This heading covers :
(A) Light-vessels, fire-floats, dredgers, floating cranes, and other vessels the navigability of which is subsidiary to their main function. These normally perform their main function in a stationary position. They include : light-vessels; drill-ships; fire-floats; dredgers of all kinds (e.g., grab or suction dredgers); salvage ships for the recovery of sunken vessels; permanently moored air-sea rescue floats; bathyscaphes; pontoons fitted with lifting or handling machines (e.g., derricks, cranes, grain elevators) and pontoons clearly designed to serve as a base for these machines. House-boats, laundry boats and floating mills are also covered by this group. (B) Floating docks. Floating docks are a type of floating workshop used instead of dry docks. They are generally structures of a U-section comprising a platform and side-walls, and are equipped with pumping compartments which enable them to be partly submerged to permit the entrance of vessels requiring repair. In some cases they may be towed. A further type of floating dock functions in a similar manner, but is self-propelled and equipped with powerful engines. These are used for the repair or transport of amphibious vehicles or other craft. (C) Floating or submersible drilling or production platforms. Such platforms are generally designed for the discovery or exploitation of off-shore deposits of oil or natural gas. Apart from the equipment required for drilling or production, such as derricks, cranes, pumps, cementing units, silos, etc., these platforms have living quarters for the personnel. These platforms, which are towed or in some cases self-propelled to the exploration or production site and are sometimes capable of being floated from one site to another, may be divided into the following main groups : (1) Self-elevating platforms which, apart from the working platform itself, are fitted with devices (hulls, caissons, etc.) which enable them to float, and with retractable legs which are lowered on the work site so that they are supported on the sea bed and raise the working platform above the water level. (2) Submersible platforms, the substructures of which are submerged over the work sites with their ballast tanks resting on the sea bed in order to provide a high degree of stability to the working platform which is kept above the water level. The ballast tanks may have skirts or piles which penetrate more or less deeply into the sea bed. (3) Semi-submersible platforms which are similar to submersible platforms, but differ from them in that the submerged part does not rest on the sea bed. When working, these floating platforms are kept in a fixed position by anchor lines or by dynamic positioning. Fixed platforms used for the discovery or exploitation of off-shore deposits of oil or natural gas, which are neither floating nor submersible, are excluded from this heading (heading 84.30). This heading also excludes ferry-boats (heading 89.01), factory ships for processing fishery products (heading 89.02), cable-laying ships and weather ships (heading 89.06).
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