ΕΥΣΤΑΘΕΙΑ ΒΑΣΙΚΕΣ ΑΡΧΕΣ

STABILITY STABILITY GEOMETRICAL MANUALS WEIGHT MANUALS STATICAL OR DYNAMIC DAMAGEINTACT LONGITUDINALTRANSVERSE LIST < 10 O LIST > 10 O

PLANES- DIMENSIONS  Longitudinal plane  Transverse plane  Horizontal plane  Waterplanes  Fore perpendicular  Aft perpendicular  Hull – Shell  Base line  Designed waterline  Length btn perprs  Length water line  Length over all  Sheer Fore – Aft  Camber  Freeboard  Beam  Rise of floor

DRAFTS  Fore draft  Aft draft  Mean draft  Even keel  Trim by bow - stern  Draft correction

TERMINOLOGY  Light ship  Light waterline  Wetted surfase  Loadline  Displasement  Light displacement  Full load displ.  Waterlinezone  Center of gravity  Center of volume  Center of buoyancy  Form coefficients  Superstructure  Deck erection  Bulkheads  Tonnage

SIMPSON RULES  First rule: h/3 ( a + 4b + 2c + 4d + e) Used when an odd number of ordinates are taken  Second rule: 3h/8 ( a + 3b + 3c + 2d + 3e + 3f + g) The rule can be used when the number of ordinates is four, or four plus some multiple of three (e.g. 4,7,10,13,16, etc)  Five eight rule: h/12 ( 5x + 8y – z) This may be used to find the area between two consecutive ordinates. We must know the length of one other ordinate, next to the area we wish to measure.

DEFINITIONS  Angle of vanishing stability : The angle at which a ship’s stability becomes 0. Numerically the same as the range of stability.  Center of buoyancy : The geometrical center of the underwater part of the ship.  Center of flotation : The point about which the ship heels and trims. The center of gravity of the waterplane.  Center of gravity : The center of all the weight in a body. The point about which the body would balance.  Deadweight : The weight of all cargo, stores, bunkers, etc, ih a ship.

More definitions  Deadweight moment : The total moment about the base line of all the components of deadweight.  Displacement : The actual weight of the ship and all aboard her at any time.  Draft : The depth of the bottom of the keel below the surface of the water.  Draft mean : The mean of the drafts fore and aft, as it would be measured amidships.  Draft at F : The ship’s draft measured at the position of the center og flotation.

More definitions  Dynamical stability : The amount of work done in inclining a ship to any given angle of heel.  Fluid KG or GM : The ship’s KG or GM, after allowance has been made for the effect of free surface of liquids.  Freeboard : The distance from the deck line to the water.  Fresh water allowance : The amount by which the ship would increase her draft on passing from salt to fresh water.  Height of metacenter : The height of metacenter above the keel

More definitions  Inertia : The resistance of a body to motion or to change of motion.  Initial stability : The statical stability of a ship at a small angle of heel. Indicated by GM.  KG : The height of the center of gravity above the keel.  KN : The righting lever which the ship would have if G were placed at the keel.  Law of Archimedes : A body immersed in a liquid appears to suffer a loss in weight equal to the weight of liquid which it displaces. From this law we conclude that a floating body displaces its own weight of water.

More definitions  Light displacement : The displacement of a ship when she’s floating at her designed light draft. The weight of the hull, machinery, spare parts and water in the boilers.  Loaded displacement : The displacement of a ship when she is floating at her designed summer draft. The light displacement plus the dead weight.  Longitudinal metacentric height : The height of the longitudinal metacenter above the center of gravity.  Mean draft : The mean of the ship’s drafts fore and aft.  Metacenter : The point at which the vertical line through the center of buoyancy, at a small angle of heel, cuts the ships center line. It is only considered to exist for angles of heel up to about 15 o.

More definitions  Metacentric height : The height of the transverse metacentre above the center of gravity.  Moment : The attempt of a force to turn a body. It is usually measured by the product of the force and the length of the lever.  MTC-1 : The moment to change the ship’s trim by one centimeter.  Moment of statical stability : The moment which will try to return a ship to the upright when she’s inclined.  Period of a ship : The time taken by a ship to roll from one side to the other and back again.

More definitions  Solid KG or GM : The ships KG or GM neglecting the effect of free surface of liquids.  Stiff ship : A ship which has a large moment of statical stability. One having a large metacentring height, or righting lever.  Synchronism : Said to occur when a ship’s period of roll is the same as that of the waves.  Tender ship : A ship which has a small moment of statical stability. One having a small metacentric height or righting lever.  TPC : Tones per centimeter of immersion. The weight which must be added to a ship in order to cause her to sink one centimeter bodily.

More definitions  Period of waves : The interval between the passages of any two consecutive wave crests.  Range of stability : The angular range over which a ship will have positive statical stability. The angle to which the ship would heel before she would tend to capsize.  Reserve buoyancy : The volume of the ship’s hull between the water plane and the freeboard deck.  Righting lever : The perpendicular distance between the center of gravity and the vertical line through the center of buoyancy. The lever of the ends of which the weight of the ship acts to turn her to the upright when she is heeled.