I was changing the fuel filter in my 115 Yamaha every six months until my boat mechanic said that I should just replace it every year unless there were other issues. I have the fuel/water seperator with the see thru bowl, Rancor I believe. I check it frequently for water and so far, there hasn't been any.
I change it annually also. Since I'm not sure what filter element you have in your F/W seperator, I suggest that you remove it, drain it and take it to your boat shop to ensure getting the correct one.