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Showing posts from December, 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.