ENGINEERING KNOWLEDGE MED3

(Contains extracts & edits of material courtesy of A.N.T.A.  publications, update version Ranger Hope © 2008,)

 

Operating Marine Diesel Engines                                                                                             

                     1.1 Checks And Procedures Before Starting Engines                                       

                     1.2 Checks To Be Made If An Engine Fails To Start                                           

                     1.3 Warm Up And Cool Down Periods                                                                  

                     1.4 Engine Overheating Symptoms                                                                       

 

Slipway Work                                                                                                                                 

                     2.1 Periodic Maintenance And Survey For Commercial Vessels                     

                     2.2 Preparations And Inspections                                                                          

                     2.3 The Function Of Sacrificial Anodes                                                                

                     2.4 Measuring Sterntube Bearing And Tail Shaft Wear                                     

                     2.5 Opening Side Valves For Survey And Maintenance                                   

                     2.6 Checking Rudder Stock And Pintle Bearing Wear                                       

                     2.7 Attaching The Propeller To The Shaft                                                             

 

Deck Machinery                                                                                                                             

                     3.1 Operation Of An Anchor Windlass And Cargo Winch                                 

                     3.2 Dangers Of Incorrect Operation                                                                       

                     3.3 Routine Maintenance                                                                                        

 

                    

 

                                                                                                                                                           

 

 

 

 

 

 


Operating Marine Diesel Engines

 

1.1  Checks And Procedures Before Starting Engines

 

The checks and procedures to be carried out before starting an engine depend on:

 

•        whether the engine has just been repaired or overhauled and

•        whether you were the last person to run the engine.

 

The person with the Certificate of Competency to operate the machinery of the vessel is the one who takes full responsibility and cannot transfer the blame if something goes wrong. To cover yourself you must carry out pre-departure checks and checks whilst the vessel is under way. The following checks cover the engine.

 

ό

Checks

 

Ensure that all work carried out to the engine has been completed and that there are no tools, materials or parts lying on the engine.

 

Ensure that there are no rags on the engine, especially the exhaust area. Check the whole engine is free from fuel and lubricating oil.

 

Gear box is in neutral.

 

Sea water strainer is clean and open the sea connection valve and, if fitted, the overboard discharge valve. Ensure there are no sea water leaks.

If the vessel has been on the slip, it may be necessary to bleed off any air at the sea water pump.

 

Water level in the fresh water header tank and ensure there are no fresh water leaks.

 

Condition of all hoses.

 

Sufficient fuel in the fuel tank for the intended voyage plus a reserve amount of fuel.

 

Open the fuel tank drain valve and drain off any sediment and/or water.

 

Open the fuel tank outlet valve.

If repairs have been carried out to the fuel system on the engine, it may be necessary to prime the fuel system and bleed off any air.

 

If a water separator is fitted, drain off any accumulated water.

 

Check the movement of the hand throttle.

 

Check the oil level in the sump shows full. In some engines, a hand priming pump is fitted so the system may be primed and prevent the major wear that takes place on starting an engine.

 

If the fuel injection pump has its own sump, check that the level in the sight glass is at the upper line.

 

If a turbo charger is fitted and has its own lubricating system, check that the level in the sight glass is at the upper line.

 

Check that the batteries are clean, charged, the electrolyte level is above the plates and the terminals are clean and tight.

 

If it is possible, bar the engine over at least one complete revolution.

This is carried out to ensure there is no fresh water in a cylinder which could hydraulic the engine. It is also to ensure the engine can turn over freely and nothing has been left in any of the cylinders and all parts are back and are in proper working order.

 

Switch on power to the starter motor. Give the engine some throttle. Engage the starter motor. The engine should rotate and fire.

 

Immediately check the oil pressure.

 

Listen for any unusual noises, especially hard metallic knocks.

 

Check for fresh water, sea water, lubricating oil, fuel oil and exhaust gas leaks. Ensure sea water is being discharged overboard. The engine fresh water temperature will slowly rise and stabilise at its operating temperature. The lubricating oil pressure will drop from its initial starting pressure to its operating pressure.

 

The revolution counter will be indicating. The throttle should be increased and decreased slightly to check its movement and that the revolution counter is functioning.

 

With the engine at its operating temperature, check the colour of the exhaust gas.

Black smoke indicates excessive fuel for the amount of air and caused by poor or insufficient combustion or engine overload.

Blue smoke indicates lubricating oil is being burnt.

White exhaust vapour indicates water or moisture. It may be in the fuel, moisture in the air or from cold cylinder liner bores when starting the engine.

 

1.2  If An Engine Fails To Start

 

This section lists some reasons for engines failing to operate correctly. There are many possibilities, so discuss these with your facilitator. Use this section as a reference guide for later use, particularly when next on your operating vessel.

 

 

Engine Will Not Start Or Is Difficult To Start.

 

If the engine does not start, the causes are mainly in the supply of fuel and/or air.

 

Remember:

 

1.      A full charge of air needs to enter the cylinder.

2.      This air must not escape as it is being compressed otherwise insufficient heat is obtained to ignite the fuel.

3.      Fuel must be injected in an atomised form into the cylinder at a precise moment.

4.      In addition, there must be no restriction in the flow of exhaust gases.

5.      An engine may fail to start, be hard to start or on starting, be irregular in its firing. It may be one or a combination of the above factors that is the cause of these problems.

 

 

Engine Not Turning Over Quickly When The Starter Motor Is Engaged

 

Battery capacity low

 

•        Check that electrolyte level is above the plates.

•        Try to start the engine on the other bank of batteries. Failing this, try to start the engine on both banks of batteries. Never continue to use a battery if the starter motor is sluggish. High discharge rates will buckle the battery plates.

•        Take the specific gravity of each cell of the battery. A fully charged battery would have a specific gravity reading in each cell of 1.26 where as a flat battery would give a reading of 1.10. The specific gravity reading should not vary more than 0.030 between cells. A lower reading on one cell usually indicates the battery needs replacing.

 

Battery connections dirty

 

•        Check that the connections to and on the battery is clean and tight. A dirty or loose connection can be identified by the heat it generates.

 

Bad electrical connection to starter motor

 

•        The starter motor draws the most load on the battery especially on diesel engines because of their high compression ratios. The electrical connections must therefore be tight and clean.

 

Faulty starter motor

 

•        The starter motor could be burnt out or the pinion is not engaging with the ring gear on the flywheel.

 

Incorrect grade of lubricating oil

 

•        If the oil is too thick, the engine will not attain sufficient speed on the starter motor to generate the amount of heat required on the compression stroke to ignite the fuel.

 

Engine has been overhauled and is tight

 

•        The parts of an overhauled engine are brought back to their correct clearances. In these clearances there will be a number of high spots and they will be worn away as the engine is run in. When the engine is run in, it will turn easily. The engine will not attain sufficient speed on the starter motor to generate the amount of heat to ignite the fuel.

•        There must be sufficient air and no restriction in the exhaust gas system.

 

Air cleaner restricted

 

•        The air cleaner is choked restricting all or most of the air required by the engine.

 

Exhaust gas restriction

 

•        Could be caused by a bucket left on the outlet of a vertical exhaust pipe to prevent rain water entering the engine or by the automatic flap valve fitted for this purpose and is stuck in the closed position.

•        Occasionally a baffle could come loose in a silencer and block the passage of exhaust gas.

 

The air must be compressed to a high enough temperature to ignite the fuel. This is usually due to low or poor compression. Compression pressure can be checked by replacing each fuel injector in turn with a compression gauge.

 

Poor Compression

 

Incorrect valve timing

 

•        The inlet valve is not opening or closing at the correct moment in the cycle because the engine has not been correctly timed after maintenance work has been carried out. (The timing of the exhaust valve would be out as well.)

 

Cylinder head gasket leaking

 

•        Could be leaking between two cylinders, between a cylinder and the outside of the engine or between a cylinder and a cooling water passage.

 

 

Fuel injector

 

•        The fuel injector body may not be sealing properly in the cylinder head allowing the compressed air to escape.

 

Incorrect tappet adjustment

 

•        The tappet adjustment is such that there is no clearance between the inlet or exhaust valve stem and the rocker arm. The inlet or exhaust valve is not closing on the compression stroke. (This is referred to as riding).

 

Sticking valves

 

•        The cam, through the cam follower, push rod and rocker arm, causes the valve to open. The spring causes the valve to shut when the cam follower moves off the lobe of the cam. A sticking valve is caused by combustion being incomplete or the engine is (or has) overheated. Carbon finds its way between the valve stem and guide until the spring cannot exert enough pressure to close the valve. On the compression stroke, air will pass the valve. It could be an inlet or exhaust valve.

 

 

Worn cylinder liner bores

 

•        Normal wear takes place on the cylinder liner where the piston rings come into contact with it. The wear is more pronounced near the combustion space where the heat burns the lubricating oil. The wear is also oval due to the thrust of the piston on the cylinder wall. The piston rings will not seal against the cylinder liner walls and, on the compression stroke, air will pass the piston rings into the crankcase.

 

Pitted valves and seats

 

•        The exhaust valve and seat is prone to being pitted. Carbon, from incomplete combustion, is hammered between the valve and seat when the valve closes. On the compression stroke, air will pass the valve.

 

Valves not seating correctly

 

•        Can be caused by the head of the valve being bent on its stem due to the head being too thin from continual grinding.

•        Can also be caused by exhaust gases scouring the valve seat and/or head. On the compression stroke, air will pass the inlet or exhaust valve.

 

Broken, worn or sticking piston rings

 

•        The piston rings expand and seal against the cylinder liner walls. Normal wear takes place and will in time become excessive. Piston rings are also subject to breakage in service or when installing. They will also stick in their grooves due to the carbon from incomplete combustion. In all cases air will pass the piston rings on the combustion stroke into the crankcase.

 

Piston ring gaps in line

 

•        Installation of the piston rings is such that the gaps were not equally separated or the ring gaps came into line during the running of the engine. Piston ring gaps in line will cause the air from compression to enter the crankcase.

 

Cold engine

 

•        Although not poor compression, the air entering the engine and the piston, cylinder liner and cylinder head are so cold that they take away the heat of the compressed air before it can reach sufficient temperature to ignite the fuel. If an engine is fitted with heater plugs, they can be utilised. Other alternatives are to use an air heater or a starting fluid to assist ignition of the fuel.

 

 

Fuel Issues

 

Fuel tank empty

 

•        Fuel piping could develop a leak emptying the contents of the fuel tank into the bilges.

 

Blocked fuel feed line

 

•        The suction valve on the fuel tank could have vibrated closed or someone could have closed the emergency fuel shut off valve.

 

Faulty fuel lift pump

 

•        Fuel is not being delivered from the fuel tank to the engine. If it is of the diaphragm type, the diaphragm could be perished or damaged.

•        The drive to the pump could be damaged.

 

Choked fuel filter

 

•        The fuel filter has choked up with foreign matter as to prevent the full flow of fuel. The filter may not have been changed at its recommended period. A bad batch of fuel may have been received. The filter may require changing at more frequent intervals until the system is clean.

 

Air in fuel system

 

•        Air is compressible where fuel is not. Air in a fuel system will cause the engine to malfunction or not start. Air usually enters the fuel system when repairs are carried out or where there is a fuel leak. This air must be bled off until a bubble free fuel is obtained. Some fuel systems have a manual priming handle on the fuel lift pump or on the fuel injection pump. In addition, there are bleed valves throughout the system, such as on filters or water separators.

 

Faulty fuel injection pump

 

•        The fuel pump is not delivering fuel to the injector.

 

Faulty fuel injectors

 

•        The valve pintle may be seized shut in its nozzle and no fuel is delivered to the cylinder. The holes or orifices in the nozzle may be blocked. The valve pintle may not be sealing on its seat causing misfiring and irregular speed, particularly on light loads.

 

Incorrect fuel pump timing

 

•        The fuel is not being delivered to the fuel injector at the precise moment in the cycle. The engine could have been overhauled and the timing of the fuel pump was incorrectly carried out. It is possible for the timing to alter whilst the engine is running due to insufficient tension on the fuel pump coupling bolts.

 

1.3  Warm Up And Cool Down Periods

 

Warm up and cool down periods are essential for assisting efficient engine operation and maintenance. All metals in marine engines expand when heated, and contract when cooled. Different metals will expand by different amounts. Thin metals will expand quicker than thicker metals of the same type when the same amount of heat is applied.

 

An engine consists of different types of metals and different thicknesses of the same metal. Castings, such as the block, cylinder head and cylinder liner must be uniformly heated up. If the heat is localised, this section will expand at a much greater rate than the remainder of the part and will most likely crack.

 

•        On starting an engine, it is necessary for it to remain at idle speed until the temperature normalises. The engine speed and load can then be gradually increased. The fresh water cooling and the lubricating oil help normalise the temperature of the engine. This is done by taking the heat away from the hottest part of the engine to heat cooler parts of the engine.

 

•        The majority of wear takes place in an engine when it is started cold. One of the purposes of lubricating oil is to put a thin film of oil between two moving metallic parts. This separates the parts and reduces friction and therefore wear.

 

•        The power stroke places a load on the bottom end bearing. The lower the revolutions of the engine, the lower the loading on the bottom end bearing and the combustion temperature. On starting, the engine should not be excessively speeded.

 

•        The thermostat in the fresh water cooling system ensures that the engine reaches its operating temperature quickly. This is done by distributing the combustion heat to the cold parts of the engine, thereby minimising unequal expansion.

 

•        If an engine is on full load and stopped quickly, the cooling water temperature will rise. This is due to the non-circulation of cooling fresh water and the heat retained in

         the metallic parts of the engine. The unequal contraction of these metallic parts has the same result as expansion and could cause cracking.

 

•        Should the engine be fitted with a turbo charger, it is necessary to reduce its speed in stages or slowly for two reasons:

 

          1.      Bearings of the turbo charger are lubricated by the main engine driven lubricating oil pump. The engine, on stopping, will cease to supply the lubricating oil to the turbo charger bearings. If time isn’t taken for the turbo charger to come to rest, damage could occur to the bearings.

 

          2.      The exhaust gas side of the turbo charger operates at a very high temperature. It is preferable to reduce the temperature gradually rather than quickly to prevent unequal contraction of the turbo charger parts as it slows down.

 

 

1.4  Engine Overheating Symptoms

 

In determining the cause of an engine overheating, consideration should be given as to whether it is a gradual process or there is a sudden rise in fresh water temperature.

 

An engine overheating can be identified by:

 

•        the fresh water cooling temperature gauge

•        the exhaust temperature and

•        by the operator’s sense of touch.

 

When tracing a fault it is helpful to follow the circuit or flow of the sea water cooling and the fresh water cooling systems, and think what may be wrong with each component that may cause overheating. Here are some possibilities:

 

A gradual rise is where the temperature rises over a period of time caused by wear; by a gradual build up of scale on the cooling water surfaces or a sea water strainer gradually becoming clogged.

 

A sudden rise in temperature could be caused by the thermostat stuck in the closed position, a pump impeller revolving on its shaft or the engine overloaded.

 

When the engine is hot and the fresh water level in the header tank is low, cold water should be introduced very slowly whilst the engine is running. The cold water will then be heated sufficiently before it circulates around the combustion space. Cold water suddenly coming into contact with the hot cylinder liner and cylinder head may crack them.

 

 

Sea Water Temperature Too High

 

An engine with poor compression usually results in the engine receiving more fuel to get the required power. This results in overheating and a high sea water temperature will

 

increase the problem. The engine speed should be reduced to bring the temperature back to its normal operating temperature.

 

 

Sea Water Intake Rose Or Grid

 

Could become clogged over a period of time so there would be a gradual increase in the fresh water cooling temperature. Reduce the engine speed until the normal operating temperature is obtained.

 

A plastic bag may get sucked onto the grid and a sudden rise in temperature would occur. Gradually slow down the engine to reduce the heat slowly and stop the engine. With no suction holding the plastic bag on the grid, and with the vessel moving through the water, the plastic bag will come away from the intake grid. Start the engine and let it idle until temperatures stabilise.

 

 

Clogged Sea Water Strainer

 

Could become clogged over a period of time so there would be a gradual increase in the fresh water cooling temperature. Reduce the engine speed gradually and stop the engine. Clean out the strainer. Start the engine and let it idle until temperature stabilises.

 

Alternately the vessel may have voyaged through matter which quickly clogged the strainer. Take the above action.

 

 

Thermostat Not Opening Fully

 

When the engine is cold the thermostat is in the closed position. Water is circulated through the engine only. As the engine reaches its operating temperature, the thermostat opens and allows the water circulating through the engine to pass through the fresh water cooler or the keel cooling pipes.

 

Should the thermostat stay in its closed position or not open fully, the engine will overheat. Feel the pipe from the thermostat housing to the fresh water cooler. This will indicate whether or not water is flowing through it. Reduce the engine speed gradually and stop the engine. When the engine has cooled down, replace the thermostat. Should you be at sea and have no replacement thermostat, the engine can be run without a thermostat. Start the engine.

 

 

Faulty Impeller In Sea Water Pump

 

A faulty impeller in the sea water pump (such as the rubber one in a Jabsco pump) could be damaged. Damage usually occurs when the pump is run dry. The discharge pipe would be warm and not at the same temperature as the sea water. Also, there would be no (or reduced) sea water discharge overboard. Reduce the engine speed gradually and stop the engine. Replace the impeller.

 

Should you be at sea and have no replacement impeller, it may be possible to reach port at reduced speed, if the impeller is only partially damaged and can still pump some water. Alternately, a sea water hose from the fire pump or the wash deck hose could be connected up to the system at the discharge side of the sea water pump to get the vessel back to port.

 

 

Keel Cooling Pipes Not Effective Due To Marine Growth

 

This causes a gradual increase in the fresh water temperature. Reduce the engine speed gradually until the normal operating speed is obtained. The vessel will have to be slipped to clean the keel cooling pipes.

 

 

Air In Sea Water Cooling System

 

On a lot of vessels, air is trapped in the sea water cooling system when the vessel re-enters the water after slipping. With the engine stopped, the air can be bled off by slackening off the backing plate on a Jabsco pump or loosening a join in the seawater cooling pipe on the suction side of the pump that is below the water line. If it is a Jabsco pump and it is run dry until the engine overheats, the rubber impeller will be severely damaged.

 

Insufficient Speed Of Sea Water Pump

On some vessels the sea water pump is belt driven from the engine. The adjustment of the belt may cause it to slip. Reduce the engine speed gradually and stop the engine. Adjust the belt tension. Start the engine and let it idle until temperature stabilises.

 

It may be that the pump does not attain sufficient speed as the driver or driven pulleys may be the wrong size. Reduce the engine speed gradually until normal operating temperature is attained.

 

 

Faulty Impeller In Fresh Water Cooling Pump

 

A faulty impeller in the fresh water pump could be damaged. Reduce the engine speed gradually and stop the engine. Replace the impeller. Should you be at sea and have no replacement impeller, it may be possible to reach port at reduced speed if the impeller is only partially damaged and can still pump some water.

 

 

Build Up Of Scale On Cylinder Water Jackets, Etc.

 

Fresh water contains impurities. They come out of solution at high temperatures and will adhere to hot surfaces. The hottest part of the engine is in the combustion space at the top of the cylinder. Scale will deposit on the cylinder liner walls in this area, on the passages to the cylinder head and around the exhaust valve. The scale will stop the transfer of heat from the combustion process to the fresh water cooling and, in the case of passages, will

 

restrict the flow. This will be a gradual process. Reduce the engine speed until normal operating temperature is attained.

 

 

Engine Parts May Be Too Tight Causing Friction

 

A new or overhauled engine normally runs hotter because it is tight. As the engine is run in, the high spots disappear. The engine turns easily, thereby reducing the operating temperature. Reduce the engine speed so that it runs at its normal operating temperature.

 

 

Fresh Water Cooling Level Is Too Low

 

A leak has developed in the fresh water system causing a loss of water in the header tank. It could be a leak in the piping, seal in the pump or a blown cylinder head gasket. Reduce the engine speed gradually and if the fresh water system is the unpressurised type, very slowly top up the header tank to its correct level.

 

If the fresh water system is of the pressurised type, reduce the engine speed gradually and stop the engine. Let the engine cool down further before placing a rag over the header tank cap. Turn the cap anti-clockwise until it reaches the position where the pressure is released. When the pressure is released, remove the cap. Start the engine and very slowly top up the header tank to its correct level.

 

If there is very little water in the header tank, it is advisable to stop the engine and let the engine cool right down before adding fresh water.

 

If possible, the leak in the piping should be stopped or the pump seal replaced.

 

 

Blown Cylinder Head Gasket

 

A cylinder head gasket leaking will be indicated by bubbles in the header tank. The extent of the leak will determine the amount of bubbles. When checking for bubbles, remember the above for pressurised and unpressurised systems. Whilst the engine is running, the pressures inside the cylinder exceeds that of the leak and the water. The heat will turn the water into steam and be discharged with the exhaust gases. However, when the engine is stopped, there is no pressure in the cylinder. The header tank is above the cylinder thereby putting pressure (a head) on the water. The water would then flow through the leak in the cylinder head gasket into the cylinder.

 

Should the piston be below top dead centre, sufficient water could flow into the cylinder and hydraulic it. The water level would drop in the header tank and the procedure would be the same as that above. However, remember that if the engine is stopped for a period of time, it may hydraulic the cylinder.

 

 

Air In Fresh Water Cooling System

 

Not normally an overheating problem when the engine is running. Air can get into the system when repairs are carried out and the cooling system is refilled. On starting the

engine, bubbles will be sighted in the header tank as the air makes its way out. As the water replaces the air, the water level in the header tank will drop. As it drops, it can be topped up slowly.

 

 

Low Compression

 

Low compression causes the engine to overheat. Some of the heat in the combustion gases by-passes the piston rings and goes into the crankcase. The cooling water is not taking away the heat caused by combustion, and overheating of the engine occurs. The engine speed should be gradually reduced until the normal operating temperature is attained.

 

 

Engine Overloaded

 

An engine that is overloaded will overheat. An engine can be overloaded by:

 

•        a dirty hull

•        a rope around the propeller

•        a bent propeller blade or

•        too large a pitch propeller.

 

The engine speed should be reduced until the normal operating temperature is attained. To stop overheating, it would be necessary to clean the hull of marine growth, remove the rope from the propeller, straighten the propeller blade, alter the propeller pitch or replace the propeller with one of the correct pitch.

 

 

Dirty Or Fouled Fresh Water Cooler

 

The sea water discharged overboard would be restricted. It is unusual for the cooler to be completely blocked. Reduce engine speed until normal operating temperature is attained. Stop engine and clean the cooler or return to port under reduced speed.

 

 

Fuel Injection Into Cylinders May Be Too Late

 

The timing of the fuel injector pump is out causing the fuel to be injected into the cylinders too late which will cause the engine to overheat. Reduce engine speed until normal operating temperature is attained. Stop engine and adjust fuel pump timing.


 

 

Slipway Work

 

 

2.1  Periodic Maintenance And Survey For Commercial Vessels

 

A vessel operates in a hostile environment being subject to:

 

•        rolling

•        pitching

•        heaving and slamming due to wave action

•        the corrosive tendencies of sea water and the marine atmosphere.

 

It is essential that regular maintenance is carried out to prevent rapid deterioration of the hull machinery and equipment.

 

Also, at sea the crew are at the mercy of the elements and have to rely on their own resources to cope with all emergencies.

 

Legislation aims to ensure that a vessel is safe and seaworthy on entering into service and remains so during its operational life.

 

To achieve these aims a vessel:

 

•        is to be constructed to the standards of and inspected during construction by a Government Authority

•        shall throughout its operational life be subject to survey by a Government Authority at periods prescribed by the Authority.

 

In Australia, the standards of construction of hull, equipment and machinery for vessels operating within 600 nautical miles seaward from the coast of Australia are those laid down in the Uniform Shipping Laws Code (amended from time to time).

2.2  Preparations And Inspections

 

There are a number of checks that are required before drydocking or slipping.

 

Drydocking

When out of the water, the ship sits in keel blocks which are horizontal.

Slipping

The vessel is positioned on a wheeled cradle, then hauled on rails up a slope. Therefore, the keel blocks and the vessel are at an inclination to the horizontal.

 


 

The majority of small vessels are slipped. It is far cheaper to construct a slip than a drydock. The drydock has an advantage over the slip. In certain operations the inclination of the slip presents problems.

 

Other ways of docking such as floating docks, synchro lifts or ship lifts are not discussed here, but the general principles apply. The preparations to be carried out by a vessel's crew are similar whether entering a dry dock or going on a slip.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2.1: Vessel in dry dock/slip

 

 

Step

Action

1

Ensure the ship is upright, i.e. the angle of heel is zero.

2

The vessel must be trimmed as near as possible to an even keel (upright).

3

Consult the dock master to ascertain requirements for docking.

4

Ensure all tanks are as full or as empty as possible.

5

Empty the bilges.

6

Lash down or secure all loose gear.

7

Shut down all machinery not required for the docking.

8

Shut down all other machinery when the dock master confirms the vessel is firmly on the keel blocks (unless there is an alternative method of cooling the diesel generators).

 

 


 

The vessel must be in a stable condition. The stability book on a vessel may in many cases include information for the docking condition. Some dock masters may want the trim to be such that:

 

•        the forefoot takes the keel blocks first

•        the stern can be swung by the aft lines connected to capstans ashore

•        the ship is centred in the dock.

 

In some cases the dockmaster may require the vessel to take the keel blocks at the stern. For a slip, the vessel must be trimmed by the stern such that the inclination of the vessel’s keel is the same as the inclination of the slip. Comments made previously regarding the dock master’s requirements also apply to slipping. If the vessel is to be surveyed and the tanks inspected, the tanks will need to be emptied and ventilated.

 

Leaving The Drydock Or Slip

The following precautions should be taken when the vessel is removed from drydock or a slip back into water:

 

1       Ensure all external hull and tank plugs are fitted tight.

2       Remove any tools, equipment and electricity supply lines which should be left on shore.

3       If the vessel was painted while on shore, confirm that the paint has dried and will not wash off and pollute the water.

4       Check that the water and environmental conditions are satisfactory for refloating the vessel.

5       Ensure that the vessel enters the water under the same stability and trim condition that it left the water.

6       Check for leaks around all sea suctions and discharges, all other ship side valves, scuppers and the stern gland.

7       Ensure the bilge system is functioning, all valves and filters are fitted and in working order.

8       Check steering system is operating correctly.

9       Open the sea suction valve/s to the salt water cooling systems for the generator engines. If vents are provided, vent the system (if not, there are often vents on sea water heat exchangers).

10     Start generator engine and its salt water cooling pump.

11     Check that sea water is circulating through the system by verifying that the water is discharging overboard.

12     Carry out Step 9 when starting the main engine.

13     Allow engine to idle for a short period.

14     Check all systems to ensure all are in working order.

 

 


 

2.3  The Function Of Sacrificial Anodes

 

Sacrificial anodes are placed at intervals on a vessel's hull to reduce corrosion of the hull.

 

 

 

Corrosion is an electro-chemical reaction. When a metal is in contact with an electrolyte, the result is that metal is corroded from the point where the current leaves the metal (the anode) and is deposited at the point where the current re-enters the metal (the Cathode).

 

 

 

The electrical potential varies at different points on the hull. As sea water acts as an electrolyte, corrosion cells are formed if there are imperfections in the paint, such as pinholes or scratches on the hull.

 

 

 

By securing sacrificial anodes at selected points on the vessel’s hull below the water line, the hull becomes cathodic. The anodes corrode and the products of the corrosion deposit on and protect the bare spots of the hull.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2.2: Sacrificial anodes

 

 

The sacrificial anode is a metal of much higher corrosion potential than steel. This is usually an alloy of either zinc or aluminium.

 

 


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2.3: Used Sacrificial anode

 

 

For optimum protection, firms who specialise in cathodic protection can be brought in to measure the corrosion potential of the hull and apply scientific principles to the size and placement of anodes.

 

Points to note:

 

•        Anodes should be in good electrical contact with the hull.

•        Anodes should not be painted.

•        Anodes should lose weight between dockings.

•        If anodes are unchanged, have a white chalky coating or are covered with weed or slime, they have reached the end of their useful life.

•        Anodes should be replaced regularly to refresh the sacrificial material.

•        Anodes will only ‘protect’ metal surfaces which are either directly wired to the anode or are contained in the same electrolyte such as sea water.

 

Accordingly, machinery which is prone to corrosion such as the engine block, the heat exchanger or bilge will need their own sacrificial anode.

 

 


2.4  Measuring Sterntube Bearing And Tail Shaft Wear

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2.4: Propeller shaft, strut and propeller

 

 

The sterntube is a steel tube which supports the propeller shaft using bearings. The sterntube also provides a seal preventing sea water from entering the vessel where the propeller shaft passes through the hull.

 

In the sterntube there are usually two bearings supporting the propeller shaft (tailshaft):

 

•        one is located at the forward end, behind the gland where the shaft penetrates the aft engine room bulkhead

•        the other is at the after end of the sterntube.

 

The forward bearing is not accessible unless the tailshaft is removed. As it only carries part of the weight of the shaft, wear is not usually a concern. The aft bearing has to take part weight of the shaft and the whole weight of the propeller and wear (if any) takes place in this bearing.

 

 


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2.5: Propeller Shaft Emerging from Stern Tube

 

 

•        Tailshafts (other names, screw or propeller shafts) are withdrawn for inspection of shaft and bearings at 4 year intervals. If the vessel is docked or slipped within that period it is standard practice to check the weardown of the aft tailshaft bearing.

•        The tailshaft can move inside the bearing up to 6% of the diameter of the tailshaft. For example, if a tailshaft is 50mm in diameter, the permissible movement between the tailshaft and the bearing is 3mm.

•        If the movement exceeds 6%, then the bearing needs to be replaced.

•        Worn bearings may result in vibration in the propeller shaft.

 

The reason for measuring wear down is that any sag of the shaft (due to the weight of the propeller) increases the stress in the shaft. The wear down is a measure of the sag (also called deflection).

 

The shipbuilder provides a maximum deflection that must not be exceeded. If exceeded the possible consequences are fracture of the shaft and loss of the propeller.

 

A common method of measuring the weardown is to clamp a dial indicator gauge to the hull or sterntube so that the pointer rests on the top of the shaft between the sterntube and propeller. Note the reading on the dial, then jack up the propeller until the resistance to jacking increases. Note the new reading. The difference is the weardown.

 

Note that the weardown as measured is the sum of the wear in the bearing and any shaft wear.

 


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2.6: Propeller Shaft and Bearing in Stern Tube

 

 

Oil Lubricated Tailshafts

 

These tailshafts have a mechanical seal at each end.

 

The standard method of checking wear is by depth gauge.

 

A collared plug in the gland housing or the stern tube just forward of the gland is removed. The depth from the face of the plug boss to the top of the shaft is measured.

 

This should be compared to the original measurement when the shaft was installed. The difference is the weardown.

 

 

Water Lubricated Tailshaft

 

The aft bearing is usually accessible via the small gap between the aft end of the stern tube and the front end of the propeller boss.

 

If a rope guard is fitted over this gap, it must be removed.

 

The tail shaft rests on the bottom half of the bearing. The gap between shaft and sterntube bush can be measured. This is done by using long feeler gauges inserted at the top of the shaft.

 

Many bearings have longitudinal grooves to allow water to circulate. Ensure the measurement is taken at the bearing surface and not the groove.

 

If the gap mentioned above is too small to allow access of the feeler gauges there is another common method of measuring the weardown. This method involves clamping a dial indicator gauge to the hull or sterntube.


The pointer needs to rest on the top of the shaft between the sterntube and propeller. Note the reading on the dial then jack up the propeller until the resistance to jacking increases. Note the new reading. The difference is the weardown.

 

Note: Weardown as measured in all cases above is the sum of the wear in the bearing and any shaft wear.

 

2.5  Opening Side Valves For Survey And Maintenance

 

As a general principle all the side valves on a vessel should be opened up and overhauled at each drydocking. These valves are sea inlet and overboard discharge valves for pumps such as:

 

•        bilge

•        general service

•        fire

•        ballast

•        sea water cooling, etc.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2.7: Side valves

 

 

This also includes all scupper pipes which have non-return valves fitted.

 

Be aware that there are different types of valves used on vessels. You should become familiar with the various types of valves used. In need, refer to your facilitator for assistance.

 


 

These steps should be followed during valve maintenance.

 

Step

Action

1

Open all valves by removing the valve cover.

2

Dismantle spindle.

3

Dismantle bridge.

4

Extract gland packing.

 

 

Follow these steps after inspection/survey has confirmed that the valves are in satisfactory working condition or that repairs have been made as required.

 

 

Step

Action

1

The valve should be lapped to its seat to ensure correct and accurate fit.

2

Fit new gland packing as per manufacturer’s instructions.

3

The gland and all parts re-assembled to the valve body.

4

Close valve (if screw down type).

 

 

It is not necessary to remove the valve body from the piping if:

 

          the body can be visually inspected

          the joint of valve to shell plating is sound.

 

 


2.6  Checking Rudder Stock And Pintle Bearing Wear

 

The rudder is used to guide the vessel’s direction. This is particularly important if the vessel has only one engine and the balancing of power from a second engine cannot be used to assist steering. It is important to include the rudder system in routine maintenance to ensure it remains in satisfactory working condition.

 

In most cases, if a rudder fails it will occur under load and at a difficult time! This may disable the vessel’s steering and result in a loss of control.

 

Rudders generally fall into three categories:

 

 

Unbalanced

Semi-balanced

 

Balanced

 

 

 

If the rudder has been poorly constructed or its condition allowed to deteriorate, the rudder stock could break loose within the rudder itself. This will result in the rudder stock effectively rotating inside the rudder while the rudder remains still. If there is any sign of separate movement between the rudder stock and the rudder, the rudder should be replaced.

 

The wear of pintles or bearings can be checked by feeler gauges. Clearance must be taken fore, aft, port and starboard as the pintles and stock are vertical and may not be lying central in the bearings. Jacking the rudder hard one way (as for shafts) is an alternative, but care must be taken to ensure that it is jacked squarely and the rudder is not canted.

 

 

If there is more than slight movement, the bearing should be replaced. If the bearing fails the rudder will be free to move violently under force from water action.

 


 

2.7  Attaching The Propeller To The Shaft

 

Unless the vessel operates with jet propulsion, you need a propeller to convert the engine power to move the vessel through the water.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2.9: Propeller and rudder arrangement

 

 

 

The most common method of attaching a propeller to the tailshaft is by machining a taper on the propeller end of the shaft and a matching taper in the bore of the propeller. The taper is usually 1 in 12.

 

A keyway and key is provided in the shaft with a matching keyway in the propeller. These act as a guide for close fit.  The small end of the shaft is extended and threaded to take a nut.

 

The propeller is pushed hard up on the shaft taper by tightening the nut. A locking device is fitted to prevent the nut from slackening. There are many methods of locking the nut. Most involve a setscrew or Allen screw that penetrates both the nut and the propeller boss.

 

Once the nuts are locked into place, the propeller is securely fastened onto the tailshaft and ready for service.

 

 


 

 

 

 

 

 

 

Figure 2.10: Propeller Assembly

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

Deck Machinery

3.1  Operation Of An Anchor Windlass And Cargo Winch

 

Anchor Windlass

 

The USL Code requires an anchor windlass to be fitted where the weight of the anchor is greater than 30kg and, where the anchor weighs more than 50kg the windlass must be power operated. Two anchors are required except for very small vessels.

 

An anchor windlass is comprised of a frame that supports a mainshaft in bearings. Mounted on the shaft are:

 

•        a cable lifter drum (often called a “gypsy”), grooved and slotted to fit the anchor cable

•        a brake drum secured to or forming part of the cable lifter, with brake band, housing and operating mechanism attached to the windlass frame

•        a clutch usually a "dog" type clutch/s to release the cable lifter and allow it to rotate freely on the shaft

•        for manual operation, a crank handle at one or both ends of the shaft

•        for power operation, a electric or hydraulic motor coupled to the shaft; where two anchors are provided the usual arrangement is for the motor to be located between the windlasses for each anchor or be located aft of the windlasses. In this latter case the motor drives the main shaft through gearing.

 

On vessels where mooring ropes/wires are too heavy to handle manually, the main windlass shaft is often extended at each end to take warping drums for handling the mooring wires/ropes on arrival/departure from port.

 

The warping drums may be locked on the shaft or are de-clutchable. The latter arrangement is the safest.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3.1: Typical anchor windlass

 

 


Safe Operation

 

Anchor Operations

 

Before starting the motor, check that the area around the windlass is clear of ropes/wires and other gear, and that there are no ropes or wires on warping drum/s.

 

In some cases, it may be necessary to start the motor to take the load. Ensure all clutches/brakes are in the appropriate positions and check that chain stoppers, devils claws and/or lashings are removed and cable is clear.

 

Start the motor.

 

At all times, stand aft of windlass and ensure you are not in line with the run of the cable. The windlass operating position is suitable.

 

Keep clear of warping drums if they are not de-clutchable.

 

When lowering cable, check that dog clutch is clear of cable lifter and release brake sufficient to control the run out speed of the cable. If lowered too quickly it may whip and jump on and off the cable lifter.

 

When riding at anchor, fit the chain stopper or devils claw and/or lashings to secure the cable. Allow some sag of the cable between stopper or claw and the windlass so that the anchor and cable weight is carried on the stopper or claw. This is so that the windlass is isolated from load and shocks.

 

When hoisting cable, ensure the dog clutch is engaged with cable lifter and brake is off. Release chain stopper or devils claw and/or lashings. Start hoisting cable. If the anchor housing is not visible from the windlass operating position, ensure that an assistant is available to signal when the anchor appears and ensure the anchor is housed securely.

 

Fit chain stopper or devils claw and/or lashings to secure the anchor. Release clutch so that anchor weight is carried on its stopper. The brake should be on in case the stopper or lashings should accidentally slacken or come adrift.

 

 

General Precautions

 

The windlass is in an exposed position on the foredeck or forecastle. The deck area is often wet and could be slippery. Wires, ropes, cable and fittings are hard to handle. Therefore as a minimum non-slip footwear, heavy duty gloves and clothing that is not to loose to get caught in the rotating machinery should be worn.

 


 

Cargo Winch

 

On smaller vessels a cargo winch is normally used in conjunction with a swinging derrick and like the windlass is comprised of a frame that supports a shaft in bearings. Mounted on the shaft are:

 

•        a winding drum fixed to the shaft, usually between the two bearings. The drum may be grooved to seat the wire rope better.

•        a brake drum secured to the winding drum, with brake band and housing attached to the winch frame. The brake is usually foot operated.

•        an electric or hydraulic motor coupled to one end of the shaft.

 

The electric motor and in many cases the hydraulic motor is fitted with a solenoid operated magnetic brake that comes into operation whenever the motor controller is brought to the stop position. This is to prevent slippage if the winch is supporting a load. The foot brake can be used for fine control or in an emergency.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3.2: Typical Cargo Winch

 


 

Safe Operation

 

Check that the end of the wire (common name: runner) on the winding drum is securely fastened to the drum. At least three turns should remain on the drum when the runner is at the maximum operating length of the rig.

 

From the operating position of the winch, take note of the run of the wire. This is to ensure that should the wire run loose, you will not be in its path.

 

Clear all loose wires and other equipment not necessary for the operation of the winch from the working area around the winch.

 

The general conditions as noted for the windlass apply to the operation of the winch.

 

 

3.2  Dangers Of Incorrect Operation

 

Some of the safety requirements and possible dangers arising from normal operation of windlasses and winches have been discussed previously. The main danger is damage to the equipment or personnel.

 

In general, deck equipment is robust and will tolerate some rough handling but care must still be taken.

 

Most safety problems that arise are from incorrect operation, such as:

 

•        Overloading the windlass when breaking the anchor from the ground, or pulling the anchor hard home into its housing.

•        Uncontrolled dropping of an anchor. The cable may whip and snake, injuring personnel who may be standing close.

•        Riding the brake when a winch is under load. This could stall the motor at a critical moment in the operation.

•        Overloading a winch such that the wire breaks. A wire breaking under load will whirl wildly in all directions and could severely injure personnel in its path.

 

Equipment will serve you well if maintained, treated and operated with respect.

 

 

3.3  Routine Maintenance

 

Deck machinery is fairly robust, but regular routine maintenance will serve you better over time.

 

 

 


 

Windlasses and winches

 

•        Grease or oil the main bearings.

•        Inject grease into all grease points.

•        Oil all linkages that do not have grease points. Use a penetrating oil if normal lubricating oil is not effective.

•        Oil or grease the threads on spindles of brake operating gear.

•        Check motors, both electric and hydraulic in accordance with the manufacturers instructions.

•        Loose gear (such as shackles, blocks, swivels, chains, and wires) should be examined regularly, stripped down, inspected and oiled or greased in accordance with the periodic inspection requirements.

•        Test and inspect all running equipment under no load to ensure it is operating freely.