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Showing posts from 2021

HRU(Hydrostatic Release Unit )

A hydrostatic release unit allows a liferaft to launch automatically if there isn’t time for crew to launch it manually.  How it works: The strong white rope is secured to the deck or liferaft cradle and attached to the liferaft lashing with a sliphook.  If the ship sinks, the water pressure will (within 4 metres) activate the sharp knife which  cuts the white rope and the liferaft will float free.  As the ship sinks, theliferaft painter line will be stretched and the liferaft starts to inflate.   The Red Weak Link breaks and survivors can board the floating liferaft. • Breaking strength of white rope sling: min 15kN. • Breaking strength of red weak link: 2.2 +/- 0.4 kN

Advantages and Disadvantages of mechanical seal

 Advantages  Lower frictional drag than traditional packing means improved pump efficiency A mechanical seal will not wear out a shaft, or sleeve, as fast as packing rings Near zero leakage is possible with mechanical seal; packing requires some leakage (usually visible) for proper lubrication Properly applied mechanical seals require less periodic maintenance than packing Specially designed mechanical seals can be applied to higher pressures and speeds than traditional packing.  Disadvantages   Less tolerant to shaft deflection and misalignment    Less tolerant to dirty or contaminated liquid; will require cyclone separator to clean the liquid  Require expensive seal piping to flush and quench   Mechanical seals are more expensive than packing rings

How two different temperatures are maintained inside a refrigerator ?

There is only coil ( capillary tube in refrigerator ) which maintains freezer temp. The refrigerator chamber is maintained using forced circulation method by a fan which uses this cold air to cool the other chamber. Or no fan is used and convectional currents gets set in due to temp difference between the freezer and refrigerator section .Thereby having two temp in refrigerator

How to Derate a marine boiler

1.Reduce max working pressure of boiler 2.Change the safety valve to larger size diameter  If you change the safety valve then need to increase corresponding waste pipe dia and also safety valve cut chest cut size need to be increased Option 2 is bit complicated so we go for option 3. 3.Reduce the firing rate by following   Change the nozzle Dp transmitter need to be recalliberated Steam cut in/ cut off will as per new max working pressure Set the safety valve for new max working pressure Accumulation pressure test to be done in presence of surveyor

Cut water clearance (Water cut )of centrifugal pump

The Portion of the volute that extends closest to the Impeller is called cutwater. So the clearance between the Vane and Cutwater portion of casing at the discharge is known as cutwater clearance Some of the liquid passes the cutwater and stays inside the pump for another trip around the volute. However, most of the liquid passes the cutwater and decides to exit the pump through the discharge nozzle.

Why tank insulation is provided on refrigerated cargo tanks?

Thermal insulation must be fitted to refrigerated cargo tanks for the following reasons: • To minimise heat flow into cargo tanks, thus reducing boil-off. • To protect the tanker structure around the cargo tanks from the effects of low temperature.   Insulation materials for use on gas carriers should possess the following main characteristics: • Low thermal conductivity. • Ability to bear loads. • Ability to withstand mechanical damage. • Light weight. • Unaffected by cargo liquid or vapour.

What is Statutory certificates and Mandatory certificates?

Statutory Certificates : Those certificates which are required by the law with respect to safety and environment protection that the vessel is required to comply with are called statutory certificates. Eg-SOLAS, MARPOL, STCW, MLC 2006   Mandatory Certificates : Certificates which are required for trading purpose. Ship’s registry certificate is a mandatory certificate however for Indian Ship’s it is Statutory Certificate. OPA’90 is a Statutory certificate for ship’s transiting in U.S waters but  mandatory for other ship’s.


One of the most important differences between LRIT and AIS, however, is that AIS is a so called broadcast system, i.e., is public, whereas LRIT data are only available to institutions which have a (governmental) entitlement to the data and guarantee the confidentiality of these data. Another main difference is that AIS is a Collision avoidance system mandated by the IMO whereas LRIT is a Reporting system mandated by the IMO.

Wilden pumps

Wilden pumps are positive displacement pumps – they move fluids using compartments or chambers with a variable volume. They have a reciprocating, or stroke-based, action; there is no rotary motion. There are few moving parts; usually only the diaphragms and the reciprocating shaft, driven by an air distribution unit, move to any significant degree. The air distribution system [2] alternately pressurises each air chamber [1] compressing one diaphragm [9] into the liquid chamber [8] on each stroke and driving the horizontal piston [3 & 4] from side to side. As the diaphragm is released, enlarging the liquid chamber, fluid is drawn into the chamber through the corresponding inlet check ball valve [5]. The following compression stroke drives the fluid back out of the liquid chamber through the outlet check ball valve and into the discharge manifold [7]. The piston has then returned to its starting position, emptying the second chamber and completing one full cycle. Since no electrical

Difference between HP and BHP

HP stands for horsepower. It is the total output power of a system. BHP stands for brake horsepower. It is the output power of the engine of a system. HP is measured for the whole system and gives the efficiency of the system. BHP is only measured for the engine of the system and gives the efficiency of the engine under ideal conditions. HP doesn’t take the frictional and other power losses into account. BHP includes the frictional and other power losses of the system. HP is measured using a simple dynamometer. BHP is measured using a brake type dynamometer. HP Measurement :The dynamometer is connected to the engine, and a torque converter is used. BHP Measurement: A brake is applied to the flywheel, and the intensity of this brake determines the BHP.

Explanation for all Notations used by MAN B&W engines

This article will provide explanation for all Notations used by MAN B&W engines till date. MAN – Germany – Maschinenfabrik Augsburg Nurnberg B&W – Denmark – Burmeister & Wain Motorfabrik A/S The merger of above two Giants is now known as Man B&W. Now, with some examples of engine name plate details and specifications, we will understand these notations. From the 1960s to present. MAN B&W ENGINE Specifications: 774VT2BF(S) 7 – Number of cylinders 74 – Cylinder diameter in cm V – Single acting 2-stroke T – Cross Head 2B – Degree of Turbocharging F – Marine applicationS – Stationary Application 7K74EF 7 – Number of cylinders K – Two stroke cross head 74 – Cylinder diameter in cm E/G – Engine model/Hydraulically Operated Exhaust Valve F – Marine application 7L80GFCA 7 – Number of cylinders L – Long stroke 80 – Cylinder diameter in cm G – Engine model/Hydraulically Operated Exhaust Valve F – Marine Application C – Constant pressure turbocharging A – Engine rating 7L80GB/

Isolation of Hydraulic system for maintance

Before carrying out any maintenance on the windlass  hydraulic unit, the entire system should be isolated.  This is to prevent any mishaps or accidents which may cause injury or loss of life and even damage the machinery. Following actions must be carried out in order to isolate the system: Stop the hydraulic pump if it is running. Switch off the electric circuit breaker and control room circuit breaker.   Shut off the pump suction and discharge valves and return line valves. If required, drain the oil from the system.   Display ‘Men at Work’ warning board.   Ensure anchors are lashed; bow stopper is in place and brakes applied.

Pneumatic coupling

 Pneumatic quick couplers (also referred to as air couplers, or pneumatic quick disconnects),  are primarily used for pneumatic applications, connecting air tools, hoses, or other implements to compressed air supplies.  The coupler half contains a shut-off valve that is automatically opened when a mating nipple is  inserted and automatically closes when the nipple is removed.   Parker pneumatic couplings come in three basic designs: general purpose/manual connect,  general purpose/push-to-connect, and special purpose.   The standard seal material for shut-off couplers is Nitrile.

Self healing property of stainless steel

The alloy nature of Stainless Steel and its thin, transparent layer on the surface provides a self   healing feature. When activated by oxygen within the air or water then it is this layer which   repairs lightly scratched or any damage to the surface.  Stainless steels contain a significant amount of chromium, which forms Chromium Oxide   when it oxidizes (rusts).  In contrast to a simple carbon steel, which forms iron oxide when it   rusts, (the flaky reddish brown oxide we typically associate with rust).  Iron oxide is brittle and  permeable, doing little to prevent further oxidation of the steel surface. In contrast, chromium  oxide does not have an objectionable appearance, being the same effective color as the base  metal, just a bit duller, and is hard and resilient.  When you scratch or mar stainless, the   exposed chromium just forms a new oxide layer, protecting the underlying metal.

Engine cylinder pressure is 120 bar why you are tightening cylinder head at 1200 bar

Pressure = Force / Area  So Force = Pressure x Area  We know that Pressure = 120 bar, Lets take cylinder bore = 60 cm  So area of head = ㄫ r x r = 3.14 x 30 x 30 = 2826 cm2   There for Force acting on cylinder head = 120 x 2826 = 339120 Ncm   In order to keep cylinder head in place we need to apply a force that is greater than 330120   Now cylinder head is tighten with 8 hydraulic nuts and assume area of one nuts as 100 cm2   For safety we take the force needed to keep head in place as 800000 Ncm  Now There are 8 nuts so total area = 8 x 100 = 800 cm2   Pressure = 800000 / 800 = 1000 bar   So we need to tight nuts around 1200 bar

Boiler water level controller : Components and Working

Fixed Carbon di Oxide extinguishing system CO2 bottle head assembly