1816.} On the Stability of Vessels. 198 
and part to the left; but if the stem be an oblique plane, the 
water, striking at the same angle of 9° or 10°, is forced downwards 
under the vessel’s bottom, instead of being divided, and cffers 57 
resistance, whereas the upright stem offers 62. If a vessel under 
sail always remain in a vertical position, the obliquity of the stern 
post would be disadvantageous to the steering; but when a vessel 
inclines, it is of moment; and the obliquity should be greater in 
small vessels, because they incline more when under sail than 
larger ships ; for suppose a vessel to incline so much as to have the 
deck perpendicular to the water (or, to use a technical expression, 
on its beam ends), the rudder, in that case, would have no other 
effect than to press down the head, and lift up the stern; but if the 
stern post was inclined aft, then the rudder would have power to 
turn the vessel. The good or bad qualities of a vessel depend greatly 
on the shape of those parts which are immersed in the water, by 
the healing or inclining of the vessel. Now it is evident that the 
upper part of a vessel may be upright, or parallel to the plane of 
the masts, or it may project outwards, or incline inwards. A com- 
bination of all these is the most advantageous for large vessels, and 
it should be observed that in all ships, especially in large ones, a 
certain proportion of a straight line near the surface of the water, 
termed straight of breadth, is necessary to prevent the vessel from 
rolling deep ; for if a constructor, with a view of making a ship of 
large dimensions stiff under sail, should make the extreme breadth 
much above the surface of the water, a wave by striking it to wind- 
ward would cause it to roll to Jeeward ; and when the sea had passed 
under the bottom, it would, by acting on the lee side, cause it to 
oscillate to windward. This double action, by making the ship roll 
deep, endangers its being dismasted; for every vessel endeavours to 
accommodate itself to the surface of the water by assuming a per- 
endicular position with regard to the fluid; for this reason, it is 
impossible to build and ballast a vessel that shall be easy in all seas. 
A ship may be considered as a pendulum, making a certain number 
of vibrations in a given time ; and if these vibrations coincide with 
the set or undulations of the waves, I do not see what can prevent 
the ship rolling to a great extent, on the same principle that a heavy 
bell is made by the ringers, with very little force, to swing the 
whole circle; and navigation would be much more dangerous if the 
cross waves did not check the rolling of the vessel. But to return 
to the shape of upper works: should the sides incline inwards, the 
stability would decrease, as is evident by the experiments with 
model 19. By the sides projecting, the vessel would be wet, be- 
cause the gunwhale in bad weather would come sooner in contact 
with the surface of the water. And another material objection to 
this shape for vessels which lay in tiers is, that the pressure would 
be totally confined to the highest part of the top timbers, which 
would cause them to break off. It may therefore be concluded, 
that to have a certain part straight (say six feet in a ship of the line) 
makes the ship easy; that by the sides inclining inwards, the ship is 
