However, approximately 15% are fabricated in steel, usually with timber head and heel posts.
Many composite gates installed in the 1960s and 1970s are nearing the end of their useful life and require refurbishment of the steelwork, in addition to new timber head and heel posts.
The head and heel posts are constructed from wood to allow for adjustment to ensure accurate sealing when the gate is being installed.
The use of sacrificial wooden parts, which are bolted into place, such as the head and heel posts, allow for ease of replacement without closure of the canal and replacement of the whole gate.
The wooden head and heel posts are vulnerable to rot at the water line, with a typical life span of 25 to 30 years before replacement is required.