A Bay Watch That Matters: ABOARD THE USS WHIRLWIND – Target No. 13 lights up as a slow-moving blip on the radar screen in the Combat Information Center of this Navy ship, a green dot that shows it is 800 yards to port and making 11 knots in the gently rolling waters of Chesapeake Bay. The target is the Gateway Bulker, a rusty coal-hauler sitting high in the water, masted under the Liberian flag and drawing the attention of both the Navy and Coast Guard ships patrolling the mouth of what has become, after Sept. 11, one of the most highly protected inland waterways in the nation.