Mould making alternatives - can you lay carbon fibre hull directly onto plug

Things might get interesting in the wrong way if you try to use prepreg without ascertaining that the chosen foam will withstand the moulding conditions.Most prepregs cure at 120 degrees and you absolutely have to ensure that your foam will not collapse if it is inside a vacuum bag at that temperature.A small test piece subjected to the moulding process will establish the likelihood of a successful outcome.Alternatively you might be able to find some LTM prepreg for a lower temperature cure,but again it would be sensible to verify that your foam will maintain it's shape.

Your proposed wet layup with bagging should be a lot less risky for the protoype.You will always have the option of using the mould to create a heavy component at a a later stage which can be used as a plug and which will save the considerable work of achieving a quality finish on a newly machined plug.Good luck.