Knotted steel

The toughness of wood is important in design for exactly the same reasons that that of steel is it determines whether a structure (a frame building, a pit prop, the mast of a yacht) will fail suddenly and unexpectedly by the propagation of a fast crack. In a steel structure the initial crack is that of a defective weld, or is formed by corrosion or fatigue in a wooden structure the initial defect may be a knot, or a saw cut, or cell damage caused by severe mishandling. 

Brearley, H. (1995) Steel-makers and Knotted String Institute of Materials, London). This book is a combination of Steel-makers (originally published in 1933) and Knotted String (originally published in 1941). 

Zinc in contact with wood Zinc is not generally affected by contact with seasoned wood, but oak and, more particularly, western red cedar can prove corrosive, and waters from these timbers should not drain onto zinc surfaces. Exudations from knots in unseasoned soft woods can also affect zinc while the timber is drying out. Care should be exercised when using zinc or galvanised steel in contact with preservative or fire-retardant-treated timber. Solvent-based preservatives are normally not corrosive to zinc but water-based preservatives, such as salt formulated copper-chrome-arsenic (CCA), can accelerate the rate of corrosion of zinc under moist conditions. Such preservatives are formulated from copper sulphate and sodium dichromate and when the copper chromium and arsenic are absorbed into the timber sodium sulphate remains free and under moist conditions provides an electrolyte for corrosion of the zinc. Flame retardants are frequently based on halogens which are hygroscopic and can be aggressive to zinc (see also Section 18.10). 

In addition to a circular cross-section (round steel), the reinforcing steels can have special shapes, e.g. twisted, knotted, ribbed, in order to produce a special adhesion effect. 

The motor fishing vessel (mfv) TIT BONHOMME, C331, (Fig. 1) was an unremarkable, coastal/ofiFshore stem trawler, rigged and equipped for bottom Irawfing for prawn and whitefish species. The vessel was bruit in 1988 in France, of steel construction, 21 meters (LOA) and powered for a service speed of about 10/11 knots. She was owned and skippered by Mr Michael Hayes, an experienced fisherman and holder of a Second Hand Special Certificate of Competency. 

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