Raft mounting consists of a sub-frame (the intermediate mass) to which major noise and vibration sources, typically the main engines and generator sets, are resiliently mounted. This sub-frame is then, itself, resiliently mounted to the ships structure. Control characteristics are dictated by the mass of the raft and choice of upper and lower stage mounts. The intermediate mass can be quite large (capable of exceeding 50% of the controlled mass), and results in a taller foundation. Consideration must be given to the integration of rafts in terms of weight, girder strength, and engine room height when fitted.