90 ECONOMICAL CARGO SHIPS. 



has investigated particular features in the cost of operation for one or more sizes 

 of ship. The scope of this series of calculations for an assumed length of route 

 of 3,500 nautical miles between fueling ports is shown herewith, each size of ship 

 being investigated for 10 knots, 11 knots, 12 knots and 13 knots sea speed, using oil 

 as fuel, except as noted: — 



A. Block coefficient chosen for each specific speed. 



1. With minimum port detention; length of ship 350 feet, 400 feet, 450 feet, 

 and 500 feet. 



2. Minimum port detention, coal burning; length of ship 500 feet. 



3. Minimum port detention, concrete ship; length of ship 500 feet. 



4. Double port detention; length of ship 350 feet and 500 feet. 



5. Minimum port detention, with 10 per cent increased resistance, 500-foot 

 ship. 



B. Fixed block coefficient for all speeds. 



6. Minimum port detention ; fine model 500-foot ship. 



7. Minimum port detention; full model 500- foot ship. 



Each of these ships was investigated for fuel rates of $6.00 and $12.00 with 

 tonnage dues, and with a fuel rate of $6.00 figures were also calculated without 

 tonnage dues. In addition to the above calculations, another series was made with 

 a steaming distance of 7,000 nautical miles between ports, but as the character of 

 the results was the same throughout, the investigation for this length of run was 

 not made so complete. Such figures as the author thinks would be of interest for 

 the 3,500 nautical mile haul are given herewith in Plate 39. 



In order to extend these calculations, a very considerable number of assump- 

 tions had to be made, as follows : — 



(a) Proportions. — The length of the vessel was taken as the water-line length, 

 which would also be the length between perpendiculars for twin-screw vessels. 

 The length between perpendiculars for single-crew vessels would be somewhat 

 greater than the figures given. 



The breadth molded was taken as equal to o.io of the length on water line, 

 plus 14 feet, this proportion giving ample beam for stability even with a consider- 

 able amount of superstructure. 



The load draught in each case was chosen to give a breadth upon draught ratio 

 of 2.25, which is approximately the best ratio for economical propulsion. 



(b) Speed and Power. — The speed in each case is such as could be maintained 

 in any ordinary weather at sea. The power was arrived at in each case from tank 

 test data, a propulsive coefficient of 52 per cent being assumed and a margin of 

 power allowed to maintain the required speed at sea. A discount of 20 per cent 

 from the figures given for indicated horse-power should be made to arrive at the 

 horse-power on a smooth-water trial trip fully loaded. 



(c) Weight of Ship. — The weight of the steel hull has been found to vary 

 slightly with the block coefficient, and this variation has been allowed for. The 

 weight of outfit corresponds to a first class specification and has been taken as iden- 



