November 15, 1917] 



NATURE 



205 



FERRO -CON CRETE SHIPS. 



THE heavy demand for steel and iron for muni- 

 tions has enforced economy in the use of 

 these materials for other purposes, and led to 

 the substitution of other materials wherever pos- 

 sfble. The shortage of shipping and the necessity 

 of making- good war losses have produced recently 

 a considerable development in the building of 

 ferro-concrete vessels of a sea-going type, especi- 

 ally in the Scandinavian countries, where the 

 losses have been great and the scarcity of metals 

 has been much felt. Reference has already been 

 made in our Notes columns to articles in Engin- 

 eering giving interesting information as to what 

 has been done in Norway in the building of such 

 vessels, and most of the experience available at 

 present has been obtained in Norwegian yards. 

 The production of concrete and ferro-concrete 



Concrete is weak under tension, and the re- 

 inforcement in ferro-concrete structures is always 

 placed so as to take the tension, leaving the 

 concrete to take the compressive stresses. There 

 is difficulty in doing this throughout the structure 

 of a ship, and lack of effectiveness in this matter 

 may produce cracks, which, in the presence of 

 salt water, may lead to trouble. Strict inspection 

 and overlooking during construction are of much 

 greatef importance in all ferro-concrete structures 

 than in buildings of other types. This is owing 

 to the nature of the materials used and to the 

 possibility of the reinforcing bars becoming dis- 

 placed during the casting and ramming process. 

 The life of the ship will depend probably upon 

 the chemical composition and water-tightness of 

 the concrete, on the proper placing of the rein- 

 forcement, and on the effect of salt water upon the 



concrete and 



upon the re- 

 inforcement if 

 there are 

 cracks. 



Ferro - con- 

 crete vessels 

 weigh c o n- 

 siderably more 

 than steel 

 vessels of cor- 

 responding 

 d i m e n s i ons ; 

 hence their 

 cargo - carrying 

 capacity is less. 

 This will prob- 

 ably make it 

 impossible for 

 them to com- 

 pete against 

 steel vessels in 

 normal times. 

 Owing, how- 

 ever, to the 

 ease with 

 which repeti- 

 tion orders for 



vessels such as barges, intended for quiet waters, 

 is by no means novel, but the problem becomes 

 complicated when the vessel is to undertake sea 

 voyages under her own propulsive power. This 

 is principally owing to the uncertainty of the loads 

 imposed on the vessel, especially when in turbu- 

 lent waters. Of course, the same difficulty occurs 

 in the design of steel vessels, but the strength of 

 these is determined almost entirely by experience, 

 and there is plenty of experience available and 

 embodied in the rules of the various registration 

 societies. Until experience has accumulated of 

 the actual behaviour of ferro-concrete sea-going 

 vessels no rules will be form.ulated. The leading 

 societies, however, are taking an active interest 

 in the development, and Lloyd's Register has 

 approved of plans up to 500 tons. The maximum 

 weight of vessel projected so far appears to be 

 1 000 tons. 



NO. 2507, VOL. 100] 



Vessel being launched, bottom uppermost. 



vessels of the same size can be executed, and 



to the reduced quantity of steel required in their 

 construction, their production will certainly be 

 useful during the war. 



Particulars are given in Engineering of several 

 of the vessels already built in Norway. The 

 Namsenfjords is 84 ft. long, 24 ft. broad, and 

 1 1 '6 ft. deep. The hull is monolithic with the 

 deck and frames round the hatches. There are 

 two large wooden fenders outside the hull, and 

 the ship has a Bolinder motor and appliances 

 for prompt loading and discharging. She 

 is well suited for carrying timber, and will 

 be put on a Norwegian coasting route. She 

 passed her trial trip on August i. Another, 

 vessel, ordered by the South Varanger Iron 

 Ore Company, will have double sides and 

 bulkheads, since ore does not take up much 

 space. 



