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Portland Harbour
between Weymouth and the Isle of Portland, Dorset
associated engineer
James Meadows Rendel
Sir John Coode
date  1849 - 1868, 1893 - 1906
UK era  Victorian  |  category  Harbour  |  reference  SY690760
ICE reference number  HEW 124
Portland Harbour is the largest artificial harbour in the UK. The Isle of Portland to the south, Chesil Beach to the west and mainland Dorset to the north protect it from gales — it's fully exposed only to the east. Classed as a primary port in the Admiralty tide tables, it has a double low water and maximum tidal range of 2.3m.
The harbour has three entrances and four breakwaters — two southern and two northern. These have a total length of 4.57km and enclose some 520 hectares. A refuge harbour was first suggested at this location in 1794, although ships had used the natural shelter of the bay for centuries. Parliamentary approval was granted in 1844, and HRH Prince Albert laid the foundation stone in 1848.
Construction of the southern breakwaters began in 1849 to the design of James Rendel, who unfortunately died in 1856. They were completed in 1868 by Rendel's then Resident Engineer John Coode. HRH Edward the Prince of Wales belatedly declared the harbour open on 10th August 1872.
These southern breakwaters are constructed of Portland stone, in all sizes from 7.1 tonnes downwards. It was heaped into a mound, tracks laid over temporary timber trestles on the mound, then more stone tipped on from loaded wagons running on the tracks, until the mound increased in length and finally became a complete breakwater. At the greatest depth, 15.2m below low water, the base width of the original breakwater was 77.7m. Side slopes were 1 in 1.5 (34 degrees), easing to 1 in 6 (9 degrees) on the seaward slope 3.7m below low water.
The harbour became a Royal Navy base with dockyard, hospital, refuelling and training facilities. The development of both the torpedo and the submarine led to Portland Harbour becoming a centre for research into underwater warfare, and a torpedo factory was built on the north side of the harbour in 1891.
As part of defence works against torpedo attack, work began on the northern breakwaters in 1893 and at that time the southern breakwaters were topped with paved roads protected by 6.1m parapet walls. All three harbour entrances were semi-circular in plan and had vertical ashlar masonry walls, granite-faced above low water.
In 1914, as a defensive measure, the battleship HMS Hood was sunk across the south entrance. Although fully submerged, it reduces swell and prevents commercial shipping from using this entrance. The north and east entrances are each some 200m wide. A flushing current enters the harbour through the north entrance, rotates anti-clockwise and exits via the south and east entrances, which keeps the harbour self scouring and reduces the need for maintenance dredging.
Portland Harbour came under fierce German air attack during World War II. In July 1940 the anti-aircraft ship HMS Foylebank was attacked by Stuka dive-bombers and sank in the harbour. Thousands of American troops from the US 1st Division embarked here for “Omaha Beach” in June 1944.
As part of the D-Day operations in Normandy, nine Bombardons (61m long cruciform steel floats) were assembled in Portland Harbour for the Mulberry Harbours. The Bombardons were designed to be moored seaward of the main Mulberry structure formed by Phoenix breakwaters (64m long open-topped reinforced concrete caissons). A number of Phoenix caissons were moored at Portland in 1944 before being towed to France.
After the war, in 1946, ten Phoenix caissons were towed back to Portland Harbour. A violent storm overnight on 31st January / 1st February 1953 caused severe flooding in southern England and the Netherlands. The Admiralty offered eight of the caissons to the Netherlands to repair breaches in the dykes, and by July 1953, six had been towed to Zealand province. It is believed that the two remaining caissons ran aground and were abandoned.
In 1959, the Royal Naval Helicopter Station HMS Osprey was formed. Royal Navy operations ceased on 21st July 1995 and the harbour closed as a naval base on 29th March 1996. Portland Port Ltd, formed in December 1994, took possession of the site immediately and their purchase was completed on 12th December 1996. Portland Port Group became Statutory Harbour Authority for Portland Harbour on 1st January 1998, replacing the Queen’s Harbour Master. In 2004 changes led to Portland Harbour Authority Ltd becoming the Statutory and Competent Harbour Authority and Portland Port Ltd the Port Operator.
The port has continued to expand; the Britannia Passenger Terminal was opened by HRH Prince Philip on 14th July 1999. In April 2000 the contract was signed for a new bunkering jetty and berth, which came into service in 2005.
An ultrasonic anemometer sited on the breakwater south of the east entrance measures wind speed and direction. These are updated on the port’s website every 10 minutes.
The sailing events for the London 2012 Olympic and Paralympic Games (July, August and September 2012) were held in either Portland Harbour or Weymouth Bay. Construction work has been carried out by contractors Dean & Dyball.
Southern breakwaters: J. T. Leather of Leeds
Research: ECPK
reference sources   CEH South

Portland Harbour