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A CAISSON DOCK GATE refers to a structure, used instead of gates, to close a lock or dock in order to maintain the water in; or exclude the water from entering into a dock, lock, basin, or reach of a canal.

Early history

This is Keppel Verolme dock

The early history is not clear. What was probably the first CAISSON was fitted at the arsenal at Rochefort in the mid 1680's for one of the dry docks, when it was described as a new and little known invention. The next mention is by Commissioner George St Lo of Chatham Dockyard; who claims to have invented "floating gates" which in 1703 the Admiralty ordered evaluating. However nothing else is heard until 1798. In that year Samuel Bentham (Inspector General Of Naval Works) revived the idea of what he called a"hollow floating dam". In 1802 The first was installed at the entrance to the "Great Basin" (now number one basin), at Portsmouth Dockyard.

You can use refs like this.

Bentham's CAISSON was mainly timber built, boat shaped, but had all the features of a modern caisson. To "close" the caisson was towed into position across the entrance, when tanks deep within the structure were flooded, causing the caisson to settle on the bottom, against flanges or in grooves. It was held in place by water pressure on it's outer face. To open again was simple, allow water levels on both sides to equalise, pump out the water from the tanks, and tow the caisson to it's storage position when it floated free from the bottom. Caissons were so successful that from the 1840'sthe British Admiralty specified Caissons, and not gates for all new docks and basins.

Advantages over gates

The advantages of caissons over gates include

1 The saving of room; in a shorteningof the length of the enterance.

2 The ability to be repaired and maintained.

3 The ability to examine the sill and masonary of the enterance.

4 Caissons also provide ability to carry road or railway across the dock enterance.

5 Fewer joints for leaks.

6 As there is no attachment of the caisson to the lock or dock wall, no stresses are transfered.

Types of caissons

THE FLOATING OR SHIP CAISSON; This is the sort built by Bentham, approximateley ship ship shaped, capable of being floated in and out of position, and moored out of way when not in use.

SLIDING CAISSON; Rectangular and box like, This Caisson slides in and out of a special recess or chamber to open the lock or dock These are popular, the chamber is often open topped to allow access for maintainance.

ROLLING or WHEELED CAISSONS are similar to SLIDING CAISSONS except they are fitted with wheelswhich run on rails fitted into the floor at the enterance to the dock.

Early CAISSONS were largely timber built, but soon gave way to Iron, and then Steel. An examples of early floating Caissons is in Belfast, In the Hamilton dock alongside the steam ship Nomadic. All three of the Graving Docks on the old Harland and Wolff site, now accesable in the Titanic Quarter are closed by Caissons' The Hamilton Dock Caisson was built of wrought iron, as ship 49; yard job number 50, and launched initially on the 14th of February 1867. The Alexandra dock (1889) was closed by floating caisson, As was the Thompson dock (1911).The Caissons for these docks were of a more box shape, but work in exactly the same way but are made of steel. The Thompson dock also exhibits another advantage of floating caissons, that of being able to be seated in two alternative locations, alowing for longer ships to be docked (The Thompson dock was built to accomadate the Titanic sisters, but only with the caisson on the outer sill). This facility also allowed the masonary of the sill to recieve attention whilst the dock was in use.

Bibliography

• Colson, Charles (1906). Notes on Docks and dock construction.

Dock and Lock Machinery; W. Henry Hunter, 1921.

Support For The Fleet; Jonathan Coad 2013.

Shipbuilders to the World; Michael Moss & John R. Hume, 1986

Belfast Built Ships; John Lynch, 2008