These are ships specially designed for the carriage of containers and are the modern equivalent of the cargo-liner of the immediate post-war years. These large vessels tend to be employed on scheduled voyages on fixed routes, travelling at high speeds of around 25 knots or more. They normally serve sophisticated container terminals where extensive shore equipment is available and, for this reason, most of them are gearless. Their turn-round time in port is very short – perhaps only a matter of hours rather than days. By their nature containerships are almost exclusively chartered by operators in the liner trades, either enhancing their own fleet or very frequently today by liner companies operating services with entirely time chartered tonnage. The greater part of the daily market activity is in the short sea and middle distance trades, the largest sizes being fixed almost exclusively on longer term time charter with the major liner companies. Containers are stowed below the weatherdeck in a secure, cellular steel framework (‘cell guides‘), in heights of eight to ten tiers, with up to three to four tiers on deck. Just as for conventional cargo-liners, however, the old stability rule of ‘heavy weights at the bottom, light on top’, holds good for containerships. These modern vessels have large hatchway openings of the same width and length as the holds they serve, and the hatch-covers are frequently steel slabs (‘pontoon hatches‘) lifted on and off by shore gear. Usually there is longitudinal framing along the main hold within a double hull; this double ‘skin’ being required to compensate for the loss of vessel strength owing to large hold areas and open hatchways.