Sunday, June 28, 2020

Timing diagram and Power card of 4 stroke cycle

  • The timing diagram shows the closing and opening of the valves. The working cycle is illustrated as a ‘P - V’ diagram (pressure-volume). The line ‘l – l’ represents atmospheric line. The piston is considered to have just moved over the ‘top dead centre’ and is on its way down. The air inlet is already open and because of the partial vacuum created when the piston moves towards its bottom position, fresh air is sucked into the cylinder. This process is represented in the 'p-v' diagram by the line ‘1-2’ which is termed suction line. This movement of the piston is called 'Suction Stroke".
  • After the piston has moved over bottom dead centre, the suction valve closes and the volume of air in the cylinder is compressed during the course of the up stroke of the piston. This is represented by the line ‘2-3’ in the above diagram and termed as compression line. This movement of piston is compression stroke.
  • The ignition takes place at point 3 and combustion continues for the duration of fuel injection, ending at point 4. After this combustion products expand to point 5 when the exhaust valve opens. Power is produced between point ‘4 – 5’.
  • The pressure drops in the cylinder to the exhaust line from 5 to 6. The exhaust valve remains open till after piston passes over the top dead center. The combustible gases are expelled. The line 6 to 1 represents this. The pressure is slightly above atmosphere, because of the resistance in the exhaust pipe. This stroke is 'exhaust stroke'.
  • A 4-stroke engine requires two complete revolutions of the crankshaft to finish working cycle.
  • This means inlet, exhaust & fuel valve must only function once for every two revolutions of the crankshaft.
  • In order to activate those valves in the correct sequence, it is necessary to operate them from a shaft, which rotates at half the speed of the crankshaft. This is called camshaft.

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Slide Valves : Simple things that mean a lot


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Exhaust valve Materials and Treatments

Material Requirements.
  • The material should retain its greatest strength at high temperatures.
  • No tendencies to air harden.
  • Critical temperature above 800*C.
  • No tendency of high temperature scaling.
  • Hot and cold corrosion resistant.
  • Able to be forged and machined easily.
  • Capable of consistent and reliable heat treatment.
  • Most diesel engines use an Austenitic heat-resisting alloy steel. The seating surface can be stellited.
Typical heat treatment: 
  • Heat up to 950*C and cool in air to give a Brinnel Hardness of 269.
Surface Treatment:
  • Surface treatment is frequently used to improve or modify valve steel characteristics. Chrome-cobalt-tungsten alloy available in various grades of hardness is widely used.
  • The hardness when deposited is in the order of 375 to 425 Brinnel.
  • The valve head is treated to more than 430*C to reduce contraction stresses.
  • The value face is now sweated by an oxyacetylene flame and the alloy deposited continually by welding (1.02 mm to 1.52 mm).
Valve Seat Inserts:
  • Alloy Irons, with high percentage of molybdenum and Chromium with a Brinnel number of Approx. 500 are best.
  • Alloy steel with stellited seating surface are also in common use.
  • The methods employed for fitting the inserts include screwing and shrinking.
Valve Guides:
  • Valve guides are mostly made of Cast Iron.
  • To avoid scaling etc at high temperatures alloy Irons are preferred.
  • Phosphor Bronze and Gun metal have also been successfully used.
  • Alloy Iron guides with Bronze linings also are in common use.
Valve Housing:
  • Mostly made of pearlitic cast iron and provided with a chamber for cooling water.

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Saturday, June 27, 2020

Construction and Working Principle of Indicator

  • An engine indicator consists of a small bore cylinder containing a short stroke piston which is subjected to the same varying pressure that takes place inside the engine cylinder during one cycle of operations.
  •  This is done by connecting the indicator cylinder to the top of the engine cylinder in the case of single-acting engines, or through change over cocks and pipes leading to the top and bottom ends of the engine cylinder in the case of double-acting engines.
  • The gas pressure pushes the indicator piston up against the resistance of a spring, a choice of specially scaled springs of different stiffness being available to suit the operating pressures within the cylinder and a reasonable height of diagram.
  • A spindle connects the indicator piston to a system of small levers designed to produce a vertical straight-line motion at the pencil on the end of the pencil lever, parallel (but magnified about six times) to the motion of the indicator piston.
  • The “pencil” is often a brass point, or stylus, this is brought to press lightly on specially prepared indicator paper which is scrapped around a cylindrical drum and clipped to it.
  • The drum, which has a built-in recoil spring, is actuated in a semi-rotary manner by a cord wrapped around a groove in the bottom of it; a hook at its lower end to a reduction lever system from the engine crosshead attaches the cord, passing over a guide pulley.
  • Instead of the lever system from the crosshead, many engines are fitted with a special cam and tappet gear to reproduce the stroke of the engine piston to a small scale.
  • The drum therefore turns part of a revolution when the engine piston moves down, and turns back again when the engine piston moves up, thus the pencil or stylus on the end of the indicator lever draws a diagram which is a record of the pressure in the engine cylinder during one complete cycle.

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Procedure for opening Main Engine Liner

Following Procedure has to be followed when opening Liner
  • Inform company and take permission.Take immobilisation certificate from port state control.
  • Read the manual and have a tool box meeting with everyone involved in the job.
  • Discuss the complete procedure.
  • Prepare important tools and spares required for overhauling liner as given in the manual
  • Prepare risk assessment and make sure all personal safety equipment are used
  • Shut starting air for Main Engine and display placards
  • Engage turning gear
  • Open indicator cocks for all the cylinders
  • Stop main lube oil pump and switch off the breaker
  • Once the engine jacket temperature comes down, shut the inlet water valve for the unit to be overhauled
  • Keep other units in Jacket preheating system to maintain the jacket temperature
  • Drain the jacket water of the concerned unit from exhaust v/v and liner.
  • Shut the fuel oil to the particular unit whose liner is to be removed
  • Dismount the cylinder head using dedicated lifting tools
  • Discard the sealing ring from the top of the cylinder liner.
  • Turn the piston down far enough to make it possible to grind away the wear ridges at the top of the liner with a hand grinder
  • Dismount the piston by following the procedure given in Manual
Liner Removal procedure for MAN engine (MC and ME engines)
Ensure the Liner lifting tool is well maintained. Two lifting screws are used with a lifting hook connected via chain. Ensure chain, screw and lifting hook are fastened together with no deformation
  • Ensure the safety strap in the lifting hook is working properly.
  • Tighten the two lifting tool screws in the liner as per the rated torque is given in the manual on both sides.
  • Measure that there is no gap between liner surface and screw landing surface after tightening, using a 0.05mm feeler gauge.
  • Disconnect the cylinder oil pipe connections. 
  • And screw of the non-return valves.
  • Dismount the four cooling water pipes between the cooling jacket and cylinder cover and clean them carefully.
  • Remove the screws of cooling water inlet pipe.
  • Attach the crossbar to engine room crane. This completes the lifting arrangement for cylinder liner.



Hook the chain from the lifting cross bar on the lifting screws and lift the cylinder liner with the cooling jacket out of the cylinder frame.

What to do if Cylinder Liner is Stuck
  • A common way to remove a stuck cylinder liner is to use hydraulic jacks on the bottom of the cylinder liner and apply hydraulic pressure.
  • Once the liner is slightly moved out of the stuck engine structure, it may be then lifted with the help of engine room crane and lifting tool
After Removing the liner from the engine:
  • Place the cylinder liner vertically on a wooden plank
  • Clean cylinder frame internally paying special attention to the contact surfaces for the cylinder liner at the top of the cylinder frame
  • Discard the O-ring on the cooling water pipe
  • Clean the pipe carefully
  • Make sure to inspect the liner for cracks and other defects

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Refrigeration Compressor Starting Unloader

  • At a star-delta start of electric motors it is often considered necessary to limit the compression work of the machine at the starting moment in order to reduce the starting torque of the electric motor. 
  • Usually, a solenoid valve is used in a by-pass arrangement which in the starting up phase short circuits the discharge side to the suction side of the compressor.
  •  At the same time, a non-return valve must be fitted in the discharge line to the condenser preventing the return flow of discharge gas to the compressor.
  • When the electric motor has reached its max. number of revolutions per minute, a switch takes place from star to delta start. 
  • The solenoid valve is closed and the compressor now works under normal conditions.

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Sludge formation in Refer system

Acid content inside a system can emulsify with the compressor oil to form an aggressive oil sludge that reduces lubrication properties. This can lead to serious compressor damage.
Sludge can also cause a variety of other problems in a system, such as blockages of strainers, expansion valves and other tiny passage

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Corrosion in Refer system

  • Moisture can cause corrosion. However, moisture in combination with a HCFC refrigerant containing chlorine (like for example R-22 or R-409A) creates much more serious corrosion, as the chlorine hydrolyses with the water to form hydrochloric acid (HCl) which is aggressive to most metals. Heat adds significantly to the problem by accelerating the acid-forming process.
  •  For HFC refrigerants (like R-404A or R-407C), it is the polyolester oils that are very hygroscopic and may decompose at high temperatures forming hydrofluoric acid with the moisture which could be introduced to the system through a sub-standard refrigerant.

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York Antwerp Rule

There is a general average act when and only when, any extraordinary sacrifice or expenditure is intentionally and reasonably made or incurred for the common safety for preserving from peril the property involved in common maritime adventure

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Certificate of Proficiency (COP) and Competency (COC)

Certificate of Proficiency (COP) refers to a certificate, other than a certificate of competency issued to a seafarer, stating that the relevant requirements of training, competencies or seagoing service in the Convention have been met.
Able seafarer deck :Person qualified in accordance with the provisions of regulation II/5 of the STCW Convention
Able seafarer engine :Person qualified in accordance with the provisions of regulation III/5 of the STCW ConventionAble seafarers whether deck or engine are given Certificate of Proficiency (COP)

Competency (COC) refers to the possession and demonstration/application of the knowledge, understanding and proficiency required of seafarers under the Convention.
Electro - technical officer :Person qualified in accordance with the provisions of regulation III/6 of the STCW ConventionETO is given Certificate of competency (COC).

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Bill of Lading

Bill of Lading (B/L)
  • The bill of lading is the declaration of the master of the vessel by which he acknowledges that he received the goods on board of his ship and assures that he will carry the goods to the place of destination for delivery, in the same condition as he received them, against handing of the original bill of lading.
  • "Bill of lading means a document which evidences a contract of carriage by sea and the taking over of loading of the goods by the carrier, and by which the carrier undertakes to deliver the goods against surrender of the document. A provision in the document that the goods are to be delivered to the order of a named person, or to order, or to bearer, constitutes such an undertaking."
The bill of lading (B/L) serves as:
  • A receipt of the goods by the shipowner acknowledging that the goods of the stated species, quantity and condition, are shipped to a stated destination in a certain ship, or at least received in custody of the shipowner for the purpose of shipment;
  • A memorandum of the contract of carriage, by which the master agrees to transport the goods to their destination; all terms of the contract which was in fact concluded prior to the signing of the bill of lading are repeated on the back of this document;
  • A document of title to the goods enabling the consignee to dispose of the goods by endorsement and delivery of the bill of lading.

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Reversing of ME-C engine

Reversing of the engine is performed electronically and controlled by the Engine Control System,by changing the timing of the fuel injection, the exhaust valve activation and the starting valves.

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Friday, June 26, 2020

Biochemical Oxygen Demand and Coliform Count

Biochemical Oxygen Demand (B.O.D)
  • Amount of oxygen taken up by sewage sample in mg/l or ppm is termed as Biochemical Oxygen Demand.
  • Measure of strength of sewage.
  • Identifies biological decomposable substances and is a test on the activity of bacteria,
  • Presence of oxygen feed on and consume organic matter.
  • Test results are expressed as amount of oxygen taken by one litre sample (diluted with aerated water)when incubated at 20°C for five days. It gauges the effectiveness of sewage treatment process.
  • B.O.D of raw sewage is 300 to 600 mg/litre.
  • I.M.O recommends a B.O.D of 50 mg/litre after treatment.
Coliform Count
  • Coliform organisms are recognised as the indicator Organisms of sewage pollution.
  • Numbers present in sewage are large. Each person contributes between 125 billion, in winter to 400 billion, in summer.
  • Coliform are present in human intestine and presence in water is taken as an indication of the pathogen count.
  • Responsible for Typhoid, Dysentery, Polimyelitis, Cholera disease.
  • I.M.0 recommends a Coliform count of 250/100 ml. of effluent after treatment.
  • It gauges the effectiveness of disinfection

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Thursday, June 25, 2020

How to prepare the IOPP Survey ?

  • Validity of the IOPP certificate checked.
  • Proper entry of ORB and, sludge disposal receipts to shore facilities attached to ORB.
  • Calculate the sludge formation, and compared with 1% of voyage fuel consumption.
  • Incinerating time, incinerated waste oil amount, remainder of waste oil in waste oil tank should be reasonable.
  • Incinerator kept ready for demonstration, such as heating of waste oil tank, alarms, control and functional test, done priorto survey.
  • OWS in good order, it’s piping free from oil leaks, overboard valve from OWS locked in closed position. If possible, one
  • section of discharge pipe removed and free from oil residues.
  • ODM checked for 15-ppm alarm and automatic stopping.
  • High-level alarms of sludge tank, waste oil tank and bilge holding tank checked.
  • Spare filter for OWS must be kept onboard.
  • USCG Notice posted near OWS and bilge pumping out station.

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Stern tube leakage

Causes
  • Misalignment of bushes 
  • Poor material, design of liner and seals
  • Contaminated oil supply with foreign materials
  • Fishing net, rope and similar material entering into seal due to defective rope guard.
  • Electro static pitting on shaft due to defective shaft earthing device.
  • Prolonged low speed operation, in which hydrodynamic oil film could not attain.
Remedies
  • Keep good alignment of bushes. 
  • Use good material and an improved seal design.
  • Always maintain L.O level due to draught condition. 
  • Keep sufficient aft peak tank water level.
  • Use good design of rope guard. 
  • Keep earthing device in good order.
Action to be taken at sea to continue the voyage
  • When stern tube seal leaks at sea, minimized as possible. To continue the voyage, following actions are to be taken.
  • Correct the vessel trim, as possible as minimum astern, to certain allowable trim
  • Use more viscous oil (e.g. Cylinder oil)
  • Use lower header tank. If not possible, reduce the oil pressure-head by using a 'temporary header tank with flexible hose to obtain only slight pressure head above SW pressure.
  • If required, reduce rpm to avoid boundary lubrication.
Repair in port
  • Repairs or renewal of aft seal done either in dock or afloat.
  • If vessel is due for dry docking survey or a dry dock facility is available, arrange to enter dry dock and renew both seals.
  • If dry dock facility is not available, renewal of shaft seals done by Bonding method in port without removing propeller and tail shaft.
  • Necessary vessel trim by ahead until propeller shaft exposed to correct position above water level and to set up "scaffolding.
  • Renewal of sealing ring done by cutting and joining it on shaft with special tool and high temperature bonding method.
Insurance Claim
  • When leakage occurs, inform to head office or owner through captain.
  • When arrive in port, invite Class Survey and Underwriter Surveyor.
  • Survey damage and by their recommendation, repair to be carried out as per Class requirement.
  • Quotation of repairs and repair cost submitted to Underwriter Surveyor to negotiate for any reduction appear necessary.
  • Both surveyors will survey the repaired work when completed.
  • For insurance claim purpose, repair cost and bills endorsed by Underwriter Surveyor, but exclude transportation charges.
For insurance claim purpose the following items are necessary,
  • Damage report
  • log abstracts
  • Damage report form for insurance claim
  • Class Surveyor recommendation 
  • Repair bills endorsed by Underwriter Surveyor

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Steam boiler water tube leakage

How to know
  • Excessive feed water consumption from cascade tank
  • Continuously running boiler feed pump
  • If large amount of leakage, boiler water level low, steam pressure drop & continuous firing of boiler
  • Some water comes out from furnace cover
  • White smoke escaping from boiler uptake
Check Leakage
For water tube boiler (Z boiler)
  • Stop firing and open combustion chamber, leakage can be seen easily.
  • For individually boiler water tube, fill up the boiler water level to full and check. If necessary, pressure test should be done.
For smoke tube boiler
  • Open the smoke side drain valve, water will come out if boiler tube is leaking.
  • After opened up the fireside cover and fill up the boiler water level until all smoke tubes are flooded, we can easily check which one is leaking ligaments.
Possible Sources of water leakage
  • Leakage from tubes
  • Distorted furnace crown plate.
  • Furnace shell plate, opposite to burner opening due to flame impingement.
  • Lower section plate of furnace, due to damage bricks works.
Possible causes of leakage
  • External wastage due to waterside corrosion and pitting caused by using bad quality feed water or improper boiler water treatment.
  • Wastage of the ligaments due to soot blowing with wet steam.
  • Due to local overheating or design fault, unequal thermal expansion between tube and tube plate
  • Due to overheating, deformation or panting tube plate
Remedy and temporary repair at sea(Ref: MIURA Z Boiler)
  • Confirm and identify the leaking water tube.
  • After confirmed, remove castable until its swaged section is exposed so that the stopper can be welded.
  • Cut off one side of the leaking tube by gas.
  • Insert stoppers upward and downward through the cut-off section and seal them all around by welding.
  • Fit anchors on the inside face of the water tube and apply castable .
  • follow the manufacturer's instructions.
This method is only for temporary damage control and the damaged water tube replaced as soon as possible 

Procedure for permanent repair in port
  • If happening in port and enough time and spares, repaired permanently by renewal of leaking tube with ship's crew or availabl e labor.
  • After cool down, inspection of leakage and opening up for renewal of tubes,
  • Cut both ends of leaking tube about 50 mm from tube plate and chisel out.
  • Remove remaining pieces by (i) chiseling and (ii) knocking out by heating and cooling to achieve shrinkage.
  • Clean polish tube holes for dye check for any cracks, minor damage at the tube hole.
  • Diametrical clearance between tube and hole about 1.5 mm.
  • The ends of new tube cleaned thoroughly and carefully expanded by rolling into the hole and tube plate.
  • New tube protruded from tube plate by 6 mm at least.
  • Bell mouthing should be 1 mm for every 25 mm of tube outside diameter plus 1.5 mm

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Damage Stability

Oil tankers 
 
Oil tankers shall be regarded as complying with the damage stability criteria if the following requirements are met:
  • The final waterline, taking into account sinkage, heel and trim, shall be below the lower edge of any opening through which progressive flooding may take place.
  • In the final stage of flooding, the angle of heel due to unsymmetrical flooding shall not exceed 25°, provided that this angle may be increased up to 30° if no deck edge immersion occurs.
  • The stability in the final stage of flooding shall be investigated and may be regarded as sufficient if the righting lever curve has at least a range of 20° beyond the position of equilibrium in association with a maximum residual righting lever of at least 0.1 m within the 20° range; the area under the curve within this range shall not be less than 0.0175 m·rad.
  • The Administration shall be satisfied that the stability is sufficient during intermediate stages of flooding
  • Equalization arrangements requiring mechanical aids such as valves or cross-levelling pipes, if fitted, shall not be considered for the purpose of reducing an angle of heel or attaining the minimum range of residual stability to meet the requirements

For Bulk Carrier: SOLAS CHAPTER XII
  • Bulk carriers of 150 m in length and upwards of single side skin construction, designed to carry solid bulk cargoes having a density of 1,000 kg/m3 and above, constructed on or after 1 July 1999 shall, when loaded to the summer load line, be able to withstand flooding of any one cargo hold in all loading conditions and remain afloat in a satisfactory condition of equilibrium
  • Bulk carriers of 150 m in length and upwards of single side skin construction, carrying solid bulk cargoes having a density of 1,780 kg/m3 and above, constructed before 1 July 1999 shall, when loaded to the summer load line, be able to withstand flooding of the foremost cargo hold in all loading conditions and remain afloat in a satisfactory condition of equilibrium
  • The assumed flooding need only take into account flooding of the cargo hold space. The permeability of a loaded hold shall be assumed as 0.9 and the permeability of an empty hold shall be assumed as 0.95, unless a permeability relevant to a particular cargo is assumed for the volume of a flooded hold occupied by cargo and a permeability of 0.95 is assumed for the remaining empty volume of the hold

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Intact Stability criteria

In port
The initial metacentric height GMo, corrected for the free surface measured at 0° heel, shall be not less than 0.15 m

At sea
The following criteria shall be applicable:
  • A-area under curve up to 30 degrees to be not less than 0.055 metre-radian.
  • B-area under curve up to x degrees to be not less than 0.09 metre-radian
  • C-area between 30 degrees and x degrees to be not less than 0.03 metre-radian.
  • x-40 degrees or any lesser angle at which the lower edges of any openings in the hull, Superstructure or deckhouses which lead below deck and cannot be closed weathertight, would be immersed
  • E-maximum GZ to occur at angle not less than 30 degrees and to be at least 0.20 metre in height
  • The maximum righting arm shall occur at an angle of heel preferably exceeding 30° but not less than 25°
  • The initial metacentric height GMo, corrected for free surface measured at 0° heel, shall be not less than 0.15 m

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Wednesday, June 24, 2020

Hydrostatic Curves

  • A series of graphs drawn to a vertical scale of draught and a base of length, which gives values such as the centre of buoyancy, displacement, moment causing unit trim, and centre of flotation.
  • In practice tables with hydrostatic parameters calculated for different draughts are used. However, only having traditional graphs it is possible to observe character of hydrostatic curves and understand ship behaviour


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Bonjean Curves

  • Curve plotted on lines plan of ship is calls bonjean curve, here the longitudinal section of the vessel is divided in 10 stations.
  • At each station transverse section and each draft, we calculate e area and moment of area., these moments then plotted on the lines plan....
  • Use: fo calculation of hydrostatics like displacement block coefficient centre of floatation TPC etc.
  • Enable the users to calculate the displacement and the centre of buoyancy for a given waterline, in an upright condition
  • curves of areas of transverse sections and their moments about the baseline of a ship used in making calculations (as to determine the force of buoyancy during launching)
  • The Bonjean curve had as its ordinate the cross sectional area at that section, up to the waterline concerned. Each curve was usually plotted with its axis The vertical axis was traditionally at ship scale.
  • Their main uses were for launching (end launching) and longitudinal strength.
  • For launching, prior to stern lift, the progressive waterlines would be set up on the ship profile with the Bonjean curves.
  • Where this waterline cut the vertical axis was the local draft at that section. Bonjean area was read at each such intersection, and then integrated longitudinally for both volume and moment.
  • These gave the volume of buoyancy and its longitudinal moment about the fore poppet for each successive waterline, to match against moment of weight force about the fore poppet, defining the point of stern lift.

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KN cross curves of stability

  • Same as the GZ cross curves and also used to get the GZ values for making the curve of statical stability.
  • The only difference being that here the KG is assumed to be ZERO.
  • This solves the problem of a sometimes positive and sometimes negative correction, as now the correction is always subtracted.
GZ = KN – KG Sine θ


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In Water Survey

Hull survey while ship is afloat done by authorized diving company with surveillance of Class surveyor as the replacement of docking survey

Requirements for IWS
  • Age not greater than 15 years. ( Ships of age 15 years and over may be permitted as special consideration)
  • All ships excluding Enhanced Survey Program (ESP) ships, such as Bulk carrier, Oil Tankers and Dangerous chemical bulk carrie rs of 15 years of age and over.
  • Ship with class “IWS” notation.
  • Need agreement of Flag administration.
  • High quality paint coating for 7.5 years extended dry docking (EDD).
  • Fitted effective anodes, fitted effective current corrosion protection (ECCP).
  • Access arrangements for - sea valves, rudder bearing & pintle clearance.
  • Stern tube wear down measurement, bow & stern thruster  -seal checking  
Documents
  • Survey plan,
  • Location and date of IWS,
  • Detail of hull marks and drawings.
Preparations in dry dock for IWS notation
  • Fitted approved Cathodic protection system.
  • Ship hull is in a satisfactory condition – shot blasted and painted with high quality paint
  • Fitted means for renewal and/or measuring of clearances of
  • Rudder bearings and bushes, stern tube wear down
  • Measures for checking of sea valves and sea chests.
  • Shell openings to be fitted gratings with hinged grid plates.
  • Hull paint color - to assist divers for inspection of hull in next IWS.
  • Mark clearly under-water hull fittings.
  • Mark transverse & longitudinal bulkheads
  • Mark tanks boundaries
  • Mark openings of shell plating for sea valves, docking plugs, thruster unit, stabilizer fins
  • Mark propeller blades with numbers
  • Mark for checking of any relative movements in next IWS
  • Liners on shaft    -bushes of rudder and stern frame
  • Drawings and folders containing above markings
  • Agreed blanking methods of any shell openings

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Tuesday, June 23, 2020

Crosshead bearing latest developments

  • Bearing Geometry - No grooves at the centre.
  • Material modification- Instead of white metal we AlSn40 are used.
  • Synthetic layer is applied on top of AlSn40.
  • Angle between two axial grooves is now 70 degree.

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Cross curves of stability

  • The Cross Curves Of Stability are used to determine the length of the righting arm at any angle of inclination for a given displacement.
  • To draw the curve of statical stability, we need GZ values for various angles of heel.
  • For this we use the GZ cross curves of stability.
  • These curves are provided for an assumed KG, tabulating GZ values for various displacements and angles of list.
  • Called cross curves because the various curves actually ‘cross’ each other.
  • Since the curves are plotted for an assumed KG, if the actual KG differs from this a correction (GG1Sineθ) needs to be applied.
  • This correction is positive if the actual KG is less than the assumed KG and vice-versa.
  • After obtaining the GZ values at various angles, the curve of statical stability is prepared

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GZ curves of stability

  • Graph where GZ is plotted against the angle of heel.
  • Drawn for each voyage condition by the ship’s officer.
  • This curve is for a particular displacement and KG.
From this curve it is possible to ascertain the following:
  • Initial metacentric height – point of intersection of the tangent drawn to the curve at the initial point and a vertical through the angle of heel of 57.3° (1 radian)
  • Angle of contra flexure – the angle of heel up to which the rate of increase of GZ with heel is increasing. Though the GZ may increase further, the rate of increase of GZ begins to decrease at this angle.
  • The range of stability – where all GZ values are positive.
  • The maximum GZ lever & the angle at which it occurs.
  • The angle of vanishing stability – beyond which the vessel will capsize.
  • The area of negative stability.
  • The moment of statical stability at any given angle of heel (GZ x Displacement of the ship).
  • The moment of dynamical stability – work done in heeling the ship to a particular angle.
Dynamical stability at è = W x A (in t-m-rad)
                                      W = Displacement (in tonnes)
                                      A = area between the curve and the baseline up to the given angle of heel (in metre-radians).
 
Assumption:
  • The ship's center of gravity does NOT change position as the angle of heel is changed.
  • The ship's center of buoyancy is always at thegeometric center of the ship's underwater hull
  • The shape of the ship's underwater hull changesas the angle of heel changes.

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Angle of loll

  • Intial unstable ship will not be upright. While heeling one side, the angle at which the G & B coincides in neutral equilibrium.
  • If GZ=0 then angle of Equilibrium = angle of loll
How to Recognize
  • Vessel will not remain upright and will assume a list to either port or starboard.
  • Vessel "flops" to port or starboard.
  • Vessel will have a very long, slow roll period about the angle of list.
  • A small GM is known to exist, plus any of the above.
Angle of Loll
  • -ve GM
  • Unstable Equilibrium.
  • G on the Centreline.
  • Corrected by lowering G below M
CORRECTION OF ANGLE OF LOLL
  • Moving cargo to a lower position;
  • Jettisoning top-weight (in an emergency);
  • Reducing FSE by pressing up/emptying tanks;
  • Filling low ballast spaces such as DB tanks
  • Top up tanks that are already slack.
  • Start with the smallest tank on the LOW side first. (If a tank on the high side is filled first, the ship will start to right herself but will then tend to roll over suddenly in an uncontrolled fashion as she passes through the upright. She will then „whip‟ through to a larger angle of loll on the other side. She may even capsize if the momentum gathered is sufficient.) When the low side is filled first, the angle of list will increase initially, but in a slow and controlled fashion. After some time, the weight of the ballast water added will be sufficient to lower the ship’s COG (despite the extra FSE), to cause the angle of list to decrease. By this method the inclining motions of the v/l take place in a gradual and controlled manner
  • Now fill the opposite tank on the high side.
  • Fill tanks alternately, low side first, until the v/l returns to positive GM.
  • Ensure that all tanks are completely filled.

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Tailshaft Survey

Tailshaft Condition Monitoring System:
  • Complete tailshaft survey will be required if the last complete tailshaft survey was carried out more than five (5) years prior to the initial survey
  • For vessels with TCM notation, tailshaft survey interval required by 7-2-1/13.1.3 will be extended up to 15 years provided:
  • Annual surveys are carried out to the satisfaction of the attending Surveyor, and
The following are carried out at each tailshaft survey due date required
  • Bearing weardown measurement
  • Verification that the propeller is free of damage which may cause the propeller to be out of balance
  • Verification of effective inboard seal
  • Renewal of outboard seal in accordance with manufacturer’s recommendation
Complete tailshaft survey may be waived subject to satisfactory review of the following records for appropriate period as considered necessary
  • Stern bearing oil analysis records
  • Stern bearing oil consumption records
  • Stern bearing temperature monitoring records
  • Tailshaft, stern bearing assembly and propeller operation and repair records
  • Stern bearing clearance and wear down measurement records
Tailshaft Survey
METHOD 1

The survey is to consist of:
  • Drawing the shaft and examining the entire shaft, seals system and bearings
  • For keyed and keyless connections
  • Removing the propeller to expose the forward end of the taper,
  • Performing a non-destructive examination (NDE) by an approved surface crack detection method all around the shaft in way of the forward portion of the taper section, including the keyway (if fitted). For shaft provided with liners the NDE shall extended to the after edge of the liner.
For flanged connection:
  • Whenever the coupling bolts of any type of flange-connected shaft are removed or the flange radius is made accessible in connection with overhaul, repairs or when deemed necessary by the surveyor, the coupling bolts and flange radius are to be examined by means of an approved surface crack detection method
  • Checking and recording the bearing clearances.
  • Verification that the propeller is free of damages which may cause the propeller to be out of balance.
  • Verification of the satisfactory conditions of inboard and outboard seals during the reinstallation of the shaft and propeller.
  • Verification of the satisfactory conditions of inboard and outboard seals during the reinstallation of the shaft and propeller.
METHOD 2
The survey is to consist of:
 
For keyed and keyless connections:
  • Removing the propeller to expose the forward end of the taper,
  • Performing a non-destructive examination (NDE) by an approved surface crackdetection Method all around the shaft in way of the forward portion of the taper section, including the keyway (if fitted).
For flanged connection:
  • Whenever the coupling bolts of any type of flange-connected shaft are removed or the flange radius is made accessible in connection with overhaul, repairs or when deemed necessary by the surveyor, the coupling bolts and flange radius are to be examined by means of an approved surface crack detection Method
  • Checking and recording the bearing wear down measurements.
  • Visual Inspection of all accessible parts of the shafting system.
  • Verification that the propeller is free of damages which may cause the propeller to be out of balance.
  • Seal liner found to be or placed in a satisfactory condition.
  • Verification of the satisfactory re-installation of the propeller including verification of satisfactory conditions of inboard and outboard seals
Pre-requisites
  • Review of service records.
  • Review of test records of:
  • Lubricating Oil analysis (for oil lubricated shafts), or
  • Fresh Water Sample test (for closed system fresh water lubricated shafts).
  • Oil sample Examination (for oil lubricated shafts), or Fresh Water Sample test (for closed system fresh water lubricated).
  • Verification of no reported repairs by grinding or welding of shaft and/or propeller.
METHOD 3
The survey is to consist of:

  • Checking and recording the bearing wear down measurements.
  • Visual Inspection of all accessible parts of the shafting system.
  • Verification that the propeller is free of damages which may cause the propeller to be out of balance.
  • Seal liner found to be or placed in a satisfactory condition.
  • Verification of the satisfactory conditions of inboard and outboard seals.
Pre-requisite
  • Review of service records.
  • Review of test records of:
  • Lubricating Oil analysis (for oil lubricated shafts), or
  • Fresh Water Sample test (for closed system fresh water lubricated shafts).
  • Oil sample Examination (for oil lubricated shafts), or Fresh Water Sample test (for closed system fresh water lubricated).
  • Verification of no reported repairs by grinding or welding of shaft and/or propeller

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Derating of engine

  • A vessel’s engine and propeller are optimized and designed for a given operational and max. speed.
  • If the operational speed of the vessel is generally lower than the one originally optimized for, it may be beneficial to consider derating of the main engine and propeller.
  • Derating as a retrofit product offers reduction of the total fuel consumption by improving the match between the operational speed and optimization speed.
  • Derating is usually an attractive option for fuel oil savings if a reduction of 10-15% of the max. speed at SMCR can be accepted.
  • It is a techno-commercial concept done at the time where shipping industry is in bad shape
Methods:
  • Readjusting fuel timing
  • Decreasing compression ratio
  • Fuel nozzle size
  • Turbocharger matching
  • t/c, propeller and shaft matching
Fuel saving originates from
  • Optimisation of the engine and propeller layout to the actual operational speed
  • Utilisation of the latest engine tuning methods
  • Utilisation of state-of-the-art high efficiency propeller design.
Derating projects includes
  • Specification of new operating/optimisation speed and max. speed of the vessel
  • Engineering
  • Design of new propeller
  • Derating of the engine
  • Rematching of turbocharger(s)
  • On board NOx measurements (parent engine)
  • New technical file
  • Torsional vibration calculation report
  • Shaft alignment calculation report.
RATE SHAPING
  • A fuel injection rate shaping control system is provided which effectively controls the flow rate of fuel injected into the combustion chamber of an engine to improve combustion and reduce emissions by controlling the rate of pressure increase during injection.
  • The injection rate shaping control system includes a rate shaping control device including a rate shaping transfer passage having a predetermined length and diameter specifically designed to create a desired injection pressure rate shape.

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Continuous synopsis record (CSR)

  • Continuous synopsis record is a special measure under SOLAS for enhancing the maritime security at the sea.
  • According to SOLAS chapter I, all passenger andcargo ships of 500 gross-tonnage and above must have a continuous synopsis record on board.
  • The continuous synopsis record provides an onboard record of the history of the ship with respect to the information recorded therein
  • Continuous synopsis record (CSR) is issued by the administration of the ship, which would fly its flag.
Following details should be present in the continuous synopsis record (CSR)
  • Name of the ship
  • The port at which the ship is registered
  • Ship’s identification number
  • Date on which ship was registered with the state
  • Name of the state whose flag the ship is flying
  • Name of registered owner and the registered address
  • Name of registered bareboat charterers and their registered addresses
  • Name of the classification society with which the ship is classed
  • Name of the company, its registered address and the address from where safety management activities are carried out
  • Name of the administration or the contracting government or the recognized organization which has issued the document of compliance, specified in the ISM code, to the company operating the ship.
  • Name of the body which has carried out the audit to issue the document of compliance
  • Name of the administration or the contracting government or the recognized organization which has issued the safety management certificate (SMC) to the ship and the name of the body which has issued the document
  • Name of the administration or the contracting government or the recognized organization which has issued the international ship security certificate, specified in the ISPS code, to the ship and the name of the body which has carried out the verification on the basis of which the certificate was issued
  • The date of expiry of the ship’s registration with the state
  • The continuous synopsis record shall always be kept on board ship and shall be available for inspection all the time.

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Load line survery preparation

The preparation for a load line survey will involve ensuring that the hull is watertight below the freeboard deck and weathertight above it
The following checks should be conducted prior to survey:
  • Check that all access openings at the ends of enclosed superstructures are in good condition. All dogs, clamps and hinges should be free and greased. Gaskets and other sealing arrangements should not show signs of perishing (cracked rubbers).
  • Check all cargo hatches and accesses to holds for weathertightness. Securing devices such as clamps, cleats and wedges are to be all in place, well-greased and adjusted to provide optimum sealing between the hatch cover and compression bar on the coaming. Replace perished rubber seals as necessary. Hose test hatches to verify weathertightness.
  • Check the efficiency and securing of portable beams.
  • Inspect all machinery space openings on exposed decks
  • Check that manhole covers on the freeboard deck are capable of being made watertight.
  • Check that all ventilator openings are provided with efficient weathertight closing appliances.
  • All air pipes must be provided with permanently attached means of closing.
  • Inspect cargo ports below the freeboard deck and ensure that they are watertight.
  • Ensure that all non-return valves on overboard discharges are effective.
  • Side scuttles below the freeboard deck or to spaces within enclosed superstructures must have efficient internal watertight deadlights. Inspect deadlight rubber seals and securing arrangements.
  • Check all freeing ports, ensure shutters are not jammed, hinges are free and that pins are of non-corroding type (gun metal).
  • Check bulwarks and guardrails are in good condition.
  • Rig life lines (if required) and ensure they are in good order.
  • De-rust and repaint deck line, load line mark, load lines and draught marks

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Friday, June 19, 2020

Enclosed Space Entry

Preparation for enclosed space entry
  • Competent person and a responsible officer to take charge of operation.
  • Carried out risk assessments, identified potential hazards
  • Space isolated and secured against ingress of dangerous substances by blanking off pipe-lines or other openings and by closing valves.
  • Clean Sludge and deposits and ventilate space thoroughly
  • Test oxygen deficiency, flammability and toxicity to confirm space is safe to entry.
  • When space is safe for entry, "Enclosed space entry permit" has to be issued.
The procedure and arrangement before entry
  • Access to and within the space should be adequate and well illuminated. No source of ignition used.
  • Rescue and resuscitation equipment should be available at the entrance to the space.
  • Arrange means of hoisting physical inability person from the confined space.
  • Select only working number of personnel entering the space to rescue the physical inability person in any accident.
  • Lifelines should be long enough to be firmly attached to the harness.
  • Enclosed space entry permit posted at work site.
Procedure and arrangement during entry.
  • Ventilation continue at all the time. If ventilation fails, all personnel leave immediately.
  • Test atmosphere periodically and if conditions deteriorate, leave the space.
  • If a personal gas detector alarms, the space leave by all personnel immediately.
  • If unforeseen difficulties or hazards develop, the work in the space should be stopped and the space evacuated.
  • Permits should be withdrawn and only re-issued
  • If any personnel in a space feel adversely affected, give pre-arranged signal by entrance and immediately leave space.
Procedures on completion
  • Everyone leave the space, carried out head count, close entrance to space.
  • Record time of completion, Responsible person & Authorized person sign in permit
  • Entry engine room log book

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Differences between MC/MC-C and ME/ME-C engines

The electrohydraulic control mechanisms of the ME engine replace the following components of the conventional MC engine:
  • Chain drive for camshaft
  • Camshaft with fuel cams, exhaust cams and indicator cams
  • Fuel pump actuating gear, including roller guides and reversing mechanism
  • Conventional fuel pressure booster and VIT system
  • Exhaust valve actuating gear and roller guides
  • Engine driven starting air distributor
  • Electronic governor with actuator
  • Regulating shaft
  • Engine side control console
  • Mechanical cylinder lubricators.
The Engine Control System of the ME engine comprises:
  • Control units
  • Hydraulic power supply unit
  • Hydraulic cylinder units, including:
  • Electronically controlled fuel injection, and
  • Electronically controlled exhaust valve activation
  • Electronically controlled starting air valves
  • Electronically controlled auxiliary blowers
  • Integrated electronic governor functions
  • Tacho system
  • Electronically controlled Alpha lubricators

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Thursday, June 18, 2020

Dampers, Detuners and Compensators

  • Every running machine has a tendency to vibrate because of several moving parts incorporated within it.
  • When in motion, the machine will have an oscillatory motion around an equilibrium point.
  • The natural frequency of vibration is always present in marine engines, but the effect can be dangerous when the vibration frequency reaches high levels. This happenswhen the natural frequency of vibration from an external source integrates with the engine vibration or when there are out-of-balance forces generated inside the engine which create 1st and 2nd order movements.
  • Such effects can result in severe damage to the marine engine’s internal moving parts, cracks in the structure, loosening of bolts and securing and damage to bearings.
Dampers:
  • Dampers are used to damp or reduce the frequency of oscillation of the vibrating components of the machine by absorbing a part of energy evolved during vibration
  • Axial vibrations: When the crankthrow is loaded by the gas force through the connecting rod mechanism, the arms of the crank throw deflect in the axial direction of the crankshaft, exciting axial vibrations which, through the thrust bearing, may be transferred to the ship’s hull
  • Torsional vibration: The varying gas pressure in the cylinders during the working cycle and the crankshaft/connecting rod mechanism create a varying torque in the crankshaft
Axial Damper:
  •  The Axial damper is fitted on the crankshaft of the engine to dampen the shaft generated axial vibration i.e. oscillation of the shaft in forward and aft directions, parallel to the shaft horizontal line.

  • It consists of a damping flange integrated to the crankshaft and placed near the last main bearing girder, inside a cylindrical casing. The casing is filled with system oil on both side of flanges supplied via small orifice. This oil provides the damping effect.
  • When the crankshaft vibrates axially, the oil in the sides of damping flange circulates inside the casing through a throttling valve provided from one side of the flange to the other, which gives a damping effect.
Torsional Damper: 
  • It is a twisting phenomenon in the crankshaft which spreads from one end to other due to uneven torque pulses coming from different units ‘pistons.
  • Consist of an inertia ring added to the crankshaft enclosed in a thin layer of highly viscous fluid like silicon.
  • The inertia ring is free to rotate and applies a lagging torque on the crankshaft due to its lagging torsional motion.
  • When the crankshaft rotates, the inertia ring tends to move in radial direction but the counter effect is provided by the silicon fluid damping the vibration
 De-tuners
  • De-tuners  are used to alter the frequency of the vibrating machinery reducing the vibration of the engine
  • Guide force moments: When the piston is not exactly in its top or bottom position, the gas force, transferred through the connecting rod, will have a component acting on the crankshaft perpendicular to the axis of the cylinder. Its resultant is acting on the guide shoe and, together, they form a guide force moment
  • Side Bracing: Normally fitted on the top of the engine which increases the stiffness and raises the natural frequency beyond the working range
  • Flexible Coupling:If the engine has a Power turbine connected to its crankshaft via a reduction gear, then flexible coupling is used to compensate for the vibration occurring during motion transfer. The Flexible elements are mainly spring or special material rubber for de tuning the vibration.
Compensators:
  • Compensator comprises two counter-rotating masses running at the same speed as the main engine crankshaft
  • The external moments are known as the 1st, order moments (acting in both the vertical and horizontal directions) and 2nd order moments (acting in the vertical direction only, because they originate solely in the inertia forces on the reciprocating masses.
  • The counterweights on the chain wheel produce a centrifugal force which creates a moment, the size of which is found by multiplying the force by the distance to the node.

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Green Engines

 The ‘G’ prefix before an engine means it has a design that follows the principles of the large-bore, Mark 9 engine series that MAN Diesel & Turbo introduced in 2006 with an ultra-long stroke that reduces engine speed, thereby paving the way for ship designs with unprecedented high-efficiency.

Specification of G-80ME-C9
            ▪    Power kW/cyl    : 4,450
            ▪    Engine speed rpm    : 68
            ▪    Stroke mm        : 3.720
            ▪    MEP bar        : 21
            ▪    Mean piston speed m/s    : 8.43
            ▪    Length mm (7 cylinder)     : 12.500
            ▪    Dry mass ton (7 cylinder)    : 960
            ▪    SFOC, L1 (g/kWh)        : 167

The G-type achieves SFOC reductions through a combination of several factors, such as:
            ▪    increased scavenge-air pressure
            ▪    reduced compression ratio (twostroke Miller timing)
            ▪    increased maximum combustion pressure
            ▪    adjustments of compression volume and design changes.

The G-type engine is characterised by:
  • low SFOC and superior performanceparameters thanks to variable,electronically controlled timing of fuelinjection and exhaust valves at anyengine speed and loadappropriate fuel injection pressureand rate shaping at any engine speedload
  • flexible emission characteristics withlow NOx and smokeless operation
  • perfect engine balance with equalisedthermal load in and betweencylinders
  • better acceleration in ahead andastern operation and crash stop situations
  • wider operating margins in terms ofspeed and power combustions
  • longer time between overhauls
  • very low speed possible even forextended duration and Super DeadSlow operation manoeuvring
  • individually tailored operating modesduring operationfully integrated Alpha Cylinder Lubricators,with lower cylinder oil consumption
  • an engine design lighter than its mechanicalcounterpart.

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Windlass requirements

  • Letting go anchor cable speed vary between 5 ~ 7 mtr/sec.
  • Heaving up speed 0.125 ~ 0.25 mtr / sec or 3 ~ 5 rpm.
  • Full loaded duty of windlass commonly 4 ~ 6 time of the weight of one anchor.
  • Warpends for mooring purpose and light line speed up to 0.75 ~ 1.0 mtr /sec

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What limit of elongation should be tighten the chain

1.5 % of original length .

Slack chain:

Symptoms:

  • Excessive chain vibration and noise.
  • Power loss in all units, indicated [by Power Card].
  • Late injection, low Pmax, [by Draw Card].
  • Late closing of Exhaust Valve, [by Light Spring Diagram].
  • High exhaust temperature and smoke.

Effects:
  • Impose heavy mechanical load, resulting fatigue failure.
  • Damage to chain system and engine frame.
  • Retardation of Fuel Pump and Exhaust Valve timings, resulting:
  • Reduced Scavenge Efficiency due to late closing of exhaust valve.
  • High exhaust temperature and smoke, due to after burning.
  • Low Pmax, due to late injection.
  • Reduced engine power


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Limitation for emission the black smoke

According to the regulation the emission from black smoke from ship
Must not come out continuously longer than 4 min:
If emission is short , total amount of time must be 3 min: in every 20 min: period.
Not more than 10 min: in total amount of time for any 2 hr period.


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Homogenizer


 
  •  The homogenizer (Vickers Type: See figure above) provides an alternative solution to the problem of water in high-density fuels. It can be used to emulsify a small percentage for injection into the engine with the fuel. This is in contradiction to the normal aim of removing all water, which in the free state can cause gassing of fuel pumps, corrosion and other problems. 
  • However, experiments in fuel economy have led to the installation of homogenizers on some ships to deal with a deliberate mixture of up to 10% water in fuel. 
  • The homogenizer is fitted in the pipeline between service tank and engine so that the fuel is used immediately.
  • It is suggested that the water in a high-density fuel could be emulsified so that the fuel could be used in the engine, without problems. 
  • A homogenizer could not be used in place of a purifier for diesel fuel, as it does not remove abrasives such as aluminium and silicon, other metallic compounds or ash-forming sodium which damages exhaust valves.
  • The three disc stacks in the rotating carrier of the Vickers type homogenizer are turned at about 1200 rev/min. Their freedom to move radially outwards means that the centrifugal effect throws them hard against the lining tyre of the homogenizer casing.
  • Pressure and the rotating contact break down sludges and water trapped between the discs and tyre, and the general stirring action aids mixing.

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Checks to Perform on Ship before Coming out of the Dry Dock

It is extremely important to maintain a checklist of things and procedure to be done before undocking and not to miss any vital point which will lead to delay in undocking.
Following things must be checked by a responsible engineer and deck officers before water is filled up in the dock:
  • All Departments in charge to confirm that repairs assigned under their departments are completed successful with tests and surveys are carried out
  • Check rudder plug and vent and also check if anode are fitted back on rudder
  • Check hull for proper coating of paint; make sure no TBT based paint is used.
  • Check Impressed Current Cathodic Protection system (ICCP) anodes are fitted in position and cover removed
  • Check Anodes are fitted properly on hull and cover removed (if ICCP is not installed)
  • Check all double bottom tank plugs are secured
  • Check all sea inlets and sea chests gratings are fitted
  • Check echo sounder and logs are fitted and covers removed
  • Check of propeller and rudder are clear from any obstruction
  • Check if anchor and anchor chain is secured on board
  • Check all external connection (shore water supply, shore power cables) are removed
  • Check inside the ship all repaired overboard valve are in place
  • Secure any moving item inside the ship
  • Check sounding of all tank and match them with the value obtain prior entering the dry dock
  • Check stability and trim of the ship. Positive GM should be maintained at all time
  • If there is any load shift or change in stability, inform  the dock master
  • Go through the checklist again and satisfactory checklist to be signed by Master
  • Master to sign authority for Flood Certificate
  • When flooding reaches overboard valve level, stop it and check all valves and stern tube for leaks
  • Instruction to every crew member to be vigilant while un-docking

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Wednesday, June 17, 2020

Name of refrigerant significance(R22,R134A)

The prefix describes what kinds of atoms are in a particular molecule, the next step is to calculate the number of each type of atom. The key to the code is to add 90 to the number; the result shows the number of C, H, and F atoms. For HCFC-141b:

One more piece of information is needed to decipher the number of Cl atoms. All of these chemicals are saturated; that is, they contain only single bonds. The number of bonds available in a carbon-based molecule is 2C + 2. Thus, for HCFC-141b, which has 2 carbon atoms, there are 6 bonds. Cl atoms occupy bonds remaining after the F and H atoms. So HCFC-141b has 2C, 3H, 1F, and 2Cl:

First, consider two-carbon molecules. For example, HCFC-141, HCFC-141a, and HCFC-141b all have the same atoms (2C, 3H, 1F, and 2Cl), but they are organized differently. To determine the letter, total the atomic weights of the atoms bonded to each of the carbon atoms. The arrangement that most evenly distributes atomic weights has no letter. The next most even distribution is the "a" isomer, the next is "b," etc. until no more isomers are possible.

A common way of writing isomers' structure is to group atoms according to the carbon atom with which they bond. Thus, the isomers of HCFC-141 are:

  • HCFC-141  :   CHFCl - CH2Cl (atomic weights on the 2 carbons = 37.5 and 55.5)
  • HCFC-141a:   CHCl2 - CH2F (atomic weights on the 2 carbons = 21 and 72)
  • HCFC-141b:   CFCl2 - CH3 (atomic weights on the 2 carbons = 3 and 90)


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Comparison between Rapson Slide Type and Rotary Vane Type


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Loadline ( Plimsoll ) Marking


Each vessel is required to hold a Loadline Certificate. Part of the requirements for this is the permanent marking of loadlines on either side of the hull arounf about midhsips. Permanent marking means that they have to be impressed or welded so that they cannot be removed by normal wear and tear. They should be white or yellow on a dark contrasting back ground. Regulations govern the number and size of these, the main ones are described below.

Danish Load mark

The Load Line Mark shall consist of a ring 300 millimeters (12 inches) in outside diameter and 25 millimeters (1 inch) wide which is intersected by a horizontal line 450 millimeters (18 inches) in length and 25 millimeters (1 inch) in breadth, the upper edge of which passes through the centre of the ring. The centre of the ring shall be placed amidships and at a distance equal to the assigned summer freeboard measured vertically below the upper edge of the deck line

Deck Mark
The deck line is a horizontal line 300 millimeters (12 inches) in length and 25 millimeters (1 inch) in breadth. It shall be marked amidships on each side of the ship, and its upper edge shall normally pass through the point where the continuation outwards of the upper surface of the freeboard deck intersects the outer surface of the shell. The location of the reference point and the identification of the freeboard deck is indicated on the International Load Line Certificate (1966). Lines to be used with the Load Line Mark

Loadline Mark
The lines which indicate the load line shall be horizontal lines 230 millimeters (9 inches) in length and 25 millimeters (1 inch) in breadth which extend forward of, unless expressly provided otherwise, and at right angles to, a vertical line 25 millimeters (1 inch) in breadth marked at a distance 540 millimeters (21 inches) forward of the centre of the ring . Aft of thevertical mark refers to loading in freshwater only. For'd refers to loading in sea water only
   
The loadline mark consists of the following marks
  • The Summer Load Line indicated by the upper edge of the line which passes through the centre of the ring and also by a line marked S.
  • The Winter Load Line indicated by the upper edge of a line marked W.
  • The Winter North Atlantic Load Line indicated by the upper edge of a line marked WNA.
  • The Tropical Load Line indicated by the upper edge of a line marked T.
  • The Fresh Water Load Line in summer indicated by the upper edge of a line marked F.
  • The Tropical Fresh Water Load Line indicated by the upper edge of a line marked TF


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Emergency fire pump requirement: - SOLAS ch II-2 reg 10,

  1.   Independent driven power operated pump
  2.  Capacity should not be less than 40%  of the total fire pump capacity required by regulation II-2 / 10.2.2.4.hj1 and in any not less than 25 m3 /hr for cargo ships 200 Gt and above.
  3. (Each of the required fire pumps (other than any emergency pump required in paragraph 2.2.3.1.2 for cargo ships) shall have a capacity not less than 80% of the total required capacity divided by the minimum number of required fire pumps but in any case not less than 25 m3/h and each such pump shall in any event be capable of delivering at least the two required jets of water. These fire pumps shall be capable of supplying the fire main system under the required conditions. Where more pumps than the minimum of required pumps are installed such additional pumps shall have a capacity of at least 25 m3/h and shall be capable of delivering at least the two jets of water required in paragraph 2.1.5.1.)
  4. Minimum pressure at any hydrant  not less 2.7 bar.( 4.0 bar for passenger ship)
  5. Space containing should not be contiguous to the boundaries of machinery spaces or those spaces containing main fire pumps. Where this is not practicable, common bulkhead between the two spaces shall be insulated to a standard of structural fire protection equivalent to that required for control station.
  6. No direct access from engine room .( if impracticable then the access should be by air lock with door of machinery space being of A60 class standard and the other door being at least steel , both reasonably gas tight , self closing and without any hold back arrangement.
  7.  If diesel  driven , should be able to start by cranking at 0 deg. If impracticable , then there should be heating arrangement acceptable to admin. Starting at least 6 times within 30 min and at least twice within first 10 minutes.
  8. Fuel should be sufficient to run for 3 hrs and sufficient reserve fuel outside machinery space for 15 hrs running at full load.

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Friday, June 12, 2020

Hull repair

Cracked weld :
  • Inform Class surveyor & seek his opinion.
  • Trace the length ok crack by DPT.
  • One inch from both sides  drill crack arresting holes.
  • Gas free the tank from inside
  • Guaging of Crack to be carried out by guaging electrode till bottom of the crack is reached
  • Welding electrode, welder & procedure to be class approved. Low Hydrogen Electrodes are used.
  • The affected portion to be heated to 200 deg C by flame torch & temp to be noted by IR sensor.
  • Carry out welding from either side
  • The weld is again to be heated by flame to rleive stress & covered with insulation tapes to reduce cooling rate.
  • Weld to be inspected & arrest holes to be welded
  • Radiography to be carried out.
  • Hose test to be carried out.
  • Primer & paint to be applied

Severe indentation in way of frame  :
  • It cannot be tolerated so has to be cropped off alongwith bend frame & renewed.
  • Put 2 small size plates & weld it to frame (tag) with actual size plate.
  • Heating & stress rereleiving to be carried out.
  • Radiograpgy & Hose test of the weld to be carried out.

Surfaces suffering from general Corrosion  :
  • Guaging to be carried out & if 20 % is eaten away plate needs to be renewed.(decided by class survyr)
  • Only thing to be done is clean the surface, coat with primer, anti fouling & anti corrosive paints.
  • Add Zinc Anodes.
Bilge Keel Fractured :
  • Crop the damaged part & renew.    

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Stern Frame


 
A stern frame may be cast or fabricated and its shape is influenced by the type of rudder being used and the profile of the stern. Sternframes also differ between twin and single screw ships, the single screw sternframe having a boss for the propeller shaft. Adequate clearance is essential between propeller blade tips and sternframe in order to minimise the risk of vibration. As blades rotate water immediately ahead of the blades is compressed and at the blade tips this compression can be transmitted to the hull in the form of a series of pulses which set up vibration. Adequate clearance is necessary or alternatively constant clearance, this being provided with ducted propellers such as the Kort nozzle. A rotating propeller exerts a varying force on the sternframe boss and this can result in the transmission of vibration. Rigid construction is necessary to avoid this. The stern post, of substantial section, is carried up inside the hull and opened into a palm end which connects to a floor plate, This stern post is often referred to as the vibration post as its aim is to impart rigidity and so minimise the risk of vibration. Side plating is generally provided with a Rabbet or recess in order that the plating may be fitted flush. The after most keel plate which connects with this region the structure od the ship serves no useful purpose and it is known as the 'deadwood'. This may be removed without ill effect on stability or performance and some sternframes are designed such that the deadwood is not present.

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Chain stopper

For anchoring operations the stopper bar is locked upright. When it is required to fix the position of the chain the stopper is lowered into the position shown. This allows the brake to be released and is typically used for stowing the anchor. chain stopper arrangements are not design to stop a runaway chain. Alternately an arrangement known as the 'devil's claw' may be used which has a forked locking piece. For smaller vessels, and where extra security is required bottle jacks with wire strops passed though the chain may be used


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Water tight doors

Vertically mounted watertight door 
To allow the passage for personnel water tight doors are fitted , openings must be cut only were essential and they should be as small as possible. 1.4m high, 0.7m wide being the usual. Doors should be of mild steel or cast steel, and they may be arranged to close vertically or horizontally.
The closing action must be positive i.e. it must not rely on gravity. Hinged water tight doors may be allowed in passenger ships and in watertight bulkheads above decks which are placed 2.2m or more above the waterline. Similar doors may be fitted in weather decks openings in cargo ships.

Hinged water tight door

 Hinged water tight doors consist of a heavy section door which when closed seals on a resilient packing mounted in channel bar welded to the door frame.
The door is held firmly in the door frame when closed by the dogging arrangements shown which allow the doors to be opened from either side.Normally six of these dogs are spread equally around the periphery

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Automatic water tight door operating gear

Automatic operating gear allows the remote operation of watertight doors. These are fitted on many vessels including passenger ships.
In the event of fire or flooding, operation of switches from bridge/fire control area sends a signal to an oil diverter valve. Oil from a pressurised hydraulic system is sent to a ram moving the door.
The door may also be operated locally by a manual diverter valve. In addition, in the event of loss of system pressure the door may be operated by a local manual hand pump
remote door position indicators are fitted as well as were appropriate alarms to indicate operation.

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"Power" terminolagies used for Main Engine

Effective Power: The Power available at the output side of the engine i.e. at crankshaft flange of the engine which connects it with the flywheel and rest of the intermediate shaft

Rated Power: It is the continuous effective power provided by the manufacturer of the engine for a desired or rated RPM of the crankshaft. Rated power includes the loads which acts on the engine due to auxiliary system running from the engine power

Indicated Horse Power: It is a theoretical power calculated with a formula
                                          (PxLxAxN)  / 4500
                                            Where    P- Mean indicated pressure of the cylinder
                                                            L- Stroke of the engine
                                 .                         A-  Cross Sectional Area of the engine cylinder
    .                                                      N- Speed of the engine in RPM
                       .                                  4500 is a constant for conversion.
              In this calculation, the frictional losses are not considered. Since it is calculated from indicated pressure of  the engine, it is called Indicated Horse Power or IHP and used for calculating mechanical efficiency of the engine

Shaft Horse Power
: The power delivered by the engine to the propeller shaft is measured by an instrument known as torsion metre which is available on board.

Brake Horse Power
: This is the power measured at the crankshaft with the brake dynamometer and is always higher than the shaft horse power. This is because the power available at shaft accounts for frictional and mechanical losses.

Gross Power: Continuous effective power provided by the manufacturer for a given RPM using defined number of auxiliaries at normal service running condition without any overloading of the engine.

Continuous Power: It is the BHP measured at the power take off end when the engine is running at continuous safe operation range outside any time limit. This is provided by the supplier.

Overload Power: It is the power excess of effective power than the rated power for a short period of time, when the same auxiliaries are used under similar service condition for limited period.

Minimum Power: The guaranteed minimum or lower most power value by the manufacturer for an approximate crankshaft RPM is the minimum power of the engine.

Astern Output Power:
The maximum power engine can generate when running in the astern direction at safe condition.

Maximum Continuous Rating or MCR: It is the maximum power output engine can produce while running continuously at safe limits and conditions.

Standard Rating: This is the power output of the engine at normal service speed which gives the highest economical efficiency, thermal and mechanical efficiency. At this speed, the wear down of the engine is at the minimum rate

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