Many thanks for the reply – it does help me when some body explains from first principles the ground rules – they seem to stick better into my muddy mind !
So it was not the centre board based on your explanation (which does make a lot of sense).
Our problem may have been that we had the balance wrong (bow,stern) which in the light wind conditions possibly messed us up.
The kicker was tight, perhaps too tight for the wind – I had not read yet that you need to apply as much kicker as to make boom and top batten partially parallel (3rd edition way farer book). I wonder does that apply on all points of sailing ?