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Annotated Photographs

Bascule bridge with annotations.
Tour graphics are heavily compressed for faster loading. Originals are larger and sharper.

There are numerous styles of bridges noted on nautical charts. In this example we illustrate the meanings of the various clearances shown in the chart symbol.

Vertical clearances are relative to the "shoreline datum" which in most cases is the mean high water level for that region. This important information must be learned from the chart itself, it is not in tide books.

The text discussion (not included here) covers the definitions of bridge types, the importance of mean high water, how to determine actual clearances in a given situation, and so forth.

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