sea room

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Unobstructed space at sea adequate for maneuvering a ship.

from The Century Dictionary.

• noun Sufficient room at sea for a vessel to make any required movement; space free from obstruction in which a ship can be easily manœuvered or navigated.

from the GNU version of the Collaborative International Dictionary of English.

• (Naut.) Room or space at sea for a vessel to maneuver, drive, or scud, without peril of running ashore or aground.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun space for maneuver at sea