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Transmissions - Coggle Diagram
Transmissions
Shaft Components
Plummer Block - support the weight of the shaft without absorbing any thrust, bolted cast steel frame, white michell pads and self contained by a ring bath lubrication system that drains down to a sump, must spin at 50 RPM
Michell Bearing - carries a load upon dynamic oil films generated by a series of pivoting white metal pads
Bulkhead Glands - maintain watertight integrity when passing through compartments, without absorbing any thrust, metal bearings lubricated by pumped grease allow for flexibility
Stern Seal - maintains watertight integrity as the shaft passes through the hull, uses a mechanical seal consisting of a rotating and stationary face held by spring bellows, also containing an emergency inflatable seal
Main and Intermediate A- Brackets - support the shaft outside the hull without absorbing any thrust, lubricated by the Hydrodynamic principle at 50 RPM
SKF Coupling - designed to separate the intermediate and tail shaft without leaving a flange, so the tail shaft can be withdrawn through the A brackets and stern seal
The SKF coupling uses an inner and outer sleeve that form an interference fit between the shafts via high pressure oil (hydraulic) between the two which is then released
GEARBOXES
They transmit power from the prime mover to the output shaft, allow for variations in speed / power and reverse thrust
Straight Spur - teeth are parallel to the shafts they're mounted on, provide low speed and are noisy
Helical - teeth are cut at an angle providing smoother meshing, useful for high speed applications and are quieter, but produce axial thrust, requiring bearings and additional wear
Double Helical - Negate Axial thrust and can be directly interchanged with straight spur gears without the need for bearings
Worm Wheel - aligned at 90*, resembling a screw with helical teeth, mating with a straight spur gear to provide a higher gear reduction and an auto lock function
GEAR REDUCTIONS
The aim of gear reductions is to reduce a primary input, e.g from a gas turbine to a manageable propellor speed
Single Gear Reduction - uses a pinion and primary wheel to reduce input, limited to a 15:1 gear ratio
Double Gear Reduction - increases the number of meshing gears, increasing overall gear reduction and allowing for smaller gears / gearbox
Dual Tandem - the loadings halved, allowing for smaller gears and further gear reduction and to combat any misalignment quill shafts are fitted
Gearbox Ancillaries
Shaft Brake - stops and holds the propellor shafts, gearing and power turbine while at idling speeds, providing checks are conducted, brake pads bolted to the upper quill shaft are applied by compressed air
Thrust Block - comprises of a thrust bearing, machined collar and michelle pads, it's purpose is to absorb the propellors hull
Turning Gear - drives the propeller shaft via the quill shaft, used for rotating the shaft for docking or for maintenance purposes, with propulsion provided by an electric motor / hand (worm and wheel), auto lock useful
Propellor Types
Fixed - blade angle cannot change, high efficiency when at high power, but underutilised when not and when going astern
CPP - pitch angle of the blades change to move ahead / astern hydraulically, taking up less room than a reversing gearbox