We had good success last month doing an open, one-mile fog-bound crossing last month, near slack low. We were originally paddling on a 110 degree heading towards the Otter Ledge #11 green day marker, from Lobster Buoy campground. http://www.charts.noaa.gov/OnLineViewer/13303.shtml I was careful to watch the stopwatch function on my "kitchen sink" watch, stopping when progress stopped, restarting when underway, figuring we'd cover the mile in about 20 minutes, given conditions and paddling pace. About midway we decided to "aim off" to 120, thinking there would be no "catching feature" or "backstop" (terms/phrases in quotations from orienteering glossary) if we were off northerly, and we'd be off to Vinalhaven. We heard gulls squawking (maybe island/ledge nearby?) and a fishing boat's diesel (all bets are off), and at the predicted "reckoning" time red#10 appeared 100 yards to starboard.
Believe your compass(es), mind your stopwatch, and be able to predict your speed/course over water under current conditions.
gary