This apparatus has been developed by my Ministry in consultation with the inventor. Its purpose is to de-foul vessels abroad which, by reason of their long- stay in tropical waters, have lost speed through marine growths and which cannot be dry-docked overseas without delay. The use of this emergency apparatus enables the vessel to be scraped, so that she can return at an adequate speed to the United Kingdom or elsewhere. The vessel can then be dry-docked in the normal way. A number of sets are already in operation overseas, and further supplies are being sent to parts where they are most required.