Lection1船舶原理英文版

Lection 1 (23.11.2011, Wednesday)
Introduction. The ship theory concept. Ship co-ordinate system. Vessel requirements. Classification societies. Ship body plan (lines plan). Ship principal dimensions.
Introduction
A crude representation of the process of creating a ship is outlined in the figure:
For determination of ship hull form geometry and position of the ship with respect to the surface of the water, the left-hand co-ordinate system, rigidly linked with the ship, is used.
An origin of this co-ordinate system, the point o, is placed upon keel line in the point of intersection of the base plane, the plane of mean transverse section of the ship body and the plane of its longitudinal symmetry.
The axis ox is pointed forward, being by line of intersection of the centre plane and the base plane. The axis oy is line of intersection of the midstation plane and the base plane; its positive direction is the direction to the right side of the ship. The axis oz is line of intersection of the midstation plane and the centre plane, the positive direction of this axis pointing upward.
Thus, the plane xoy is the base plane, plane xoz is the centre plane, and plane yoz is the midstation plane.
Co-ordinate system
The ship theory concept
The ship theory is the science of its seakeeping (seaworthiness): buoyancy, stability, insubmersibility, propulsion, maneuverability, motion (rolling).
Buoyancy – the vessel's ability to swim in a certain position relative to the surface of the water, carrying all designed according to his service loads.
The stability of the ship – the ability to swim in a live situation and return it as soon as the will to act by external forces, had rejected a vessel from the situation.
Insubmersibility –the vessel's ability to maintain buoyancy and stability when sinking one or group of compartments.
Propulsion – the vessel's ability to develop a certain speed with the power of main engines and corresponding pumped propulsion systems. The ship's engine is a special device (e.g., propeller), which transforms the energy of the main engine driving the ship.
Control –the vessel's ability to change direction when transferring the rudder and move in a straight line with the position of the rudder on the centerline.
Rolling – fluctuations of a vessel concerning balance position.
Seaworthy qualities, at which studying the vessel is considered as a motionless body (buoyancy, stability, insubmersibility), unite section "Statics ship".
Seaworthy qualities, at which studying the vessel is considered as a moving body (propulsion, control, rolling), unite section "Dynamics ship".
Vessel requirements
Vessel –floating structure, capable of performing certain tasks: transportation of people and goods, towing of other vessels, etc., therefore, each vessel must comply with its intended purpose and have a range of qualities, among which are:
– the overarching sufficient navigation safety in terms of seaworthiness, and taking into account the effects of other factors (e.g. fire safety);
– optimum speed in the selected direction, taking into account the purpose of the vessel;
–sufficient strength, durability and reliability of the hull, mechanisms, equipment, etc. with a minimum of their weight;
– minimum freight ton or per passenger for a certain distance – for cargo and passenger ships; minimum cost of production of one tonne of fish –for fishing vessels, etc.;
– the largest payload capacity in data sizes and for cargo vessels; maximum passenger capacity for passenger vessels, etc.;
–mechanization and automation of management of ship power plants, support mechanisms and the ship as a whole;
–the availability of high-performance devices that provide the ability to perform basic tasks ship ship means, for example, cargo handling operations;
– good working conditions and welfare team;
–the lowest cost of construction of vessel.
Classification societies
The authorities with the most profound influence on shipbuilding, merchant ship design and ship safety are the classification societies. Among the most dominant are Lloyd’s Register of Shipping, det Norske Veritas, the American Bureau of Shipping, Bureau Veritas, Registro Italiano, Germanische Lloyd and Nippon Kaiji Kyokai. These meet to discuss standards under the auspices of the International Association of Classification Societies.
The standards to which the ships must be built and maintained are laid down in the first of the two major publications of Lloyd’s Register, Rules and Regulations for the Classification of Ships. The other major publication is the Register Book in several volumes, which lists every known ship, whether classed with the Society or not, together with all of its important technical particulars.
Ship body plan (lines plan)
At first superstructures and deckhouses are ignored and the hull of the ship is considered as a hollow body curved in all directions, surmounted by a watertight deck.
Most ships have only one plane of symmetry, called the middle line plane which becomes the principal plane of reference.
The shape of the ship cut by this plane is known as the sheer plan or profile.
The design waterplane is a plane perpendicular to the middle line plane, chosen as a plane of reference at or near the horizontal: it may or may not be parallel to the keel.
Planes perpendicular to both the middle line plane and the design waterplane are called transverse planes and a transverse section of the ship does, normally, exhibit symmetry about the middle line.
Planes at right angles to the middle line plane, and parallel to the design waterplane are called waterplanes, whether they are in the water or not, and they are usually symmetrical about the middle line. Waterplanes are not necessarily parallel to the keel.
Transverse sections laid one on top of the other form a body plan which, by convention, when the sections are symmetrical, shows only half sections, the forward half sections on the right-hand side of the middle line and after half sections on the left. Half waterplanes placed one on top of the other form a half breadth plan. Waterplanes looked at edge on in the sheer or body plan are called waterlines. The sheer, the body plan and the half breadth collectively are called the lines plan or sheer drawing and the three constituents are clearly related.
It is convenient if the waterplanes and the transverse planes are equally spaced and datum points are needed to start from. That waterplane to which the ship is being designed is called the load waterplane (LWP) or design waterplane and additional waterplanes for examining th e ship’s shape are drawn above it and below it, equally spaced, usually leaving an uneven slice near the keel which is best examined separately.
A reference point at the fore end of the ship is provided by the intersection of the load waterline and the stem contour and the line perpendicular to the LWP through this point is called the fore perpendicular (FP).
The after perpendicular(AP) is frequently taken through the axis of the rudder stock or the intersection of the LWL and transom profile.
The distance between these two convenient reference lines is called the length between perpendiculars (LBP). Two other lengths which will be referred to are the length overall and the length on the waterline.
The distance between perpendiculars is divided into a convenient number of equal spaces, often 20, to give, including the FP and the AP, 21 evenly spaced ordinates. These ordinates are, of course, the edges of transverse planes looked at in the sheer or half breadth and have the shapes half shown in the body plan. Ordinates can also define any set of evenly spaced reference lines drawn on an irregular shape. The distance from the middle line plane along an ordinate in the half breadth is called an offset and this distance appears again in the body plan where it is viewed from a different direction. All such distances for all waterplanes and all ordinates form a table of offsets which defines the shape of the hull and form which a lines plan can be drawn.
A reference plane is needed about mid-length of the ship and, not unnaturally, the transverse plane midway between the perpendiculars is chosen. It is called amidships and the section of the ship by this plane is the midship section.
The moulded draught is the perpendicular distance in a transverse plane from the top of the flat keel to the design waterline.
The moulded depth is the perpendicular distance in a transverse plane from the top of the flat keel to the underside of deck plating at the ship’s side.
Freeboard is the difference between the depth at side and the draught. It is the perpendicular distance in a transverse plane from the waterline to the upperside of the deck plating at side.
The moulded breadth (beam) extreme is the maximum horizontal breadth of any frame section.
Tumble home is the tendency of a section to fall in towards the middle line plane from the vertical as it approaches the deck edge. The opposite tendency is called flare.
Deck camber or round down is the curve applied to a deck transversely. Sheer is the tendency of a deck to rise above the horizontal in profile.
There are special words applied to the angular movements of the whole ship from equilibrium conditions. Angular bodily movement from the vertical in a transverse plane is called heel . Angular bodily movement in the middle line plane is called trim .
A ship is said to be in position without heel (upright) if the heel angle is equal to zero.
A ship is said to be in position without trim (on even keel) if the angle of trim is equal to zero.
The volume of displacement is the total volume of fluid displaced by the ship.
Ship principal dimensions
Principal dimensions:
L – length between perpendiculars or length of ship on DWL;
B – width of ship or width of ship on DWL;
T – draught of ship or draught of ship on DWL.
For the characteristic of all volume of ship body the following parameter will be used:
Н – depth, which is understood as length of interval from the line of keel up to the upper watertight deck measured on the projection "Profile plan" in the section of a middle frame.
For determination of overall dimensions of ship body the next designations will be used max L , max B and max H .。