Propeller & Sistem Perporosan

References :Introduction to Marine Engineering

Marine Auxiliary MachineryMaritime Engineering Reference Handbook

Marine engineeringPrincipal of Naval Engineering

Dedi Budi Purwanto ST.,MT.

Sistem Permesinan

Introduction

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Sistem perporosan penggerak utama peralatan yang diperlukan untuk mengubahtenaga putar yang dihasilkan main engine kedalam daya dorong kapal bergerak

Sasaran :

Menyalurkan tenaga dari main engine ke propeller

Menyangga alat penggerak

Menyalurkan gaya dorong yang dihasilkan oleh propulsor ke badan kapal

Mampu menerima beban operasional sesaat (kec.tinggi saat maneuver)

Bebas dari gangguan getaran

Dapat di andalkan untuk seluruh daerah operasi kapal

Sistem pemeliharaan yang rendah

3 Poros yang terletak di dalam kapal dinamakan line shafting sedangkan bagian porosyang diluar badan kapal disebut wet shafting dirancang berbeda tergantunglokasinya

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Untuk mengontrol bocor/banjir di pasang watertight bulkhead di dalam kapal stuffing box dipasang menembus bulhead

Bantalan berfungsi menyangga poros dalam keadaan kelurusan poros antara main engine dengan propeller

Line shaft bearing

Steady bearing

Spring bearing

Stern tube bearing

Strut bearing

Gaya dorong propeller di salurkan ke badan kapal dengan sebuah thrust bearing, bilamain engine menggunakaan reduction gear dipasang didepan maupun dibelakang darislow speed gear

Pertimbangan dalam Penyusunan

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Posisi ME ditetapkan pada saat tahap preliminary design

Pemilihan main engine (rpm) reduction gear??

Jumlah main engine

Sistem transmisi

Konvensional

Electric propulsion

Lokasi motor induk

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Lokasi propeller dihitung berdasar diameter propeller, clearance yang cukup antarapropeller dan baseline kapal, clearance yang cukup antara propeller dan badan kapaldan pada bidang letak propeller

Lokasi propeller

Tipe gaya getaran yang ditimbulkan opropeller

Naik turunya tekanan padabadan kapal karena naikturunnya tekananhidrodinamik yang disebabkan daun propeller

Naik turunnya gaya padabantalan propeller dan poroskarena wake iregularty(wake tak teratur)

Naik turunnya gaya yang ditransmisikan melewatisistem perporosan terutamadisebabkan oleh wake iregularty.

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Kemiringan pemasangan poros ( kearah vertical) diijinkan

Untuk kapal dengan propeller 2 atau lebih (kearah vertical dan horizontal)diijinkan

Shaft rake

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Metode pelepasan poros untuk pemeriksaan atau reparasi harusdipertimbangkan saat membangun susunan poros

Shaft with drawl

Perancangan Poros

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Material poros

Material

mild steel

High strength steel

Untuk high power, tetapi untuk wet shafting memakai mild steel

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Faktor yang menentukan lokasi jumlah bantalan poros;

Ships structure & arrangement

Equality of the line shaft bearing reaction

Bearing unit load and L/P ratios

Shafting flexibility

Lateral vibration natural frequency

Bearing location

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Sambungan poros dengan poros lain memakai bolted flange coupling atauremovable coupling

Shaft Coupling

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Gerakan axial poros relative terhadap elemen yang fix pada badan kapal harusdipertimbangkan menetapkan clearance antara propeller-hub dengan stern frame, antara rumah bantalan dengan elemen yang berputar.

Faktor yang berpengaruh:

Thrust bearing clearance

Gaya dorong propeller

Submerge pressure

Hull hogging & sagging

Perbeadaan temperature

Shaft axial movement

Bearing (Bantalan)

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Line shaft bearing bantalan yang terletak didalam kapal pelumasan minyak

Thrust bearing

Steady bearing / Spring bearing

Outboard bearing pelumasan dengan air atau minyak

Stern tube bearing

Strut bearing

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The propeller thrust is transmitted to the hull by thrust bearing.The main thrust bearing may be located either forward or aft of the slow speed gear

Thrust bearing: absorbs the axial thrust transmitted by the propulsion shaft from the propeller and delivers this thrust to the hull of the ship

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Line Shaft bearing

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Type Bearing

Plain bearing

Tilting pad bearing

Roller bearing

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1. By a lignum vita bearing

2. By a white metal bearing

Outboard bearing

The two usual methods of supporting the propeller shaft in the stern tube are:

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Oil lubricated outboard bearing

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Oil Lubricating

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Water lubricated outboard bearing

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Sea water Lubricating

Bulkhead stuffing boxes are installed where the shafting passes through bulkheads. This is to control flooding, in the event of a casualty.

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Accurate alignment ( Bearings, mechanical seals, packing, and couplings) vital to the operating life of rotating equipment.

The proper shaft-to-shaft distance must be maintained, particularly when a limited end float coupling is being used

Torsional effect, or machine torque, may also need to be considered when aligning the equipment.

It has been found that 50 to 70% of all vibration problems in machines are caused by misalignment

Shaft Alignment

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Types of Misalignment

There are two basic types of misalignment: parallel (or offset) and angular.

Both types can be found in the vertical and horizontal planes.

Typically, a combination of offset and angular misalignment is found in both directions.

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Indications of Misalignment

Some of the indications of misalignment are:

Excessive vibration

Excessive bearing temperature

Noise

Bearing wear pattern

Coupling wear

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The four most popular methods of controlling shaft alignment are:

the gap and sag method

optical or laser sighting

jacking

the strain gauge (bending moment) method.

These methods can be used either singly or in combination.

Controlling shaft alignment

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The gap and sag method uses pre-calculated flange measurements to establish the alignment, to be carried out whilst the flange couplings are disconnected.

The advantages of this method include the simplicity of the measuring equipmentand the ease of control in both the horizontal and vertical directions.

The disadvantages are limited accuracy and the lack of applicability in the service condition.

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Gap and sag method

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The optical sighting or laser sighting methodIs more accurate than the gap and sag method. It uses high-quality sighting equipment and is generally used before the shafts are installed and coupled up.

Optical sighting is often used to establish the reference line and the position of the engine supports and for determining how to borethe stern tube.

Alignment and verification follows by means of the gap and sag method and finalalignment control by the jacking and/or strain gauge method.

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Optical sighting or laser sighting method

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The jacking method lifts the shaft line clear of each bearing in turn by means of a hydraulic jack and calibrated load cell. The shaft is lifted in steps, whilst deflections are recorded on a dial gauge and plotted against the applied load.

This method uses simple equipment and is employed when the shaft line is coupled up, ready for operation.

However, it is not suitable for the control of horizontal alignment and the yard may need to arrange for special supports for the jacks. Finally, as the jacks have to be positioned beside the bearings, adjustments have to be made to therelevant calculations to evaluate the true bearing load.

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Jacking method

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The strain gauge method requires a combination of computation and strain measurements.

If a shaft line rests on a number of bearings, a theoretical distribution of bending stress may be calculated.

If the bending stresses, determined from the measured strains at an appropriate number of stations, deviate from the theoretical, this is taken to be caused by an alignment that differs from the theoretical straight-line case.

Using the strain gauge method, both the horizontal and the vertical direction may be controlled. Loads on normally inaccessible bearings can sometimes be determined. Readings can easily be taken after the gauges are fitted, and the effects of oil film formation and propeller thrust may be studied.

The disadvantages are that the method requires the skilled fitting and operation of strain gauges and suitable data acquisition and analysis software and time is required for calculations after taking the strain readings.

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Strain gauge method

Reduction Gear

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Reduction gear is needed for medium and high speed engine proplusion drives, to bring the propeller efficiency to a reasonable level.

Reduction gear size is described with the distance between input and output shaft.

Gear ratio is = driving shaft speed divided by driven shaft speed = inverse ratio of their teeth number. Reduction gear ratio is always >1.

Shaft generator drive is often connected to the reduction gear. In some cases shaft generator drive is very complicated

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Propeller

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Pemilihan tipe awal perancangan kapal

Mayoritas propulsor yang digunakan dikapal tipe Fixed pitch propeller

Tipe propeller :

Fixed- pitch propellers

Controllable Pitch Propellers (C.P.P.)

Propeller in Nozzle

Contra-rotating propeller

Contra rotating propeller

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Hampir semua propeller di buatdari pengecoran tunggal

Eumumnya mempunyai efisien, biayadan kesederhanaan disbanding tipeyang lainnya

Mempunyai mekanisme didalamhub yang dapat dikendalikan darijauh u tuk merubah pitch propeller

Pitch dapat diubah saat propeller berputar

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fixed pitch propeller Controlable pitch propellers

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Pump jet

Propeller diletakkan padanozzle

Kort nozzle

Mempunyai keuntunganeffisiensi dalam aplikasi bebanpropeller tinggi tug boat, fishing vessel, large slow speed ship

Banyak digunakan pada tug boat bollard oull dan towing bertambah 30~40 %

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Propeller in Nozle

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Contra-rotating propeller

Baling-baling jenis ini mempunyai dua-coaxial propellers yang dipasang dalam satusumbu poros, secara tersusun satu didepanyang lainnya dan berputar saling berlawananarah.

Overlapping propeller

Konsep dari baling-baling ini adalah duapropeller tidak dipasang/diikat secaracoaxially, tapi masing-masing propeller memiliki sumbu poros pada sistemperporosan yang terpisah

Ship's propulsion layout

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All commercial ships have a common thread. Within the ship, there is a power plant and, generally, a propeller which converts mechanical energy into motion in turn propelling the ship through the water.

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Deep sea vessels

The engine is generally a slow speed two stroke engine, such as a B&W or Sulzer. It is directly connected to the propeller shaft.

This set up is simple, efficient and "easy" to operate and maintain.

Specialized vessels

Two four stroke, medium speed engines are used here for their low size to power ratio

Having two engines also offers a level of redundancy. They can be operated simultaneously or individually because of the clutch.

The gear box will compensate for the high speed of the engines and allow the propeller to turn a more efficient slower speed

This setup is very common on medium size specialized vessels, such as Stand By Vessels (AHST) Research, cable ships and such

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Coastal vessels

One four stroke medium speed Diesel engines which is geared and can berun without turning the shafting because of the clutch.

The CPP offers aresponsive level of control and reverse! The set up is straight forward and easy to maintain.

This set up is common on larger fishing boats, coastal freighter, some

medium size tugs (~4000 hp).

Small boats

The Diesel engine can be a two stroke or a four stroke. It is almost always a high speedengine which requires the marine gear

The gear has a built in clutch, actually two clutches, one for forward and one to obtain reverse.

The gearbox also has the thrust bearing built in.

The fix pitch propeller is attached to the end of the shaft.

This is typical set up of small vessels. Yacht, tugs, fishing boats, small ferries etc.

It is very common to see this in vessels having less than 2000 hp.

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Cruise ships

The engines are usually four stroke medium speed engines, this isbecause of their bigger size to power ratio

The propulsion is done via electrical motors which are built into pods controlled by cyclo-converters

Icebreakers

They require large horse power but often encounter shock loadingfrom hitting big pieces of ice and such. Diesel engines do notappreciate shock loading.

The motors are controlled by two cyclo-converter. Cyclo-converters are a web page unto themselves, but basically,allow the electric motors to turn, forward or reverse, at any given power (speed) required

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Double ender ferries

They carry large quantities of vehicles andpassengers on short runs in calm waters

The shafts are quite long, as they must go to both ends of the ship down the centerline; and they clutched as well, to allow both engines to drive one shafts or both.

With a CPP system as well, and two rudders, this type of vessel is veryresponsive.

Naval vessels and tankers

Naval vessels and other military ships have other priorities than fuel

The power feeds into the gear box reducing the rpm, then into a propeller

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