Tuesday, December 4, 2007


Many rivers cannot be negotiated by larger ships without a fair tide since a head current hinders them in making turns. A fair current helps the stern around a bend when it strikes the quarter, so the stern comes around at a greater rate. At the same time the bow is assisted by the eddy currents reflected out of the bend and the lack of current on the bow on the point side of the bend. For a given speed over the bottom, a ship stemming a tide has a greater flow of water passing between her and the bank, retarding the stern's motion around a turn and forcing the bow and ship towards the bank.
Since a ship that is closer to the bottom is more difficult to control, high water makes the pilot's job easier-aside from just putting enough water under a deep loaded ship to assure that she is in the desirable state of being always afloat! By moving with a rising tide to ensure a fair current and deeper water, a ship is using both tide and current to her best advantage.
The current changes at each area of a channel at a different time, and is affected by several factors such as freshets from heavy rains upriver, and strong offshore or onshore winds, so tides may occur at different times than predicted. Keep a seaman's eye on the current. Develop the habit of looking at pilings, buoys, and other fixed objects to check the actual current against that which has been predicted until the practice becomes as natural as breathing.