(How they work)
The sequence to descend a lock goes
thus: If the lock is empty, you must
first shut the bottom gates and close
the bottom paddles. Then fill the lock
by opening the top paddles. When the
lock is full you open the top gates and
the boat can enter the lock.
With the top paddles down and the top
gates closed, you now open the
bottom paddles and the water level
inside the lock equalises with that of
the level in the pound below the lock.
There is usually a cill underneath the
top gates which extends out into the
lock. Care must be taken to avoid
getting caught up on the cill or else
disaster can overtake the unwary. The
furthest extent of the cill is normally
marked in white on the side of the lock
and can be up to 6 feet or more from
the lock gates.
Lastly, once the water
level inside the lock is the
same as that below the
lock, you can open the
bottom gates and the boat
sails off into the distance.
Normally all gates and
paddles are left closed
unless on rivers, where
the exit gate is often left
Ascending is the reverse of the above, taking care not to snag the boat on top or bottom gates.
The term paddle covers all the different types of devices for filling and emptying the locks.
These are usually found at the top of locks and are a simple rack and pinion system. The water
enters via the base of the lock chamber and causes the boat to surge backwards initially and then
surge forwards as the level rises.
These come in various designs, some rack and pinion via a gearing wheel, some hydraulic (found
a lot on the K&A) and can sluice the water in above or below the water level. These need treating
with respect, as opening fully, too soon, can cause the flooding of a boat which is well forward in
the lock. With full length boats this is a major detail as they must position themselves to the front
of the lock, because of their length. ( Dawn has her own name for some of the more difficult