Caissons versus movable dry-dock gates

What is the difference between a movable caisson and a gate system for a dry dock?

The arrangement described uses pumping and cranes to remove the caisson; a gate has its own movement system and is easier to operate repeatedly.

In the crane-handled arrangement described here, a caisson is pumped out before being lifted clear of the dock entrance. Several deliberate steps are therefore needed to remove the barrier, making accidental movement difficult. A powered gate is easier to operate repeatedly and avoids the lifting work. Its moving mechanism can jam or fail to close properly. The choice depends on how the dock will be used and the relative importance of convenient operation and a barrier that is difficult to remove inadvertently.