Sail in the Gulf Stream (English Channel or similar) and you can bet behemoths abound there too. They will often be steaming at twenty to thirty knots.
Consider that a freighter or tanker pushing 20 knots will eat up liquid real estate–and anything in its path–at 2000 yards every three minutes. Or 2 nautical miles every 6 minutes. If you pick up a ship on the horizon at 6 miles, you may have just minutes before it’s on top of you.
Your number one determinant for risk of collision will be drift bearings. This action will always be in addition to other means (i.e. AIS or radar if installed). Again, the electronics are not a substitute for visual bearings. The Navigation Rules are quite clear on the requirement of bearings in collision risk situations. Train your sailing crew or partner in the sea-tested, works-every-time, no-batteries-required techniques described below.