An elongate article (100) such as a prefabricated pipeline of several kilometers length is towed through water. The article is provided along its length with buoyancy adjusting material (102) fitted closely to the article. The buoyancy adjusting material is sufficient to give the article overall a positive buoyancy so that it will not sink to the seabed, and is distributed unevenly along the length of the article so as to create regions of negative buoyancy. This causes the article to adopt a wave profile with peaks (+) and troughs (−) along its length. The article is connected at its extremities to lead and trail tugs (104, 106) for controlling movement of the article through the water. Intermediate peaks are optionally coupled to intermediate tugs (108) or buoys (702) via self-adjusting ballast chains (110). The wave profile allows the towed structure to extend without undue tension on the article itself. The article can be laid to the seabed progressively removing buoyancy elements (102) using an ROV (302).