80 STRESSES ON VESSELS OF THE GREAT LAKES 
limited in its application and that it was never intended to apply to ocean-going vessels of 
such extreme proportions. This standard section modulus was determined from an analysis 
made into the 1913 Rules of the various classification societies and is probably quite safe to 
use within the limits specified, although so eminent an authority as Dr. Bruhn seems to con- 
sider the standard somewhat low for vessels carrying heavy deadweight cargoes. Compar- 
Lf 
ing the longitudinal strength of vessels on an —> basis is convenient, but such a method can 
Ne 
only be a safe guide in the determination of scantlings if their proportions of D are some- 
what Suu Tp not being a complete measure of the longitudinal strength as the relative stiff- 
ness to resist deflection is neglected. In other words, if the Freeboard Committee had been 
required to legislate for ocean-going vessels of proportions in the neighborhood of twenty 
depths to length, the standard laid down for longitudinal strength would probably have been 
very different. 
I have had the M. I. of the section of a large bulk freighter 580 by 60 by 32 feet 
if 
worked out and find that the Y is 21,600 and that, on the basis of the freeboard strength 
standard for ocean-going vessels of ordinary proportions, the allowable draught would be 
about 17 feet. An addition of 45 square inches to the sectional area of the deck would sat- 
: Jf 
isfy the y standard for a draught of 19 feet, but the most optimistic naval architect would 
hardly be satisfied with this additional scantling to O.K. the vessel for operation in the 
winter North Atlantic in the ore trade. The point I wish to make is the necessity for caution 
in the application of the Freeboard Committee’s strength standard to seagoing vessels hav- 
ing dimensions and proportions outside of the limits defined. 
These big lake freighters are well designed for their intended service, i. e., the carriage 
of ore, coal and grain on the Great Lakes. The longitudinal structural strength, however, 
could be improved by extending the wing tanks to the deck, but this again would reduce 
the deadweight carrying capacity for grain cargoes. 
One consideration which should not be lost sight of is the absence of serious deteriora- 
tion through corrosive action in the steel hulls of lake vessels, and although a margin for cor- 
rosion is not evident in the strength standard of ocean-going vessels it is there nevertheless, 
so that on this ground alone lake vessels could have lighter scantlings and a lower initial 
strength standard. 
It is in the practical effect of the proposals of Dr. Sadler as indicated in Plate 19 (Pro- 
posed Standard for Great Lakes Vessels) that I am especially interested. In applying these 
to the 580-foot vessel already mentioned and using an f value of 15 equivalent toa BM factor 
of 64 in association with a nominal stress of 8.2 tons, the allowable draught would be in- 
creased from 19 to 24 feet; and conversely, if the present draught of 19 feet were retained, 
a considerable reduction from the present topside scantlings could be allowed. It should be 
i If 
also remembered that in the application of the Freeboard Committee’s standard the —> 
i 
in the way of a section abreast of the hatch openings is only required to be 90 per cent 
of the full standard expressed by f X b X d, and if it is Dr. Sadler’s intention to allow a 
