68 THE DETERMINATION OF THE RESISTANCE OF SHIPS. 



at any rate to a relative degree, very easily in experimental tanks, and it is quite common 

 to find, for instance, that the addition of bossing to the stern will add anyhere from perhaps 

 6 to 10 per cent to the resistance of the net hull, and even in connection with the bossing and 

 the angle at which the bossing is placed, we have found differences amounting to as much 

 as 3 or 4 per cent, depending on the angle. 



The cruiser stern was mentioned, and I am afraid my experience bears out Mr. Rigg's — 

 there is no doubt that that type of stern gives you a form of less resistance than the ordinary one 

 we have been using in the marine service for so long. I have recommended it in quite a num- 

 ber of cases, and recently, about a year ago, without altering the lines to any great extent, 

 we could actually reduce the resistance of a model between 5 and 6 per cent by adopting the 

 cruiser stem. 



Even with our typical lake freighters, which are usually looked upon more or less as 

 boxes with the ends slightly shaped, we have been able to make a difference something like 5 

 and 6 per cent with a very small modification of form, comparatively small, and a very slight 

 reduction in displacement. 



I just mention these few facts in confirmation of what Mr. Rigg has said, and I should 

 like to thank him for the kind remarks he has made about the work which has been done in 

 this country. 



Sir Archibald Denny (Communicated) : — The system of notation used by us in our 

 experimental tank is to plot all our resistance results as rate curves for vessels of a standard 

 length of 100 feet, the rate being the estimated horse-power multiplied by 100 and divided 

 by the wetted surface. 



When we publish any data we publish them as estimated horse-power spots, or curves, 

 for the actual vessel under consideration, and anyone can convert this data into his favorite 

 system of notation. I think it might be useful to adopt a uniform system of notation through- 

 out the technical world for the publication of results, but this would not necessarily involve a 

 change of system for any individual experimental tank in the filing of data. It would be in> 

 possible to get all the experimental works to agree to the uniform system of notation within 

 their own gates, as the accumulated data are very considerable and the trouble of converting 

 them to any agreed-upon notation woidd not be faced. If that be so, then an attempt to intro- 

 duce a uniform system of notation for publication throughout the technical world would also 

 be difficult because the staff of each experimental works would naturally wish their particular 

 system to be adopted so as to save themselves trouble; that is only human nature. 



I concur with the author that the benefit which has been derived from model experiments 

 has been very great, not only to those who possessed an experimental tank themselves, but 

 also indirectly to the whole shipbuilding business, as the exceptionally efficient vessels pro^ 

 duced by means of these tests showed what might be done and led to further improvement. 



The Effect of Temperature on Resistance. — The exact amount which should be allowed for 

 this is not yet definitely fixed, but at present we use 3^ per cent for 10°F. on the gross resist- 

 ance; that is, we take 3^^ per cent upon both the skin friction and wave-making. We are still 

 working at this, but we believe that ultimately this figure will not be greatly departed from. 

 It would be interesting if some well-known fast passenger vessel could be tried on a proper 

 measured mile in the depth of winter, and in the height of summer, care being taken that in 

 both cases she is freshly out of dock and painted properly with precisely the same paint. I 

 should be glad if my American friends would show the way in this and report progress. 



