Measurements master Course

Port Said UniversityFaculty of Engineering

Naval Architecture and Marine Engineering Department

Sea Trial Measurement’sUT (thickness measurements and crack detection)

Vibration Measurements

Post Graduate Course:

Measurements

Course Code:

000

Supervisor:

Dr. Waleed Yehya

23th MAY. 2013

Prepared By: Mohamed ElmaadawyDesign engineerN.A.M.E. B.Sc.Port Said Shipyard Suez Canal Authority

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Sea Trial Measurement’sMEASUREMENTS Code: 000

Contents

1. Introduction 3

2. Typical trials. 43. Nautical trials measurement’s. 5

3.1. Ship speed measurement 53.2. Ship turning circle diameter and tactical diameter measurement 53.3. Water depth measurement 6

4. Equipment installation measurement’s. 74.1. Engine power measurement 74.2. Shaft RPM measurement 7

Prepared by: M.Elmaadawy

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1. Introduction

Before being commissioned, each vessel classified by any classification socity has to undergo sea trials in the presence of a competent class Surveyor.

A sea trial is the testing phase of a marine vessel. It is also referred to as a "shakedown cruise" by many naval personnel. It is usually the last phase of construction and takes place on open water, and it can last from a few hours to many days.

Sea trials are conducted to measure a vessel’s performance and general seaworthiness. Testing of a vessel’s speed, maneuverability, equipment and safety features are usually conducted. Usually in attendance are technical representatives from the builder, governing and certification officials, and representatives of the owners. Successful sea trials subsequently lead to a vessel’s certification for commissioning and acceptance by its owner.

Although sea trials are commonly thought to be conducted only on new-built vessels (referred by shipbuilders as 'builders trials'), they are regularly conducted on commissioned vessels as well. In new vessels, they are used to determine conformance to construction specifications. On commissioned vessels, they are generally used to confirm the impact of any modifications.


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2. Typical trials

Sea trials are fairly standardized using Technical Bulletins published by IACS, IMO, ITTC, SNAME, BMT, regulatory agencies or the owners. They involve demonstrations and tests of the ship's systems and performance.

Speed trial:

The vessel is ballasted or loaded to a predetermined draft and the propulsion machinery is set to the contracted maximum service setting, usually some percentage of the machinery's maximum continuous rating. (ex: 90% MCR) The ship's heading is adjusted to have the wind and tide as close to bow-on as possible. The vessel is allowed to come to speed and the speed is continuously recorded using differential GPS. The ship is then turned through 180° and the procedure is followed again. This reduces the impact of wind and tide. The final "Trials Speed" is determined by averaging all of the measured speeds during each of the runs. This process may be repeated in various sea states.

Crash stop:

The vessel is ballasted or loaded to a predetermined draft and the propulsion machinery is set to the contracted maximum service setting, usually some percentage of the machinery's maximum continuous rating. The trial begins once the order to "Execute Crash Stop" is given. At this point the propulsion machinery is set to full-astern and the helm is put hard-over to either port or starboard. The speed, position and heading are continuously recorded using differential GPS. The final time to stop (i.e.: ship speed is 0 knots) track line, drift (distance traveled perpendicular to the original course) and advance (distance traveled along the original course line) are all calculated. The trial may be repeated at various starting speeds.

Endurance:

The vessel is ballasted or loaded to a predetermined draft and the propulsion machinery is set to the contracted maximum service setting, usually some percentage of the machinery's maximum continuous rating. The fuel flow, exhaust and cooling water temperatures and ship's speed are all recorded.

Maneuvering trials:

A number of trials to determine the maneuverability and directional stability of the ship may be conducted. These include a direct and reverse spiral manoeuvres, zig-zag, and lateral thruster use.

Seakeeping:

Was used exclusively for passenger ships but now used in a variety of vessels. Involves measurements of Ship motions in various sea states followed by a series of analyses to determine comfort levels, likelihood of sea sickness and hull damage. Trials are usually protracted in nature due to the unpredictability of finding the correct sea state and the need to conduct the trials at various headings and speeds.


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3. Nautical trials measurement’s.

3.1. Ship speed measurement. (units : knots)

Today, sea navigators measure their ship's speed using modern GPS (Global Positioning System) driven devices.These signals, each travelling at the speed of light, arrive to a GPS receiver at slightly different times due to distance to satellites differences. After receiving signals from at least four different GPS satellites, the receiver can calculate its position in all three dimensions (based on time delays between signals). Once the receiver knows exact position at any given time, the internal electronics tracks that position in time and calculates ship's speed.Current position accuracy of the GPS system is about 10-20 meters with most standard receivers and can be as good as 1 meter or less with special ground based repeaters.

A classical way of measuring ship speed is to use a stop-watch to calculate the time required for a ship to move a known distance, This way also has an error as it depends on the human factor and should be repeated for more than once and the average speed to be taken as the final measured speed.Q: ship speed measurement trial one of the most important sea trials and a major contract item explain two procedures used to measure ship speed and state the data and information should be collected during measurement.

3.2. Ship turning circle diameter and tactical diameter measurement (units : meters)Turning ability is the measure of the ability to turn the vessel using hard-over rudder the result being a minimum “advance at 90° change of heading” and “tactical diameter” defined by the “transfer at 180° change of heading”. A turning circle maneuver is to be performed to both starboard and port. The rudder angle must be the maximum design rudder angle permissible at the test speed, but is not required to be more than35 degrees.Q: explain how ship turning circle trial would be performed and indicate the most important parameters to be monitored and support your answer with illustrative drawing


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3.3. Water depth measurement (units : meters)Water depth can be obtained either by digital or classical (analog) techniqueEcho sounding is the digital technique of using sound pulses to find the depth of water. The interval from the emission of a pulse to reception of its echo is recorded, and the depth calculated from the known speed of propagation of sound through water. This information is then typically used for navigation purposes or in order to obtain depths for charting purposes.

A simple and old fashion method for finding the depth of water is to lower a weight attached to a rope over the side of the vessel. When the weight touches the bottom, the rope becomes slack. The rope is then pulled back on-board and the length of the rope needed to touch the bottom is determined. This is a slow method and is not very useful if the vessel is moving very fast. If the water is very deep, it is difficult to retrieve the rope unless a mechanical winch is used.

Q: Water depth on of the critical parameters in most of the sea trials explain two methods for measuring water depth and support your answer with illustrative drawing,

Q: Explain how would the water depth would affect the bollard bull trail


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4. Equipment installation measurement’s

4.3. Engine power measurement. (units : KW or HP)To measure the horsepower of an engine, hook the engine up to a dynamometer. A dynamometer places a load on the engine and measures the amount of power that the engine can produce against the load.If you attach a shaft to an engine, the engine can apply torque to the shaft. A dynamometer measures this torque. You can convert torque to horsepower by multiplying torque by rpm/5,252.

Q: Explain engine power measurements procedure

4.4. Shaft RPM measurement. (units : 1/Min)Shaft revolution can be measured using tachometers, The idea behind most digital counting device, frequency meters and tachometers, is a micro-controller, used to count the pulses coming from a sensor or any other electronic device.In the case of this tachometer, the counted pluses will come from proximity sensor, which will detect any reflective element passing in front of it, and thus, will give an output pulse for each and every rotation of the shaft, as show in the picture. Those pulses will be fed to the microcontroller and counted.

Q: Explain one method for measuring shaft rpm and support you answer by illustrative drawing showing the concept of shaft RPM measurement.


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UT (thickness measurement crake detection)

Q. 1. Ultra-sonic one of the most common and reliable methods of thickness measurement and crack detection, Explain the main principles of ultra-sonic and support your answer with illustrative drawing and write down the governing equations of this method.

Q.2. Explain in detail how crack could be detected using ultra-sonic testing

Q.3. Right or wrong (comment and correct the wrong answer)

1- Ultrasonic testing is mainly used for surface testing

(Wrong) ultra-sonic is mainly used for internal testing as it uses high frequency sound waves, typically above 2MHz to pass through a material.

2- the higher the frequency of the sound wave the smaller the wavelength

(Right) according to the governing equation wave length decrease by increasing frequency

3- The smaller the wavelength the higher the sensitivity

(Right) In UT the smallest detectable flaw is half the wavelength, so decreasing the wavelength increase the possibility of detecting small cracks

4- Sound velocity in material depend on the frequency of sound wave

(Wrong) The velocity of sound in a particular material is CONSTANT and it is the product of DENSITY and ELASTICITY of the material

Q.4.state the advantages of Ultrasonic Testing

Q.5.explain the limitations of Ultrasonic Testing

Q.1. what the oil mist detector & what is its benefit?


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Q.2. what the devices used to determine the ship's heading?

Q.3. How Machine Vibration is generated & what factors could affect its amount?

Q.4. In brief describe the time waveform for a complete propulsion system (gearbox, shaft, & propeller) & its frequency

Q.5. Plot recommended points for fixing vibration measuring instruments explaining vibration directions to be measured.

Q.6. what the damages & consequences of vibration?

Q.7. Amplitude is an indicator of the severity of vibration; explain how the amplitude can be expressed in engineering?

Q.8. explain in brief the Types of Vibration

Please take notes on the following:-Recommended trial water depth-NDT types only -Near Zone length calculation-Oil mist detector (think wisely in its efficiency)Concerning Vibration part please read carefully the file previously uploaded in this subject


Measurements master Course

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