Performing work over water has always been more difficult and expensive than performing the same work on land. And when the work is performed below water, the difficulties and cost difference can increase geometrically with the depth at which the work is performed. The key to carrying out marine construction work efficiently is to minimise work over water, and perform as much as possible on land. The use of float-in cofferdams to construct marine bridge foundations is a successful application of this principle and one of the first projects on which it was used was the Bath-Woolwich Bridge in Maine, over three years ago (Bd&e issue no 14). Caltrans recognised the advantages of this construction method and applied it to the design of the main tower foundations for the new suspension bridge across the Carquinez Strait.