STABILITY THEORY II

Author : Professor C.D.J.Yarg.

TABLE OF CONTENTS :                                                                 

| angle of loll | Carriage of timber | corrections tabular to assigned freeboard | critical instant dry docking stability | damage stability | difference between type A and B | free trim wrt offshore supply vessels | improvement of stability on roro ships | inclining experiment | load line rules | loadicator | Loadline surveys | natural rolling period | passenger vessel flooding requirement | stability of offshore supply vessel | stability on ro ro ships | Statical stab curve derived fm KN values | stiff tender vessels | still water rolling period | Stress and stability data | synchronous rolling | Type A Ships Loadline rules | Type B Ships Loadline rules | up thrust | virtual loss of GM | windage |

List stability and stress data required to be supplied to ship under the current Load line Regulations, stating for each how such information might be used.

The load line regulations require the master of the ship is to be provided with information relating to the stability of the ship. This usually takes the form of Stability Information Booklet which contains all that is needed to safely manage the vessel’s stability.

The required information is as outlined as below:-

1)      General Particulars

              This includes the ship’s name, official number, and port of registry, tonnage, dimensions,              displacement, deadweight and draught to the Summer Load line. Useful as a reference in               supplying information to various official organizations such as Port Authorities, canal                             authorities etc

2)      General arrangement Plan

              This usually consists of a profile and plan views of the ship showing the location               of all               compartments, tanks, store rooms and accommodation. Used to locate and identify               individual compartments.

3)      Capacities and Centre of Gravity of cargo, fuel, water, stores etc:

              This will show the capacity and the longitudinal and vertical centre of gravity of               every               compartment available for the carriage of cargo, fuel, stores, fresh water and water               ballast.

              This information is required for

a)      transverse stability calculations (to calculate ship’s KG) and

b)      Longitudinal Stability calculations (to calculate ship’s LCG).

              Also used to calculate the space available for items of deadweight such as fuel,               water,               cargo etc.

4)      Estimated weight and disposition of passengers and crew:

              Of particular relevance to the passenger ships. For use in transverse and               longitudinal               stability.

5) Estimated weight and disposition of deck cargo including 15% allowance for               timber deck cargo)

              For use in transverse stability calculations involving calculation of the ship’s KG               and               GM. Used effectively so as to ensure vessel complies with the load line regulations               throughout the voyage..

6)      Deadweight scale

              A diagram showing the load line mark and load line corresponding to the various               freeboards, together with a scale showing displacement, TPC and deadweight for               a range               of draughts between Light and Load condition.

              Particularly useful when loading cargo (eg., comparing draught to estimate cargo               loaded)

7)      Hydrostatic particulars  (Displacement, TPC, MCTC, LCB, LCF, KM)

              A diagram or table showing the hydrostatic particulars of the ship such as               Displacement, TPC, MCTC, LCB, LCF, KM et.

              Particularly useful for a variety of stability calculations including transverse stability and               longitudinal stability (eg., worksheets for the calculation of GM, trim and draughts               forward and aft)

8)      Free Surface Information (including an example)

              Usually in the form of Free Surface Moments (FSM) for each tank in which liquids               can be carried. The FSM given will be for a stated relative density of liquid (often 1.00)               which will need to be adjusted if the liquid is of another density.

              Used in transverse stability calculations in order to find the ship’s fluid KG and               fluid               GM.

              There should also be a worked example.

9)  KN tables / Cross curves (including an example)

              This will take the form of a diagram or table showing the righting levers for an               assumed KG (the KN is the GZ of the vessel assuming the KG is zero). There should               also be a worked example showing how a GZ curve can be obtained using the tables /               cross curves.                           

              KN tables are used to obtain the value of GZ (as GZ = KN=-KGsinθ)

              Cross curves are used to find the GZ of the vessel for any angle of heel.

10) Pre-worked Ship conditions (Light ships, Ballast Arr/Dep, Service loaded Arr/Dep,

       homogenous loaded Arr/Dep, Dry docking etc)

              To include for each condition:

a)      a profile diagram indicating disposition of weights.

b)      Statement of light weight plus disposition of weight on board.

c)      Metacentric height (GM)

d)      Curve of statical stability (GZ curve)

e)      Warning of unsafe condition.

              Very useful in cargo planning since it is easier to use a ship condition similar to

              the proposed load condition. Also useful where the ship’s tables are presented in a               form unfamiliar

              to the ship’s officer who can now follow the method of calculation normally used on that               vessel.

              Dry dock: Enables officer to plan the stability condition for entering dry dock.

                 Loaded: Provides officer an example to establish stability condition of the vessel              

              when loaded with relation to draught, trim, displacement, stress (SF & BM) and ...