FACULTY OF MECHANICAL, UNIVERSITI TEKNOLOGI MALAYSIA

SKMM 3623 ENGINEERING MATERIAL (SECTION 01)

SHIP RUDDER

LECTURER: ENGKU MOHAMMAD NAZIM BIN ENGKU ABU BAKAR

GROUP MEMBERS:(1) NADZMER AZRAI BIN MOHD FAUZIA12KM0170(2) MUHAMMAD AZAM AZRAEI BIN ABDUL RAHIMA12KM0163(3) MUHAMMAD NAJEE BIN JUNAIDIA12KM0168

Table of ContentChapterTitlePage Number

11.0Introduction2

1.1Type of Materials4

1.1.1Rudder Stock and Rudder Shaft4

1.1.2Rudder Bearings6

1.1.3Rudder Framework7

22.0Operational Condition8

2.1Type of Failure8

2.1.1Deformation8

2.1.2Fracture8

2.1.3Wear9

2.1.4Cavitation10

2.1.5Fatigue10

33.0Failure Analysis11

3.1Type of Rudder Failure11

3.1.1Stock Failure11

3.1.2Framework Failure12

3.1.3Delamination12

3.1.4Bearing Failure13

3.1.5Cavitation14

3.2Rudder Failure Repairs16

3.2.1Rudder Stock Repair16

3.2.2Delamination Repair16

3.2.3Cavitation Repair18

3.3How to Extend The Lifespan of the Rudder19

44.0Conclusion22

55.0References22

1.0 IntroductionShip rudder, or just rudder in short, is a device used to steer a ship, boat, submarine or other conveyance that moves through a medium such as air or water. Rudder also widely used in hovercraft or aircraft, but we will focusing the rudder used in ship. A rudder operates in which by redirecting the fluid past the hull. Of all parts of a ship, rudder is one of the most important parts in a vessel, due to its use in maneuvering. After hull integrity, rudder integrity is the most vital component of a seaworthy vessel.Basically, rudder is a flat plane or sheet of material which attached with hinges to the ships after end. The rudders are shaped like flat plane as to minimize the drag called hydrodynamic drag. On smaller vessels, a tiller, a stick or pole acting as a lever arm, which may be attached to the top of the rudder to allow it to be turned by a helmsman. Meanwhile, in larger vessels, cables, pushrods, or hydraulics may be used to link rudders to steering wheel.Rudders always go through a lot of stress in normal use. With every turn, the skin on each side of rudder is subjected to a cycle of compression and tension. Years of sailing can accumulate a lot of these fatigue cycles. Shock loads, groundings, competitive sailing and a rudder that been under-engineered are all contributing to rudder failure.To maintain the rudder integrity, it is very hard, because of its situated position around the ship. To running maintenance or repair process, the ship required to dry docking at shipyard. There are already a lot of reported cases of breakdown of ships rudders. These problem caught the attention of the seafaring industry. They try to solve this issue because of the damages caused by ships rudder breakdown such as collision, grounding, and even worst, loss of lives.There are basically 5 components within rudder, which are rudder stock, rudder framework, rudder bearings, rudder shaft, and rudder brace. Rudder stock is the vertical member at the forward edge of a rudder, hinged at the sternpost and attached to the helm or steering gear. Rudder framework firmly attached to the stock with long, strong welds. Rudder bearings is used to support rotating shaft against either transverse or thrusts loads. Rudder shaft is the central shaft around which the rudder turns. This is the shaft of the rudder to which the tiller or steering mechanism is attached. Rudder brace is the system aligned gudgeons and pintles which form a pivot for the rudder.

Figure 1: Modern ship Rudder (Source: http://en.wikipedia.org/wiki/Rudder)

Figure 2: Cross section of ship Rudder (Source: http://dynamicdivers.gr/services/tailshaft-rudder-clearance-measurements/)1.1 Type of Materials1.1.1 Rudder Stock and Rudder Shaft

Figure 3: Rudder Stock and Rudder Shaft (Source: http://www.pyiinc.com/jefa-rudder/rudderstock.html)Generally, there are four materials that can be used in the production of rudder stock. The materials are:

Aluminium AIMgSi1 (EN 6082): The tensile strength is 340 N/mm, the 0.2% proof stress is 280 N/mm2, the specific weight is 2.700 Kg/m.

Aluminium AIZnMgCu1, 5 (EN 7075): The tensile strength is 520 340 N/mm, the 0.2% proof stress is 460 N/mm, the specific weight is 2.700 Kg/m.

Stainless Steel aisi 316 (1.4401): The tensile strength is 600 N/mm, the 0.2% proof stress is 200 N/mm, the specific weight is 7.900 Kg/m.

Stainless Steel aisi 329 (1.4460): The tensile strength is 750 N/mm, the 0.2% proof stress is 450 N/mm, the specific weight is 7.900 Kg/m.

Stainless Steel aisi 630 (1.4542): The tensile strength is 1.100 N/mm, the 0.2% proof stress is 900 N/mm, the specific weight is 7.900 Kg/m.

Historically Stainless Steel 316 has been the preferred for rudder shaft material, due to its non-corrosive and relatively strong and widely available. At the end of last century alternative rudder stock materials like Aluminium and High Strength Stainless Steel became widely available. Driven by the aircraft and space industry, new high quality Aluminium Alloys were developed.The mechanical and anti-corrosion characteristics of Aluminium depend on the alloy elements. Pure Aluminium is not usable for a high strength purpose like a rudder shaft. The most popular Aluminium Alloy for rudder shafts is AlMgSi1 (EN 6082). The addition of the Alloy element Manganese extremely increases the mechanical properties proof stress and tensile strength. The addition of the Alloy element Silicon extremely increases the corrosion resistance of the Aluminium. A hard and strong layer of Silicon Oxide SiO2 protects the Aluminium even against the most hostile seawater.The mechanical and anti-corrosion characteristics of steel depend on the Alloy elements and the heat treatment. By adding Carbon, Chrome and Nickel to Iron and heat treat it correctly, one achieves the Alloy Stainless Steel. The protection against corrosion is not achieved by an oxide layer like Aluminium, but the added Chrome and Nickel make sure the metal itself will not oxidize.To be able to evaluate the mechanical properties of metals, one should first know that four of many mechanical properties of a metal are important for rudder stocks:

0.2 % proof stress: As soon as forces are applied to a metal, it will deform. Up until the 0.2% proof stress, this deformation is called elastic deformation. This means that after the forces are taken away, the metal will come back to its original shape with a maximum permanent deformation of 0.2%. The value of the 0.2% proof stress is given in Newton per square mm (N/mm). Projected on a rudder shaft, this figure will determine the point of permanent damage. When the forces on the rudder shaft will rise above the 0.2% proof stress, the rudder shaft will be permanently bend and practically unusable.

Tensile strength: Tensile strength or breaking strength determines the point where the stress level in the metal has risen so high that the metal is torn. The value of the tensile strength is given in Newton per square mm (N/mm). For rudder stocks, this figure is not very important. From the proof stress point, the metal will flow and the rudder shaft will heavily bend permanently and eventually break at the tensile strength point.

Specific weight: The specific weight of a metal is used to calculate the mass of a product with a given volume and is specified in Kg/m3. Very dense metals such as Stainless Steel will have a high specific weight, meanwhile light metals such as Aluminium will have a low specific weight.

1.1.2 Rudder Bearings

Figure 4: Ship's Rudder and its Bearing (Source: Material Selection in Mechanical Design, Michael F. Ashby)

ParameterDescription

FunctionSliding bearing

Constraints Wear resistant with water lubrication Resist corrosion in sea water High damping desirable

ObjectiveMaximize life, meaning minimize wear rate

Free variables Choice of material Bearing diameter and length

Table 1: Design requirements for Rudder Bearings (Source: Material Selection in Mechanical Design, Michael F. Ashby)Rudder bearings of ship operate at under the most unpleasant conditions. The sliding speed is low, but the bearing pressure is high and adequate lubrication is often difficult to maintain. The rudder lies in the wake or front of the propeller, which will generates severe vibration and consequent fretting. Sand and wear debris tend to get trapped between the bearing surfaces.Ships rudder bearings are traditionally made of bronze. The wear resistance of bronzes is good, and the maximum bearing pressure is high. Other materials such as polymers which are suitable for rudder bearings due to clearly superior are listed below:

MaterialComment

PTFE, Polyethylenes, Polypropylenes, NylonLow friction and good wear resistance at low bearing pressures.

Glass-reinforced PTFE, Filled Polyethylenes, PolypropylenesExcellent wear and corrosion resistance in sea water. A viable alternative to bronze if bearing pressures are not too large.

Silicon Carbide SiC, Alumina Al2O3, Tungsten Carbide WCGood wear and corrosion resistance but poor impact properties and very low damping.

Table 2: Materials for Rudder Bearings (Source: Material Selection in Mechanical Design, Michael F. Ashby)

1.1.3 Rudder FrameworkRudder framework is one of the component in rudder, which firmly attached to the rudder stock with long, strong welds. It is made out of stainless steel, rather than mild steel.

2.0 Operational ConditionThe operation of rudder are given the maneuvering to the ship, this rudder located at the stern (back) of the ship and directly behind the propeller because to give the ship maximum maneuvering. the condition for rudder operation are wet atmosphere because all part of the rudder are immersed into the seawater, therefore it will faced several type of failure like corrosion, wear, fatigue and other type.

2.1 Type Of Failure2.1.1 DeformationDeformation failure is the phenomena where the structure or the rudder part like rudder blade, rudder stock and rudder horn change it shape due to overload and reducing of the material strength.

Figure 5: Deformation on rudder blade (Source: http://www4.hcmut.edu.vn/~dantn/Marine/surveypractice/2013/01/rudder-rudder-stock-and-pintle-survey.html)

2.1.2 FractureFracture occur due to development of certain displacement discontinuity surface within the material. The high stress apply on the material will cause the material to crack. There are several type of crack that can occur on ship rudder that is sheer crack, slip band and dislocation.

Figure 6: Crack appear on rudder blade (Source: http://www4.hcmut.edu.vn/~dantn/Marine/surveypractice/2013/01/rudder-rudder-stock-and-pintle-survey.html)

2.1.3 WearWear is sideways displacement that occur when two component are contact to each other, this will cause friction if the component move in opposite direction. The friction will wear off the side that touch each other. On the ship rudder this can be find on steering gear, main rudder bearing.

Figure 7: Areas where wear can occur (Source: http://www4.hcmut.edu.vn/~dantn/Marine/surveypractice/2013/01/rudder-rudder-stock-and-pintle-survey.html)2.1.4 CavitationThe movement of the ship are depend on the propeller, the rotating propeller will cause the water flow become a turbulent flow and also reduce the water pressure, this phenomena will generated hydrostatic cavitation. Cavitation or corrosion can occur by two factor, is by hydrostatic cavitation and different corrosion properties of the materials.

2.1.5 FatigueFatigue of the structure of material happen due to repeatable stress applied on the materials, the strength of the material will reduce with the stress applied. There are several type of stress that can be determine, as example is compression, tension and torsion. In rudder part, rudder stock undergo torsion that can make it fatigue.

Figure 8: Area where fatigue can occur (Source: http://officerofthewatch.com/2013/08/16/incident-information-on-broken-rudderstock-due-to-corrosion-fatigue/)

3.0 Failure Analysis3.1 Types of rudder failureRudder failure may occur due to many reason and their characteristics of failure are differ from one type of failure to another failure. Certain type of failure could cause an instant damage to the ship while others may give effect on long term of ships lifetime. Below is the example of rudder failure.

3.1.1 Stock failureStocks can fail in several ways, all related to inadequate strength. A bent metal stock can result in a rudder being jammed off-center, which will prevent or give useless to any efforts to steer a boat with sails, drogues, and a jury rudder or by towing lines. Composite rudder stocks, meanwhile, will break rather than bend.

Figure 9: Stock-Rudder Failure (Source: www.cruisersforum.com/forums/f55/rudder-stock-failure-129234.html)

Under normal operating conditions, a rudder stock is subject to repeated and reversing torsional stress, which it can easily handle if it is sized correctly. However, corrosion changes everything. Stainless steel, in particular, suffers when deprived of oxygen, which is exactly what happens up inside a rudder tube full of seawater. This gives bad effect where the shaft comes in contact with a solid bearing surface, which rubs away the oxide film that protects the steel. Hidden from view, the stock begins to corrode.Over time, its strength is low enough that an impact or strong twist hit towards it will make the rudder falls away.3.1.2 Framework FailureIn the weakest configuration, the stock extends only just below the top of the rudder where its end is welded to a mild-steel plate. A stock that extends deep into the blade is better compare to the multiple welds to resist the twisting stresses and absorbing the bending stress. Also, the rudder will not necessarily fall away when these welds fail.A well-engineered interior framework is made out of stainless steel, rather than mild steel, and is firmly attached to the stock with long, strong welds. However, even if the interior frame is a single stainless plate that is welded to the stock for almost its entire interior length, it is almost impossible to maintain a perfect seal between the composite blade and the metal stock. Water eventually penetrates into the blade and fosters corrosion, especially where welding has altered the molecular structure of the metal. As the water inside the rudder is trapped, this type of deterioration continuously occur even in a boat stored on land. If corrosion weakens the framework to its breaking point, rotating the stock will fail to turn the rudder blade.

3.1.3 DelaminationDelamination is the peeling from undercoat or substrate. Delamination can occur anywhere in the rudder but will most likely show up in this same area where the metal mandrel inside the rudder ends. The stress cracks and delamination can go unnoticed for a season or two and the problem may not be identified until water begins weeping from the rudder after the boat is pulled from the water.

Figure 10: Delamination on rudder surface. (Source: elizabeth1981oday34.blogspot.com/2011/09/keel-rudder-and-bottom-work.html)

In northern climates, delamination can be caused by freezing water. A slight leak at the top of a fiberglass rudder will allow moisture to enter. A drop or two of water per day adds up over time. Once inside, the water will freeze during the winter. When it freezes, it expands and can crush the foam core and, in some cases, cause the rudder to delaminate and even split apart. It may take several seasons for a problem like this to reveal itself.

3.1.4 Bearing FailureOutboard rudders pivot on pintles that joint with gudgeons. This type of bearing is extremely reliable and mostly fails due to predictable and often obvious wear, although corrosion in a stainless steel pintle, as opposed to a bronze one, can result in sudden failure.The stock on an inboard rudder, on the other hand, typically penetrates the hull through a laminated tube. The interior surface of the tube serves as the bearing surface for the turning stock, with a second fixed bearing up high on the stock countering the bending loads. Some rudder tubes are fitted with a grease fitting or at least a grease cap that allows lubricant to be forced between tube and stock to reduce wear. While uncomplicated and durable, a raw tube can suffer wear, hastened by infrequent lubrication, which will result in excessive play, worrying clunks and difficulty steering. The raw tube also subjects a metal stock to corrosion-encouraging abrasion, particularly if grit finds its way into the tube.To eliminate the need for lubrication, some rudder tubes are sleeved with low-friction plastic bearings. Unfortunately, two common bearing materials, polyamide (nylon) and polyacetal (Delrin), absorb water and swell, causing the bearings to grip rather than guide. Even a stable plastic such as UHMW can be distorted by a corroding aluminum carrier. Either circumstance can make for stiff steering or freeze rudder movement entirely.With an even larger opening in the hull, the rudder tube can be fitted with a roller bearing. This type of bearing tends to create a lighter helm and is easier on the rotating stock than solid bearings. However, roller bearings tend to fail suddenly rather than gradually, which will result in significant binding.

3.1.5 CavitationA ships rudder, placed directly behind the propeller to give the ship maximum maneuverability, is particularly prone to erosion followed by corrosion. The erosion in this case is caused by hydrodynamic cavitation. Hydrodynamic cavitation is a phenomenon that accompanies turbulent fluids. The turbulence in the fluid, in this case, is caused by the ships motion through the water but more particularly by the action of the ships propeller which results in areas of greatly reduced fluid pressure.Due to the low pressure, the water vaporizes. This causes small vaporfilled cavities or bubbles in the fluid up to about 3 mm in diameter. The cavities travel through the water and the pressure around them increases, causing them to collapse suddenly. The implosion of the cavities is accompanied by a complex set of physical processes.It is the collapse of the cavities which is accompanied by very high pressure pulses, speeds and temperatures in the water, that cause the damage. The forces involved are very large. It is as if the surface affected has been subjected to repeated, heavy blows from a hammer, as well as high temperatures. This causes what is known as cavitation erosion as the surface material, first paint and then steel, begins to flake away. This process can be greatly magnified by the presence of gravel or other hard particles in the water. One need only examine a ships rudder that has been subjected to cavitation damage to see that, whether one understands or subscribes to the theory, in practice very real damage is caused by this phenomenon. Rudders become deeply pitted; paint coatings and hard steel simply disappear; whole plates can fall off and the rudder practically disintegrates altogether, all as a result of this cavitation damage. So the rudder is subjected to cavitation damage from two main sources: the turbulence caused by the propeller and that caused by the water flowing over the rudder itself.

Figure 11: Cavitation on rudder surface. (Source: http://www.motorship.com/news101/ships-equipment/quantifiable-results-from-hull-coatings)

Cavitation damage is not limited to the ships rudder. The propeller is also subject to the phenomenon, as are stabilizers, the vessels hull and other parts of the underwater vessel where the water flows are particularly swift or turbulent. But the rudder is particularly prone to this phenomenon due to its position and form. The process is gradual, but not necessarily slow. This process can occur in a remarkably short period of time. Sometimes six months is all it takes for serious rudder damage to be present.The first step is that the cavitation causes the paint coating on the steel to erode, eventually exposing bare steel. The erosion of the steel is then accompanied by the electro-chemical process of corrosion because the steel is no longer protected. The effect is multiplied as the cavitation continues and the erosion it causes is added to by the natural corrosion of bare steel exposed to water the electro-chemical process and the oxidation which this brings about.

3.2 Rudder Failure RepairsRudder component that has been defect can be repair by using a proper process of work. Repairing work are done to solve the problem occur to the rudder and to longer it lifespan. It is also be done to avoid any further damage to the rudder that can lead to unexpected incident and total loss.

3.2.1 Rudder Stock RepairAccording to Marketendia, a company expert in rudder failures, here are the following procedures for repairing a damaged rudder stock:1. View the stock: The best way to tell if your stock is sound is to get a look at it where it is most likely to fail, in the area hidden by the rudder tube. This is like examining through-the-deck chain plates by extracting them. In the case of a rudder, dropping it a few inches to expose the critical part of the stock should be adequate. This applies equally to composite stocks, which can suffer from hidden wear or damage just above where they enter the hull.2. Check vertical alignment: Aside from its adverse effect on sailing performance, a bent rudder stock will have been weakened, and straightening it will weaken it more. The force that bent the stock may also have damaged the rudders bearings, internal frame, outer shell or even the structure of the hull and rudder tube. A spade rudder that is not vertical or does not rotate in place at the bottom of the blade requires a careful and complete evaluation.

3.2.2 Delamination RepairThere are two approaches one can take to restore strength to the delaminated area.1. The first and easiest option is the drill and fill approach.2. The second option involves removing the fiberglass skin in the delaminated area, repairing the core, gluing the skin back in place and structurally repairing the original cracks in the skin if any and the cuts made in the fiberglass skin to gain access to the core.

Figure 12: Drilling and Filling of Delaminated Area. (Source: NYK-TDG Maritime Academy; Report on the Causes of Ships Rudder Breakdown, January 2013)

The drill and fill method is the easiest of the two repairs. It involves fewer steps but takes more time to complete the repair because of the longer time required to dry out the wet core before the repair can be attempted. The repair may not be as reliable as the second method because there is no opportunity to inspect or prepare the delaminated areas inside the rudder for optimum bonding. Even so, this method has worked well when the damage is not too extensive.

Figure 13: Removing the Skin and Repairing the Core. (Source: NYK-TDG Maritime Academy; Report on the Causes of Ships Rudder Breakdown, January 2013)

Most repair facilities use the second option and cut off the fiberglass skin in the delaminated area. They remove and repair the voided core before gluing the rudder skin back in place. This method allows the rudder to be repaired over the period of days rather than weeks. It is also a more reliable repair because you get to see what you are bonding to. Surfaces can be dried quickly and thoroughly, and damaged core can be removed and replaced with new core.

3.2.3 Cavitation RepairCavitation is the first major problem that causing ships rudder failure. There are many ways on preventing the damage caused by cavitation. The most common practice is to use a conventional type of rudder, place it directly behind the propeller and coat it with a typical epoxy coating or antifouling scheme consisting of primer, epoxy coats, midcoat and biocidal AF paint; the rudder area is often also surrounded by a number of sacrificial anodes for cathodic protection. Depending on the design of the rudder, the usual cruising speed of the vessel and the presence or absence of abrasive particles in the water, cavitation erosion sets in rapidly or not so rapidly; the paint is eroded away leaving bare steel; the steel is then subjected to the combined damaging effects of cavitation erosion plus corrosion; the rudder becomes pitted and damaged, usually in a specific pattern; inspection reveals the damage, hopefully before it is too late, and the rudder must be repaired or replaced before it disappears completely.The repair usually consists of welding to restore and build up the surface where the metal has eroded or corroded away, followed by repainting. Plates may need to be entirely replaced. This usually takes the form of lengthy and expensive hot work performed in drydock. Alternatively, it can involve expensive, drawn out underwater repairs to the rudder to keep it functioning until the next opportunity to drydock the ship. Repairs done under water can only be considered a temporary measure since the steel and the welds must of necessity be left bare.

Figure 14: Typical repairs to a rudder that has suffered cavitation damaged. (Source: The Hydrex Group; Hydrex White Paper No.6, 2011)The vessel sails and the repaired rudder is subjected to further cavitation. Weaker now, the damage occurs more rapidly. Before too long the rudder must be replaced entirely. This all adds up to a continuing economic nightmare for the shipowner/operator. Drydocking is expensive in many ways, not the least of which is the off-hire time it entails.

3.3 How To Extend The Lifespan Of The RudderSymptoms of rudder failure are not easily detected, but you can lower the risk of failure with a proper program of rudder care and maintenance, hence increase its lifespan.

Know your rudder: Is it outboard or inboard? Spade or skeg-mounted? Is the stock aluminum, stainless steel or composite? Solid or hollow? A thin-wall aluminum stock might be fine for bay sailing, but is unlikely to survive an encounter with a drift net or a coral head. Recognizing a rudders obvious weaknesses should keep from taxing it beyond its capabilities.Service the bearings: Grit trapped inside a rudder tube abrades a stainless steel stock and opens the door to virulent corrosion. There is usually little water flow inside a rudder tube, so grit will likely remain there unless its flushed out. Give the rudder tube and bearings a thorough high-pressure flush every time the boat is hauled. Pintles and gudgeons can also benefit from flushing.If the rudder tube has grease points, give them a squirt of grease at least once a year. Roller bearings should be cleaned but never lubricated, although a bit of grease on the bearing carrier can retard corrosion and make future servicing easier. Worn bushings or bearing rollers should be replaced. Worn rudder tubes can be rejuvenated by injecting graphite-thickened epoxy into the tube interior with the stock coated with mold-release wax in place. Check vertical alignment: Aside from its adverse effect on sailing performance, a bent rudder stock will have been weakened, and straightening it will weaken it more. The force that bent the stock may also have damaged the rudders bearings, internal frame, outer shell or even the structure of the hull and rudder tube. A spade rudder that is not vertical or does not rotate in place at the bottom of the blade requires a careful and complete evaluation.Test for ease of rotation: Rudders should turn smoothly from stop to stop. Any roughness or drag suggests corrosion of the stock, swelling or distortion of a solid bearing, flattened rollers in a roller bearing or other corrosion, wear or alignment issues.Smooth action is eaasily checked if it have tiller steering, but it may need to release the rudder from the steering mechanism on a wheel-steered boat. Make sure that any observed drag is not caused by the support bearing under the pin or nut that prevents the rudder from dropping out of the boat. Testing rotation with the boat afloat rather than on the hard should eliminate this issue.Confirm strong stops: Rudder movement beyond around 35 degrees either side of center is undesirable. The absence of strong stops that prevent the rudder from exceeding these angles exposes it to the risk of being slammed over by a following sea or when powering in reverse. This risks jamming the rudder as the broadside position of the blade subjects the stock to a violent bending force.Check for play: Outboard rudders and rudders with a bottom bearing should be checked regularly for wear of pintles, gudgeons and other hardware by trying to rattle the rudder in its bearings. Spade rudders are supported by bearings inside the boat, so push the bottom of a spade rudder side to side to check for tube wear or other bearing problems. Check inboard rudders of all types by locking the tiller or quadrant rigidly against a stop and trying to move the back edge of the rudder blade. Any movement indicates failure of the internal structure or deterioration of the filler.Examine the blade: Pay particular attention to the edges of the blade, looking for any signs of cracking or separation. Use a mirror and a light to get a look at the top of the blade, particularly where the stock enters it. Any splits or cracks here will allow water into the interior of the rudder. Because hardened resin eventually loses its grip on a metal stock, I like to run an O-ring-like bead of flexible polyurethane sealant (3M 5200) around the stock where it enters the top of the blade. This is best done with the rudder out of the boat or at least dropped.Drain: When sailboats are hauled out of the water, the rudder often drips long after the hull is dry, something that is noticed by far too few owners. Water inside a rudder is the enemy. It is corroding the metal framework and delaminating the blade; in freezing weather it will shatter things. When the boat is hauled,watch for continuing drips or rivulets from the bottom fitting. After the hull has been pressure-washed and is dry, feel the bottom of the rudder. If it is wet, wipe it with a white towel. Rust color is a clue to what is going on inside.

If the rudder does not drip, that doesnt necessarily mean it is dry inside. It is almost always enlightening to drill into the interior of the blade at or near the bottom. Do this with a battery-powered drill so it dont get electrocuted when water comes trickling out.Again, the color of this water will serve as a clue to the possible extent of interior corrosion. Try to drill 1/8in holes in several locations. These are easily repaired before launch with a bit of epoxy putty. Water inside a rudder does not condemn it, but an absence of water is reassuring. Tea-colored water pouring from your rudder is cause for concern.View the stock: The best way to tell if the stock is sound is to get a look at it where it is most likely to fail, in the area hidden by the rudder tube. This is like examining through-the-deck chainplates by extracting them. In the case of a rudder, dropping it a few inches to expose the critical part of the stock should be adequate. This applies equally to composite stocks, which can suffer from hidden wear or damage just above where they enter the hull.

4.0 ConclusionThe rudder of the ship played an important role in ship maneuvering and motion. It is crucial to always inspected and monitored the ship rudder constantly to prevent from any unwanted breakdown or problem later on. In conclusion, ship rudder failure can happen in five different type of failures, which is stock failure, framework failure, delamination, bearing failure and cavitation. All these kind of failures can lead to unexpected loss, disturbing the ship operation and can harm the lives of the seafarer. Hence, a certain prevention method such as rudder stock repair, proper material coating and some repairing work should be applied and practiced so the rudder can work perfectly, thus longer the lifespan of the rudder.

5.0 ReferencesWebsite:1. http://www.sailmagazine.com/boatworks/know-your-rudder2. http://www.slideshare.net/silvercyril/ship-rudders3. http://www.cruiserlog.com/forums/f12/rudder-stock-failure-leading-to-yacht-sinking-1845.html4. http://www.cruisersforum.com/forums/f55/rudder-stock-failure-129234.html5. http://sfbaysss.org/forum/showthread.php?1190-Rudder-Failure6. http://officerofthewatch.com/2013/08/16/incident-information-on-broken-rudderstock-due-to-corrosion-fatigue/7. http://www.pyiinc.com/jefa-rudder/rudderstock.htmlOthers:1. A Report on the Causes of Ship's Rudder Breakdown by NYK-TDG Maritime Academy, January 20132. HYDREX White Paper No.6, Rudder Cavitation Damage Solved by The Hydrex Group, 20113. Material Selection in Mechanical Design, Michael F. Ashby

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