peed, but a good mean speed would be 500 to 750 ft. for conveying and
200 to 300 ft. for hoisting. A cableway used in excavating work in
Chicago was credited with a capacity of 400 to 600 cub. yds. per day at
a total cost of 2d. per yard, including labour, coal, oil, waste, &c.

_Coaling Ships at Sea._--In the coaling of ships at sea the cableway has
rendered great service. The conditions under which this operation has to
be carried out present many difficulties, especially in rough water. One
of the chief obstacles is the maintenance of the necessary tension on
the cable used in conveying the coal from the collier to the ship. The
first test in coaling ships at sea, made by the British admiralty, took
place in 1890 in the Atlantic at a point 500 m. south of the Azores in
water 2000 fathoms deep. Ten ships of war were coaled, each vessel
taking enough coal to enable it to steam back to Torbay, 1800 m. away.
In this case the collier was lashed alongside the battleship it was
feeding, thick fenders being interposed to prevent damage, but
nevertheless as the colliers got light they pitched considerably, and
one or two sustained dents in their sides. The ships did not roll, being
kept bows-on to the swell, which became heavy before the coaling was
completed. The coal was taken in by derricks at the main deck ports. It
is clear that had the sea been really rough coaling in this fashion
would have been impossible.

The most practicable method of coaling at sea yet devised is the marine
cableway of Spencer Miller, which has been tried with some success in
the American navy. It is intended for use between vessels 350 to 500 ft.
apart. The ship being coaled takes the collier in tow, steaming at the
rate of 4 to 8 knots; it has been found that a speed of five knots in
moderately rough water will keep the cableway taut and maintain a
sufficient distance between the crafts. The collier is fitted with an
engine having double cylinders and double friction drums, which is
placed just abaft the foremast. A steel rope 3/4 in. in diameter is led
from one drum over a pulley at the mast head and thence to a pulley at
the head of shear-poles on the vessel being coaled, and brought back to
the other drum. The engine moves in the same direction all the time and
keeps on winding in both the strands of the conveying rope. Should the
two vessels increase the distance between them during the operation of
conveying the coal bags, of which two, wei