SECTION A-AThe correct protective grid.Among other reasons, protective grids are fitted to reduce the ship drag resistance because of the transfer pipes. Travel in ice also requires protective grids. Not too many grid bars shall be used. Standards, for installations up to approximately tunnel diameter 1,50 m, 4 vertical bars and 3 horizontal bars., for larger installation 5-7 vertical bars which are interconnected with 5 horizontal bars. The type of protective grid must be known for the design of the propeller. Five grid bars win reduce the thrust of the installation by approx. 9%, seven bars by approx. 10%. At the same time the installation requires more power. The protective grid shall have no large "cover".Cover in these terms signifies the ratio between the area of the bars and the tunnel opening.Grid area = 10 -15% of tunnel area.
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