hWAPR
Ca PRh )5.2(0147.0' 2
Representation of surface roughness (continued) In case of FR coated propellers, use of fully turbulent (ks) – as in the
ITTC’78 method- is not valid because:
- Actual propeller roughness are different than sand roughness
- FR surfaces do not correlate only based on a single roughness
parameter, texture parameters are also important
Review of propeller coatings
As old as Holzaphel (1904) – Preventing fouling and G/corrosion
Kan et al (1958) – Fouling prevention simulated by rubber sheets
Dashnaw (1980) – To protect scarced (cheap) alloys for economy
Heatcock et al (19790; Angell et al (1979); Akhtar (1982) –
Ceramic coating research to prevent cavitation damage
Foster (1989) – Full scale reports with vinyl coating for positive
fouling and G/corrosion prevention
Coldron & Conde (1990) – Positive report on full-scale ceramic
coating applications but not so on TBT-SPC application.
Matsushita et al (1993) – First application of FR coating on
FS propellers and positive impact on fouling and cathodic protection
Anderson et al (2003) – Positive report on reduced ICCP current
output due to coating
Atlar (2004) – Opinion on complex corrosion issue and economy
trade-off between coating and surface finish
Newcastle University research (2003 – present) – to report later
Propeller coating applications are growing since the introduction of
Foul Release (FR) coatings
FR applications currently about 5% but increasing (e.g. 250 ships)
Smoother; may reduce drag; durable; non-biocidal
Promoted by paint companies
Control fouling
Further anectodal claims (fuel saving, reduced cavitation/vibration)
Reality is that frictional losses in a propeller’s efficiency can be
as high as a 15% compared to potential (axial & rotational) losses
So keeping the propeller smooth and free of fouling is saves energy
Rest needs to be proven
Review of Foul Release coatings
Non-biocidal; Fouling is released by weak hydrodynamic shear
forces over “low surface energy” silicon based coated surfaces
Bio-adhesion is strongly correlated with , Brady & Singer (2000)
Silicon (and other PDMS) materials have an order of magnitude
lower , Singer et al (2000)
Candries (2001) demonstrated reduced drag properties
of FR coatings as opposed to TBT free –SPC coatings
Candries & Atlar (2003) indicated the importance of texture
parameters in correlations with drag for FR coatings
EC
,
EC
Foul Release coatings R&D as applied to propellers
Effect on propeller efficiency:
- Atlar et al (2002, 2003) used Musker’s equivalent roughness parameter
based on the measured surface parameters of newly painted FR surfaces
- The equivalent roughness value was related to Rubert scales and they
were used to represent various surface finishes
- The equivalent roughness was also related to the blade sectional drag
coefficients and hence to the propeller performance in a lifting surface
analysis code
- Simulations for a typical merchant propeller after 2 years of service
indicated a 5-6% gain due to coating - High speed propellers can take advantage of the foul release coatings further due to their relatively large blade surface area and higher shaft speeds
,
,
0.4 0.5 0.6 0.7 0.8 0.9J
0
0.1
0.2
0.3
0.4
0.5
0.6
KT,
10K
Q,
O
KT
10KQ
O
Design
Rubert D
Rubert E
Rubert F
Rubert F
Design
DesignRubert F
Figure 1. Propeller Open Water Characteristics
Ship type Medium Tanker
Deadweight 96920 tonnes
Length Overall 243.28 m
Max Draught 13.616 m
Speed 14.86 knots
Shaft RPM 139.5
Power (installed) 9893kW
Built 1992
Full-Scale Propeller Dimensions:
Diameter 6.85m
Mean Face Pitch 4.789m
Expanded Blade Area Ratio 0.524
Design Advance Coefficient, J 0.48
- Model tests in Emerson Cavitation
Tunnel with freshly applied F/R
coatings on a commercial tanker
propeller showed no conclusive
evidence of any undesirable effect
on efficiency (including damage to
paint),
Effect on propeller efficiency
The Effect of Coating Damage upon the Propeller Open Water Characteristics
(Confidence Limits 95%)
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8
Advance Coefficient, J
KT, 10K
Q, E
ffic
ien
cy
Intact Coating KT
Intact Coating 10KQ
Intact Coating Efficiency
Damage Scenario 1 KT
Damage Scenario 1 10KQ
Damage Scenario 1 Efficiency
Damage Scenario 2 KT
Damage Scenario 2 10KQ
Damage Scenario 2 Efficiency
Damage Scenario 3 KT
Damage Scenario 3 10KQ
Damage Scenario 3 Efficiency
Effect on Cavitation Inception
LOADED CONDITION (J) -
Uncoated Coated % Change
Inception Inception Inception
0.517 0.505 -2.32 (Delayed)
Dissidence Dissidence Dissidence
0.513 0.510 -0.58
BALLAST CONDITION (J)
Uncoated Coated % Change
Inception Inception Inception
0.542 0.590 8.86 (Earlier)
Dissidence Dissidence Dissidence
0.540 0.557 3.15
LOADED CONDITION BALLAST
Cavitation number,
= 0.50
0.320
Propeller Immersion,
H = 10.0m
4.66m
RPM = 100 104
Advance Coefficient,
J = 0.48
J = 0.486
Loaded
J= 0.5
Coated uncoated
• Some evidence of
coating altering the
inception /
dissidence of tip
vortex cavitation
• But trend in
delaying or earlier
inception is mixed
Effect on fully developed cavitation
uncoated Coated Coated uncoated
J= 0.45
J= 0.40
Loaded, = 0.50 Ballast, = 0.48
UNCOATED PROPELLER:
Well defined (thicker) tip
vortex , more stable (&
slightly larger extent) sheet
cavitation patterns.
COATED PROPELLER:
Less well defined tip
vortex and less stable
sheet & hence more misty
cavitation patterns
• Depending upon the advance coefficient (J) some beneficial effect of
coating (waterborne noise reduction), mainly in non-cavitating condition (at
high J’s) is observed
SPL
(dB) uncoated coated
Cf (Hz)
J=0.7 J=0.6 J=0.4
Loaded condition, = 0.50 10 100 1000 10000
60
100
140
140
SPL
(dB)
Cf (Hz)
uncoated
coated
J=0.6 J=0.4 J=0.7
Ballast condition, = 0.48
SPL
(dB)
100
60
10 100 1000 10000
Effect on noise
Final Power Curve ComparisonErrors estimated at 10%
0.00
20000.00
40000.00
60000.00
80000.00
100000.00
120000.00
140000.00
6.00 6.50 7.00 7.50 8.00 8.50 9.00 9.50
Tide Corrected Speed over Ground (knots)
Co
rre
cte
d S
ha
ft P
ow
er
(Wa
tts
)
Uncoated Trial
Coated Trial
Coated
Uncoated
• Despite the weather
effecting the coated
trials, the results
showed little
difference between the
performance of the
coated and uncoated
propellers
Full scale trials with uncoated vs coated propeller
Full-scale observations
Application of F/R coatings on propeller
keeps the propeller free from major fouling
as clearly observed in full- scale and
prevents the increase in roughness over
the time (next slide)
14 months uncoated
Newly coated
After 24 months
After 12 months
After 36 months
• Roughness and texture
characteristics of coated
propeller are similar after
2 years in-service
Roughness in service
Full scale observation shows that FR
coatings can prevent major biofouling
but not slime which attaches more
strongly to FR coatings than other
fouling mechanisms
Modelling of roughness in the presence
of biofouling is a complex issue
requiring further research with
experimental data. One such research
study by Schultz (2007) using
Granville’s approach (1958, 1987)
presents interesting findings that may
be exploited for propeller applications.
However it requires further data on
roughness-drag correlations
Interaction with biofouling
Newly applied
37 months
later
CONCLUSIONS – Propeller coating (TASK 2.2 – 2.4)
Propeller coating has always been attractive and FR coating applications
are increasing
There is no credible evidence that propeller coating demonstrates gain/loss
in efficiency. But there is limited evidence that coating keeps the roughness
and texture levels similar as newly applied as well as preventing macro fouling
Limited model tests (Newcastle University) on efficiency, cavitation and
noise do not display any major favourable or unfavourable effect of coating.
Model test requires care for the coating thickness effect
Semi-empirical expressions used for blade section drag coefficient requires
modification to take into account the coating effects properly
There is a need for standard measurement tools and procedures for surface
measurements and model testing with coated propellers
There is a need for dedicated full-scale trials and observations with coated
propellers
TASK 3 - Review the existing measurement
methods for surface roughness at model
scale and at full scale
Surface roughness parameters:
Amplitude parameters (Rt, Rz; Ra, Rq; Rsk, Rku, etc)
Texture parameters (Sm; Sa)
Spectral parameters (ACF; PSDF)
Fractal parameters (FD)
44
Surface measurement techniques & equipment
In full scale Direct measurement using portable
Stylus (contact) type equipment
Optical (non-contact) sensor equipment
Indirect measurement by taking
Representative impression (print) of old applications
Sample plates during coating for new applications
& measuring them using non-portable or portable devices
In model scale Direct measurement using portable
Stylus (contact) type equipment
Optical (non-contact) sensor equipment
Other sophisticated photogrammetry techniques
45
46
BMT Hull Roughness
Analyser (HRA)
47 Typical output from BMT HRA
48
Lab based non-portable
laser profilometer
(OSP 100 – UNISCAN)
Sample coated
surfaces
49
Foul Release Roughness profile:
Ra = 1.10
Rq = 1.21
Rt = 4.50
Sk = -0.87
Ku = 5.04
Sa = 0.23
-15
-10
-5
0
5
10
15
20
0 5 10 15 20 25 30 35 40 45 50
mm
mic
ron
SPC Roughness profile:
Ra = 3.26
Rq = 4.04
Rt = 19.98
Sk = 0.01
Ku = 3.29
Sa = 1.90
-15
-10
-5
0
5
10
15
20
0 5 10 15 20 25 30 35 40 45 50
mm
mic
ron
Typical output from lab based laser profilometer (OSP 100 – UNISCAN)
50
Surtronic3+
Portable
stylus device
Typical output from SURTRONIC3+ on a propeller blade
51 New prototype BMT-HRA using a laser sensor developed by BMT - Newcastle University
Laser sensor based
prototype BMT – HRA
52
New BMT- HRA device Non-portable Laser profilometer
TASK 3 – Conclusions
Ship hull and propellers coated with new generation coatings, especially with the FR types, cannot be reliably measured by current mechanical contact devices at drydocks. There is a need for non-contact, portable, robust device.
New generation coatings need more surface parameters to be known than just AHR and hence such devices need to be more sophisticated to provide such ability
A new portable non-contact prototype device has just been developed requiring to be proven by marine industry
Roughness measurements on ship models are carried out but the results of the measurements are used for quality assurance and not for further investigation.
Most of the model basins do not measure the roughness of the model hull and propellers.
53
TASK 4 - Propose methods that take into
account surface roughness and other
relevant characteristics of coating systems;
check the need for changes to the existing
extrapolation laws.
Measurement Equipment
Test Procedure Recommendations
ITTC Rough Skin Friction Database
54
Flat plate in towing tank (still the best)
Flat plate in cavitation tunnels (in atmospheric)
Flat plate in open water channel
Pipe friction device
Flow cell
Couette cell (two coaxial cylinders)
Other shapes than flat plate in towing tank or the like
(such as axysymmetric body or model ship)
Full scale tests
Friction Measurement Equipment
55
Best combination of accuracy and complexity
Direct measurement of flat plate drag (majority of cases) or
a floating small cell (edge effects!)
Longer and thinner the better
Towing speed is limited (usually 5 m/s)
Re-rigging for each new surface test requires care
Orientation and time between the tows are important
Flat plate in towing tank
56
Mostly boundary layer measurements using LDV to
estimate measure wall velocity, velocity shift (roughness
function) and hence friction coefficient
In some cases direct measurement of friction drag of the
plate or even a floating cell in the flat plane (edge effect!)
are used
Overall expensive but accurate method
Flat plate in cavitation tunnel
57
Cost effective, practical and also well suited for bifouling effect
investigations
It is an indirect method, average values based on pressure drop and
hence lower accuracy for less rough surfaces. BL is not free confined
in pipe radius and hence correction will require for flat plate skin
friction
Couette cell, rotor apparatus Simple, practical and cost economical but experience non-uniform BL
development as well as temperature issues. Some complexities in
calculating skin friction based on torque measurements
Friction pipe
58
Flow cell
High aspect ratio channel provides fully developed shear and hence turbulent flow on very small testing surfaces using micro slides They are mainly used for biofouling adhesion tests using seawater but can be exploited for friction tests though complex.
59
Other shapes
Using other shapes than flat plates will bring further complexities introducing much higher residual and wave making, hence are recommended.
However some simple shapes without free surface for convenience and higher Re number (e.g. Axy-symmetric body in high speed channels) may be preferred
60
Friction test procedures – recommendations
High Re-numbers should be preferred (Lower the Re no higher the risk of surface being hydraulically smooth). At least 2m/s above
It is imperative that all measurements should be completed with reference to a hydraulically smooth (practically polished) surface, y+ ~ 5 (i.e. h ~ 5-50m)
Reproducibility is essential without and with re-rigging during coating changes. Strict uncertainty procedures should be followed
Representative coating applications should follow the same procedure as in the real world application (in shipyards)
Roughness measurements should be taken as precise as possible using appropriate devices and as many as possible roughness parameters
61
ITTC Rough (wall) Skin Friction Database (RSFD)
STC proposes to start an International database for skin friction measurements including coated surfaces with/without biofilms by following a harmonised procedure
Submission:
SSPA and Newcastle University will maintain a website for submission of data that will be publicly available
Submitted data will be evaluated to meet required confidence level to be included in RSFD
Cf, DU+, h will be made public compared to Cf,ITTC
62
63
Velocity shift (roughness) function can be used for each friction line with
more than one roughness parameter
will be replaced by
RSFD Analysis and comparison procedure
Efficiency parameter C will be defined by LSM for each surface and
fairly constant values of C can be devised for different surfaces to be
used for full scale predictions
All measurements will be referred to a reference “Hydraulically Smooth”
surface for comparisons
and velocity function can be evaluated using a known smooth skin friction line
e.g. Cf, ITTC
64
ITTC Skin Friction Data Submission Form
Company/institution Phone
Contact person Adress
e-mail Submission date
Appended material (raw data, analysed data, reports, papers)
File name (description) Public (Yes/no)
1.
2.
3.
Test description
1. Equipment (see document XXX, section 1.1, 1-8). If other please specify
2. Reynolds number range
3. Flow speed range
4. Roughness height measurement type (device and parameter)
Short description of test equipment if not standard
Surfaces tested
Deliverables Description Roughness height Other parameters
1. (name or description)
2.
3.
Additional information
RSFD Submission Form
Extrapolation Methods:
Conclusion: No changes to Powering Performance
Prediction regarding the use of the Townsin roughness
allowance due to lack of data.
Recommendation: It will not be possible to generate a
new formulation without an extensive database of skin
friction measurements: ITTC Rough Skin Friction
Database (RSFD) initiative is proposed
Conclusions and Recommendations
65
Model test procedures:
Conclusions: Most accurate method for skin friction
measurements probably is the flat plate in tow tanks but
others can be used by paying attention to high Re no,
and reproducibility. There is a need for accurate
measurements of roughness characteristics with
more parameters.
Recommendation: Establishment of comparative
skin friction database development following
coherent test procedures
66
Propeller Coatings
Conclusions: No credible evidence from full-scale
measurements to prove any gain or loss from a vessel
fitted with a coated propeller compared to a newly
polished uncoated propeller.
There is evidence that these coatings can maintain the
blade surface free from major fouling for long time
without any maintenance
Propeller model tests with coated blades suffer from
appropriate paint thickness in model scale due to
application methods with commercial coatings.
67
Propeller Coatings
Recommendations: More dedicated model tests, full-scale trials and progressive docking observations to accurately assess the effect of coatings on the propeller efficiency, cavitation and noise performance should be conducted
As a generic problem of the foul release type coatings, investigations on the application and measurement of coatings on model and full-scale propeller should continue
As a generic problem of any coating the investigation on the effect of slime on propeller coatings should continue.
68
69
State-of-the-art-coatings Coatings
Conclusions:The applications of Foul Release (non-
biocidal) type antifoulings are increasing worldwide and
require further attention and hence further investigation.
Different model evaluation, application and measuring
techniques make it difficult to compare measurements for
which reason most of the measurements are only able to
state that this coating is xx% better than another coating
Recommendation: Methods measuring FR coating
surface characteristics in drydocks should be developed
based non-contact technology. Investigations on the drag
performance of these coatings should continue.
70
