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Seal solution

Limpet dams were the last thing on Martin Lavers mind when he returned from Ghana in 1967 after two years as a junior resident engineer for Halcrow on the Tema port project. With a long leave ahead of him, Lavers plan was to invest his savings in setting up a classical guitar school. Then came the phone call that was to change his life.

It was from John Rochester, who I had first met on the Great Ouse flood protection scheme in 1961, when he was with Sir Lindsay Parkinson & Company and I was a peg-bashing graduate, says Lavers.

Since then he had set up as a small contractor. But while John is a very practical man and a great motivator, he needed an engineer/administrator to make the company work.

Lavers admits he knew nothing about contracting at the time I didnt even know what an invoice looked like but Rochester convinced him. John Martin Construction was set up later the same year, ostensibly as a traditional regionally-based general civil engineering contractor.

But we always had a bias towards river and marine works, Lavers says. And our long term plan was to compete at the difficult end of the market where technical competence really counted.

This philosophy paid off, because the new company avoided the pitfalls into which so many similar companies fell, and survived its early years. By 1987 JMC was turning over 3M annually, and even making modest profits in good years. Then came the chance Lavers had hoped for.

We were working on a conventional quay restoration in Harwich when the client was letting a new contract to repair badly-deteriorated sheet piling on a busy quay nearby. Everyone assumed the work would have to be done with divers, but I was sure there was a better solution.

Lavers idea was a moveable cofferdam, a development of the tailor-made limpet dam JMC had used around smooth tubular piles on an earlier contract. What was needed at Harwich was a dam which could seal on to unprepared irregular surfaces very quickly, thereby minimising disruption to ships using the quay. And it needed to be operated without divers.

He told the client that JMC would develop the concept at its own expense, a major gamble for such a small company. To make the challenge even more daunting, the quay in question had no walings and the line of sheet piles was extremely irregular. And I had no idea if it had ever been done before, and no idea if we could do it, Lavers adds.

Then as now, the secret was in the seals. That very first limpet dam used simple plastic foam seals, which, even though they were rapidly abraded by the corrosion products on the piles, worked well enough for JMC to be awarded the 200,000 contract to repair the quay.

Ten years on, and with eight basic designs of limpet dam now in use, Lavers reckons the company has solved the seal problem. He says he would be happy to build dams up to 12m deep any deeper than that and we would have to look very carefully at seal design and is still convinced of the benefits of innovation.

JMCs latest baby is a pregnant dam design which provides enough room for the installation of ground anchors through existing quay walls. This allows quays to be upgraded to take heavier ground loadings, or to be reinforced against the effects of bow thruster scour. Other designs are sure to follow. Nearly every contract needs its own purpose-built dams, Lavers reports. But they all follow the same principles, and offer the same benefits.

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