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Full Scale Measurements – Sea trials

Experimental Methods in Marine Hydrodynamics Lecture in week 46

Contents: •Types of tests •How to perform and correct speed trials •Wave monitoring

•Measurement •Observations

•Motion measurement •Hull monitoring •Propeller cavitation observations

Covers Chapter 11 in the Lecture Notes

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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) – Mainly seakeeping and sea loads tests

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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

• 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 Guidelines for the assessment of speed and power performance by analysis of speed trial data

• 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 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 wind

direction

•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 Conditions – max 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*Am

2 and h>½V2

– Smaller depths require corrections for shallow water • Current

– Current of more than a few knots is unacceptable

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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: h>6.0*(Am)½ and h>½V2

• 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 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 Procedure for the Analysis of Speed/Power Trial Data

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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 – 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)

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Shaft measurements

Torque measurement Thrust measurem.

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Bollard Pull Tests

Good location Poor location

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Maneuvering trials

• Trial types and execution same as in model scale • Measurements:

– (D)GPS position measurement – Gyro compass course – Rudder angle – Propeller revs

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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 (high risk of loosing it)

• Fixed weather station – Good solution if one is nearby

• Wave radar (Wavex) • Bow-mounted altimeter

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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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Directional wave radar

• Microwave radar • On fixed or on moving “platforms” • Big and expensive • Used on offshore installation, not on ships

SM - 050

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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 Max0 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 1.5 5 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 >1614 9 Hurricane Exceptionally high waves 80 89 >14 >1615 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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Measurement of motions

• Accelerations: Conventional accelerometers • Angles: Gyros, magnetic 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

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Measurement of forces: Hull Monitoring - Sensors

• 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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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