232 NOTES ON FUEL ECONOMY. 



These are for ten knots in each case. In addition to less first cost, the 

 shorter boat will be handier at sea, more easily taken care of as regards sta- 

 bility, and occupy less space at piers. There was no question of repeating 

 an order. 



EXAMPLE NO. 3. 



In heavy bulk carriers it is desirable to know how full a vessel can be 

 made, keeping capacity down and so having no more ship than is necessary. 

 A majority of ship designs on this coast are prepared for light cargoes occupy- 

 ing large space, where ship dimensions run large per ton deadweight; hence 

 the saving in ship dimensions possible when carrying ore, for instance, is apt 

 to be overlooked. 



These vessels are frequently run at only nine knots, even though they 

 have some margin of power; the problem resolves itself into one of finding 

 the range of dimensions where the total resistance remains constant, even 

 though the component parts vary. In a design to carry 7,000 tons dead- 

 weight it was found practicable to increase block coefficient from .75 to .78 

 and reduce length from 360 to 340 feet for the same effective horse-power at 

 nine knots; this represented a 5 per cent saving in steel hull. Beam and 

 draught remained constant. 



This problem and the preceding one are merely examples of searching 

 for the economical limit of speed, on which subject a good deal has been 

 published from time to time. 



While the temptation to keep power down by fineing the ship is a strong 

 one, especially when owners expect a very low coal per diem rate, ship 

 designers should never allow the dimensions to run up beyond what this 

 somewhat elusive economical limit requires. 



EXAMPLE NO. 4. 



Quadruple expansion machinery versus triple for long voyages. 



The author recently had a very forcible example of the saving possible 

 if quadruple expansion machinery were fitted in a cargo steamer designed to 

 carry 7,000 tons of paying freight for a distance of 14,000 miles, oil burning. 

 The figures came out as follows : — 



