Duck diving fail is getting annoying D:

I'm starting to get really eff-ed off at my attempts at duck-diving. My board just seems to veer off at an angle when I try, and that's when I even manage to get it anywhere close to underwater!
I'm on a 6'4" bic funboard/mini-mal, and weigh 140 lbs.. am I just not going to be able to ever achieve a good duck-dive on this board (and in which case should I start trying to turtle-roll instead) or am I still doing it wrong?
It's totally frustrating me right now, I'm bloody knackered by the time I even get out to start catching waves, and my arms end up feeling like noodles!
I'm on a 6'4" bic funboard/mini-mal, and weigh 140 lbs.. am I just not going to be able to ever achieve a good duck-dive on this board (and in which case should I start trying to turtle-roll instead) or am I still doing it wrong?
It's totally frustrating me right now, I'm bloody knackered by the time I even get out to start catching waves, and my arms end up feeling like noodles!
