The Press., 1892-06-30
IRON AND WOOD SHIPS
MATERIALS USED IN sHipDuILDING
 AND THEIR VALUE.

Tho Points in Which. Iron a.Ad Steel Are
 Superior to yy.od-Their LiEbtness
 and Durability and tiAe Comparative
 Safety of All Kinds of Vessels.
 The three materials used in the con- ,struction of ships in general are wood, iron and steel. Wood has been in use from time immemorial. Iron is only about fifty years old and steel is easily within the memory of every man of moderate years. The importance of the three materials are inversely as stated steel being the most valuable, then iron and last wood. Noticeably is this so ill the construction of swift steamships, for wood is unsuited to the great engine power nowadays put into ships; it can not properly stand the strain.
 Iron ships are superior to wooden ones in the following particulars: Lightness mbined with strength, durability when properly treated, ease and cheapness of construction and repair and safety when properly constructed and subdivided. In wooden ships it has been found that about one-half of the total weight of the ship is required for the hull, whereas in iron ships only from 30 to 40 per cent. of the weight is thus taken up. For in- stance, in a wooden armored warship, the weight of the hull being 50 per cent of the displacement leaves 50 per cent. for the weights to be carried. In an iron armored warship the weight of the hull is only 40 per cent, leaving 60 per cent. for weights to be carried.
 The tensile strength of iron is from 40, ,000 pounds to 60, ,000 pounds per square inch, and this strength can be secured throughout all the metal used, so that the material worked into the ship is uni form and homogeneous. These are quali- ties wanting in wood; the greatest care cannot eliminate such weak spots as are due to the presence of knots, crossgrain, hidden defects, etc. Generally good sound timber may be said to have a strength to resist pulling apart (tensile strength) of about 10, ,000 pounds.
 IRON FAR SUPERIOR TO WOOD. When in shipbuilding 1t comes to fastening pieces together, as, for in- stance, in making ships keel or her deck beams, the weakness caused by scarfng the pieces of wood together be- comes an element of strength in riveting the iron. No matter how it may be nec- esssary to treat the pieces of metal, whether by rlveting or welding or by angle irons, the iron stands far above the wood in resistance to tensile strains. It is only when resisting strains of com pression that there is 8 tendency of iron plates to buckle, and this is guarded against by making the plates thicker than is required for other strains or by re-enforcing them.
 Durability is a quality of iron that is not yet thoroughly determined. In gen. eral, a wooden ship may be said to last about fifteen years. Some last longer but there will be much patching and re. newing to be done. The rules of Lloyds allow about fourteen years as the aver. age durability of the best built timber vessels.
 Iron is not subject to the internal sources of decay to which wood is liable Worms and marine animals cannot in jure it, nor will it rot from imperfect ventilation. Neither can the parts work loose from the motion and straining ot the ship, allowing water to get in and cause decay. The danger to iron lies in the rusting or corrosion, especially ill the under water parts-outside from the sea water and inside from the bilge water. The only prevention is careful watching, cleaning and painting. and even with all this supervision galvanie action is likely to do some damage Therefore the life of an iron ship is linn, tied, and in the present state of knowl edge of the subject may be set down as approximately thirty years, for, though a ship will last longer, extensive repairs will have to be made that will cost con- siderable money.
 STEEL BETTER THAN IRON. If io alsn oaoio,. to ,.or,o;r. ', iro,, sl,ir,