The small crack, in the Wave, above the gudgeon is not repairable. The material is cross-linked polyethylene. It is not weldable. There is a thickish inner layer of foamy polyethylene that would keep it from leaking and you might be able to add a back up plate inside the transom.

Wave or 14? The 14 would be a good trainer, but the Wave is easier to sail. Not much racing available in either. If it is a time on the water sort of thing and his skills are not quite there... Wave. If he is competent I think the 14 might be a good choice.