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Determine Initial Stability How Location of Center of Gravity Is Fixed by Inclining the Ship —Initial Stability in Any Condition Can Then Be Calculated HE introduction of the inclin- | ing experiment by the United States steamboat inspection ser- vice for determining the position of the center of gravity of a vessel, from which the metacentric height which is the initial measure of stability may be determined, is a notable triumph in the promotion of safety of life at sea. But before the position of the center of gravity can be determined by an inclining experiment, the dis- placement, center of buoyancy, and metacentric, radius must be established from the lines of the vessels. For all vessels of any pretentions these quantities have been determined as a part of the necessary calculations in the design. The primary purpose of an inclining experiment, is to determine the posi- tion of the center of gravity of the light ship. The hull and machinery should be complete in every respect and all equipment permanently located All extraneous weights, such as fuel, stores, and fluids of all kinds, except water in the boilers at working level, must be excluded from the vessel in preparation for an inclining experi- ment. The metacentric height is the initial measure of the stability and the emer- gencies encountered by vessels of various characteristics require a cer- tain factor of safety if you like, of which it is a true index. Upon an ocean-going ship, loaded and ready : for sea, 20 inches in metacentric height may be considered a good measure for comfort and safety, while an in- land steamer with 20 inches in meta- centric height may be unsafe. Obvi- ously a standard limit of metacentric height for all vessels cannot be spec- ified by law. With every alteration of displacement, the metacentric height and the behavior of the vessel are affected, and it is dangerous to gen- eralize and it is therefore, necessary to investigate the stability for, a variety of conditions. In order for a ship to be successful, she must be economical and dependable in opera- tion, but first of all she must stand up, and possess that quality of resist- The author, Capt. Chester Willett of the United States steamboat inspection service has been in charge of conducting inclining ex- periments on vessels since the inception of this rule by the government. An article in the September, 1925 issue of MARINE ReEvIEW treated the general subject. BY CAPT. CHESTER WILLETT ing a change from rest, which tends to return her to the upright: position upon being disturbed and _ buffeted about by dynamic forces. There is considerable preparatory work to an inclining experiment in order to conduct the test expeditiously and ensure accuracy of results, and many precautions must be _ strictly adhered to and sundry details properly arranged. A preliminary inspection is made to ascertain the condition of the vessel and a careful list is made of all items necessary to complete the ship, together with their weights and permanent locations on_ board. A list is also made of all weights on board to go ashore, such as inclining weights, dunnage, staging, and tools; and of all weights on board but not in their respective positions. This may be determined with suf- ficient accuracy by the formula wxd GM = and solving for w, D x tan 9 GMxDxtan9 v= d where w is the amount of inclining weight required, GM is the metacen- tric height (estimated at a reason- able desired amount), d is the dis- tance the weight or weights can be moved from the center line of the ship, D is the displacement of the ship, and tan 9 is the angle of inclina- tion which may be 3° degrees. The inclining weights may be of any local material suitable for han- dling transversely over decks and should be divided into any number of equal units and placed on the center line or on the outboard sides of the deck. Use At Least Two Pendulums At least two pendulums should be suspended from suitable locations, and on large vessels three pendulums are used. The pendulums are suspended in buckets of oil to dampen their os- cillation for the purpose of more ac- curate readings on a batten, which is prepared on a wooden hors?, or trestle, to record the throw -r swing of the pendulum when the weij.hts are moved across decks. The perdu- lum line should be about 15 or 20 feet in length and must pivot from a sharp suspension point so that ac- 17 curate measurements of the lergth of the line between the pivot and the batten can be made. The draft of the vessel is taken from a small boat, where the merks are measured with accuracy and tec- orded as draft at inclining condition, for use in determining the weight of the ship from the displacement curves. The density of the water is de- termined by taking a sample of the water at the surface and a sample from near the depth of the ship amid- ships, and the mean density accurately determined by analysis, or hydrometer tests, for use in the correction of the weight of the ship as predeter- mined. After the preliminary examination, the vessel is put in an upright posi- tion. All the necessary measurements and data are taken and _ recorded, the mooring lines are slackened and all persons on board stationed at their assigned positions on the center line, and the zero readings are marked on the various battens. After the zero readings have been marked, the inclining weights are moved; the first movement is gener- ally from port to starboard, and the men on board again take up their re- spective positions on the center line and the first readings are recorded on the battens. In the particular case under discussion here 15.97 tons of weight was moved across decks 386 feet, and the vessel heeled slightly. On referring to the data sheet, it was found that the draft at the in- clining condition was 14 feet 2.5 inches aft and 10 feet 1.125 inches forward. After corrections were made for the base line, they worked out to a mean draft of 12 feet 1.81 inches. The true displacement. at the above drafts, with correction for density of water, shell, and appendages, was found to be 4590 tons, which repre- sented the weight of the ship as in- clined. Upon making calculations for the metacentrie height, it was found that: 15.97 x 36 182.625 GM =—=————- x 4590 14.44 = 1.60 feet which subtracted from the height, of me (Continug-of the Columbia S.S. Co. * ~ ~ : bs : Fe gage SE Net PER SPR AT RN I rE OIE SO A al A ve =~ DET 8 ME Sane en RIES Ae BEESON SESS SSS SS