We're no longer down, but from past experience by boat:
Off Dart Haven Marina - so you get to see the candles & smaller cakes
Off the visitors pontoon near the Higher Ferry where you'll get a better view of the shells.
Or if you want not to rsik falling over the side from looking up too much - land on Higher Ferry slip Kingswear side (beach on the N side).
Member of the Macmillan Round the Isle of Wight Club