(Ranger Hope © 2008, contains edits of material courtesy of A.N.T.A. publications)
Corrosion and Deterioration
Methods of Docking and Slipping
Advantages of Planned Maintenance
Elements of a Planned Maintenance Program
Breakdown of wood by fungi, commonly called rot or decay, can occur in timber whenever the moisture content rises above 20 to 25 percent. The fungi which cause decay spread by means of microscopic spores which are usually present in the air, so that any moist susceptible timber, even in almost completely sealed cavities, is subject to attack.
Warning signs of decay are:
• Paint or varnish failure
• A musty smell like mushrooms
• Fruiting bodies, like toadstools, spongy growths, or soft incrustations of various colours
• Mycelium, generally white threadlike growth, sometimes thick like cotton wool
• Any softening, cracking or other physical breakdown of the wood
Marine Insect Attack
Timber may be attacked by any of the following, depending upon conditions:
• Subterranean types
• Tree dwelling type
• Dry wood type
All three of these varieties dislike the light and may be exterminated by the use of proprietary poisons.
These only attack hardwoods which have sapwoods containing a high starch content. Fortunately 33% of Australian hardwoods are immune from attack. The attack becomes evident when an accumulation of fine flour dust appears on the surface of the timber. This borer may be exterminated by the use of proprietary poisons.
• The pill bug - a crustacean
• The gribble - a crustacean
• The shipworm or toredo - a mollusc
The crustacean borers cause the typical “hour glass” type of wastage seen in neglected piles of wharves, etc. If allowed to go unchecked they are responsible for considerable damage to the underwater section of wooden vessels. Sometimes they are referred to as “putty borers”.
The toredo commences life as free swimming larvas which attach to submerged timber and immediately begin to bore. In Australian waters they may reach a length of up to 1 metre. They use the attached wood as habitation, the worm feeding on minute marine life in the surrounding water. For the owners of wooden vessels these borers are a constant worry. Prevention of attack from both forms of marine borer is possible by deep and total impregnation of the timber with creosote or proprietary preservatives. An alternative by costly procedure is metal sheathing.
Corrosion is the alteration and decomposition of metals or alloys by direct chemical attack or by persistent electrochemical reactions. Corrosion can be classified as:
1. Chemical corrosion.
2. Electrochemical corrosion.
This is the attack of metals by solutions of acids or alkalines which will chemically combine with the metal to form entirely new products. The material can be considered as being dissolved in the solution. Such attack is usually caused by spillage of liquids such as battery acids, galley refuse, or in toilet areas.
This is the most common type of corrosion. It is caused by very small electrical currents flowing between one metallic area to another. These electrical currents cause the material which is being corroded to change to a completely different substance; for example, steel changes to rust. Whether the corrosion takes place below the waterline, or above the waterline, the presence of both oxygen and an electrolyte (i.e. a conducting solution) play an important part. Saltwater is a liquid which encourages corrosion because it is an excellent conductor of electricity.
Corrosion is indicated by the presence of rust or wastage of a metal.
The following precautions will keep the risk of fungal and insect attack to a minimum.
• Ensure good ventilation throughout the boat, particularly when it is lying idle.
• Make sure rainwater cannot get in.
• Prevent condensation by ventilation. Where it is unavoidable e.g. on insides of windows, use water-repellent preservative on woodwork.
• Use a water soluble preservative in the bilge water. A cheap and effective one can be made by dissolving 0.65 Kg of borax and 0.45 Kg of boric acid in 4 litres of hot water. This mixture is non-corrosive and harmless to animals.
• Inspect the vessel’s timbers for decay regularly, at least every 6 months. If decay is found act at once, a few weeks in summer is enough for major damage to be done.
• Use a preservative from a variety of preservatives that have been developed for the successful treatment of timber for decay resistance.
• Use a proprietary poison for extermination of marine insects.
There are two ways of preventing corrosion.
1. By providing a piece of material which will corrode in preference to the vessel. Such a substance is usually found attached to the hull near the propeller or attached inside a tank, in the form of a sacrificial anode. When two metals in contact with each other result in one of the metals corroding, the metal which is preserved is called more “Noble” than the metal that corrodes.
In such cases aluminium will corrode in preference to steel; steel will corrode in preference to brass; brass will corrode in preference to stainless steel. Different metals should not be used in close contact unless there is good insulation between them; for example, it is bad practice to connect a steel valve to an aluminium hull, without insulation. The aluminium may corrode around the steel.
Lead, in contact with aluminium will cause rapid wasting of the aluminium. For this reason, lead based paints must never be used on aluminium hulls. Lead incidentally, is more noble than steel, but the problem is not nearly as noticeable.
2. By coating the surface with a substance such as paint. Paint sticks closely to any surface to which it is applied and prevents corrosion. In order to ensure that the bond between the paint and the surface is good the surface must be properly prepared.
In particular -
• Any cracked or flaking paint should be removed.
• The surface should be clean, dry and free from salt, oil, grease etc.
• Any corrosion should be removed.
• Any internal repairs to the surface should be completed.
It is beyond the scope of this learner’s guide to describe every type of paint there is, but some of the common types of paints are as follows:
Anti-Corrosive Paints - used on metal surfaces to prevent corrosion from occurring.
Heat Resistant Paints - either sprayed aluminium or aluminium/graphite pigments.
Fire Retardant Paints - the action of these paints is that as they burn, gasses are given off which blanket the flame and slow or stop the combustion reaction.
Anti-Fouling Paints - used on the hull to prevent the growth of marine organisms.
Barrier Paints - in the case of painting an underwater section with a new coat of anti-fouling, unless the old system is completely removed, it is essential that a coat of barrier paint is used between the old and the new coats of anti-fouling.
This is because the solvent in the new paint will react with the old and some of the poison will leach down through the old paint thereby reducing the amount available to come out of the new coat to seaward.
Likewise when using a ‘high performance’ 2 part paint over the top of a coat of conventional paint, the coats must be separated by a coat of barrier paint. The chemical reaction occurring in the HP paint will damage the underlying conventional paint.
Non Skid Paints - used on decks and steps to prevent slippage. Generally around door entrances, windlass area, boarding areas and on steel step ladders.
Figure 1.1 Spray Painting Antifouling
Paints can be applied by brush, roller or spray gun. In all cases you should refer to the manufacturer’s instructions on the recommended procedure, materials and safety precautions. This information is usually available from the paint container itself.
This method does not require a slipway or dry dock, so it is suitable for repairs in an isolated area or in an emergency. The only requirement is a tidal range greater then the vessel’s draught.
The vessel is driven to a flat, cleared section of the beach or river bank and positioned parallel to the shore or bank, to give even support along its length as the water level falls and rises. The bank should not be too steep, and must be clear of obstructions. The vessel must fall up hill if flooding on the incoming tide is to be avoided. It may be positioned between poles driven into the bed or simply weighted to fall up hill. Hawser lines may be tied to solid sections of the vessel, e.g. the foot of a mast, and secured to points on-shore to help prevent the vessel from falling downhill. When the water level is low enough, shoring is installed on the downhill side to prevent rolling over.
In this method, a vessel is heeled over, while afloat, by means of tackles set up between its masts and another ship, or shore attachments.
This method is not as successful as careening in exposing the hull, but since the vessel is afloat, there is little hull stress, and the dangers, through touching the bottom, or damage to the hull and the intakes, are minimal. It must be remembered that by heeling a vessel you increase its draft and you should be sure that there is sufficient under-keel clearance for the job.
The graving dock is excavated from the land and closed to the sea by means of a large watertight door or gate known as the “Caisson Gate”.
The edge of the dock bottom beneath the gate is referred to as the sill. The dock bottom has a very rigid construction and is usually made of reinforced concrete. The dock bottom always has a slight slope towards the sill to aid drainage. The sides of the dock are usually terraced to enable side shoring.
Along the centre line of the dock are blocks of concrete topped up with timber. They form the keel blocks. Two parallel rows of blocks on either side form the bilge blocks or side blocks. Depending on the size of the vessel and the shape of the underwater hull, the blocks are repositioned to suit the particular vessel.
On the sides of the dock at ground level are rails on which winches travel along the length of the dock. Wires from the winches are used, two on the forward beam and two on the after beam, to help position the vessel over the keel blocks when the vessel is brought in. Cranes are used for heavy lifting.
When the vessel is in position the lock gates are shut and pumping out commences. A diver may be employed to ensure that the vessel’s keel is in line with the keel blocks. As water is pumped out the diver keeps checking that the vessel is taking to the blocks as planned. Sometimes blocks are shifted so that maintenance can be done on a sea chest valve, drain plug, etc.
The basic structure of the floating dry dock is a very strong and rigid double walled “U”. The bottom is constructed very similar to the bottom structure of ships. The sides of the dock are vertical wing tanks. Keel blocks and bilge blocks are laid on top of the double bottomed structure. The whole dock forms a floating, watertight structure which can be submerged by flooding the double bottom and wing tanks.
The vessel to be dry docked is simply floated into the dock and positioned above the keel and bilge blocks by use of mooring lines. Shores are fitted to provide support and as the dock tanks are pumped out the dock rises until the pontoon deck is dry.
Figure 1.2 Floating Dock
Operates along the same lines as the floating dock in that the vessel is floated in over a submerged platform and is then lifted clear of the water by raising the platform. The synchrolift however, is a land-based platform which is lowered into the water by a series of synchronised winches lining either side of the dock.
Figure 1.3 Vessels on Synchrolift
Figure 1.3 shows a vessel on a synchrolift. Note the keel and bilge blocks. On the left of the picture, just clear of the bow you can see one of the lifting winches.
One of the most common methods of removing a small vessel from the water involves the use of the patented slipway. This is basically a sloping, reinforced concrete runway which extends well below the low water mark. On the slip itself is built a set of railway tracks set well apart. Wheeled carriages run on these tracks and depending on the size of the vessel being dry docked, carriages can be linked together to form a single unit. Cradles are fitted onto these carriages with keel blocks on the centre line atop the carriage. The entire assembly is made up to suit the vessel being dry docked.
The vessel is manoeuvred onto the cradle under its own power and is secured with “springs”. As the vessel settles onto the cradle bed, wedges are inserted to keep the vessel upright. The entire assembly is slowly winched up the slipway. As the vessel takes to the keel blocks, securing beams are drawn tight and any shores, if required, are fitted. The vessel now secure in its cradle on the carriage is slowly winched out of the water.
A narrow dock is excavated and then opened to the sea. The vessel to be lifted manoeuvres slowly into the dock and secured temporarily with mooring lines while a mobile straddle carrier is positioned above the vessel. Broad slings which will eventually distribute the weight of the hull are then put in place. The weight is taken up by the slings. The moorings are released and the vessel is lifted clear of the water. The straddle crane, under its own power, carries the slung vessel to a suitable position in the shipyard, where it is lowered on blocks and shored and the slings removed.
The main advantage of this system is that many vessels can be docked at the same time and the slipping facility is not laid up for the duration of the vessel’s stay.
Figure 1.4 Travel Lift
Prior to docking or slipping, a complete repair list of all work to be done while in dock should be made up. Several copies should be made so that all those directly involved in the work can monitor the progress being made and cross off the completed jobs.
When docking or slipping your vessel, the entire weight of the vessel will be supported at a few localised points, instead of uniformly over the hull, as is the case when the vessel is afloat. Most small vessels have sufficient strength to withstand these localised stresses without additional support. However, it should be remembered that external keel coolers, echo sounders, log and sonar transducers could be severely damaged if the bilge or keel supports came into contact with them. It is important that the dockmaster is supplied with up to date and accurate information regarding their location.
If you are using a patent slip for docking your vessel, then stability is not a major problem provided that the vessel is snugly secured in the cradle and the side support beams are drawn up tight before it is pulled clear of the water. The same is true of the travel lift.
If however, you are using a synchrolift, floating dock or graving dock, then you must be sure that your vessel has as much stability as possible. Tanks should preferably be empty so as to remove any free surface effect. The critical moment occurs just before the vessel settles on the keel blocks. Usually your vessel will be trimmed slightly by the stern. As the water level falls, the keel will touch the blocks at the stern first. This results in an upthrust on the stern which increases as the water level falls. This has the effect of reducing your vessel's GM by causing an apparent rise in the centre of gravity. If it did not have sufficient initial stability, it could topple off the blocks, with disastrous consequences. It’s happened before, make sure it never happens to you. Most shipbuilders will supply a recommended docking condition with the stability data for the ship. You should ensure that your stability condition is equal to, or better than the recommended condition.
All moveable weights should be secured, and all unnecessary weights on deck should be removed.
General Precautions In Dry Dock
• Transducers and impressed current anodes should be covered with grease and then masking tape.
• Remove drain (docking) plugs from all tanks that need to be drained. Put them in a safe place and keep a written record of which plug goes where. Ensure that plugs are all replaced prior to flooding the dock or entry into the water.
• Ensure that safe access is provided to and from the vessel.
• Ensure that fire safety precautions are adhered to.
• Ensure that all tanks, void spaces etc are opened, vented and ready for inspection by surveyors at the appropriate time.
• Ensure that all pollution control requirements are met.
In a dry dock the vessel may be unable to use its fire fighting system. Note the position of the fire hydrants ashore and the site of the dock supplied fire extinguishers. Keep a close watch on any hot work being done and stop any unsafe practices.
• all docking plugs have been replaced
• all intake gills/grates have been replaced
• all transducers are uncovered and wiped clean
• all tanks are boxed up (manhole/inspection covers are replaced)
• anchors are secured
• all loose gear is secured
• new paint is dry to manufacturer’s specifications
• shore power supply is disconnected
• there is sufficient water depth to unslip
• sea cocks are open
The survey requirements of commercial vessels are laid down in the State Marine Acts and the USL Code. In this section, we will only deal with the requirements are per USL Code. Specifically, we will consider the surveys carried out for the issue of a “Certificate of Survey”.
Survey a thorough examination performed by, or in the presence of a surveyor or an authorised person or society.
Inspection a visual inspection performed by an approved person.
The Certificate of Survey is issued on completion of an Initial Survey. The surveyor submits a report, detailing the condition of the hull, machinery and equipment, and makes a written declaration of such condition.
The main purpose of this survey is to ensure that the vessel will be able to perform the tasks for which it is intended.
All aspects of the vessel’s construction are examined to ensure that it meets the requirements of Section 5 of the USL Code. After the construction is complete, the Authority surveys the vessel once more and if satisfied, issues the owner with a “Certificate of Survey”.
The Certificate of Survey or its evidence (plasticised document or metal plate) should be displayed:
• near the steering position, except on passenger vessels, where the evidence should be displayed in such a position that it is readily visible to passengers, or if the Authority requires,
• in a position on board that it shall be visible from outside the vessel.
Periodic Surveys And Inspections
All vessels must under go ‘Periodic Surveys and Inspections’ to satisfy the Authority that the vessel continues to comply with all its laws and regulations.
The survey schedule for vessels of less than 35 metres in length is given in Section 14 of the USL Code and is reproduced below:
• Running trial of each main engine and associated gearbox.
• Operational test of bilge pumps, bilge alarms and bilge valves
• Operation test of all valves in the fire main system.
• Operational test of all sea injection and overboard discharge valves and cocks.
• Operational test of main and emergency means of steering.
• Running trial of all machinery essential to the safe operation of the vessel.
• Inspection of all pipe arrangements.
• General examination of machinery installation and electrical installation.
• All safety and relief valves associated with the safe operation of the vessel to be set at the required working pressure.
• Pressure vessels, and associated mountings used for the generation of steam under pressure or the heating of water to a temperature exceeding 99 degrees Celsius
• Inspection of the liquefied petroleum gas installation.
• Inspection of cargo handling, fishing and trawling gear.
• Inspection of escapes from engine room and accommodation spaces.
• Inspection of personnel protection arrangements in machinery spaces.
• Inspection of casings, superstructures, skylights, hatchways, companionways, bulwarks and guard rails, ventilators and air pipes, together with all closing devices.
• Inspection of ground tackle (anchors and chains).
Two Yearly Surveys
• Hull externally and internally except in way of tanks forming part of the structure.
• Sea injection and overboard discharge valves and cocks.
• Inspection of propellers, rudders and under water fittings.
• Pressure vessel and associate mountings of an air pressure/salt water system having a working pressure of more than 275 kPa.
• Each screw and tube shaft.
• Anchors and cables to range.
• Chain locker internally.
• Tanks forming part of the hull, other than oil tanks, internally.
• Void spaces internally.
• Compressed air pressure vessels having a working pressure of more than 275 kPa and associated mountings.
• Pressure vessel and associated mountings of an air pressure/fresh water system having a working pressure of more than 275 kPa.
• Cargo handling, Fishing and trawling gear.
• Insulation test of all electrical installations above 32V A.C. or D.C.
• Each rudder stock and rudder stock bearing
• Steering gear.
• Hull in way of removable ballast.
• Selected sections of internal structure in way of refrigerated space.
• Fuel oil tanks internally
The master is responsible for the seaworthiness of the vessel and must ensure that all national and international requirements regarding safety and pollution prevention are being complied with. Effective planning is required to ensure that the vessel, its machinery systems and its services are functioning correctly and being properly maintained, including dry-docking to maintain hull smoothness.
Planned maintenance is primarily concerned with reducing breakdowns and the associated costs. Planned maintenance is of two kinds:
Preventative maintenance is aimed at preventing failures or discovering a failure at an early stage.
Corrective maintenance is aimed at repairing failures that were expected, but were not prevented because they were not critical for safety or economy.
• Fewer breakdowns and repairs.
• Equipment operates efficiently at all times.
• Fewer hazards to the crew when working with well maintained equipment.
• Vessel complies with survey requirements at all times.
• No areas of the vessel or items of equipment are overlooked or neglected.
You can develop a basic maintenance program for your vessel by taking the following steps:
Step 1 Determine what items need to be maintained.
Step 2 Determine the type of maintenance tasks required on each item.
Step 3 Determine the frequency of carrying out particular maintenance jobs.
Step 4 Prepare a maintenance schedule.
Step 5 Develop operational and recording procedures.
You will need to consider the following issues in the planning process
• Is an item worth maintaining? What would be the real cost of failure to maintain that item?
• Equipment manufacturers instructions.
• Statutory survey requirements.
• Classification society requirements.
• Maximum length of survey cycle.
• Magnitude of maintenance task.
• Maintenance/inspection that can only be carried out when the vessel is out of water.
• Resources required.
• Length of voyages, routes and trades the vessel is involved in.
• Spare parts replacement.
The plan must be adaptable to various weather conditions and must be flexible enough to accommodate changes in vessel’s trade.
It is convenient to draw up a maintenance schedule by breaking down the plan into various ‘time phases’. Two suggested categories are:
(a) Short-term maintenance.
(b) Long-term maintenance.
Short-term maintenance may include weekly, fortnightly or monthly inspections and greasing routines. Long term maintenance will involve major overhauls and surveys. Remember too that some operational maintenance tasks will only be carried out as and when necessary.
The actual operation and documentation of the plan will vary from vessel to vessel. Many vessels use a card index system or computer program for this purpose. Usually, a job sheet is prepared for each job. The job sheet contains a description of the work and a list of relevant spare parts and references to drawings and instruction manuals. On completion of the job, relevant details are entered in the job sheet.