230 NOTES ON FUEL ECONOMY. 



only 13,100 indicated horse-power for the same speed. This means that for 

 10,000 miles the saving in coal amounts to some 1,100 tons at 18 knots; this 

 can be fairly credited to the experimental tank and its able staff. 



Our destroyer designs are also good examples of efficient propulsion; 

 the way in which the recent vessels have gone through their trials compared 

 with those of twelve years ago needs no comment. 



The best speed at which to run a merchant vessel is not a question that 

 the builder has much to do with. The distance between ports, propor- 

 tionate values of passenger and freight business, the nature of the cargo, 

 mail-carrying requirements, character of the waters traversed, and the com- 

 petition to be met are the prime factors in determining this speed. Once it 

 has been decided upon, the builders should be allowed to settle the dimen- 

 sions best suited to the speed and the work (passenger and freight accom- 

 modations) expected of the vessel. It is surprising how many vessels are 

 run at unsuitable speeds, some unavoidably so on account of passenger 

 accommodations; but the majority could well have been reconciled in the 

 design stage as regards the dimensions, speed, capacity, stability, trim and 

 deadweight. 



When the owners decide on their real service speed, the builders should 

 not be required to run a measured mile trial reaching a top speed out of all 

 proportion to the service speed ; it can only be done at a sacrifice of efficiency 

 elsewhere, probably in the fineing of the ship and consequent reduction in 

 carrying capacity. 



In fast passenger liners the proper reconciling of speed and dimensions 

 may very well spell success or failure to the whole venture; this should be 

 recognized and some time devoted to preliminary design work and model 

 tank tests. The preliminary work on the Mauretania designs furnishes a 

 case in point. Why should not corresponding care and attention be devoted 

 to less ambitious designs? That many owners are seeking to get the maxi- 

 mum out of their investment is evident when we consider the number of 

 special types lately coming to the front, all designed with a view to the 

 utmost efficiency in their particular line, not only for driving but more 

 especially for cargo handling and storage. 



The following examples have been collected from recent experience in 

 general design work, with the hope that others will be brought forward in 

 discussion by those whose daily experience has been along similar lines. 



EXAMPLE NO. I. 



Advantage of model tank experiments on hull forms and of careful 

 propeller design. 



