For a single GRP skin hull over a male mould, the building of the mould follows the same procedure as for a cored hull. Instead of using a PVC foam core you will now use cheaper urethane foam which is removed once the hull is turned. This is a rigid foam and is purchased in sheet form similar to PVC. It is usually removed with a shovel and the interior of the hull has to be sanded in preparation for further laminating, stringers, bulkheads etc.
Single skin may be a bit cheaper to build than sandwich but there are a lot of advantages in using sandwich so consider all aspects and design features before deciding which you will use.
