Lifting forces required to salvage a sunken vessel and caisson and their response to bottom friction, buoyancy release, surface tension, water capture and water release

Two field tests were carried out to measure the lifting forces required to salvage a sunken vessel and caisson, and force histories were obtained to assess their response to bottom friction (BF), surface tension (ST), buoyancy release (BR), water capture (WC) and water release (WR). The test results for the two fully sunken objects showed rather different force profiles. The effect of BF on the caisson, at 1.27 MN, is much larger than that (0.086 MN) on the vessel due to the greater weight of the caisson, whereas the effect indices are almost identical. During separation from the surface water, the vessel was affected by the WC within the vessel as well as by BR and ST. Once fully salvaged, the lifting force of the vessel gradually reduced to 0.71 MN from the maximum of 1.38 MN, owing to WR. The maximum lifting forces of the vessel and the caisson correspond to two and one times the initial lifting forces of 0.69 MN and 9.41 MN, respectively. It was found that the salvage process of the vessel resulted in a more complicated lifting force history than that of the caisson, primarily because the vessel structure allowed WC and release.