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Mulberry harbours

Excerpts from the Society's Transactions

The paper entitled "Mulberry harbours" by Professor Sir Alan Harris, is published in the Transactions of the Newcomen Society, 1989-90 Vol 61.

Spud pontoon with LST buffer © copyright

Sir Alan Harris himself had a role at Mulberry, as he describes at the beginning of his paper. He landed at Port-en Bessin as Officer in command of the advance party, 933 Port Construction and Repair Company, Royal Engineers, as soon as the village had been liberated. He and a crew of ten divers worked from French fishing boats, each with a skipper and crew. Their job was clearing the sea-bed for incoming caissons, disposing of UXBs and mines, and inspecting the various structures under water.

This great feat of design and of construction had begun with Churchill's famous memo of 30th May 1942 to Lord Mountbatten:

Piers for use on beaches
They must float up and down with tide. The anchor problem must be mastered. Let me have the best solution worked out. Don't argue the matter. The difficulties will argue for themselves.

In the following short extract, the author describes some of these practical issues and challenges:

"A breakwater alone would protect the beaches during onshore winds, thus permitting the continuation of unloading beached craft. Given the right site (tides, nature of sea-bed, depths etc), ships and barges could have continued to discharge cargo onto rafts and DUKWs. But beaching meant waiting for twelve hours, whereas the floating pierhead could turn around an LST in 40 minutes. Unloading on to rafts and DUKWs meant a slow trip from ship to shore, as well as double handling. A pierhead provided rapid unloading straight on to road transport.

On that coast, however, the pierhead needed to rise and fall with the tide. A rigid pierhead, however constructed (and caissons could have been used), would at low tide have been some 20 ft above the ship's deck, whose derricks could thus not have operated. Mobile cranes could have been used on the pierhead but were in short supply, would have occupied space and were slower. Cargo had, moreover, then to be got ashore; a rigid pier was out of the question and a floating pier would require an immense span connecting to the rigid pierhead to give a practical slope at low tide.

The anchor problem was also vital. A large scope on a classic cable and anchor would be needed at high tide; at low tide the pierheads would drift around and the cables would risk fouling the ships. Bruce White responded to Churchill's memo by describing a particular type of dredger used for mineral extraction. It consisted of a pontoon carrying robust vertical piles in guides; at the desired location these piles, which carried load bearing slabs at their feet ('spuds'), were allowed to drop on to the sea bed and the pontoon then jacked up to maintain negative buoyancy and transfer load to the piles. The pontoon thus firmly founded, the dredging gear would work from a stable platform."

Clearly, the scheme could 'float up and down with the tide'. Moreover, the anchor problem had been mastered!

The author in his paper goes on to describe the Whale pierheads; the Spud pontoons; Whale floating roadways; Bombardon breakwaters; Phoenix caissons; Corncob blockships; Mulberry A and B; Gooseberry - and the very many components eventually used in this extraordinary project, which he sums up as follows:

"The audacity of Mulberry lay in its magnitude, the complexity of the means needed to fulfil its functions, the vagueness with which, of necessity, the site was known and the phenomenal speed with which the component parts had to be constructed in the UK and assembled on the far shore."

Biographical Note: Alan Harris (1916-2000), a pioneer of prestressed concrete, worked with Freyssinet in France 1946, managed the Prestressed Concrete Company in Britain until 1955, then senior partner in Harris & Sutherland, 1955-1981 and Professor of Concrete Structures at Imperial College 1973-80; a prolific writer and frequent lecturer receiving many honours and awards. As a Royal Engineer his connection with Mulberry started on D-Day+1.

The complete text of this paper can be purchased on line from our archive.

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