10 
POPULAE SCIENCE EEVIEW. 
the resistance of a ship is due to friction, this is one obstacle. 
In the next place, every vessel carries before it a wave of dis- 
placement and a frictional wave. These diverge from each 
bow, whether one side of the bow be flat or not. A flat bow 
certainly diminishes the wave of displacement, but it does not 
annihilate it, and it scarcely diminishes the frictional wave at 
all. From these two causes there is a heaping of the waves in 
the channel, which forms a great source of extra resistance. In 
sailing vessels of this form the extra resistance is compensated 
for by the extra sail-carrying power of this type, but there is 
no such compensation in a steam-vessel. Then, again, the mode 
of propulsion is so bad — I should have said the worst possible, 
were it not that one of the directors of the Dicey Company has 
proposed to substitute a water-jet propeller for the paddles. 
There can scarcely be a worse position for a paddle-wheel than 
half-way along a rectangular channel. The propulsion is 
affected by the reaction of the water, whose backward velocity 
relatively to the ship is greater after it leaves the paddle-float 
than before it meets it ; otherwise there would be no propul- 
sion. Now the sectional area of a stream of water is inversely 
proportional to the velocity — for the quantity of water that 
passes any section of it is constant — and if the section is uni- 
form, there must be a difference of level, or eddy-disturbance, 
or waves, either of which take up part of the work which ought 
to be expended upon propulsion. This occurs to some extent 
with outside paddles ; but it is very much enhanced when the 
paddle is placed in a conflned channel — not to mention the 
increased frictional resistance of the paddle race. I believe I 
am within the mark in predicting that, for the same speed, 
Captain Dicey’s boat will require twice the engine power of that 
designed by Mr. Keed and Mr. Bessemer. It is not probable to 
my mind, that with such a ship, and such a propeller, a speed 
of twenty or twenty-one miles could be reached at all, no mat- 
ter what the engine power might be. 
Besides the danger from want of steering power, there is 
great danger of the paddle being carried away or disabled by 
a great wave, the effect of which would be guarded from dissi- 
pating itself laterally by the sides and roof of the canal in 
which the paddle works. 
As regards the connection of the two hulls by means of the 
platform, I do not think that this presents any mechanical or 
practical difficulty, except that it will require a great weight of 
iron, and that this will have to be met by increased draught of 
water. This is itself an evil where tidal ports have to be 
entered ; and it also takes up engine power. 
In short, I have come to the belief that Captain Dicey’s 
twin ship will be easy, but that it will not be fast, economical, 
or safe. 
