Marine Engineering Lec 4

8/18/2019 Marine Engineering Lec 4

1/23

Marin EngineeringMarin Engineering

Lec. 4Lec. 4

Dr. Arwa HusseinDr. Arwa Hussein


2/23

Transmission Line


3/23

The purpose of a thrust block on a large marine engine is to transmit the

torque produced by the rotating propeller through the housing hold-down

bolts into the ship’s structure.

Thrust Block


4/23


5/23

• The structure under the thrust block is reinforcedwith steel plates and I-beams above and inside the

double bottom tanks or cofferdams.

• The thrust block itself consists of a housing which

contains a number of wedge-shaped white metaledpads with generous helical oil grooves cut intothem.

• The pads are arranged and fixed around a steelsupport, holding them against a machined collar onthe drive shaft.


6/23

• The pads are prevented from overheating andpremature wear by a fluid film of oil between them

and the collar, with the oil supply being hydrodynamic(self-pressuried! due to the rotation of the drive shaft.

• There is an oil reservoir in the bottom of the housingwhich may contain an oil-cooling coil through whichseawater is circulated.


7/23


8/23


9/23


10/23


11/23


12/23

"ropeller #rive $haft• The propeller shaft is bolted to the main engine flywheel, passing through

the thrust block then along the shaft tunnel. %ere it is supported by theshaft bearings before passing through the stern tube to drive the ship&s

propeller.


13/23

• The shaft is manufactured from forged steel, complete with

coupling flanges. It is machined leaving a larger diameter at the

location of the shaft bearings' this section has to have a fine finishto run within the white metal bearing.

• The shaft coupling flange faces are accurately machined and the

bolt holes reamed to accept fitted bolts. They are bolted together

using high tension bolting, which is tightened using hydraulic

tensioning gear.


14/23

• The supporting bearings are cast in two halves and are

usually white metal lined. These have oil scrolls cut into

them to distribute the splash lubrication.

• owadays ball bearing shaft supports are being used,

but they have been reported as being )uite noisy with a

tendency to run hot


15/23

$tern Tube


16/23

• The stern tube, as the name suggests, is a hollow tube-likestructure at the stern or rear part of the ship. * ship needs apropeller to drive it forward against the waves.

• The propeller, located outside the ship, needs to be connected tothe engine inside the ship+s engine room.

• * long shaft known as the propeller shaft is used for connectingthe ship+s engine and the propeller.

• The stern tube is a narrow hole in the hull structure at the rearend (aft peak! of the ship, through which the propeller shaftpasses and connects the engine and propeller.


17/23

• The stern tube is used to support and seal the propeller shaft as it passesthrough the aft hull.

• It consists of a cast iron tube welded into the stern frame. In the old days,the shaft inside the tube was brone coated and run against a longitudinalbearing.

• %owever nowadays, the propeller shaft has a I (copper nickel alloy!liner shrunk onto it. Babbitt metal is applied over this and then machined,providing the bearing surface between the cast iron stern tube and thepropeller shaft.


18/23

• It is lubricated and cooled by lube oil supplied from agravity tank located under the aft peak. The propeller shaft

has mechanical andor ad/ustable gland seals fore and aft toprevent the ingress of oil to the sea and the aft bilge well.


19/23

Sealing arrangement of sterntube• The lubrication system for ships with variable draught (due toloading and unloading of cargo) consists of header tanks located at

around to ! meters above the water line so that the differential

pressure ensures no water ingress.

• "ifferent sealing arrangements are used to prevent water ingress andoil leakage. They are as follows#

– $tuffing boxes consisting of packing material.

– 0ip seals in contact with shaft to prevent passage of oil or water alongthe shaft.

– 1adial face seals supported with springs fitted radially around the

shaft$ aft bulkheads and after end of the stern tube.


20/23

Stung Box


21/23

0ip seals

• %adial shaft seals$ also known as lip

seals$ are used to seal rotary elements$

such as a shaft or rotating bore.

&ommon e'amples include strut seals$

hydraulic pump seals$ a'le seals$ power

steering seals$ and valve stem seals.


22/23

Radial face seals

• face seal is a seal in which thesealing surfaces are normal to the

a'is of the seal.

• ace seals are typically used in staticapplications and are used to prevent

leakage in the radial direction with

respect to the a'is of the seal.

• ace seals are often located in agroove or cavity on a flange.


23/23

End of LectureEnd of Lecture

Marine Engineering Lec 4

Documents

Transcript of Marine Engineering Lec 4