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Full Scale Measurements – Sea 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 vessels – compliance 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 craft – requirements 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 speed

and 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

• ITTC Recommended procedure 7.5-04-01-01.2 Analysis of

Speed/Power Trials Data

• IMO: 2000 HSC Code (IMO 185E) – Requirements for

testing of high speed craft

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http://ittc.info

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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 for instance 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 charge of handling the ship

– There is usually one or more ship masters hired by the shipowner who is going to take over the ship

• Measurements are performed by shipbuilder or by third party (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 wave

direction

•Steady Approach

> Min. 10 minutes

•Steady Approach

> Min. 10 minutes

Waves

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Measured mile

Leading marks («overettmerker»)

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Trial Conditions – max acceptable

• Sea state

– When wave spectrum is measured:

– When wave height is visually observed:

• Wind

– ≤ Beufort 6 (20 knots) (for ships with L>100 m)

– ≤ Beufort 5 (for ships with L ≤ 100 m)

• Water depth h

– If or correction is required

– Tests shall not be performed in waters whereor

• Current

– In cases of current time history deviating from the assumed

parabolic/sinusoidal trend and the change of the current speed

within the timespan of one Double Run is more than 0,5 knots,

tests shall not be carried out

1 3 2.25 100PPH L

1 3 1.5 100PPH L

3 Mh B T 22.75 Sh V g

2 Mh B T 22 Sh V g

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Trial Conditions – Contractual

• 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: and

• Current

– No current

– No practical limit for when corrections are made. Use of double runs

means that corrections are always included

3 Mh B T 22.75 Sh V g

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Correction of trial results

• When trial conditions are not fulfilled corrections must be made

• Typical corrections:

– Draught – interpolation in model test results on two draughts

– Wind – calculation of wind resistance using empirical drag coef. or results from wind tunnel tests

– Shallow water – empirical formulas

– Waves – calculation 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 Recommended procedure 7.5-04-01-01.2 Analysis of

Speed/Power Trials Data

– STAWAVE by Marin

• Comes with a free software package for performing the analysis

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ISO 15016 correction flow chart

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ISO 15016 correction method

• Compute resistance correction:

• Compute power correction:

• The propulsive efficiency is assumed to vary linearly with

the added resistance:

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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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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

• 10º/ 10º to both sides

• 20º/ 20º to both sides

– Turning circle test

• 35º 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

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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 (DP) 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 horizontal 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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Measurements – environmental 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 360º turning test at low speed

– The difference between log speed and GPS speed

• often, one doesn’t 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 position – for a drifting buoy

this can be used as an estimate of current

– Can be brought along for a full scale test

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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

doesn’t move

• Problematic when heading, speed or other operational

parameters change

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Beufort wind scale with related sea conditionsSea Description term Wind sp. [knots] Wave height [m] Sea

Beufort state Wind Wave min max Probable Max Description

0 0 Calm Calm 0 1 0 0 calm; like a mirror

1 0 Light air Ripples 1 3 0.1 0.1 Ripples with appearance of scales:no foam crests

2 1 Light breeze Small wavelets 3 6 0.2 0.3 Small wavelets; crests of glassy appearance, not breaking

3 2 Gentle breeze Large wavelets 6 10 0.6 1 Large wavelets; crests begin to break; scattered whitecaps

4 3 Moderate breeze Small waves 10 16 1 1.5 Small waves, becoming longer numerous whitecaps

5 4 Fresh breeze Moderate waves 16 21 2 2.5 Moderate waves, taking longer form; many whitecaps; some spray

6 5 Strong breeze Large waves 21 27 3 4 Larger waves forming; whitecaps everywhere; more spray

7 6 Near gale Large waves 27 33 4 5.5 Sea heaps up; white foam from breaking waves begins to be blown in streaks

8 7 Gale Moderately high waves 33 40 6 7.5 Moderately high waves of greater length; edges of crests begin to break into spindrift; foam is blown in well-marked streaks

9 8 Strong gale High waves 40 47 7 10 High waves; sea begins to roll; dense streaks of foam; spray may reduce visibility

10 9 Storm Very high waves 47 55 9 12.5 Very high waves with overhanging crests; sea takes white appearance as foam is blown in very dense streaks; rolling is heavy and visibility is reduced

11 9 Violent storm Exceptionally high waves 55 63 11.5 16 Exceptionally high waves; sea covered with white foam patches; visibility still more reduced

12 9 Hurricane Exceptionally high waves 63 71 14 16 Air filled with foam; sea completely white with driving spray; visibility greatly reduced

13 9 Hurricane Exceptionally high waves 71 80 >14 >16

14 9 Hurricane Exceptionally high waves 80 89 >14 >16

15 9 Hurricane 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

– European Centre for Medium-Range Weather Forecasts ECMWF

– National Oceanic and Atmospheric 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 state

and wind in your area

– You can of course not get wave elevation time series!

• Localized information for the Norwegian coast:

Norkyst 800 http://thredds.met.no/thredds/catalog/fou-

hi/norkyst800m-1h/catalog.html

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European Centre for Medium-Range

Weather Forecasts

• An independent intergovernmental organisation founded in

1975 and supported by 34 states

• Produces global numerical weather forecasts for users

worldwide

• Offers hindcast data for wind and waves freely available

for download

• Data in GRIB file format – requires a suitable routine for

reading and interpreting

http://www.ecmwf.int/

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Ocean current

• Important to correct speed-power related measurements for

the effect of current

• Dedicated speed trials aim at cancelling the effect of

current by using double runs

– For ship monitoring (monitoring performance during normal

operation) this is not an option

• Direct measurement possible by using buoys

– Not a practical solution for ship monitoring!

• If accurate speed-through-water measurement on the ship

was available, problem would be solved, but it isn’t!

• Hindcast data available from OSCAR

– Ocean Surface Current Analyses Real-time

http://www.esr.org/oscar_index.html

• The Norkyst 800 model gives current forecast and hindcast

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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 IMU – for 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 to

damage, gauges work

loose

• Sensors based on fiber-

optics - polarimetric and

bragg-grating suggested as

alternative

Hull Monitoring System:

Strain gauge in protective casing:

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Rolls-Royce Health and Monitoring

System - HEMOS

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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

• Many other types of performance monitoring coming up

– Ref. Rolls-Royce HeMOS system

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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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Sample picture from full scale propeller cavitation observation

Summary:

•Types of tests

•How to perform and correct speed trials

•Wave monitoring

•Measurement

•Observations

•Motion measurement

•Hull monitoring

•Propeller cavitation observations