A Treatise On The Principles And Practice Of Dock Engineering

DURABILITY. 3°7 •when they were built. Owing to the deepening of the lock, new verticals had to be introduced, but the old horizontal ribs were replaced, and are now doing duty as effectively as the new tiniber, with every prospect of an indefinite existence. The greenheart storm-gates of the Sandon entrance, built about the year 1848, were taken to pieces in 1902 and found to be in excellent condition. The Bramley-Moore Dock gates, of English oak, built about 1835, were overhauled in 1902; below the water-line, the wood was in perfect preservation, but decay had occurred in some sapwood in the upper part of the gate, which had to be made good. The greenheart gates at the Delamere Dock, at the entrance to the River Weaver, were constructed in 1862. No repairs of any kind have been executed to them, and they are still in admirable condition.* The greenheart gates at the sea entrance to Hendon Dock, Sunderland, were constructed in 1866. With the exception of some caulking to the planking, no repairs have been carried out, and the gates are still practically as good as new.f Where the timber is of less trustworthy character the same durability cannot be reasonably expected. Continental gates often contain a large proportion of ordinary pine and pitchpine, timbers which do not possess the lasting qualities of oak and greenheart. It is not surprising, tliere- fore, to find that the average life of such gates is about twenty-five years, though, with constant care, Mr. Nelemans states that very good results have been obtained, after nearly forty years’ triai, with creosoted pine, “although the gates concerned are not usually worked, excepting those in the old Ymuiden Locks. It should be observed, however, that gates which are nearly always in their recesses do not last longer than those which are regularly worked.” J The one really weak point in the argument for the longevity of wooden gates is their liability to the depredations of sea worms. The Limnoria terebrans and the Teredo navalis (vide Chapter iv., p. 151) are two extremely persistent and troublesome borers, but they do not infest sewage-polluted waters, at any rate to any serious extent, and greenheart appears to be little, if at all, susceptible to their ravages,§ possibly on account of a poisonous oil which it contains. A splinter of greatheart in the flesh will * Hunter on “ Dock Gates of Greenheart and Steel,” Int. Nav. Gonq., Düsseldorf 1902. + Ibid. + Nelemans on “Iron and Wooden Look Gates,” Int. Nav. Gong., Düsseldorf, 1902. § The testimony on this point is not altogether unanimous. Mr. Squire states that Greenheart offers, perhaps, the best resistance to the ravages of the Pholas and imnoria on the exterior, and of the Teredo on the interior, of the wood, but it is by no means invulnérable. In the Bombay Docks, greenheart gates were freely attacked by all these animals, especially on the seaward side of the gates and on the underside of the ribs. For the first few years they appeared only in the corners of the large ribs where the less mature timber would be found, but ultimately they penetrated the heart- wood. On “Lock Gates,” Ninth Int. Nav. Cong., Düsseldorf, 1902.