Neither would I anymore...
The problems start at launch. Shorter ships such as Visby and the Indonesian trimaran can have hullform proportions and interactions with the seaway that mean that the most significant load case for the hullform structural design may not in fact be longitudinal bending, as is the case for a larger hullform. In some cases, the local loading due to engine installations etc may be far more significant.
This means that unconventional materials such as composites can be used as the bending loads are much less severe. Build a frigate out of composites and suddenly we are using the materials in a new way, where the anisotropic nature of composite strength, fatigue resistance etc will greatly complicate structural design.
Of course, this is not to say that one could not build a large vessel from composites - rather that it increases the risk, and thus expense, associated with doing so.