The size and design of the subbase depends on the engine involved and its use. In many installations, the engine and the mechanism that it drives are mounted on a common subbase. One advantage of mounting both units on a common subbase is that misalignment is less likely to occur than when the units are mounted separately. Diesel-driven, electrical generator sets are usually secured to a common subbase. A different type of mounting or subbase involves the use of handfitted chocks, or blocks, between the engine and the supporting structure of the ship.
Bolts are the devices used to secure the engine rigidly in place and to maintain alignment.
The securing devices that are used to fasten a subbase to the structure of a ship may be classified, in general, as rigid or flexible. Engines that drive auxiliary equipment such as fire pumps or generators 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 used between the subbase of a generator set and the structure of the ship. Flexible devices may also be placed between the engine and the subbase.