Bottom Material Since the self-cleaning effect can be expected to the bottom materials under the floating structure due to the existence of the current same as that around it, little difference is found between the bottom materials under and around the floating structure. The Experiment According to the result of The Experiment little difference is found between the bottom materials under and around the floating structure. Investigation on Existing Floating Structure According to the investigation on the floating structure built more than several ten years before, no remarkable difference to the bottom materials can be found between under and around the floating structure.