vessels, where the rivets require to be close to each other, the edges of the plates are weakened to that extent. In this estimate we must however take into consideration the circumstances under which the results were obtained, as only two or three rivets came within the reach of experiment: and again, looking at the increase of strength which might be gained by having a greater number of rivets in combination, and the adhesion of the two surfaces of the plates in contact, which in the compressed rivets by machine is considerable, we may fairly assume the following relative strengths as the value of plates with their riveted joints : 100 Taking the strength of the plate at 56 These proportions may therefore in practice be safely taken as nearly the standard value of joints, such as used in vessels where they are required to be steam- or water-tight, and subjected to pressure varying from 10 to 100 lbs. upon the square inch. Since the above was written, I have ascertained, on a recent visit to Bristol, that the large steam-ship * now building there is double-riveted, the plates being three-fourths of an inch thick over the bottom and bilge, and five-eighths thick up to the waterline. These plates are joined together with double rivets of 1 inch diameter, and inserted at distances of 3 inches apart. The proportions appear to be good; and conceiving the workmanship to be equally so, I should infer that this fine vessel would fairly establish the principle, that iron, in all the ramifications of shipbuilding, is an article of paramount importance to the war as well as to the mercantile navy. In the pursuit of the foregoing inquiry, I was naturally led to the consideration of the best proportions and best forms of riveting plates together. I investigated this subject with great care and from my own personal knowledge and that of others, I have collected a number of practical facts, such as long experience alone could furnish. From these data I have been enabled to complete the following Table, which for prac *The Great Britain steam-ship. tical use I have found highly valuable in proportioning the distances and strength of rivets and joints requiring to be steamor water-tight. TABLE EXHIBITING THE STRONGEST FORMS AND BEST PROPORTIONS OF RIVETED JOINTS AS DEDUCED FROM THE EXPERIMENTS AND ACTUAL PRACTICE. The figures 2, 1.5, 45, 6, 5, &c., in the preceding Table are multipliers for the diameter, length, and distance of rivets, also for the quantity of lap allowed for the single and double joints. These multipliers may be considered as proportionals of the thickness of the plates to the diameter, length, distance of rivets, &c. For example, suppose we take three-eighth plates and required the proportionate parts of the strongest form of joint, it will be •375 × 2 -375 x 4 = 750 diameter of rivet, •375 × 5 inch =1.688 length of rivet, 12 inch =1.875 distance between rivets, 1 inch •375×51+3=3-438 quantity of lap for double joints, 3in.. •75, 1.68, 1.87, 2:06, and 3.43 are therefore the proportionate quantities necessary to form the strongest steam- or water-tight joints on plates three-eighths of an inch thick. In the preceding pages I have endeavoured to investigate almost every circumstance having a practical bearing on the question of the strength of rolled plates, and the best methods of uniting them together. In conclusion, I would venture a few remarks on the value and judicious use of this material, in its adaptation to ship-building, and other purposes to which it may be successfully applied. It is not my intention to enter into the question as to whether wood or iron be the preferable material, as a number of circumstances, such as cost, durability, &c., must be considered in order to form a correct decision. * I would, however, observe, that, in ship-building alone, it appears from the facts already recorded, that iron is very superior in its powers of resistance to strain; it is highly ductile in its character, and easily moulded into any required form without impairing its strength. It is also stronger in combination than timber, arising from the nature of the construction; and the materials composing the iron ship become a homogeneous mass when united together, forming as it were a solid, without joints, and presenting as a whole the most formidable powers of resistance. These are some of the properties which appear to distinguish iron from other materials, and which give it an ascendency of combined action, which cannot be obtained in the union of timber, however ingeniously contrived. It moreover possesses the property of lightness along with strength; in fact, its buoyancy, strength, and durability constitute the elements of its utility in the innumerable cases to which it may be applied. In ship-building it possesses other advantages over timber. Its hull is free from the risk of fire; and in case of shipwreck, either on rocks or sandbanks, it will resist the heaviest sea, endure the severest concussion, and with proper attention to the construction, it may *Since the above was written we have had many examples of the enormous strength of iron ships, and amongst others we may instance an iron vessel which took the ground with nearly one-half of her length at the stern hanging over a shelf for a whole tide; another, the Vanguard iron steamer, which for several hours (under the action of a heavy surf) was beating upon sharp shelving rocks without going to pieces; and lastly, the Great Britain steam-ship, which was stranded in Dundrum Bay, and resisted the force of the winter storms for many months. be the means of saving the lives of all on board. It moreover has the advantage of bulkheads, which, made perfectly watertight, not only strengthen the vessel, but give greater security to it, and by a judicious arrangement in the divisions will float the ship under the adverse circumstance of a leak occurring in any one of the compartments. These are the qualities and powers of the iron ship; and I trust the present research into the strength and proportions of the material of which it is composed, will not only give increased confidence in its security, but will lead to an extension of its application in every branch of marine and mechanical architecture. PART III. Resistance of Wrought-iron Plates to Pressure by a Blunt Instrument at Right Angles to the Surface of the Plate. Irrespective of the experiments made to determine the strength of wrought-iron plates and the relative strength of the joints by which they are united, the investigation would be incomplete if we omitted another inquiry of equal importance, namely, the resistance offered by plates to a crushing force, such as exhibited in the injuries received by vessels when stranded on rocks, or taking the ground in harbours where the surfaces are uneven. Such a Almost every person connected with nautical affairs is acquainted with the nature of the injuries received by timberbuilt vessels when placed in circumstances affecting their stability, or when resting on hard and unequal ground, such as frequently occurs in tidal harbours at low water. position is attended with danger under every circumstance; and in order to determine the relative values of the two materials, wood and iron, it was considered desirable to institute similar class of experiments on both, and thus to afford the means of comparison between them. English oak, as the strongest and best material used for the construction of firstclass vessels, was selected for this purpose; and the results obtained from both are given, under circumstances as nearly similar as the nature of the experiment would admit. They are as follows: In each of the experiments the plate was fastened upon a frame of cast iron, 1 foot square inside and 1 foot 6 inches outside, its breadth being 3 inches and thickness half an inch. The sides of the plates, when hot, were twisted round the frame, to which they were firmly bolted. The contraction, by cooling, caused it to be very tight, and the force to burst it was applied in the centre. This was done in order that the force might in some degree resemble that from a stone or other body with a blunt end pressing against the side or bottom of a vessel a bolt of iron, terminating in a hemisphere 3 inches in diameter, had thus its rounded end pressed perpendicularly to the plate in the middle. The results are given in the following tables : TABLE XIII. EXPERIMENTS TO DETERMINE THE RESISTANCE OF PLATES OF WROUGHT IRON TO A FORCE TENDING TO BURST THEM. |