I must admit when I played SHII, I used to just guess the right time to fire, and I got about a 70% hit rate, not bad i must say for pure guesswork!
OLC is absolutely a must if your for manual targeting. I can't play without it now, with the "aim-bot" that is auto-aim theres no real satisfaction when you hit something. When you've worked everything out yourself, there is a real sense of satisfaction when you see those fish hit home! Also a sense of frustration when you find yourself in rough seas which makes it bloody hard to get the data with the sea, and sometimes you make a mistake like do the speed etc wrong and its just like god damnit!
GWX 2.0 is a must too! can't forget that!