Thrust Block Position & Support :-

Main thrust block is placed closed to the propulsion machinery in order to reduce any problem due to differential expansion of the shaft and the hull. The low hull temperature of midship engined refrigerated cargo ships can cause a contraction of upto 20mm relative to the shaft whereas water temp, change or heating of fuel tanks can cause expansion of hull. Other problems include whirling of tail shaft, relative movement of the hull and misalignment due to droop from propeller weights. Deformation produced by the thrust load can cause misalignment problems, unless suitable stiffening is employed (particularly with an end of gearbox installation).

Support :-

The substantial double-bottom structure under the main machinery provides an ideal foundation for the thrust block and is the reason for siting the thrust block close to the engine. The upright thrust block and any supporting stool must have adequate strength to with stand the effect of loading which tends to cause a forward tilt. This results in lift of aft journal of the block and misalignment of the shaft. Axial  vibration  of the   shaft   system,   caused  by  slackening of propeller blade load as it turns in the sternframe or by the play of diesel engine crankwebs, is normally damped by the thrust block. Serious vibration problems sometimes cause thrust block to rock, panting of the tanktop and structural damage.

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