80 AN ANALYSIS OF THE ISHERWOOD SYSTEM 



the case he has under consideration, of about 1 per cent. This will be appreciated by refer- 

 ring to the midship section and considering that the framing is 2 feet 2 inches apart, whereas 

 in the Isherwood systaTi it is 12 feet apart. The extent of the saving to this end would 

 probably be close to 20 tons. 



There is another item of saving which has escaped Mr. Flodin's notice. This will also 

 be appreciated by referring to the section — that is, the amount of cement chocks that are re- 

 quired between the frames in the transversely framed vessel, whereas in the Isherwood sys- 

 tem the necessity of this cementing does not exist. 



The saving in this weight would depend upon the amount of coke breeze, or like ma- 

 terial, that may be fitted in with the cement, but I should say it must be worth about 10 tons. 



These savings, added to the amount as calculated, namely, 142 tons, would increase the 

 deadweight carrying capacity of the vessel and also the saving in weight. The percentage 

 of saving would then be relatively higher than indicated in the paper. 



With regard to his remarks where he has touched upon the tankers, it may be advis- 

 able to point out that the saving in weight in these vessels run up as high as 15 per cent and 

 even more. 



This varies with the bulkheading arrangements. This is now appreciated sufficiently 

 that over 90 per cent of the tankers building are on the Isherwood system and that saving 

 in weight is obtained without impairing the strength of the vessel. In fact, the section modu- 

 lus of the Isherwood system is almost 20 per cent better than the transverse system, and to 

 that extent the vessel's longitudinal strength is increased. 



Regarding the failure of bottom through collapsing, the figures Mr. Flodin has taken 

 out are on the basis of floors on every frame in the case of the transversely framed vessel. 

 As it is evident and well known that there is consideralble surplus of strength where floors 

 are fitted on every frame, classification societies have agreed that floors can be fitted on every 

 third frame with bulb angle or channel intermediates. Further, the frame spacing has been 

 approved up to 36 inches, and Lloyd's has allowed a concession of the thickness of the bot- 

 tom plating on this construction as well as in the case of the floors on every frame. 



Regarding the longitudinal strength or bending strength, which Mr. Flodin has so care- 

 fully and diagrammatically set forth, it appears that 5 per cent advantage to the Isherwood 

 system was considerably on the low side. In fact, from calculations I have made, the sec- 

 tion modulus shows about double that amount. 



There is one thing that probably he has given the transversely framed vessel the ad- 

 vantage of, and that he has doubtless left out of the Isherwood vessel. I refer to the con- 

 tinuous deck girders. In a strict comparison, of course, the deck girders should be treated 

 alike in both cases, that is, either included in the Isherwood vessel or excluded in the trans- 

 versely framed vessel. 



Regarding the strength of the decks it would be necessary to have the figures before me 

 so as to exactly see how the comparison was made for deck loads. I am not, however, in a 

 position to discuss this point in detail, but I am certain that the decks of the Isherwood ves- 

 sel are as well supported to sustain a similar load as the transversely framed vessel. This 

 has been borne out by experience. 



Regarding the shell plating, it is not correct to say this is in accordance with Lloyd's 

 rules. The material in an Isherwood vessel is better distributed and disposed in the right di- 

 rection. This is conceded by classification societies, and they have found it possible to re- 

 duce the plating in Isherwood vessels slightly. 



