The majority of sailboats have a keel, a lead-filled blade that extends from the bottom of the boat to provide straight line tracking and acts as a counterbalance for the wind blowing against the sails. When the "Mistral" takes a wave and rolls 360-degrees, there is no keel visible.
At the beginning of the movie, when the Andrea Gail and the Hannah Bowden enter Gloucester Harbor together, a Leisure Casino Cruises casino boat is tied up at a pier in the background. Leisure Casino Cruises started running out of Gloucester in 1998.
When the captain is about to tell the crew about the broken ice machine the camera pans out to the crew who all stop what they're doing. Murph is holding two fins that apparently have just been cut from a fish. When the captain says the ice machine's "had it" the fins are no longer in Murph's hands, nor are they by his feet (in the event that he dropped them).
A fishing hook is caught in Murph's hand. When Billy starts to take it out, Murph puts a big wooden spoon in his mouth, with the scooping part to the right. When Billy jerks the hook out, Murph's reaction shot has the scooping part of the spoon to the left.
Just before the Andrea Gail is overturned and sunk, she is shown from above approaching a giant wave, with her stablizing "out-riggers" deployed. The next shot she is shown head-on and they are not in view. Finally, she is shown from above again, climbing the wave, and the stablizers are again deployed.
After the ship has been bashed by the rogue wave, the crew is forced to replace the windows on the starboard side of the bridge with either plywood, or some other form of sheeting. A crew member is picked up by the wind underneath the covering and tossed overboard. Wires are very visible when the man is airborne.
When the Andrea Gail enters the eye of the storm, the waters become calm. In reality the air would be calm and the skies clearer, but the seas would be just as bad as ever, on account of churning from the surrounding hurricane's eye-wall winds.
The sailboat rescue was performed by the US Coast Guard; not the Air National Guard as shown in the film. Also ANG helicopters don't usually carry the type of rescue basket shown in the rescue since their primary mission is the rescue of military personnel.
(Confirmed by citation of the book and USCG reports and news sources.)
The Andrea Gail has an all-around (light shows 360 degrees) green masthead light over an all-around white masthead light. According to COLREGS Rule 26 part C: "A vessel engaged in fishing, other than trawling, shall exhibit: I: two all around lights in a vertical line, the upper being red and the lower white." Trawling vessels display green over white. The Andrea Gail was long-line fishing, not trawling, and would require a red over white light.
When the Hurricane Hunter flies through Hurricane Grace, the man reading the wind speed gauge says "winds over 140 knots, category 5." Grace was never higher than a CAT 2, with maximum winds of 100 mph.
Although Tyne, Shatford, and Sully were the only fisherman from Gloucester who died at sea, the wall lists the names of all men who lost their lives while working as professional fisherman who sailed out of Gloucester, regardless of where they actually lived.
Early in the movie, the body of a Gloucester fisherman who died at sea is removed from a rival fishing boat. At the end of the film, he is not listed on the wall of lost fishermen for 1991. The wall lists only those lost at sea, not those whose bodies were recovered.
In the middle of the storm, the TV in the Gail's lower room keeps showing a perfect image because it's playing a video. The TV's anchor bracket could be behind the TV, much like a removable car stereo.
On the USCG Cutter, the officer is referred to as "Captain," but his hat shows the insignia of a Commander in the USN & USCG. Any commanding officer of a seagoing vessel is called "Captain" while on board.
During the later storm sequences in the pilot house of the Andrea Gail, after the windows are broken out, the water droplets falling from overhead fall vertically with the pull of gravity. That means the camera was tilted, and the actors were leaning to heighten the appearance of rough seas.
When the weatherman is reviewing Hurricane Grace and the weather front covering New England, he clicks on the New England area to zoom in. When the new window opens, 447992x.tif is in the top left corner. A .tif is an image file, meaning the weatherman is looking at images, and not a real radar screen.