DESIGN AND CONSTRUCTION OF PASSENGER STEAMERS. 277 



DEPTH AND DRAUGHT. 



This subject is one calling for special mention. It can be stated at once that the draughts 

 adopted for large liners are not those that the naval architect would choose if he had a free 

 hand ; neither are they the ones dictated by considerations of the limitations of steel as a ship- 

 building material. Terminal harbors and canals are the main deciding factors, and while a 

 discussion of harbors, existing and projected, is not within the scope of this paper, neverthe- 

 less it may be noted in passing that the improvement and deepening of harbors are again 

 being taken up seriously, the extensions to the facilities of the port of London recently opened 

 being a case in point. The late Sir W. H. White contributed a valuable paper bearing on 

 this subject, among other things, to our Society in 1911 ; Sir J. H. Biles has shown in 

 several papers the advantages of increased draught in large carriers, also Lord Pirrie has 

 contributed to our knowledge on the subject. In order not to take up space with repetitions, 

 the interested reader is referred to these papers and to the report of the Canadian Royal 

 Commission on Oversea Communications, dated 1914, an extremely valuable document, the 

 importance of which has evidently been masked by the war. Suffice it to say that the eco- 

 nomics of the ship can benefit by increased draught up to the point where such increase im- 

 poses excess costs on harbor authorities, which would have to be passed back to the ship in the 

 form of increased and excessive harbor chai;ges. 



A really first-class harbor should nowadays have a depth of at least 40 feet, and Lord 

 Pirrie advocates 45 feet; with such depths and corresponding draughts of about 37 feet 6 

 inches to 42 feet 6 inches economics of transport are available. Mr. J. F. King's forecast in 

 1912 referred to above under "Length" is worth noting; his figures gave a 1920 draught 

 of 36 feet 6 inches for Atlantic liners and for average passenger ships. The predicted Suez 

 Canal depth of 30 feet came very close to being a mean draught for such ships, which showed 

 steady increase up to a 25 to 34-foot range. Draught increases relatively and actually more 

 slowly than length, it is hardly necessary to say. 



The Panama and Suez canals are bound to exercise a profound influence on the draughts 

 of passenger liners, the figures for which now stand as follows : 



1. Panama. — ^A minimum depth of 40 feet in the canal, with 40 feet in the Atlantic and 

 35 feet in the Pacific approaches at mean low water, which means an available draught of 

 about 38 feet. 



2. Suez. — ^At present the available depth is 32 feet and permissible draught is 30 feet ; 

 the authorities are dredging for 34 feet 6 inches and 31 feet figures respectively. 



It is to be noted that Suez has gradually been deepened by dredging from 19 feet in 

 1870 to 32 feet in 1920. 



Liners of the future will probably not be able to avail themselves of all the draught eco- 

 nomically desirable, for we are now approaching the region of excessive dredging costs in 

 certain harbors. 



Another big factor in restricting draught is the River Plate; many vessels now trading 

 there on a 26 feet 6 inches limit could well have been designed for 30 feet. 



SPEED AND POWER. 



Looking back on the not so distant days when it was necessary to plead the advantages 

 of experimental tank work, it is gratifying to reflect on the conditions of today. The last 

 decade has witnessed a decided modification of attitude. 



