206 REPORT—1858. 
piston per minute. This speed of piston, when working at full pressure, gave 100 
effective horse-power for the larger, and 50 horse-power for tugs of less power. The 
former, under such circumstances, took a load of 500 tons of cargo, or a gross load of 
650 tons at a speed of 3 miles per hour in the canals and 43 miles in the river portion 
of the navigation. The latter hauled a load of 220 tons of cargo, or a gross load of 
325 tons at the same speed in the canals, and 3} miles per hour in the river. On an 
experiment with one of the more powerful tugs, twelve vessels, containing with the 
cargo in the tug 832 tons, or a gross tonnage moved of 1222 tons, were taken in the 
river portion of the navigation a distance of 44 miles in 1} hour, or, allowing for cur- 
rent, 21 miles per hour. On another occasion the same tug took nine vessels, con- 
taining with the tug 552 tons of cargo, or 852 tons gross, over the same portion of 
the river (allowing for current), a speed of 4-87 miles per bour. The dynamical effect 
on the tow-rope in the former case varied from 28 to 34 ewt., and in the latter ave- 
raged about 271 ewt. These tugs were also very useful for breaking up and contending 
against ice; and there was also a diminished consumption of fuel as compared with 
the previous tugs employed,—which were paddle-boats. The commercial results were 
as follows :—9d. per boat per mile by the paddle tugs; 7d. by horse haulage, &c. ; 
and 4:15d. by screw tugs. The economic proportionals were consequently 1, 1°68 
and 2:15. The trip of 36 miles was thereby accelerated two hours, and increased 
certainty was obtained. 
Description of a Floating Dry Dock. By G. BAYLry. 
The dock in question was designed in 1836 for a South American Government ; 
it was intended to be moored in deep water, and ride with a ship of war in it with 
safety during ordinary gales. 
The port, or rather open roadstead, in which it was proposed to place the floating 
dock, had arise of tide of about 6 feet. To meet the peculiarities of the place, it was 
proposed to construct the dock so that it could be immersed or sunk down to any 
depth that might be required to admit the ships of various classes, and be strong 
enough to ride with them, without straining the ship. 
Three things had to be combined—strength, rigidity, and buoyancy. The needful 
strength and rigidity were to be secured by a very simple system of bracing and 
trussing, and the whole framing covered with planking well secured and made water- 
tight. This space was subdivided longitudinally and transversely, so as to obviate 
any risk from the rushing of the water from side to side or from end to end of the 
dock; and at the same time, these longitudinal and transverse partitions would add 
to the strength and rigidity of the entire fabric. 
A transverse section of the dock would show that the floor of the dock is a framed 
beam, consisting of two tie pieces about 4 feet apart, with queen posts in the centre, 
under the ground or lower tier of keel blocks, with tie bolts introduced where neces- 
sary. The sectional area must be proportioned to the entire weight of the dock with 
the ship, so that, if desired, it may float with its upper internal surface above the 
level of its external waters. The angular or rectangular space between the outer 
and inner planking of the sides must be of sufficient volume to allow the dock to be 
sunk to any required depth to receive the ship. 
The dock itself must be ballasted with sufficient weight to render it specifically 
heavier than water, in order that it may be readily sunk to the required depth, 
It was proposed to have an engine fixed on the deck forward, to pump out the 
water from the subdivisions, and also to drive saws and any other tools required 
for carrying on the repairs*. 
It would be desirable to construct such docks of iron, which is peculiarly suited 
to meet all the requirements of such structures as to strength, rigidity, and buoyancy, 
at less cost than timber under almost every combination of circumstances. 
The peculiar advantage of the kind of dock now suggested is its adaptation to 
places, where, from local circumstances, it is difficult, if not impossible, to build 
secure and substantial dry docks on the shore. 
* The paper was illustrated by a model, showing the general construction and proposed 
arrangement of the engine, pump, &c. 
Seem 
