Functional and constructional difference between torsional and axial vibration dampers:

Torsional vibration damper: A torsional vibration damper (or detuner) is fitted to the free end of the crankshaft (or on the flywheel) to control torsional vibration - the twisting oscillation of the crankshaft about its axis caused by the periodic torque from the cylinders. Construction: it consists of a heavy inertia ring (a flywheel-like mass) connected to the crankshaft hub by a rubber element (or by a viscous fluid, e.g. silicone oil, in a viscous damper). Function: the inertia ring tends to remain at constant speed while the crankshaft twists; the relative motion between the ring and the hub is resisted by the rubber/fluid, which dissipates the vibrational energy as heat, damping the torsional oscillation. The damper is tuned so that its natural frequency absorbs the critical torsional frequency of the crankshaft, preventing resonance and the high stresses that would otherwise crack the crankshaft.

Axial vibration damper: An axial vibration damper controls the axial (fore-and-aft) vibration of the crankshaft - the longitudinal oscillation of the shaft along its axis, which is a separate mode of vibration. Construction: it is fitted at the free end of the crankshaft and consists of a mass (a heavy ring/plate) connected to the shaft by a spring/rubber element, arranged so that the mass can move axially relative to the shaft. Function: the axial motion of the mass is resisted by the spring/rubber, damping the axial oscillation of the crankshaft and preventing the axial vibration from being transmitted to the engine structure and the thrust bearing. It reduces the axial vibration amplitude and the associated stresses.

Difference: The torsional damper acts on the twisting (rotational) oscillation about the shaft axis, using an inertia ring and a rubber/fluid element; the axial damper acts on the longitudinal (fore-and-aft) oscillation along the shaft axis, using a mass and a spring/rubber element. Both dissipate energy to control the respective vibration mode.

Function of the side and top bracing of the main engine:

The main engine is braced to the ship's structure to control the vibration and the forces transmitted to the hull.

Side bracing: The engine is braced laterally (athwartships) to the ship's side structure by side stays/braces. Function: to control the transverse (lateral) vibration of the engine and to transmit the lateral forces (from the engine's inertia and the propeller) to the ship's structure, preventing excessive lateral movement and vibration of the engine and reducing the stress on the engine bedplate and the hull.

Top bracing: The engine is braced at the top (the upper part of the engine, e.g. the cylinder head/entablature) to the ship's structure by top stays/braces. Function: to control the fore-and-aft and lateral vibration of the top of the engine, which would otherwise sway, and to transmit the forces to the hull, reducing the vibration of the engine and the hull and preventing damage to the engine and the exhaust system. The top bracing also helps to control the axial vibration of the engine.

Both bracings are designed to be adjustable (with turnbuckles) and are set to a specific preload so that the engine is held firmly but not over-constrained, allowing for thermal expansion while controlling vibration.