Monday, 2 January 2012


Bow Line

Oily Water seperators - OWS


The most common type of oily water seperators found on ships are of the gravitational type. these rely on the difference in SG of the mix to seperate out the oil from the water 

Shown above is a gravitational type seperator capable of very good quality effluent discharge. A safety valve (not shown) is mounted on the unit as are test cocks and a drain valve.


The unit is initially filled with purge water. The discharge from the pump has a sample line take of to a 15ppm monitor. This is lined up and in used with flushing water used until the pump is running. The unit activation button is pressed, the oil outlet valve is closed, the suction valve is opened and the discharge pump is started. Bilge water is drawn through the unit over a vertical arranged plate stack. The 15pp monitor is lined up to the pump discharge sample line 

Terms Used In Ship Construction

 The hull form of a ship may be defined by a number of dimensions and terms which are often referred to during and after building the vessel. An explanation of the principal terms is given below.
After Perpendicular (A.P.): A perpendicular drawn to the waterline at the point where the aft side of the rudder post meets the summer load line. Where no rudder pot is fitted it is taken as the centre line of the rudder stock:
Forward Perpendicular (F.P.): A perpendicular drawn to the waterline at the point where the foreside of the stem meets the summer load line.
Length Between Perpendicular (L.B.P.): the length between the forward and aft perpendiculars measured along the summer load line.
Amidships: A point midway between the after and forward perpendiculars.
Length Overall (L.O.A.): Length of vessel taken over all extremities.

Freeboard: The vertical distance measured at the ship’s side between the summer load line (or service draft) and the freeboard deck. The freeboard deck is normally the uppermost complete deck exposed to weather and sea which has permanent means of closing all openings, and below which all openings in the ship’s side have watertight closings.
Moulded Beam: Measured at the midship section is the maximum moulded breadth of the ship.
Scantlings – the sectional dimensions of various parts of a vessel.
Strake – A line of vertical plating, extending forward and aft.
Sheet. Curvature of decks in the longitudinal direction. Measured as the height of deck at side at any point above the height of the deck at side amidships.
Stringer – A line of horizontal plating, extending forward and aft.
Floor – Transverse vertical stiffeners which strengthen the ship’s bottom plating and which may be enclosed to form double bottoms.
Pounding – When a ship meets heavy weather and commences hearing and pitching, the rise of the fore end of the ship may synchronise with the trough of a wave. The fore end then emerges from the water and re enters with a tremendous slamming effect, known as pounding. This may cause damage to the fore end. The shell plating must be stiffened to prevent buckling.
Panting – As waves pass along the ship they course fluctuations in water pressure which tend to create an in and out movement of the shell plating. The effect of this is greatest at the fore end where the shell is relatively flat. This is know as panting and can lead to metal fatigue; the structure at the ends of the ship is therefore stiffened to prevent excessive movement of the shell.

Heat exchangers


A heat exchanger is a component that allows the transfer of heat from one fluid (liquid or gas) to another fluid.   Reasons for heat transfer include the following:
  1. To heat a cooler fluid by means of a hotter fluid
  2. To reduce the temperature of a hot fluid by means of a cooler fluid
  3. To boil a liquid by means of a hotter fluid
  4. To condense a gaseous fluid by means of a cooler fluid
  5. To boil a liquid while condensing a hotter gaseous fluid
Regardless of the function the heat exchanger fulfills, in order to transfer heat the fluids involved must be at different temperatures and they must come into thermal contact.  Heat can flow only from the hotter to the cooler fluid.

Types  of  Heat  Exchanger  Construction

Although heat exchangers come in every shape and size imaginable, the construction of most heat exchangers fall into one of two categories: tube and shell, or plate.  As in all mechanical devices, each type has its advantages and disadvantages.

Ac Motor


General Operating Principle

1.   A revolving magnetic field is set up when a 3 phase voltage is applied to the stator of an induction motor.
2.   The revolving field induces a voltage in the rotor bars
3.   The induced voltage creates large currents which flow in the rotor bars and end rings
4.   The current carrying rotor bars are immersed in the magnetic flux created by the stator. Because of that current carrying rotor bars are subjected to strong mechanical force.
5.   The sum of mechanical forces on all the rotor bars produce torque which tends to drag the rotor along in the same direction as the revolving field.
6.   As the rotor picks up speed, the relative velocity of the field with respect to rotor diminishes progressively
7.   This causes magnitude and frequency of induced voltage to decrease as the rotor bars are cut more slowly.
8.   Thus the rotor current is very large initially but decreases rapidly as the motor picks up speed.
9.   But the rotor will never be able to catch up with rotating field as this will reduce induced voltage to zero and consequently mechanical force acting on rotor will also become zero.
10. Difference in rotor magnetic field speed and rotor speed is called slip, its normal value is less than 0.1% of synchronous speed.

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