Brian Moseley, Plymouth
Webpage created: June 28, 2019
Webpage updated: June 28, 2019

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Plymouth's At the most northerly extremity of the North Yard Extension to the Royal Dockyard, just before Weston Mill Creek, was constructed Basin number 5, known during building as the Closed Basin.  At 34 acres 9 perches, this was the largest Basin in the Dockyard.

It measured 1,550 feet in length and about 1,000 feet in width.  Various figures have been quoted for the depth of water inside the Basin: it has been claimed to be 32 feet 6 inches at low water of ordinary spring tides, 48 feet at high water, while the Ordnance Survey map of 1912 gives it as 45 feet at Mean High Water of Spring Tides (MHWST).

The walls of the Basin were constructed of concrete faced with limestone and they were 30 feet thick at the base.  The height from the floor  of the Basin to the coping was 55 feet but the walls actually extended up to 90 feet deep into the subsoil from the original surface.

Two entrances were provided, one 95 feet wide via North Lock, the other direct from the Hamoaze via Sliding Caisson R.  This entrance was said to be 95 feet wide in 1907 but was shown as 125 feet wide on the Ordnance Survey map of 1912.  Caisson R slid into the wall of Wharf number 8.  The depth over the sill at this entrance was 32 feet at low water ordinary spring tides or 47 feet 6 inches at high water.

At the northern side of this Basin is a pier, 500 feet long by 75 feet wide.  This increased  the wharfage inside the Basin to 5,000 feet and also provided a base for an Air Capstan to help manoeuvre warships around the Basin.  An MTE Workshop was erected on the Pier.

On the eastern side of the Basin an 160-ton Crane was installed along with some 20-ton Travelling Cranes.  75-ton Steam Crane number 1 was installed on the western side, a short distance from the North Lock, and number 2 was placed on the Coaling Ground area for Number 8 Wharf. 

When His Royal Highness the Prince of Wales (later to become King George V) declared the Basin open and the North Yard Extension works finished on February 21st 1907, he named this the Prince of Wales Basin.