Existing comment:
How the screwpile lighthouse got its name:
A screw like this one was at the bottom of each of the seven pilings (legs) of this lighthouse -- allowing the leg to be screwed down into the soft Bay bottom. Although it would have been easier to drive the pilings into the mud, screwing them in gave the lighthouse a much more stable foundation.
The Bay goes through many environmental changes throughout the year; ice tends to freeze around lighthouse pilings and as the tide rises up it often lifts the legs. The pilings' screws eliminate this unwanted damage.
You would have seen screwpile lighthouses like this one on the Chesapeake Bay, Delaware Bay, and in North Carolina where the rivers and estuaries have soft bottoms and it is possible to screw the pilings down.
Ten-inch solid wrought-iron pilings were screwed twenty five feet into the Bay floor to prevent shifting. |