Not always ultra-fast, but I find that shooting for the bow, rather than trying to hit the "critical" spots in the middle, allows for a faster sinking. By flooding the bow you induce a negative angle on the boat, that combined with the forward momentum of the ship, drives it underwater faster than hits anywhere else. This is especially important, IMO, in GWX were flooding (rather than damage) is the primary mechanism of ship sinking. A hit in the middle floods, but does nothing to affect the angle of the ship. A hit in the rear causes a positive bow angle, which is unaffected by the forward momentum of the ship. But if you ever encounter a ship sailed in reverse, I'd then target the stern.
