TAPTER 
VI 
TAY CRANES. 
‘DAL INFLUENC 
THE use of the quay crane is prevalent at British and certain 
European ports on account of its adaptation to special 
physical conditions on the Eastern littoral of the North 
Atlantic Ocean. The principal factor which influences, and, 
in fact, dominates, the situation is the phenomenon of the 
tides. In Great Britain, the waters of the principal ports, 
such as London, Liverpool, Bristol, Cardiff, Hull, New- 
port, and Swansea are characterised by very pronounced 
variations of level at different periods of the day, due to 
tidal ebb and flow. 
These variations are of the order of 20 to 40 feet, and so 
great a change in the respective levels of a ship’s deck and 
the wharf, or quayside, renders it impossible to depend 
entirely upon ships’ booms and whips for the transfer of 
goods between ship and shore. A vessel's deck may he so 
far below quay level that her derricks cannot command 
the quay. Moreover, when the tidal current is running 
strong, say on the ebb, accentuated possibly by the river 
discharge, it is very difficult to keep barges, or lighters, 
securely attached alongside for the purpose of receiving 
goods overside. 
These adverse circumstances have led to the construction 
of docks at tidal ports, for the purpose of providing quiescent 
areas, undisturbed by tide or current, within which vessels 
may not only lie afloat at periods of low water, but may also 
be maintained at a fairly uniform level of flotation, so that 
there may be no attention required to moorings and no 
interruption in cargo-handling operations.