Flash lock

[3] In England the "gate" was similar to a temporary needle dam: a set of boards, called paddles, supported against the current by upright timbers called rymers which normally kept the level of water above it to navigable levels.

Considerable skill was involved both in removing the paddles in a timely manner and navigating the boat through the lock.

[5][6] Flash locks were commonly built into small dams or weirs where a head of water was used for powering a mill.

As navigation increased in importance, improvements were made to the basic design, and they came to be known by various names according to where they were located.

The gate was opened by operating a large spoked wheel, connected by chains to a toothed drum.

The paddles are of differing lengths allowing a very fine adjustment of the amount of water flowing through the weir.

A drawing of a boat passing downstream through a flash lock [ 1 ] [ 2 ]
Detail from 16th century Abingdon Monks' Map showing Abingdon Lock as a flash lock
Sketch map of a flash lock on the River Thames between Whitchurch-on-Thames and Pangbourne around 1786, showing method of winching a barge up over a weir . Flash locks were common on the Thames above Staines .
Capstan Wheel near Hurley , England that was used to winch boats upstream past a flash lock. It is said to be the only one left in England and was restored in 1999.
Paddle and Rymer weir on the Thames
Paddles stored for use at Northmoor Lock