1884.] Stability with Draught of Water in Ships. 435 



fixed draughts of water and with given positions of centre of gravity. 

 The curve of metacentres gives the height at all draughts of water 

 above which the centre of gravity cannot be raised without making 

 the ship unstable when upright, and causing her to lie over more or 

 less to one side. The ordinates of the curve of stability represent the 

 lengths of the righting arms, which, multiplied by the- weight of the 

 ship, give the righting moments at all angles of inclination from the 

 upright. The stability of numerous vessels, both of the Royal Navy 

 and Mercantile Marine, have been investigated in this manner for 

 certain draughts of water, and a great amount of information obtained 

 respecting the variation of stability with inclination at such draughts, 

 and the angle at which the stability vanishes in many classes of ships. 

 The peculiar dangers attaching to low freeboard, especially when 

 associated with a high centre of gravity, have been fully discussed and 

 made known. 



Curves of stability having been chiefly constructed for deep and 

 moderate draughts, the character of the stability which is often to be 

 found associated with very light draught, appears to have hitherto 

 escaped attention. As a matter of fact, light draught is often as 

 unfavourable to stability as low freeboard, and in some cases more so. 

 The general opinions that have till recently prevailed upon the subject 

 appear to have been based upon a vague impression that so long as a 

 vessel has a high side out of water, and any metacentric height, she 

 will have great righting moments at large angles of inclination and a 

 large range- of stability. It was shown at the " Daphne " inquiry, held 

 by Sir E. J. Reed, in July last, that these opinions largely prevailed 

 and were erroneous. 



It fell to my lot to make some investigations respecting the stability 

 possessed by the " Daphne " at the time of the disaster which 

 happened to her, and to give evidence respecting the same. I after- 

 wards pointed out, by way of explanation of my evidence, in a letter 

 to the " Times" of the 1st September last, some of the considerations 

 which obviously apply to light draught stability. The first, which so far 

 as I am aware had never before been stated, is that any homogeneous 

 floating body which is symmetrical about the three principal axes as 

 the centre of gravity — such as a rectangular prism or an ellipsoid — 

 will have the same moment of stability at equal angles of inclination, 

 whether floating at a light draught with a small volume below water, 

 or at a deep draught with a similar volume above water. For 

 instance, if a homogeneous prism of symmetrical cross-section 5 feet 

 high float at a draught of water of 1 foot, it will then have precisely 

 the same moment of stability at equal angles of inclination, and 

 consequently the same curve of stability throughout, as if it were 

 loaded — without altering the position of the centre of gravity — till it 

 had 4 feet draught of water, and 1 foot of freeboard. From this it 



vol. xxxvi. * 2 H 



