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Showing posts from 2023

Mooring winch Brake holding capacity

 Determined at the design stage based on vessel size, number of mooring lines , wind area and tidal conditions and the mean braking load of mooring lines. After selection of the  MBL of the mooring line, the winch heaving load will be set to a lower value than MBL to prevent the winch motor from applying excessive loads

Working of a Chain Block

The chain block contains two cogs or gears in which the chain is wrapped around. Both electric chain blocks and manual chain blocks have the same fundamental functions - when the chain is pulled, it wraps around the wheels which adds torque to the lifting mechanism, pulling the item that is on the other end of the chain (usually with a strong hook) and lifting it off the ground - the wheels inside the block are how they are able to lift heavy loads - even when operated manually. when the chain is release a braking mechanism kicks in and holds the load where it is until the chain is pulled again. A chain block has a strong chain for lifting objects and attaching hooks to, manual lifting blocks have a hand chain which can be used for pulling by hand to bring the load up (these are powered by motors in electric chain blocks), they also have a grabbing load hook for attaching the load . 

Rudder Trunk

Rudder stock is carried in the rudder trunk which as a rule is not made water tight at lower end , but water tight gland at top of the trunk ;ie, where the stock enters the intact hull. Trunk kept short so that the stock has minimum unsupported length.  Watertight opening for inspection

Bedplate alignment - Piano wire method

 A 0.5 mm diameter piano wire is stretched along each side of the bedplate. The wire is loaded with 40 KPa horizontal force. At the centre line of each cross girder , the distance is measured between the wire and the machined faces of the bedplate top outside oil grooves It will thus be revealed whether the later has changed compared with values during engine installation. The measurement are taken by micrometer with laser light when touches wire.

Sewage checks by PSC inspector

Chlorine content on effluent STP is operational or not Corrosion or hole on the tank holding to tank Aeration blower working and checking the pressure Overboard valve locked and sealed. Seal number recorded on logbook Validity of international sewage pollution prevention certificate Proper air lift from settling tank to aeration chambers Working of high level alarms and auto cut off Presence of Chlorine tablets or UV lamp 

Why Full Astern Power is usually less than Full Ahead Power

Propeller blade system is designed for maximum efficiency in ahead direction In astern direction angle of attack is high on the back of the blade. Propeller will absorb very little available power. Severe eddying occurs on face(efficiency is low) Hence if 80% of Full ahead power is available for astern then boosting it to 100% will have minimal return in thrust

Difference between air coolers for shipboard reciprocating main air compressor and Large slow speed two stroke Marine diesel propulsion engines

In both cases the  air coolers are  for increasing the efficiency of the compressors by inter cooling.   Both T/C and Reciprocating compressors are meant to increase pressure , however to a different degree ( T/C : 4 for single stage , and 10 bar for 2stage turbo chargers)  During the compression the air temp raises when the pressure is increased, and need to be cooled.  Cooling is by fresh water / sea water / air in the Main Air Compressors and  Either Sea water or Fresh Water(LT) Cooling is controlled in Engine Coolers to maintain the Air Temperature to the required value, to reduce water impingement on to the liners. Cooling is not controlled in air coolers of Main Air Compressors ( the lower the temp is better for the efficiency), hence there will be control valves for Engine Air Coolers and no control valves for Air Compressor coolers. Engine Coolers are very large in comparison to Main Air Compressors as the air flow is very large ( depend on the Engine power rating) Engine coole

Types of keys used in keyed propellers

Parallel Keys : These keys have a rectangular cross-section and are used in straight keyways. They provide a simple and effective means of transferring torque between the shaft and the hub. Sunk Keys : Also known as rectangular keys, these keys fit into keyways that are cut into both the shaft and the hub. They have tapered sides that fit tightly into the keyway, preventing movement. Woodruff Keys :These keys have a semi-circular shape and are often used in applications where axial movement of the propeller on the shaft needs to be prevented. They fit into a curved keyway on the shaft and a corresponding slot on the hub. Tapered Keys :Tapered keys are used in tapered keyways, providing a wedging action that helps secure the propeller onto the shaft tightly. Gib Head Keys :Also known as feather keys, these keys have a projection, or gib head, that fits into a slot in the hub, preventing axial movement. The type of key used depends on factors such as the design of the propeller hub and s

Safety features and considerations for windlass operations in hydraulic systems

Emergency Stop Button : Install an easily accessible emergency stop button that immediately halts all windlass operations when pressed. This allows operators to quickly stop the system in case of emergencies or unexpected situations. Pressure Relief Valves :Hydraulic systems should be equipped with pressure relief valves that prevent the hydraulic pressure from exceeding safe limits. If the pressure reaches a dangerous level, the valve will open to release excess pressure and protect the system from overloading. Pressure Gauges : Install pressure gauges at appropriate points in the hydraulic system to allow operators to monitor hydraulic pressure. This helps ensure that the system operates within safe pressure ranges. Limit Switches :Use limit switches to automatically stop the windlass when the anchor chain reaches its upper or lower limit. This prevents overextension of the chain or damage to the equipment. Flow Control Valves :Flow control valves regulate the flow rate of hydraulic

Why stainless steel not used for cylinder liners

SS is Difficult to machine for high finish Galling or friction welding when moving up and down(like piston & cylinder; valve stem & gland etc)  Most of the engines work in the range 400 to 900°C and it is called Sensitization zone and SS will lose Chromium and SS becomes steel and start rusting and cracking. Stainless steel has high thermal expansion(1.6times steel/CI) and low thermal conductivity(SS has low thermal conductivity , 25% of CS. The bore area will have high temperatures and high thermal expansion and distortion and mis-alignment of cylinder piston and engine bore are expected.

Power to weight ratio. Explain

The power-to-weight ratio represents the ratio between a vehicle's power and its total weight.  The higher the PWR, the faster the vehicle will accelerate. It is for this reason that motorbikes accelerate quicker than most cars.  PWR calculations are commonly used to predict vehicle speed.  It's very easy to calculate a power-to-weight ratio. Simply divide the power output of a vehicle by its weight.  If you have a car that weighs 2000 pounds and has 250 hp, the PWR will be as follows: 250 / 2000 = 0.125 hp for every pound of car.

Sulzer fuel pump timing adjustment

Engine should have run 30 mins of diesel oil before stoppage Open the indicator cocks, shut the main air starting valve and engage the turning gear close the fuel supply and ruturn valve on the fuel pump Drain the remaining fuel from the fuel pump Inspect the cams and rollers The stagnation pressure control valve has to be dismantled Note the valve desiganation S-suction , D- delivery and U- for spill valve Remove the valve cover and the springs Pressure bushes are released using special wrench The vavles are removed using a withdrawal device Examine valve seats and contact surfaces. Defective should be reconditioned or replaced The valve contact surface in fuel pump block should be in good condition.Damaged surfaces must be reconditioned After cleaning the fuel pump block throughly the suction and spill valves are cleaned in diesel oils and fitted back respectively without their springs The pressure bushes are tightened to 300Nm The dial gauges should be inspected before mounting it t

Shaft earthing device

A turning propeller is electrically insulated from the hull by lubricating oil film in bearings Electrical potential is generated between the shaft and the hull  As a result the cathodic protection of the ship will not protect the propeller Electrical potential can cause currents in the bearigngs resulting in pitting of the bearing surfaces Problems can be avoide if the shaft is earthed with a propeller shaft slip ring This shaft earthing assembly comprises a pair of high silver content\graphite compound brushes mounted in a balanced brush holder, running on a copper slip ring with solid silver track

Overboard valve regulation

Should not be of cast iron Must be Class approved Fitted at easily accessible location as far as practicable readily visible Indicators are to provided local to the valve ie ,showing whether they are open or shut Valve spindle are to extend above the lower platform. Valves and distance pieces extended for the installation on the ship side below the load water line are to be tested by hydraulic pressure not less than 5 bar.

Problems associated with welding cast Irons:

1) Cast iron is that the metal is filled with impurities. When you melt the metal the embedded dirt and sand contaminated the weld and tend to not mix well with the cast iron filler rod.What you end up with is not a fused intermixed metal bead but a porosity filled weld that can be easy to chip away with a chisel because it has not bonded to the base metal.  2) Pre heat & Post Heat required.And different as per its composition.Pre heat to stress relieve & post heat to control rate of cooling.  3) The large amount of carbon in the base metal tends to segregate itself along grain boundaries as the weld puddle solidifies and cools. What this does is lower the tensile strength even lower so that in the weld fusion boundary the shrinkage force pulls the metal apart as it cools, ie it tends to crack along the weld when cools.  4) Cracking. If it cools down too quickly you will get cracks along the weld.  5) Proper selection of filler rod & flux required as per the grade and compo

Why Negative cam or Inward cam used in Air distributer of MAN B&W starting air system .why not a possitive cam

The cam for the air distributer serves its purpose only while starting the engine . Actually if you see there is no other requirement of this particular cam while the engine is continue in operation.  Therefore if a cam ( normal possitive ) is used then wear of this particular cam will be abviated and will be expensive to repair / replace this cam. So when the engine has started and the vessel is enroute a voyage , then this particular cam turns without any running gear touching it. It comes into play only starting

Boiler Turndown

Boiler Turndown Boiler turndown is the ratio between a boiler’s maximum and minimum output. Depending on the burner’s design, it may have a turndown ratio between 4:1 and 10:1 or even higher.  A 4:1 turndown means the boiler’s minimum operating load is 25% of the boiler’s full capacity (100% capacity divided by 4).  A 10:1 turndown means the minimum operating load is 10% of the full load capacity (100% capacity divided by 10). Why is Boiler Turndown Ratio Important? Turndown ratio is important for boilers that are required to operate at a wide variation of capacities. A boiler with a higher turndown ratio will usually handle fluctuating loads more efficiently than one with a low turndown. A boiler’s burner will modulate or “turn down” as the demand for hot water or steam decreases, in an attempt to meet only the required load. The turndown ratio tells you the minimum output the boiler can handle before turning off and then cycling on and off frequently. If the demand goes below the bur

Function of Hooper tank in Bulk carrier ?

Hopper tanks are classified into bottom hoppers and top heavy wing tanks. For bottom hoppers, the main purpose is to take ballast, so as to rapidly increase the vessel immersion, simultaneous reduction in metacentric height, and a change in Centre of gravity. For top heavy wing tanks, the idea is to rapidly correct list of the vessel and act as active ballast tanks, for vessels such as Lakers where passages are narrow and cargo loading is often scattered. Except for this, they contribute in cargo loading also because the side slopes allow the cargo to slide off and collect at the centre, thereby making the cargo collection easier at the end Also, the hoppers are strengthened by additional transverse and longitudinal members, thereby supporting the port and starboard fuel tanks, and also distributing the cargo loading in a dynamic way to make sure the load is not concentrated at one point for higher loading speeds

Stamping on CO2 bottles

  W - Manufacturer stamp/symbole + - fill 10% excess on psi ✬ - 10 years testing, if no ✬ then every 5years hydrostatic test. 2005/03 - year/month of manufacture 6831611 - serial number pw200 - cylinder pressure 5L- cylinder capacity Stamp for testing lab 

Secondary Injection in fuel pump and fuel valve

Reopening of the fuel valve after the main injection id terminated is secondary injection . The sudden closing of the injector needle cause a pressure wave to be setup which reflects from the delivery valve back to the injector needle . If the residual pressure and reflected pressure together exceeds the injector lifting pressure , secondary injection takes place.

Why con rods are I sections ?

Con rods during operation are subjected to buckling loads Buckling strength is directly proportional to moment of inertia. So , I section is having maximum area moment and least weight. Hence introduce the vibration of conrod and also reduce side thrust acting on the cylinder. I section can be easily manufactured

Shroud Ring

Shroud ring is a component in turbocharger which forms a part of the inner exhaust gas casing adjacent to the turbine The area around the turbine is always in contact with highly corrosive exhaust gas. If no shroud ring is fitted , the turbine inner casing will be slowly wasted and complete housing to be renewed for repair . Otherwise only shroud ring can be replaced with new one

How piston rings are manufactured ?

Manufactured using Pot casting method , producing a short cylinder of oval cross- section from which the rings are machined in a cam turning lathe. This produces a balanced and homogenous casting around the entire circumference of the ring. The lathe is equipped with an interchangeable copying cam , which controls the cutting tool By changing the shape or ovality of the cam , the circumferential pressure distribution at the ring can be altered

Why air compressor valves are concentric ?

They have a low inertia of moving parts and good flow characteristics. It is highly efficient at higher rotational speed. Concentric valve is compact and a combination of suction and discharge valve , which make it compact and space saving with the lowest possible clearance volume. Plate type suction and discharge valve , whose larger diameter and small lift after the least resistance to the flow of gases

Fire in drydock

The possibility of fire aboard the ship or elsewhere within the dockyard complex is always unwelcome, but the fact remains it is a possibility at virtually any time of day or night. In the event that the possibility becomes reality, common sense and past training should automatically come into the equation.  As with any other fire incident the alarm should be raised as soon as possible after the discovery of the fire and the following procedure is suggested. Assuming that the crew have remained on board and the fire is on board the vessel, after the alarm has been raised:  Muster an emergency fire party and attempt to contain and extinguish the fire immediately following its discovery. Non-essential personnel should be evacuated to the shore and the fire brigade should be contacted. A gangway watch should be set to ensure that the access to the vessel is not blocked which as such would deny accessibility to fire fighters. The minimum water volume should be used when tackling fires in d

VEC and VEO of sulzer RT Flex engine

  VEC (Variable Exhaust - valve Closing ): Adopting compression pressure to keep the firing ration (Pmax / Pcomp) within permitted range during injection. VEO ( Variable Exhaust - valve Opening ): Keeps the exhaust gas pressure blowback constant by earlier valve opening at higher speed for fuel economy and less deposit at piston underside

Advantages of Electronic Oil Record Book ( e ORB )


Matching of Turbocharger

It involves matching of reciprocating engine to rotary compressor and turbine of Turbocharger. Impellor of compressor is chosen to provide desired airflow at engine power 80 - 90% MCR , thus taking into ( a ) Operating temperature and Engine room pressure ( b ) Pressure drop across air cooler. Once impellor output is fixed , diffuser is chosen which will provide compressor efficiency high , but ample surge margin. When compressor side design is final , turbine power requirements are known. The main variable on the  turbine side is nozzle size and this is matched to provide required compressor work and minimum restriction to exhaust gas flow. Smaller nozzle area: ( a )Work output increase   ( b ) T\C speed increase ( c ) Air delivery pressure increase

Why check bumping clearance in Main Air Compressor but not in Aux Engines

 In air compressors requirement is to discharge the maximum amount of compressed volume of air out of 1st stage cylinder so that maximum cool fresh air should come in. If the bumping clearance is more then air left inside stage will be more and at higher temperature after discharge so less mass of air will get inside in the suction stroke now due to this there will be increased suction temperature of air and consequently less work done and reduced efficiency of air compressor. Where as in Aux Engine we need maximum air to remain in cylinder head at TDC for better and efficient combustion of the fuel . Thats why enough clearance is provided between piston top and underneath of cylinder head . No danger of contacting or banging of piston to cylinderhead.

Anemometer / Wind vane

A wind vane is an instrument that measures wind direction while anemometer measures wind speed.   PRINCIPLES OF WIND VANE AND ANEMOMETER The measuring principle of anemometer is simple: the stronger the wind blows, the faster the half-open plastic cups turn. The speed of the cross rotation determines the wind speed. The cup anemometer records the number of rotations per minute and thus the wind speed very accurately. Information obtain by wind vane and anemometer are converted and can be read directly form ship’s bridge.   HOW THE DATA IS CONVERTED                                                     Information generated by wind vane and anemometer are converted and can be read directly form ship’s bridge. Through advance technology, wind speed and direction can be seen directly through a display unit in the ship’s bridge and no need for manual calculation.

Torsional vibration damper .Diagram


Sulzer Reversing servo motor mechanism . Diagram


Electrical safety requirements for pump rooms on ships

Power supply : The electrical supply to the pump room must be protected by over-current devices, and the wiring must be properly installed and maintained. Lighting : Adequate lighting must be provided in the pump room, with emergency lighting available in the event of power failure. Equipment : Electrical equipment in the pump room must be approved by a recognized testing organization and properly maintained. Earthing and bonding : The pump room must have a proper earthing and bonding system to prevent electrical hazards. Fire protection : Fire protection measures must be in place, including automatic fire detection and fire suppression systems. Ventilation : Adequate ventilation must be provided in the pump room to ensure proper functioning of electrical equipment and prevent hazardous buildup of gases. Accessibility : The electrical equipment and wiring must be easily accessible for maintenance and inspection. Testing : The electrical equipment in the pump room must be regularly test