Chapter 3-STABILITY AND BUOYANCY 



(r 



10 20 30 40 50 60 70 



ANGLE OF HEEL, IN DEGREES 



vSO 90 



8.59 

 Figure 3-15. — (A) Uncorrected stability curve 

 taken from cross curves. (B) Corrected sta- 

 bility curve. 



and a horizontal batten or an inclinometer device 

 designed for this purpose, usually does not ex- 

 ceed two degrees. The metacentric height is 

 calculated from the formula 



GM 



wd 



Wtan^ 

 where 



w = inclining weight, in tons 



d = distance weight is moved athwartships, 

 in feet 



W= displacement of ship, including weight w, 

 in tons 



tan 6= tangent of angle of list 



The results of this experiment are calculated 

 and tabulated in the Inclining Experiment Data 

 Booklets , which consist of two parts. Part 1, 

 Report of Inclining Experiment , contains the 

 observations and calculations that determine the 

 displacement and location of the center of gravity 

 of the ship in the light condition. Part 2, Stability 

 Data for surface ships and Stability and Equi- 

 librium Data for submarines, contains data 

 relative to the characteristics of the ship in 

 operating condition. These booklets are prepared 

 by the inclining activity, and Part 2 is issued to 

 the ships for their information. 



The KG obtained from the inclining experi- 

 ment is accurate for the particular condition of 



loading in which the ship was inclined. This is 

 known as Condition A, or the "As-Inclined" 

 condition. The ship may have been in any condi- 

 tion of loading at the time of the experiment, 

 and this may not have been in operating condi- 

 tion. In order to convert the data thus obtained 

 to practical use, KG must be determined for 

 various operating conditions. The standard load- 

 ing conditions as found in the Inclining Experi- 

 ment Data Booklets are as follows: 



Condition A— Light ship 



Condition Al — Light, without permanent bal- 



last3 

 Condition B— Minimum operating condition^ 

 Condition C— Optimum battle condition^ 

 Condition D— Full load 



Other special conditions, including special 

 low stability operating conditions, conditions of 

 light load with water ballast, and similar condi- 

 tions may be included. 



Condition A— Light Condition assumes that 

 the ship is complete and in all respects ready 

 for sea, but with no load aboard— no fuel oil, 

 stores, crew and effects, ammunition, water, 

 gasoline, JP-5, or water or oil in machinery. 

 Although not an operating condition, Condition A 

 is the basic condition from which other condi- 

 tions are calculated. 



After obtaining the displacement and locating 

 the center of gravity for the ship in Condition A, 

 corresponding values may be computed for other 

 standard conditions of loading. The weights and 

 vertical moments of all consumables to go 

 aboard are determined and, starting with the 

 displacement and KG for Condition A, a new 

 displacement, KG, and GM are calculated for 

 each of the other conditions of loading. The GM 

 thus obtained is in each case corrected for the 

 free surface assumed to exist in the ship's tanks 

 for that particular condition of loading. (Free 

 surface is discussed later in this chapter.) 



Having determined displacement and KG, it 

 is possible to draw a curve of stability for each 

 condition of load. Additional information con- 

 cerning inclining experiment data can be ob- 

 tained from chapters 9290 and 9880 of the Naval 

 Ships Technical Manual. 



This condition is listed only when ships have perma- 

 nent ballast. 

 4 



For ships without underwater defense systems. 



5 

 For ships with underwater defense systems. 



43 



