A Treatise On The Principles And Practice Of Dock Engineering

DISTRIBUTION OF PRESSURE ON KEEL-BLOCKS. 487 4 feet 6 inches apart from centre to centre. The amount of overhang forward was very great. At one-fourth of the vessel’s length, measured from the stem, the keel rose f inch and continued to rise as it proceeded forward. The condition of things is shown in fig. 479, the black blocks indicating the extent of the supported part of the keel. The exact sequence of the occurrence was never clearly ascertained, the evidence being somewhat conflicting, but the most competent witness stated that he found the blocks flying out at the after end of the ship first, and then the forward blocks came down. On the other hand, Dr. Elgar, who was called in as a consulting expert by the Mersey Docks and Harbour Board, inclined to the opinion that the catastrophe was due to the great pressure imposed on the forward blocks by the excessive overhang of the vessel’s stem, and, therefore, that disruption began in that quarter. In a paper* read before the Institution of Naval Architects the same year, Dr. Elgar gave the reasons for his decision, and entered very minutely into the question of the probable amount of stress produced in the foremost loaded block, deducing a pressure of 178^4 tons. Without desiring in the least to depreciate the care and skill with which the mathematical calcula- tions were carried to their conclusion, it cannot but be felt that the postulates were too hypothetical to justify any definite numerical result. It is, in faet, only possible to approach the question by means of certain assumptions, none of which may be accurately, or even approximately, true. For example, it has to be taken for granted, either that the blocks were elastic or that they were rigid, the keel flexible or inflexible, and the probability is that no one of these conditions prevailed throughout. It is useless to go into the matter again in^o far as the “Fulda”is concerned. Whether the blocks were sheared at the forefoot or abaft the middle (and it is a stränge complication of the whole affair that the blocks had been in use for 40 years and the “ Fulda” docked several times before without mishap), the faet remains that the pressure upon the keel-blocks is very unevenly distributed, and is certainly very great on the forward blocks under any ship of ordinary design. About the time of the “ Fulda ” disaster, the author made a number of careful observations of the actual profile assumed by the keels of various vessels in graving dock. In all cases he found two regions of great de- pression—one immediately abaft the forefoot and the other amidships under the machinery. In these localities, the keels had crushed the soft wood caps to a much greater extent than elsewhere, there being a maximum difference of level in some cases of as much as 1J inches. The intricacies of the problem are too numerous for any exact solution, but if we choose to confine our investigation within certain limits, we may arrive at a result which will have some relative value. We will therefore briefly deal with the general case of the distribution of stress under a system of irregular loading, making the following assumptions : — * Elgar on “ The Supporting of Ships in Dry Doeks,” Min. Proc. Inst. X.A., 1899.