Hello,
Sounds like you are surfing off the wind and overtaking waves. since you are sans spi. shouldn't the boards be mostly up? They don't do much good in the situation that you desribe. you want side slip not traking. also a badly oversheeted jib would give problems surfing. also the better the rudders are suited to the boat, the better the steering. more mast rake may help, but that is an uninformed suggestion.