The curves do not apply to skew layouts. If in these the piers are to be square, Fig. 30f can be used by making a layout and finding the re- quired distance from center to center of piers, subtracting therefrom a length varying from 20 feet for a 100-foot span to 30 feet for a 200-foot span, and entering the diagram with the results as the "clear-channel" width. If

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skewing piers is permissible, both can be skewed for the vertical lift, but only the rest-pier for the bascule. This condition favors the vertical lift materially.

For deep and expensive piers, a bascule layout, such as is shown in Fig. 30d is not economic, that indicated in Fig. 30g being cheaper. The