Home » » Describe a single collar thrust block. How would it be fastened to the ship hull?

Describe a single collar thrust block. How would it be fastened to the ship hull?

Describe a single collar thrust block. How would it be fastened to the ship hull? How would
it compare with a multicollar thrust block? What care and attention does it require and how is
clearance measure?

The thrust shaft is connected to the main engine crank shaft. In the case of a direct drive
reciprocating engine, to the main gear wheel shaft. In geared installation; it functions as well as
transmitting the engine torque also to the next shaft, is to transfer the thrust of the propeller, to
the thrust block, which being securely fitted to the hull of the ship. The shaft is comparatively
short with a coupling at each end a thrust collar in the middle of its length and a ? at each side
of the thrust collar.

The journals run in bearings housed in the thrust block which is secured. Each side of the collar
bears upon a number of kidney shaped white metal faced pads supported in the thrust block
those on the forward face of the collar being to take the astern thrust. The back of each kidney
piece has a hump or step to allow the pads to pivot and the slightly so that the lubricating oil,
picked up by the collar from the bottom of the block can squeeze its way as a wedge shape film
between the pad and collar surface and be dragged over the whole surface. Thus there is always
a film of oil maintained between the faces and there is consequently no metallic contact.
Thrust pressures in the region of 24 bar can therefore be carried without danger of overheating
due to friction. Particular attention is giving to the strengthening of the structure of the double
bottom heavy loads be supported and vibration minimized, but the thrust from the thrust block
is to be transmitted to ship’s hull.

All structure below the boiler and engine rooms is increased in thickness, additional longitudinal
girders are incorporated so that they are pitched closer together, all girders have double angles
and all parts are bearing fit. A tank top plate of extra thickness ( 40mm or more ) runs
continuously from under the engine bedplate to under the thrust block seating, the forward
edge of the thrust block base either contacts the engine bedplate or chocks are fitted to have
the same effect of spreading thrust load over a greater area of the ship’s hull.

Chocks are also fitted at the after edge of the thrust block. Most medium diesels have the thrust
block as an appendix to or integral with the engine. When the engines are going ahead the
thrust force is taken up by the surface of collars. This reduces the length of the block and it will
be obvious that this is not a drawback as the engines only need to run astern for short period.
The thrust block is secured to the hull of the ship by means of a pedestal made up of plates and
angle iron, the hull being strengthened at this part so to transfer the thrust and distribute it over
the hull. The shoes are usually held in position by large adjusting screws each shoe having
separate jam nuts to permit the load to be distributed evenly over the various collars. The faces
of the shoes are usually filled with white metal which permits about 70lbs per sq in of effective
surface when the engine are running at full speed ahead.

On many ships the shoes are water cooled while on others they are contained in an oil bath. the
modern Mitchell thrust block only one collar, the collar having kidney pieces or rolling fitted,
and the pressure that can be carried may be as high as 500psi this style of thrust is fitted in all
modern ships having either turbine, reciprocating or diesel machinery, as the friction is greatly
reduced and the size and weight of the thrust block is greatly reduced.

Base and covers are made of cast iron, while the bearing at each end are made of gunmetal.
Lubrication carried out by means of an oil scraper, fitted in the collar which intercepts the oil
brought up by the rotating collar from the oil bath below, so forming a cascade of oil over the
thrust pads. The end bearings are self lubricated and oil deflecting rings are fitted at each end to
prevent oil escaping.
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