STRESSES ON VESSELS OF THE GREAT LAKES DUE TO WAVES OF 
VARYING LENGTHS AND HEIGHTS. 
By ProFressor HERBERT C. SADLER, MEMBER OF COUNCIL, AND Proressor A. LINDBLAD, 
MEMBER. 
[Read at the thirtieth general meeting of the Society of Naval Architects and Marine Engineers, held in 
New York, November 8 and 9, 1922.] 
When the Committee on Bulkheads and Freeboard met to consider the various problems 
upon which it was to report, the question of the possibility of including the vessels on the 
Great Lakes in the assignment of freeboard arose. 
As little or no systematic investigation into the strength of this type of vessel had been 
made, it became necessary to make several strength calculations for the conditions met with 
in this region. As information of this character may prove of value in other fields, it was 
thought advisable to have the same in the permanent records of our society. The results 
of the principal parts of these investigations are submitted herewith. 
In the first place, it became necessary to find out what lengths and heights of waves 
might be expected. Little or no data upon this subject existed, so a series of instructions was 
issued to captains of vessels in order that they might observe and report upon the waves 
encountered. Although all possible care was taken on the part of the observers, there was 
still a chance of error. On the whole, however, the data obtained were sufficiently reliable for 
the purpose in hand. 
A few of the general conclusions are as follows: 
1. As a rule, waves over 250 feet in length are rarely encountered. In one case, a 
report was made of waves in the neighborhaod of 350 to 400 feet after a severe storm on 
Lake Superior, but although the height was not observed it was evidently not of the usual 
magnitude, judging from other comments on the behavior of the ship. 
2. The heights of the waves appear to be somewhat larger in proportion to their lengths 
than the usual ratio of 1/20, and probably vary between this figure and 1/15. The actual 
heights did not appear to exceed 20 feet as a maximum. 
The following waves were therefore used in the calculations: (a) 325 feet by 20 feet; 
(6) 300 feet by 20 feet; (c) 250 feet by 16.7 feet and two special cases, 325 feet by 15 feet 
and 350 feet by 20 feet, in order to obtain some intermediate data. As these waves are con- 
siderably shorter than the usual run of vessels on the Lakes today, it was necessary to per- 
form two sets of calculations, one with the crest and one with the hollow at the bow. 
Three types of vessels were chosen of the following dimensions: (a) 420 feet by 52 feet 
by 28 feet; (b) 504 feet by 56 feet by 30 feet; (c) 590 feet by 64 feet by 33 feet. 
The wave profiles and corresponding positions of maximum bending moment are shown 
in Fig. 1, Plate 13, for all of the above cases; and the detailed shearing force and bending 
moment curves in the following Figs. 2 to 4, Plates 14 to 16. 
As these vessels tend to sag when uniformly loaded, it is customary to put some addi- 
tional cargo in the forward and after ends. This method of loading has been assumed as the 
proper one, although calculations were also made for uniform loading. 
