Magnetic compass

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Image
The magnetic compass is fitted on the upper bridge exactly center line of the ship   It is referred to as standard compass     1. D ry C ard    2. W et C ard   A compass point north because all magnets have two poles north pole, south pole.   The north pole of the one magnet attracted towards the south pole of another magnet     DRY CARD COMPASS   A light aluminum ring about 254mm in diameter is attached to a brass hub by silk cord which is threaded in and out through holes in the ring.   This tight silk cord is act like bicycle wheels.   There is no other connection or support between the ring and the hub.   Silk cord is used because it doesn’t shrink or stretch due to moisture or change in atmospheric temperature.     Card support: -     The bottom of the hub has small cap fi tt ed with a sapphire bearing surface.   This rests on a pivot tipped with iridium which is hard nonmagnetic metal....
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WATER TIGHTNESS OF HATCH COVERS(TEST)

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The water tightness of hatch cover is imperative to protect the cargo and avoid large cargo claims. Mainly there are three methods for testing the weather tightness of hatch covers.
1)chalk test
2)water hose leak detection test
3)ultra sonic leak detection test.
4)Visual inspection.


1)CHALK TEST:-
  • The top edge of every compression bar is covered with chalk.
  • Hatches are then fully closed and reopened .
  • The rubber packing is examined for a chalk mark, which should be run continuously along the packing's center. Gaps in the chalk mark indicate lack of compression.
  • Chalk testing merely indicates if the hatch is aligned and compression achieved .
  • It will show whether compression bar is adequate and therefore it is not a test for weather tightness.
2)WATER HOSE LEAK DETECTION TEST:


  • Water hose test is used to determine weather tightness of hatch cover.
  • The general procedure for hose testing is to apply a powerful jet of water from 20-50mm diameter hose fitted with a 12mm diameter nozzle held at a distance of 1-1.5 m from a hatch joint at a speed of 1m at every 2 sec.

  • Problem with this test is it cannot be performed in sub zero conditions and also it cannot pinpoint leaks accurately.


3)ULTRASONIC LEAK DETECTION TEST :-
  • Is an alternative to the hose test for testing hatch cover, access doors and access hatches for weather tightness accurately locate the potential point of leakage.
  • This test involves placing an electrical signal generator inside the cargo hold. A sensor is then passed around the outside of all the compression joints. Reading taken from the sensor indicates the points of low compression or potential point of leakage.
  • these are three methods to check the water tightness of hatch covers.

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