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Note: Shelter Deck and Full Scantling Types. Full scantling was the default type, with maximum hull strength (scantlings) and the entire hull below the top continuous deck (the upper deck) enclosed and watertight. The shelter deck type was developed to exploit a regulation that allowed the exclusion from gross and net tonnage calculations of any space on or above the upper deck that was sheltered but not enclosed, giving shipowners considerable savings on canal tolls, etc. In a shelter deck ship the top continuous deck (the shelter deck) covered a 'tween deck space that had openings in its internal bulkheads and in its after overhead deck to make it "not enclosed," and the deck below it (the upper deck) was the top of the enclosed and watertight portion of the hull. Lowering the top watertight deck (also called the freeboard deck) one level however increased the required freeboard of the ship by the same amount, reducing its maximum draft and its ability to carry heavy weights. On the other hand this also reduced the need for maximum strength in the ship's scantlings. Shelter deck ships were best suited to carry relatively light, bulky cargo for which a deep draft was not required, while full scantling ships were better suited for heavy, dense cargoes. In the freighter designs presented here, the larger ones (except for Design 1133) were of the shelter deck type while the smaller ones were of the full scantling type. Note that two large tanker designs also had shelter decks. |