236 NOTES ON FUEL ECONOMY. 



vessel. Unfortunately, this series does not include ships of all of the proportions 

 which we may be called upon to design. I think that comparatively few models 

 are taken to Washington by shipbuilders as preliminary designs, and the results 

 of the tank tests of these models compared with the results of the standard series 

 from which the contours of residuary resistance were derived, without finding that 

 improvements have to be made in these models in order to obtain as good results 

 as the standard series shows to be possible. 



I accept every statement which Mr. Rigg has made, without taking exception 

 to any of them, but would like to ask him for more data on some of the information 

 he has put before us. I think it is of as much interest to the members of the Society 

 to know why and how things are done as to know the simple fact they have been 

 accomplished. I hope Mr. Rigg will be able to give us more information with 

 regard to some of the interesting examples he has presented. 



If we take Example No. i, we see there two ships, one of which has a displace- 

 ment 46 per cent in excess of the other, and we find that at a speed of 11.5 knots 

 it takes practically the same power to drive these two ships. Of course, that is 

 very striking — that you can drive with the same power 46 per cent more weight 

 at the same speed. The question arises: Are these results given the results of 

 model tank tests, or are they the combined results of model tank tests and actual 

 trials ? If so, were the trials of these ships run under the same conditions ? Is the 

 data, as far as it goes, strictly comparable — assuming that the results are abso- 

 lutely correct, which I do assume? Although we have not the full data of these 

 ships, if we look at the dimensions given, we find in the case of the oil tank ship, 

 in the left-hand column, under the heading "1903," that the ratio of length to 

 beam is 7.78, and we find in the case of the ship in the right-hand column, under 

 the heading "1909," that this ratio is 7.26. That is not much difference. We 

 find the ratio of beam to draught for the left-hand column ship is 2.245, ^^^d in 

 the case of the right-hand column ship 2.146, in other words, the ship described as 

 the better ship has a shghtly smaller ratio of beam to depth. At the speed of 1 1 .5 

 knots, at which these ships take practically the same power, the speed-length ratio 

 ^ in the case of oil tanker class is .606, and in the case of the navy collier class 

 is .586; that is to say, the speeds at which these two vessels are run in proportion 

 to their lengths are practically the same. The block coefficients of these two 

 vessels are almost identical. The ship described as the poorer one, the oil tanker 

 built in 1903, has a displacement-length coefficient, or coefficient of fatness, of 165, 

 and the other ship, which has proven superior, has a coefficient of fatness of 197, 

 in other words, is a fatter ship than the first vessel. I hope the author of this 

 paper will present us with the curves of resistance, residuary and frictional, in 

 the case of these two ships, also the trial trip data, so that we can see how it is 

 possible to obtain this very remarkable economy which he has presented for our 

 consideration. More data is necessary to make this example complete and com- 

 prehensible. 



Example No. 2 refers to two ships which require the same total horse-power 



