My partner and I are booked to stay on the island for a week shortly, are there bag size restrictions to take on the transfer boat?
On a boat I would not think so. Internal flights yes.
I wouldn't think so, but if the luggage is bigger than the flight checked bag requirements then it may be best to contact Leleuvia just to be safe as it is a small-ish boat.... I am a little jealous though, Leleuvia is my most favourite resort & island in Fiji!! Enjoy your time there!!
I have taken multiple suitcases on the island transfers on boats and they have been business class sizes and 30 kilos in weight and had no problems at all.