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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BASIC DEFINITIONS

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BASIC DEFINITIONS


Length Overall (LOA): Length of vessel taken over all extremities measured from the tip of the bow in a straight line to the stern.


Length Between Perpendiculars (LBP): The length between the forward and aft perpendiculars measured along the summer load line. When there is no sternpost, the centerline axis of the rudder stock is used as the aft end of the length between perpendiculars.


Forward Perpendicular (FP):A perpendicular drawn to the waterline at the point where the fore-side of the stem meets the summer load line.


After Perpendicular (AP):A perpendicular drawn to the waterline at the point where the after side of the rudder post meets the summer load line. Where no rudder post is fitted it is taken as the center line of the rudder stock.


Amidships: A point midway between the after and forward perpendiculars.


Breadth extreme: The maximum beam taken over all extremities.Measured from outside of shell plating to outside of shell plating.


Breadth moulded: Measured at the midship section, this is the maximum moulded breadth of the ship measured from inside of shell plating to inside of shell plating.


Depth moulded: The vertical distance measured from the top of the keel to the top of the freeboard deck beam at side.


Depth extreme: Depth of vessel at ship's side from upper deck to lowest point of keel.


Draft: Distance between the ship’s keel and the waterline of the vessel. Keel is the lower most longitudinal part (considered as backbone of the ship) and the waterline is the location on the hull where the air-water interface occurs.


Freeboard: Freeboard is the distance measured from the waterline to the upper edge of the deck plating at the side of the freeboard deck amidships.


Camber: Curvature of decks in the transverse direction.Straight line camber is used on many large ships to simplify construction.

  Main Purposes:

a) to facilitate drainage of water

b) Increase the resistance to deflection under load.


Sheer: A rise in the height of the deck (curvature or in a straight line) in the longitudinal direction i.e. height of deck will be slightly more in forward and aft compared to height of deck amidship.

The forward sheer is usually more than the aft sheer to protect the forward anchoring machinery from the waves. The purpose behind such a construction is to allow flow of water from forward and aft to midship and then drainage of water to bilges.


Stem Rake(Rake of Stem): Inclination of the stem line from the vertical. 

Raked stern posts will give better manoeuvrability in harbour. 


Rise of Floor (Deadrise): The rise of the bottom shell plating line above the baseline. This rise is measured at the line of molded beam.


Air Draft: Air draft is the distance from the surface of the water to the highest point of the ship.


Flare (Flare of Bows): The outward curvature of the side shell above the waterline. It promotes dryness and is therefore associated with the fore end of the ship.

Purpose:

a)  Increases reserve buoyancy at forward part and thus helps to provide a better seaworthiness and reduces pitch.


b) Gives more spaces for the fitting off machinery such as the windlass.


c)  Allows anchor to be dropped without causing any damage to the ship.


Tumblehome: The inward curvature of the side shell above the summer load line. This is opposite of flare. This design is due to a wider beam than the uppermost part.

The main advantages are:

  1. In heavy weather tumblehome reduce the amount of water ingress to bow.

  2. When the ship is rolling,a broader beam displaces more water and thus more buoyancy.


Parallel Middle Body: The length over which the midship section remains constant in area and shape.


Entrance: The immersed body of the vessel forward of the parallel middle body.


Run: The immersed body of the vessel aft of the parallel middle body.


Base Line: A horizontal line drawn at the top of the keel plate. This line is taken as reference for the purpose of measurement of  all vertical moulded dimensions.


Bilge Radius: The radius of the rounded portion of a vessel’s shell that connects the bottom to the sides.

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