FIG. 16.
MODEL IN UPRIGHT POSITION
FIG. 17.
MODEL IN INCLINED POSITION
A further method of arriving at results by experiment, involving principles not unlike those of the “paper section” method just described, has recently come under the author’s notice, and through the courtesy of its inventor—Mr John H. Heck, of Lloyd’s surveying staff at Newcastle—the following general description of the apparatus and fundamental principles is made public for the first time:—
By means of a “stability balance,” roughly illustrated by Figs 16 and 17, in conjunction with either an outside or inside model of the vessel, the moments of stability can be practically determined. In practice, an inside model has been found the most convenient to employ. This consists of a number of rectangular pieces of yellow pine of any uniform thickness, out of which a portion has been cut, respectively to the form of the vessel at equidistant intervals of say 15 feet. These pieces, together with two end pieces, are kept together by four or six bolts, thus forming a contracted model, the inside of which is of a similar form to that of the vessel. If this model is filled with water to a height corresponding to any draught, it will represent a volume of water having the same form, and proportional to the displacement of the vessel at that draught.
The stability balance consists of a frame A attached to a steel bar Z, having knife edges working upon the support C; a table D attached to a spindle working freely in the bearings E, and capable of being turned through any angle; a sliding weight F to balance the weight of the model when empty; a sliding weight H to balance and measure the weight of the water contained in inside or displaced by outside models; a sliding balance weight K which by adjustment will locate the centre of gravity of the combined weights of the table D, the model and the weight K in the axis of the table D, so that the model will remain when empty in any inclined position, and be balanced by the weight F.
In order to determine the moments of stability, the model is first fixed on the table D, and the weights F and K so adjusted that F will balance the model at all inclinations. The table is then brought into the upright position, and water is poured into the model to the height corresponding to the desired draught of water, and the weight H shifted until the whole is balanced. The weight of water in the model will evidently be = weight H × its distance from the fulcrum ÷ distance centre of model is from fulcrum.