Magnetic compass

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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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DIFFERENT TYPES OF VENTILATION.

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 1.THROUGH VENTILATION.

This is done by trimming the leeward ventilator into the wind and windward ventilator away from wind. The direction used here is apparent wind direction.


2.SURFACE VENTILATION.

 This is done by the ventilator turned into the wind and the leeward turned away from the wind . This is necessary for certain cargoes where only the surface cargo is to be ventilated.


eg:- coal…


3.FORCED VENTILATION.

It is achieved by using mechanical fans and there by the air in the hold is dried and recirculated. 

 

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