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Full Scale MeasurementsSea trials
Experimental Methods in Marine Hydrodynamics
Lecture in week 45 Contents:
Types of tests
How to perform and correct speed trials
Wave monitoring
Measurement
Observations
Motion measurement
Hull monitoring
Propeller cavitation observations
Performance monitoring
Covers Chapter 11 in the Lecture Notes
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Dedicated sea trials are conducted under the
following circumstances:
Delivery of newbuildings (Contractual Trials)
Speed-power (compliance with contracted performance)
Bollard Pull test (tugs and offshore vesselscompliance with
contracted performance) Maneuvering (compliance with IMO criteria)
Sea keeping (only high speed craft)
If a special problem has arisen, for instance:
Propeller noise and/or erosion
Steering problems
Excessive fuel consumption
For research purposes (quite rare due to high costs)
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Delivery Sea trials (Contractual trials)
Ship building contracts contain specific requirements for
speed-power performance
Failure to meet requirements means fees to be paid and ultimately
that the ship owner has the right to refuse to accept the ship
For tugs and offshore vessels, there will be requirements
for bollard pull as well
There might be requirements also for maneuvering trials :
Emergency stop test Turning circles
Zig-zag tests
High speed craftrequirements also for seakeeping tests
IMO: 2000 HSC Code (IMO 185E)
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Applicable standards
ISO 19019:2005 Sea-going vessels and marine technology --
Instructions for planning, carrying out and reporting sea
trials
ISO 15016:2015(E) Guidelines for the assessment of speedand power performance by analysis of speed trial data
Replaced previous version in 2015. Significant differences!
ITTC Recommended procedure 7.5-04-01-01.1 Preparation
and Conduct of Speed/Power Trials IMO: 2000 HSC Code (IMO 185E)Requirements for
testing of high speed craft
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IMO HSC testing requirements
Stopping
Normal stop from max speed to zero
Emergency stop
Crash stop
Cruise performance in two sea states
Normal conditions
Worst intended conditions
Measurements of accelerations, speed, relative wave heading
Failure tests
Check that the ship, crew and passengers are not at risk if forinstance the steering fails
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Organization of Delivery Trials
The Shipbuilder is responsible
Trial Leader From the shipbuilder
Responsible for the execution of all phases of the trial
Ship masters
There is one ship master hired by the shipbuilder who is in chargeof handling the ship
There is usually one or more ship masters hired by the shipownerwho is going to take over the ship
Measurements are performed by shipbuilder or by thirdparty (like Marintek or Maskindynamikk)
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Execution of speed trials
Always run back and forth at same engine setting
Run back and forth at the same track
Perform runs at different speeds (at least three)
If possible, orient the track with and against the winddirection
Steady Approach
> 5 min and 1 mile
Steady Approach
> 5 min and 1 mile
Wind, current
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Measured mile
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Trial Conditionsmax acceptable
Sea state
Preferably sea state 3
Ultimately sea state 5 (or up to sea state 6 for ships with L>100 m)
Wind Beufort 6 (20 knots) (for ships with L>100 m)
Beufort 5 (for ships with L 100 m)
Water depth h
h>6.0*Am2
and h>V
2
Smaller depths require corrections for shallow water
Current
Current of more than a few knots is unacceptable
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Trial ConditionsContractual
Sea state
No waves
In practice: Beufort 1 (Wave height 0.1 m)
Wind No wind
In practice: Beufort 2 (Wind speed 6 knots)
Water depth h
Deep,
In practice: h>6.0*(Am) and h>V2
Current
No current
No practical limit for when corrections are made. Use of double runs
means that corrections are always included
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Correction of trial results
When trial conditions are not fulfilled corrections must bemade
Typical corrections:
Draughtinterpolation in model test results on two draughts Windcalculation of wind resistance using empirical drag coef. or
results from wind tunnel tests
Shallow waterempirical formulas
Wavescalculation of added wave resistance and speed loss
Standards for how corrections shall be performed: ISO 15016 Guidelines for the assessment of speed and power
ITTC Procedure for the Analysis of Speed/Power Trial Data
STAWAVE by Marin
Comes with a free software package for performing the analysis
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IMO Energy Efficiency Design Index -
EEDI Increases the need for standardized trial and correction
procedures
The speed at 75% MCR in calm water must be accurately
determined
Now longer just a matter for yard and ship owner
Shall be approved by classification society
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Recent developments
The ISO 15016 is about to be discarded
Too complicated to use
Too much freedom to manipulate results
Outdated correction methods
IMO has tasked ITTC to develop a new standard
ITTC works with Marin, and the new guideline is based on
the STAWAVE methods
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Speed measurement
Speed over ground and Speed through water
Timing a measured mile
the old-fashioned way, only applicable to dedicated speed trials
Gives speed over ground
GPS
The obvious choice, always used
Gives speed over ground
Speed log
Device to measure speed through water
Always installed on ships
Doppler log is most common on large ships
Measures speed at about 10 m below bottom, close to bow
The accuracy is questionable!
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Measurement of shaft power
Strain gauges glued directly to the shaft
Calibration factor must be calculated, so shaft dimensions and
material properties must be known exactly
Tachometer to measure shaft speed
Commercial power meters
Made for permanent installation The best, but most expensive alternative
Poor, but cheap alternatives are
fuel rack measurements (measurement of fuel consumption,
combined with supplier data for fuel quality) measurement of cylinder pressure (used on large, slow speed
engines)
For diesel-electric drive-trains, the frequency converter (drive)
will usually be able to output information about power supplied to
the electric motor
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Shaft measurements
Torque measurement Thrust measurem.
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Optical torque sensor
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Optical thrust and torque measurement
Required accuracy for thrust measurement is
25 naonometers!Challenging, but possible, according to
supplier VAF Instruments
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Bollard Pull
Tests
Good location Poor location
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Bollard pull test
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Bollard pull test
2x460 kW
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Maneuvering trials
Trial types and execution same as in model scale
Measurements:
(D)GPS position measurement
Gyro compass course
Rate of turn (if possible)
Rudder angle
Propeller revs
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Types of Ship Maneuvers
IMO standard maneuvers:
Zig-zag tests
10/ 10 to both sides
20/ 20 to both sides
Turning circle test
35 rudder angle
Full astern stopping test
Additional maneuvers:
Spiral test Reverse spiral test
Pull-out maneuver
normally added at the end of a turning test
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Zig-zag test
i
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Test 2011: 20-20 zig zag
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Turning circle
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Testing of position-keeping ability and
thruster performance at zero speed
Important for vessels that have requirements to Dynamic
Positioning performance
No standard tests or commonly recognised procedures
There is a need for development of standardized tests and analysis
procedures for this purpose
A way to characterise thruster performance at zero speed:
Run the thrusters in different combinations (one by one, and in
specific combination) for a short time Measure the acceleration of the ship in the horisontal plane
Compute the impulse required to create the acceleration
Compare the effective impulse with the impulse provided by the
thruster(s) to arrive at a kind of efficiency
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Measurementsenvironmental conditions
Water depth
Echo sounder (ship instrument) or nautical charts
Water quality
Temperature: Cooling water intake temperature can be used
Density: From nautical charts or density measurements
Wind Velocity and direction from anemometer
A separate, calibrated instrument is preferable
Watch out for influence of superstructure on the measurement
Current
Nautical charts and tables
the difference in speed between double runs
a 360 turning test at low speed
The difference between log speed and GPS speed
often, one doesnt trust the speed log sufficiently for this purpose
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Wave measurements
Visual observation and estimation
Estimates by yard representative, ship-owner representative, and
possibly a neutral third party are compared and averaged
Mobile wave buoy Accurate (but only at a single point)
Recovery of the buoy is difficult (risk of loosing it)
Fixed weather station
Good solution if one is nearby
Wave radar (Wavex)
Bow-mounted altimeter
Wave information without measurement: Hindcast data
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Wave buoys
Fugro Oceanor Wavescan
Directional wave spectrum
Wind
Current
Water temperature and salinity
Must be moored; large, heavy, costly Smaller, spherical buoys
Drifting or moored
Simple buoys measure wave height only by use
of an accelerometer
Advanced buoys can measure the directional
wave spectrum through use of the Doppler shift
of the GPS signals
Usually measures positionfor a drifting buoy
this can be used as an estimate of current
Can be brought along for a full scale test
http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=aMG0sltdNOuyxM&tbnid=UVcwN3lXp4O-tM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.channelcoast.org%2Fsouthwest%2Fsurvey_techniques%2Fwaves%2F%3Flink%3Dwave_measurement_at_nearshore_buoys.html&ei=KCJxUsuhOquZ0QX80YHABg&bvm=bv.55617003,d.ZGU&psig=AFQjCNFDWEg9vhfKhWgK0WWzZhpCGFy5Rw&ust=1383232384105471http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=aMG0sltdNOuyxM&tbnid=UVcwN3lXp4O-tM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.channelcoast.org%2Fsouthwest%2Fsurvey_techniques%2Fwaves%2F%3Flink%3Dwave_measurement_at_nearshore_buoys.html&ei=KCJxUsuhOquZ0QX80YHABg&bvm=bv.55617003,d.ZGU&psig=AFQjCNFDWEg9vhfKhWgK0WWzZhpCGFy5Rw&ust=13832323841054717/25/2019 Full Scale Measurements- Sea Trials
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Wavex by Miros AS
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Bow-mounted altimeter
Measures relative wave motion
Ship motions must also be measured
in order to calculate absolute wave
height
SM - 055
SM - 094
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Using the ship as wave buoy
Measurement of ship motions and accelerations
Knowledge of ship motion transfer functions can be used
to find the wave spectrum from the measured ship motion
power spectrum
Current research topic
Can hardly work for short waves, since then the ship
doesnt move
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Beufort wind scale with related sea conditions
Sea Description term Wind sp. [knots] Wave height [m]Beufort state Wind Wave min max Probable Max
0 0 Calm Calm 0 1 0 0
1 0 Light air Ripples 1 3 0.1 0.1
2 1 Light breeze Small wavelets 3 6 0.2 0.3
3 2 Gentle breeze Large wavelets 6 10 0.6 1
4 3 Moderate breeze Small waves 10 16 1 1.55 4 Fresh breeze Moderate waves 16 21 2 2.5
6 5 Strong breeze Large waves 21 27 3 4
7 6 Near gale Large waves 27 33 4 5.5
8 7 Gale Moderately high waves 33 40 6 7.5
9 8 Strong gale High waves 40 47 7 10
10 9 Storm Very high waves 47 55 9 12.5
11 9 Violent storm Exceptionally high waves 55 63 11.5 16
12 9 Hurricane Exceptionally high waves 63 71 14 16
13 9 Hurricane Exceptionally high waves 71 80 >14 >16
14 9 Hurricane Exceptionally high waves 80 89 >14 >16
15 9Hurricane Exceptionally high waves 89 99 >14 >16
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Illustrations of Beufort wind (and wave) scale
From: http://en.wikipedia.org/wiki/Beaufort_scale
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Hindcast data
Information about wave and wind condition in the past
Data collected by meteorological institutes
From wave buoys, weather stations, satellites, observations
Many different sources
Might be hard to find the right source for your test
National Oceanic and Athospheric Administration www.noaa.gov
is the main source
Many different applications are using their open data
From hindcast data you can get information about sea stateand wind in your area
You can of course not get wave elevation time series!
Generally only available for open ocean areas
http://www.noaa.gov/http://www.noaa.gov/7/25/2019 Full Scale Measurements- Sea Trials
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Measurement of motions
Accelerations: Conventional accelerometers
Angles: Gyros, compass, accelerometers
Rate gyro to measure rate of change of angles
Inertial Measurement Units (IMU)
Consists of a number of accelerometers built into one compact unit
Gives out accelerations, velocities and motions at any point
Konsberg Seatex MRU is a good example of a commercial IMU
Kongsberg Seapath
Combination of DGPS and IMUfor accurate position
measurement
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Kongsberg Seatex MRU 5+
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Kongsberg Seapath 330
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Measurement of forces:
Hull Monitoring
Strain gauges most
common sensor
Short and long gauges
Cabling exposed todamage, gauges work
loose
Sensors based on fiber-
optics - polarimetric and
bragg-grating suggested as
alternative
Hull Monitoring System:
Strain gauge in protective casing:
R ll R H lth d M it i
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Rolls-Royce Health and Monitoring
System - HEMOS
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Example: Monitoring of loads
on an azimuthing thruster of a
seismic vessel
Measurement of ship motions andposition with Seapath
Measurements on the portazimuthing thruster
Automatic triggering of data storage
Data acquisition system remotelymonitored from land
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Performance monitoring
Typical merchant ship application:
To monitor the development of speed and fuel consumption
over time, in order to detect need for maintenance
Challenges:
Monitoring and correcting for environmental conditions
Waves, wind, water temperature
Accurate measurement of shaft power and speed through water
Measuring and correcting for loading condition Data processing
Setting-up and running automatic data transmission
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Propeller Cavitation
Observations
Seen from below Seen from the side
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Cavitation observation techniques
1. generation borescope
2. generation borescope
Source: marin.nl
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