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174
HARBOUR ENGINEERING.
and harbour walls, and the space between was occupied by two lines of railway
for conveying men and materials ; and in this way the whole width of the top
of the stage, viz., 70 feet, was occupied.
“ About the middle of May in every year the first block was lowered by the
helmet divers’ gantry to its place. The helmet divers’ stage was suspended
by iron rods from the beams of the main stage, and hung about 10 feet below
it. To this stage wrought iron ladders were attached for the convenience of
divers descending to their work. Six divers were under water together—four
on the seaside and two on the harbour side. They remained down four hours
at a time, when there was a shift; and there were three shifts in the day.
The life-line men and pumpers remained on the work all day, but the pumpers
were relieved every half-hour. The divers’ apparatus and the stage were
removed every night, so treacherous was the sea, for even in summer it was
not safe to leave anything at the level of the divers’ stage; but at the height
of the main stage, 10 feet higher, or 20 feet above high water, the sea seldom
disturbed anything. The mode of bringing the work up was by taking
advantage of the spring tides ; thus it was expected of the divers that, in a
fortnight, they would bring the diving work up to the level of low water, for
a distance seaward of 60 feet, ready for the masons. Whatever excavation
was required for the lowest course, it being a great deal more at some times
than others, or however rough the sea had been, the divers never failed to
prepare a length of 60 feet ; but they frequently went down a second time for
an extra shift to accomplish this. The average day’s work of a diver in the
year 1860 was 8J cubic yards of building; in 1861 it was 11 cubic yards; and
in 1862 it was 14 cubic yards. Their work was excavating foundations,
receiving the granite face-stones for the sea-wall, and setting the granite and
concrete blocks of the sea and harbour walls. The stones and blocks were
speedily lowered by a single chain 45 feet from the top of the stage by the
gantry crabs and a rope-break. This latter was a piece of rope, with rope
yarn twisted round, made fast to the frame of the crab and then fastened to
the pinion shaft of the single and double gear. The chains employed were of
the best charcoal iron ^ inch thick, and they were only used for two seasons.
“ The divers’ work being ready for the masons, to the level of low water of
spring tides, two days before full or new moon, the resident engineer gave
orders to commence setting the face-stones in cement, if, in his opinion, the
tide fell low enough ; otherwise he could stop the works. The masonry of the
breakwater on the sea face was of granite and native Alderney stone • on the
harbour side it was of native stone, and the space between was filled in with
backers and small rubble. The backers were as large as the machinery would
lift, and were set in Medina cement and sand, in the proportion of 1 part of
cement to 2 parts of sand. Sand suitable for building occurred in abundance
in the island. No better cement could have been had for the purpose, for
very often the masonry, ten minutes after it was built, was covered with water.
No large stock of cement was laid in, as its quick setting qualifies were
impaired by time. The masons endeavoured to keep the work done at each