OF SHIP CONSTRUCTION. 73 



all three periods. Enough work has not been done in this field to make it possible 

 to predetermine any one of these three vibration periods, except in so far as recip- 

 rocating machinery may be regarded to be likely to vibrate in synchronism with the 

 period of the stroke, and it consequently seems decidedly advantageous to reduce 

 the amplitude of the vibrations wherever that is possible. 



PRACTICAL CONSIDERATIONS AND OPINIONS OF SHIPBUILDERS AND SHIPOWNERS. 



Among the advantages claimed by the Isherwood supporters are that the ships 

 built to this system are more easily cleaned and repaired, and that the ventilation is 

 improved. 



It is unquestionably true that the Isherwood ships are more easily cleaned and 

 painted, especialy so in the double bottom. With the floors spaced 24 to 30 inches 

 apart, as is usually the case in transversely framed ships, the cleaning and paint- 

 ing of the spaces between the floors become both an expensive and unpleasant task, 

 whereas with the floors spaced from 5 to 6 feet apart, as is the practice in Isher- 

 wood ships abaft the three-fifths length, there is ample space and better air for the 

 men to work in. 



It is not so easy, however, to draw a conclusion as to the ease of repairing the 

 vessel. This is a point on which the results of years of experience alone can throw 

 light. This is also true of the question of ventilation. 



In order to obtain information on these points, as well as general expressions 

 of opinions and criticisms, inquiries were sent out both to shipowners who were or 

 had been operating Isherwood ships and to shipbuilders who had had extensive ex- 

 perience in this field of work. In all forty-eight letters of inquiry were sent out, 

 the field covered including, besides American firms, several European countries, 

 Australia, and China. The results were, unfortunately, not very satisfactory. Many 

 of the inquiries, or the letters sent in answer to them, were perhaps lost or mis- 

 carried because of the war-time irregularities in the mail service, and of the rela- 

 tively few answers that were received a considerable number were non-committal, 

 or the writer had the impression that the Isherwood system had certain advantages 

 but admitted that he did not know this from his own experience. With but one 

 exception (see reference to letter from a European firm in paragraph on torsion), 

 all the answers received were favorable to the Isherwood system, and some of them 

 contained statements of sufficient value and definiteness to be worthy of quoting 

 here: — 



From W. R. Grace & Co., New York City: — 



"The Isherwood system has advantages and disadvantages compared with the 

 ordinary system of framing. The advantages are, that in way of the cargo hatch- 

 ways the Isherwood transverses form an arched system of construction, giving better 

 support to the deck and dispensing with girders and, to a great extent, pillars. One 

 disadvantage is that the transverses take up more depth than the ordinary frames. 



