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Showing posts from 2024

Insert plate in welding

An insert plate is used to replace any damaged steel plate of ship's hull. The insert plate must have identical characteristics with the original steel plate ( type /grade/thickness etc). The damaged part of the steel plate has to be cropped-out and renewed by welding using the same welding consumables. The minimum consumable grades. All ship's Class Societies consider the above mentioned requirements as permanent repairs for maintaining the ship’s Classification Certificates fully valid. On the contrary, doubler steel plates which are welded on top of a damaged structure plate is considered as temporary repaired with a short limit date until the full permanent repairs are dealt with

How is engine frame attached to the ships shell plate

For engine seating a plate floor is required every frame  Main engine seatings are in general integral with this double bottom structure.  Inner bottom in way of the engine foundation has a substantially increased thickness.  Often the machinery is built up on seatings forming longitudinal bearers which are supported transversely by tripping brackets in line with the double bottom floors, the longitudinal bearers being in line with the double bottom side girders.  There are transverse plate floors at each frame. The thickness of the engine seating is governed by the power, weight, and length of the unit

What is dual class ? Why

A dual class vessel is one which is classed by two Societies between which there is a written agreement regarding sharing of work, reciprocal recognition of surveys carried out by each of the Societies on behalf of the other Society and full exchange of information on the class status and survey reports.  All the ships of "The shipping corportation of India" used to have dual class.  Out of two, one classfication society was "Indian Registrar of shipping".  Indian ships were required to have IRS as its classification society but as IRS was then not a member of IACS, ships were forced to have a second classification society which was member of IACS.  So in this case, these ships would have certificate of class from each classification society.  In 2010 when IRS became the member of IACS, Indian ships were no more required to have Dual class.  More than 50 classification societies. But only 12 are IACS members  A double classed vessel is one which is classed by two

Pressure testing of DB tank

Both Leak & Structural test  Test head :  The greater of –  Top of the overflow To 2.4m above top of tank   To bulkhead deck    Procedure: Fill tanks by gravity to sea level. A ballast pump can be used if the vessel wishes, but is not recommended. If there are scuppers, then block scuppers as would be required for bunkering operations.  Close sounding pipes tightly if these are at deck level.  Open, or take off, air vent tops.  Top up tank through air vents by fire hose until (assuming stern trim) water level is close to top of aft air vents.  Ensure that fire hose can be stopped quickly as water level nears top of air vent.  Check by sounding or ullage through the air vent, that water level in forward air vents has also risen towards top of air vents. Hold level for 30 minutes minimum and check if level in vent is falling or steady.  Look for leaks.

Rudder clearances

 Pintle  For a ship in service, Maximum allowable clearances between Pintle and bush is 6 mm.   IF the actual clearance exceeds 6mm, the bush should be renewed.  Measured using the thickness gauge. The clearance is taken in four sides: forward, aft, port, and starboard.  The measurements are taken through the inspection cover, usually on the port side.  The normal clearance is about 1 to 2 mm.   Neck bush clearance Between the rudder stock and the neck bush (rudder stock upper side) is measured using the thickness gauge.  The clearance is taken in four sides: forward, aft, port, and starboard.  The measurements are taken from top of the rudder.  The normal clearance is about 1 to 2 mm.  Jumping Clearance: The designed clearance is 2.0 mm maximum.  If the clearance measured is found to be large, it can be concluded that the rudder has moved down. The clearances can be taken from rudder trunk – between the stopper and carrier bearing

Drydock 50 hz supply, ship 60 hz .What should be done

 50 Hz will make motors run slower. 50/60=83% that will have the effect on the efficiency and the connected load .  If we supply a reduced frequency then we also need to reduce the voltage accordingly to prevent the motor to draw more current.  Voltage/frequency of ship equals to Voltage/frequency shore. That’s gives us a calculated voltage of 366 volts, which closer to the standard 380 volts 50 Hz, that can be accepted.  By doing so the through put of the pumps will be reduced, and we definitely have to keep an eye on the temperatures of the motor windings.

Hull roughness measurement

Hull Roughness Analyser  Computer is connected to the hand held carriage having a stylus measuring head.  Stylus head is moved around the hull surface to measure and record the hull roughness profile.  One traverse of the head at any point on the hull will collect information from 10 samples having length of 50 mm.  For each 50 mm sample, the micro processor will assess the mean gradient through the peaks and valleys to give highest peak to lowest valley measurement for that sample.  This measurement is known as Rt (50).  Approx. 100 selected locations which must include bow, stern, mid ship, and boot topping area (area between load line and ballast water line).  A number of traverses for stylus will give ‘n’ readings, hence the Mean Hull Roughness (M.H.R) at that station is average of Rt (50)  There will be ‘m’ stations around the hull of the ship. Hence Average Hull Roughness (AHR) will be average of Mean Hull Roughnes