672 Transactions. — Miscellaneous. 



the moment of the solid of immersion and to reduce that of 

 emersion. This draws the centre of buoyancy to windward, 

 and so increases the length of the righting-lever. 



The first method merely acts upon the ship's centre of 

 gravity, whereas the second acts upon her centre of buoyancy 

 as well. 



The same principle might be adopted to add to the stability 

 of a sponsoned ferry-boat. Such a balk might be secured to 

 each side of the boat above the stays which support the 

 sponsons. With a light load of passengers this would be 

 above water, but the ends should nevertheless be eased off to 

 reduce the resistance when it is immersed by heavier loads. 

 In any case where this might be deemed insufficient the range 

 of stability could be very much more increased by planking 

 over the outside of the stays from the hull right up to the 

 sponsons and making this watertight. The weight thus 

 added would possibly not lower the centre of gravity of the 

 steamer, but it would very greatly increase the moment of the 

 immersed solid when she was careened to the edge of the 

 sponsons, and thus draw the centre of buoyancy to windward, 

 and greatly lengthen the righting-lever. 



It is hardly safe to give any arbitrary rules for stability, 

 but it may safely be affirmed, where a vessel's initial stability 

 is satisfactory, that if the width of her water-line goes on in- 

 creasing as the angle of heel gets larger she must have a good 

 range of stability. A ferry-boat's lading is peculiarly danger- 

 ous, because it is not only generally carried high above her 

 centre of gravity, but is a live weight, which in case of panic 

 is almost sure to rush to the lee side. Hence a large range of 

 stability, in the interest of public safety, is imperative. As 

 such boats usually ply in smooth water, there is not the same 

 objection to a great fall-out above the water-line which would 

 attach to a sea-going vessel. In the latter the great leverage 

 which it would afford to the waves would result in heavy 

 rolling, and the receipt of very ugly blows from the seas. 



A rather telling illustration of the great stability afforded 

 by a large fall outwards above the water-line is afforded by 

 the preference which a square log shows when floating. If a 

 number of these are rafted together they can be made to float 

 on their flat sides, but if one is floating by itself it will always 

 lie cornerwise. Here is a section of one, and I will place it 

 in water. You will see that it cannot be got to float in any 

 other way than with one corner down. We may first see why 

 it will not float on its flat by referring to fig. 6, Plate LI. As 

 it is a square figure, and is homogeneous, its centre of gravity 

 will be at the intersection of lines drawn cornerwise. Similarly, 

 the under- water portion being rectangular, the centre of buoy- 

 ancy will be at the half-height and half- width of this portion. 



