PORT ECONOMICS 
drawback, however, may be unduly emphasized, because 
the cost of pumping, in the majority of cases, is small in 
comparison with the capital charges, that is to say, interest 
and depreciation. The cost of pumping probably does 
not amount to more than 10 to 15 per cent of the total 
annual expenditure. 
A great point in favour of floating docks is their mobility, 
as they can be transferred from one port to another. 
Moreover, a floating dock is constructed in detachable 
sections and can be lengthened or shortened, whenever 
circumstances so require. Against this must be stated 
the fact that a floating dock, as a buoyant structure, is 
liable to the perils of a ship—it may founder or be wrecked. 
Under all the circumstances, it is found in practice that 
there is scope for the employment of both types. There 
is a floating dock at present at Southampton with a lifting 
capacity of 60,000 tons, which has repeatedly docked the 
second largest existing vessel, namely, s.s. Majestic, a 
vessel of 56,000 tons gross register, and there are several 
floating docks with lifting capacities of 20,000 to 40,000 
tons. Quite a large number of graving docks have 
dimensions in excess of any vessel now existing. The 
largest at present is a graving dock at Bahia Blanca, 
which has a length of 1,300 ft., a width of entrance of 
115-133 ft., and a depth of 43 ft. over its entrance sill. 
In all, there are six graving docks which have lengths of 
1,150 ft. and over, although the thousand-foot vessel has 
not yet materialized. The length of the Majestic is 
g1z'ft. 
Having discussed floating and graving docks, we need 
not devote much time to Slip Docks, which in this country 
are small chambers for ship-repairing purposes. The 
vessel requiring treatment is floated over a cradle, or 
1 The s.s. Leviathan, of 59,000 tons gross register, is nominally the 
largest in tonnage, but, being a U.S. vessel, its tonnage has been 
computed on a slightly different basis. There is little difference 
Pies the two in point of size. The Majestic is actually longer 
26