yup, i made a hull in 2 halfs. it was a fantasy style vessel, , the original was sculpted and then i made a mould in plaster, i used a hard dental style plaster,
i then laid up a GRP hull from the plaster mould, , finer details such a hull plate lines were generally ok, one of two sections of plate lines were not perfect, but were sorted with dremel and tools !
downside of plaster is they are generally only any good for one GRP hull - so if you wish to make several the quality drops off quickly, small details may be compromised,
you must use release agents- the righto nes in the right quantity- plaster is very porous !
positives are you can layup some unusual shapes with a plaster mould- inlcuing major undercuts the mould can be split/ broken/ cracked off - hence plaster moulds are often referred to as a waste mould.....
plaster is cheap and can set quickly
ideal for mock up or test moulds.......
good look