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Measure Stability of Ships With Instrument By W. Selkirk Owen* LL ships under all conditions A loading should have the proper amount of stability; not too much and not to little. No exact means of determining stability di- rectly or easily has heretofore been available, There has now been per- fected a truly remarkable instrument for automatically measuring stabil- ity. This instrument is known as the stability meter and was invented by J. Lyell Wilson, an American navai architect. This stability meter can be con- veniently installed in the machinery space on the vessel and its dial, which may be located anywhere, will register the existing amount of G@M or the metacentric height, in feet or inches, and it can be read by anyone at any time. It is a compact, high- class, electric instrument and _ oc- cupies but little more space than a man’s suitcase, Stability Determined The theory upon which the instru- ment works is based on mathematical deductions. Metacentric height has a definite mathematical relation to the maximum angle of roll, however small, that occurs at any instant to- gether with the maximum agular ve- locity of the ship during that roll. This information the stability meter automatically records and combines with a given constant setting of the instrument which is determined by ealculation, once and for all, for the particular ship upon which it is being used. The net result is that a final and conclusive answer to the ques- tion of what the metacentric height is in feet and inches can be read di- rectly upon the dial of the instru- ment. The maximum angle of roll is de- termined by a small damped pendu- lum and the maximum angular ve- locity is recorded as the result of the tilting or precessional movement in- duced by the ship’s velocity upon a small gyroscope revolving at high speed. These two movements are in turn transmitted independently to each branch of a logarithmic slide rule, arranged on transparent con- centric cylindrical shells and the an- swer becomes available immediately as the result of this virtually auto- matic manipulation of the slide rule by the electrical devices in the in- strument, *The author, W. Selkirk Owen, is pro- fessor of naval architecture, Webb In- stitute of Naval Architecture. 30 A calculation of the mathematical expression known as the radius of gyration of the material of the ship and its contents must be made to de- termine the constant setting for the instrument for each particular vessel. This, of course, is work for the ex- pert and when once done and the in- strument is installed ready for use its setting need never be disturbed again so long as it remains on that ship. If an instrument should be re- lceated at any time on another ves- sel, it would only require a proper re- setting to give correct readings for the new ship. Stability is a changing thing even during the same voyage of the ves- sel, Fuel and stores are consumed on a trip and may cause a vital change in the position of the center of grav- ity. It may be necessary to correct such a condition by adding water ballast to the vessel before arrival. The value of the stability meter to the operating personnel on_ ship- board is obvious. It would give them at all times the exact metacentric height, and thus indicate the neces- sity for water ballast and the effect —Photo by Fairchild Wilson stability meter. Direct reading indicator, giving metacentric height of vessel in feet and inches MARINE REVIEwW—December, 1934 on stability produced by such ballast. The necessary minimum amount of stability of a merchant vessel is a matter of vital concern to the gov- ernment in its responsibility for the safety of life at sea of the crew and passengers who embark upon _ the vessel. The bureau of navigation and steamboat inspection must have the assurance of satisfactory stability qualities of a vessel, along with other matters that affect her sea- worthiness. Without such assurance the vessel would not be allowed to depart from port, It is now required by law that each vessel shall have her stability quali- ties determined by a satisfactory in- clining experiment performed under the direction and supervision of rep- resentatives of the bureau of naviga- tion and steamboat inspection. There- after it remains for the marine su- perintendent, after solving his own problems of stability for each voy- age, to convince a skeptical govern- ment official of the wisdom and cor- rectness of his own judgment in the matter. It is no wonder that differ- ences of opinion arise in such a high- ly specialized and abstruse technical question. Especially is this so when the opinions of two persons of pos- sibly different temperaments, experi- ence and methods of approaching the subject are required to harmonize. Save Excessive Ballast Excessive and unnecessary ballast, with all its attendant economic loss, is too often the only way out. In this instance the government may be polite but it is firm. In the absence of definite and complete information no chances are taken and to make certain to be on the safe side on goes the ballast. At the international safety of life at sea conference, held in London, in 1929, at which all of the import- ant maritime nations of the world were represented, a great deal of earnest thought and attention was given to the matter of minimum sta- bility requirements for vessels, J. Lyell Wilson, inventor of the stability meter, is well known among technical men of the shipping in- dustry. He is the assistant chief sur- veyor of the American Bureau of Shipping. In 1926 he was appointed technical assistant to the committee on stability. As a result of his special preparatory studies and _ investiga- tions of the subject of stability, he recognized the need and advantage of an instrument for its direct deter- mination. This instrument has now been perfected after years of patient effort and experimentation, and its practical value has been demonstrat- ed on various vessels. Shipowners’ have co-operated in making it pos- sible to obtain valuable data pertain- ing to the economical operation of the vessel,