Paddy,
Beginners usually need flat water, that's why the river is so good. Put up with it is my suggestion, clean your board after, it's only a bit of river sediment.
The best ocean sailing for beginners is Safety Bay, but it might be a bit far you

TOW (Time on water) is important when a beginner, but in ideal conditions preferably, which means flat water.
Hardie SoftBoy