PURPOSE:To carry out complete onboard desalination by effectively using the time required for returning to a port from a resources gathering place by providing a filter layer on the base of a hold and providing a drain chamber below the layer. CONSTITUTION:A hold 2 of a hull 1 has a filter layer 3 at the base. A drain chamber 4 is disposed in the lower portion of the hold equipped with a drainage pump. A fresh water sprinkler device 5 is provided in the upper portion of the hold 2, thereby supplying fresh water from a ballast tank 6 by a fresh water pump. The fresh water for desalinization is used also for a ballast for an outward trip, and the salt-containing water after desalinization is completely filterated by the filter layer 3 to be made limpid and then be thrown away in the sea. The area of the filter layer 3 is made larger than that of the hold bottom by 40% or more, so that drainage can be accomplished without blinding so as to conduct desalinization completely. Accordingly, during the time required for returning to a port, the desalinization for granular marine resources so as to be used immediately after landing.
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