60 AN ANALYSIS OF THE ISHERWOOD SYSTEM 



In other words, are the claims, not only as to increased cargo capacity, but also as 

 to strength, true? It is the first purpose of this paper to endeavor to answer these 

 questions in the case of one specific type of vessel, the choice of which depended 

 on the fortunate circumstance that a western shipbuilding firm, with which I was at 

 the time connected, changed from the transverse to the longitudinal system of con- 

 struction. Other advantages claimed for the Isherwood system will also receive 

 consideration. 



The particulars of the design under consideration are: — Length between per- 

 pendiculars, 380 feet ; length, over all, 395 feet ; length, Lloyd's, 380 feet 3 inches ; 

 breadth, mottlded, 53 feet ; depth, moulded, 29 feet 3 inches ; load draught, about 23 

 feet 6 inches; block coefficient, .790; deadweight cargo capacity, about 7,500 tons. 



The two vessels are, as shown by the profiles (Plates 34 and 35), of the poop, 

 long bridge and forecastle type, and both are built to the highest class of Lloyd's 

 Register of Shipping. 



In making this change in the system of construction, several minor alterations 

 became necessary or desirable. Thus, for example, the engine and boiler casings 

 and the deck-houses were changed, the fore-peak bulkhead was moved forward, 

 and a bulkhead was added in hold number two, at the forward end of the bridge. 

 But since these alterations are not chargeable to the change in the system of con- 

 struction, they have either been disregarded or their effect has been equalized. 



Notwithstanding the necessity to make these departures from the working 

 drawings, this opportunity for direct comparison offers very considerable advan- 

 tages. Vessels of both designs have been built and are at the present time in actual 

 operation, so that the case cannot be regarded as a hypothetical one. We have, 

 further, the advantage of being able to obviate reduction to standard conditions or, 

 in the case of steel weights, to a basis of tons of deadweight capacity per ton of 

 steel, since the vessels are of identically the same dimensions. 



In this connection attention is called to the absence of side stringers in the trans- 

 versely framed vessel, this omission having been compensated for by increased 

 stiffness of side framing and greater thickness of shell plating. Since this simpli- 

 fication is now quite commonly adopted, both ships may be regarded as typical of 

 the system of construction that they represent, but it should be borne in mind that 

 the transverse framing construction has gone through a long course of develop- 

 ment, while the Isherwood system is relatively very young and may consequently 

 be regarded as being in a rather rapid state of evolution. 



COMPARISON OF WEIGHTS AND CAPACITIES. 



Rather careful calculations of the net steel necessary to complete the two ves- 

 sels show that 2,023 tons were used for the transversely framed vessel and 1,881 

 tons for the Isherwood ship. These figures, which are in tons of 2,240 pounds, do 

 not include scrap ; that is, deductions have been made for lightening holes, notches 

 in the plates where continuous members pass through, etc., and no allowance has 



