126 Transactions of the Royal Canadian Institute 



vessels. As a matter of fact, we find that large ships are adequately 

 strong when their stresses, calculated in the somewhat semi-empirical 

 method indicated above, are nearly twice those of small ships. This does 

 not mean that steel in a twenty thousand ton ship is twice as strong as 

 steel in a five thousand ton ship, but simply that our standard methods 

 do not apply in similar ratio to large and small ships. 



While the greatest strains upon a vessel afloat in service occur in 

 rough water, there is one operation during the btiilding which is liable 

 to tax severely the strength of the vessel unless careful investigation and 

 preparations are made in advance. I refer to the launch. Except on 

 the Great Lakes of America, the almost universal practice is to launch 

 vessels stern first in the direction of t^eir length, which means that 

 supported on a wooden sled they toboggan, as it were, down a timber 

 slide, lubricated with tallow and oil or the equivalent. The length and 

 inclination of the ways upon which the vessel slides, and the inclination 

 of the keel of t'he vessel to the horizon in the posit*ion in which she is 

 built, must be carefully calculated to insure, first, that the vessel does 

 not tip over the end of the ways and lift her bow, which would result in 

 crushing her, due to concentration of weight at the end of the ways, and, 

 second, that the vessel does not lift her stern so soon as to produce a 

 bending moment which would break her in two. A third minor factor is 

 that it is undesirable to have the bow ot the vessel, as she clears the end 

 of the ways, drop too far, although this is not a matter of importance if 

 the two major matters referred to above have been properly taken care of. 

 All of the calculations necessary to insure a satisfactory launch must be 

 made, and the launching ways fully planned before the keel of the vessel 

 is laid. 



The launching weight of a 33,000-ton battleship will be abou't 15,000 

 tons, and the transfer of this large mass from quiescent repose, upon 

 blocks shored to keep them thoroughly rigid and stable, to the condition 

 afloat, is one of the most spectacular incidents in shipbuilding. A 

 successful launch is a very pleasing sight and apparently a very simple 

 and easy performance. Few of the spectators realize that it was planned 

 virtu'ally to the last detail before the first keel plate of the vessel was laid, 

 or for that matter, before the keel blocks themselves were located and 

 graded. 



I will say a few words in conclusion concerning one branch of naval 

 architecture which during the last fifty years has, I believe, profited more 

 than any other by the applicatioa of science both in the establishment 

 of correct theories and the abolition of older and in many cases grotes- 

 qu^ely erroneous ideas. I refer to the question of speed and power. 

 Our modern ideas on t<his subject are due primarily to William Froude, 



