5-31. The securing devices used to fasten a subbase to the structure of a ship may be generally classed as
rigid or flexible. Propulsion engines are secured rigidly to avoid misalignment between the engine, reduction
gear (or other driven mechanisms), and propeller shaft. Engines which drive auxiliary equipment may be
secured by either rigid or flexible devices. In installations where rigidity is of prime importance, bolts are used
as the securing devices. Flexible securing devices are generally between the subbase of a generator set and the
ship’s structure. Flexible devices may be placed between the engine and the subbase. Although flexible
devices are not necessary for every type of generator set, they are desirable for generator sets mounted near the
side of the hull to reduce vibration. Flexible devices also aid in preventing damage from shock loads imposed
by external forces. Two general types of flexible securing devices are the vibration isolator and the shock
absorber. Both types may be incorporated in one device