VV hard to comment without knowing the type of vessel , its hull layup and the temperature of the water where she lives. If when inspected out of the water there are no obvious blisters I would not be too concerned about the underlying laminate. An often overlooked area is has the bilge had water / diesel lying in it for any period ? His best bet is to try and talk to other owners of sisterships -that will often point the way for further investigation or if it is warranted.