basically for products with "minimal risk" the manufacturer prepares a declaration of conformity and labels the products with the CE Mark. (Self certification). If the product is found to not meet the requirements of the relevant directives then the product is withdrawn from the market and the manufacturer fined.
for products with greater risks they have to be indepedently certified.
I didnt see what size of boats require to be independently certified though.
basically the CE product means that the product meets the relevant EU legislation for that type of product. So you have to determine which legislation is relevant.
i guess that one of them is 94/25/EC
Directive 94/25/EC of the European Parliament and of the Council of 16 June 1994 on the approximation of the laws, regulations and administrative provisions of the Member States relating to recreational craft link
if you are going to manufacture a series you really should find a consultant to advise you on this while you are still in design stages.