1842.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



begins to take a uniform force througli the vessel, and neutralising or 

 turning into one cliannel the multitude of conflicting currents, Mr. 

 Grantham has undertaken to make experiments on the subject. It 

 has been supposed that the course of the magnetic current is deter- 

 mined during the operation of rivetting, or that its intensity is con- 

 siderably increased, its force being also influenced by the polar direc- 

 tion of the sliip's keel while on the stocks, but Mr.' Grantham states 

 that helms been led to doubt tliis. The polarity of the ship, he con- 

 siders, is not affected by rivetting, but seems to be dependent on the 

 quantity or quality of the iron, and he thence deduces that there is 

 reason to believe that time will have but little effect in increasing or 

 diminishing the magnetic intensity. Captain Johnson, we may add, 

 has observed, that the compass placed a few feet above the deck is 

 not much attracted by the iron, and it is a common practice for the 

 captains of iron ships to place a compass in the cross-trees at the top 

 mast-head, by wliich to ascertain the correctness of the one placed in 

 the binnacle. Sir Howard Douglas has raised the question whether 

 the changes of climate are likely to affect the intensity of the electric 

 current. We think they might in a slight degree, but experience has 

 proved not to such an extent as to interfere with the safe action of the 

 compass. The long voyages to the East and West Indies, and to South 

 America, have abundantly proved the efficiency of the compass in iron 

 vessels. As to iron vessels being more subject to drift to leeward, and 

 steering ill, as these are circumstances dependent on form, thev can be no 

 peculiar defects of iron shipping. The navigable powers of iron vessels, 

 when properly constructed, are as perfect as those of timber vessels ; but 

 it is the case that many iron ships being built for a light draught of 

 water, are flat-floored, and very full, without adequate and counteract- 

 ing depth of keel. This, however, has nothing to do with a deep-sea 

 ship. Fouling in the case of iron ships has been much exaggerated, 

 for it can be entirely got rid of by the application of a scraper, such 

 as Mr. Grantham has invented and described. The corrosion of the 

 iron plates by the action of sea-water proves a groundless alarm — no 

 case of destruction from this cause in many vears' experience has yet 

 occurred. Mr. Grantham remarks, that so slight is the apparent decay 

 of the vessel when in use, and so much slower in its progress than 

 is exhibited by iron when applied to other purposes in salt water, 

 that many who have observed the fact, are led to suppose that some 

 occult and preservative law is in operation peculiar to iron so em- 

 ployed. The phenomena of iron rails on a railway will occur to our 

 readers on this occasion, and also those affecting wood pavement. 

 As oxidation is promoted by heat, Mr. Grantham recommends that in 

 ■steam-boats the boiler should be kept as far as possible from those 

 ports of the vessel which are above water, or means should be adopted 

 to keep them cool by interposing non-conducting substances. The 

 connection of copper pipes with the shell is also to be avoided, and 

 for this purpose the same gentleman states that he has latterly made 

 short lengths of wrought iron pipes, with flanges, and rivetted them 

 to the vessel.* It was assumed that iron vessels would be found un- 

 suitable for warm climates, as subjecting the crew to a greater heat, 

 but neither in the Niger, or the Euphrates, nor in the China Seas, has 

 this proved to be the result. Even at home ship-owners have been 

 deterred from the use of iron by the fear that the public were preju- 

 diced against it, although the experience of the Glasgow and Liver- 

 pool steamers, and other large vessels, shows no such unwillingness. 

 We agree with the author before us in regarding stiff'ness of hull as 

 an advantage and not an injury to the sailing power of a vessel, pro- 

 vided the elasticity of the rigging is sufficiently secured. The preju- 

 dice of the underwriters with regard to iron vessels, will most likely 

 turn out very much in the same way as that with regard to chain 

 cables. They would .not formerly insure a vessel which had chain 

 cab'es ; then it came to the use of one cable of hemp and another of 

 iron, and now most probably underwriters would oliject to a ship as 

 insufliciently found if she had no chain cable on board. If the under- 

 writers do not give way with regard to iron ships, the owners and 

 builders have the remedy in their own hands, for it is in contempla- 

 tion on their part to form a marine insurance companv of their own. 



Having now disposed of the objections to iron shipping, we shall 

 refer to some of its merits. The first cost is perhaps the feature of 

 primary interest : on this subject Mr. Grantham sums up. 



" From a careful consideration of the question of cost, I have arrived 

 at the following conclusions: — 



" 1st. That a good serviceable iron sailing vessel, not exceeding 300 

 tons burthen, will be equal in cost to an English-built twelve years 

 timber-built ship, of the same external dimensions, without includiug 

 the price of copper sheathing for the latter. 



' On the subject if corrosion of iron, and ihe means of rempclying it. see 

 Mr. Mallett's Papers in this Journal, vol. i, p. 312 ; and vol. iii, p 387 • Mr. 

 Neilson's Patent, vol. iii, p. 303 ; and Mr. Wall's, vol. iii, p. 429. ' 



"2nd. That iron vessels of above 300 tons have the advantage of 

 being rather less expensive than wooden vessels. 



" 3rd. That for very large merchant vessels and ships of war, iron 

 will also be found to be much less expensive than wood. 



"4th. That iron sea-gaing steamers bear also about the same pro- 

 portion according to their different sizes. 



" 5th. That iron vessels, for rivers, may be built at a light expense, 

 but so built are unfit for sea service." 



The prime cost, presenting this immedi ite advantage, is not the 

 only pecuniary benefit; for iron shipping, from the durabilitv of the 

 material, requires few repairs, and when broken up is more produc- 

 tive than timber. Repairs, the great source of profit to otlier ship- 

 budders, can never accrue to the iron ship-builder to an equal extent. 

 The hulls of some of the large Clyde steamers have not cost 1/. these 

 five years, while the usual calculation for a timber-built steamer is 

 that the expense of repairs will in ten or twelve years have equalled 

 the iirst cost. The advantage, in case of breaking up, is in fivour of 

 iron as against timber, four to one. Turning to their physical merits, 

 we should premise that malleable iron is one of the strongest mate- 

 rials,* while it may be converted into any shape ; on the other hand, 

 timber for curved parts must be grown with great trouble in an 

 unnatural form, or else scarfed, and its strength consequently impaired. 

 The ease, moreover, with which iron beams and frames of any di- 

 mensions and in one piece can be wrought, overcomes one of the 

 greatest difficulties in ship-building. As regards the mode of fastening, 

 copper and iron bolts must be used to secure the frames of a timber- 

 built ship, and are so badly contrived that they have little hold, while 

 they are the source of destruction to the ship, as being of a different 

 substance. Mr. Creuze sums up well on this point. He savs of iron, 



" Among the advantages are the greater durability of the material, 

 not only from its relative durability with that of timber, but from its 

 requiring no such metallic sheathing to ]>rotect it from the ravages of 

 worms. Also the greater durability of the structure, as a whole, in 

 consequence of the greater permanency in the perfect combination of 

 its several parts, arising from the fiistenings being of the same texture 

 as the portions of materials brought into connexion. The metallic 

 fastenings to a timber-built vessel act, it must be remembered, not 

 only chemically, but also mechanically, to accelerate her destruction 

 so soon as the close connexion of the several parts is at all diminished." 



A wood ve.ssel is compared by Mr. Grantham to an arch, being made 

 up of a great number of parts of various forms and sizes, placed in 

 diff'erent directions, and being dependent on each other for support. 

 If one becomes loose, the whole structure is more or less endangered. 

 In consequence, a most elaborate system of bracing bv iron straps, 

 knees, and bolls with nuts, is now pursued. The bolts do not accord 

 with the materials they fasten together, and the wood is so soft that 

 when a severe strain arises, a general yielding takes place, by the 

 boltheads sinking into it, and the wood itself 5;iving wav to the pres- 

 sure it receives from the neighbouring parts. In the iron vessel, on 

 the other hand, the outer shell of the vessel is composed of a series 

 of plates so rivetted together that its strength is nearly equal to that 

 it would be if formed of one plate. The consequent strength of iron 

 vessels needs little to be said in proof. On the canals the iron boats 

 are put to the severest service, as carrying iron stone, pig iron, and 

 refined iron from the blast furnaces. Mr. Grantham refer; to many 

 instances of vessels getting aground and on rocks without injurv, and 

 several cases of their being left resting on one or two points of support, 

 without any strain to the framing. A large casting, weigliing four 

 tons, is mentioned as having fallen into the hold of the Princess Royal, 

 Glasgow iron steamer, in consequence of the tackle having given way, 

 but without damage to the vessel. Greater capacity for stowage is 

 one of the grand points on which iron shipping claims superiority. 

 Mr. Grantham treats it thus: — 



"The shell of a timber-built vessel is so much thicker than that of 

 an iron vessel, that, with the same outside dimension^, the l.itter is 

 frequently IS inches wider and 12 inches deeper in the hold than the 

 former. Taking the most^^avourable part of a vessel — n imely, in the 

 centre of the length — in a vessel of 20U tons, the proportion in favour 

 of the iron vessel will be as 5 to G; but in the ends, which are drawn 

 finely off", the disparity is much increased, m.ikiiig the proportion of 

 the whole contents about as 5 to 4. Supposing, therefore, that a 

 vessel built of timber could stow 200 tons, she would, if ni.ide of iron, • 

 have room for 2o0 tons. The total capacities of the largest vessels 

 will probably not approximate nearer than as 5 to 6; tnakii.g the iron 

 ship of GOUtons not to exceed in outward dimensions the timber one 

 of 500 tons. The advantage of this is very great, and enables an iron 



' Vide Mr. Fairbairn on the Strength of Iron, with respect tcS .ip-buikling, 

 in our third Vol., p. 388. 



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