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NYK-TDG Maritime Academy Report on the Causes of ShipsKnowledge Avenue, Carmeltown, Canlubang Rudder BreakdownCalamba City 4037, Laguna, Philippines

1

Report on the Causes of Ships Rudder Breakdown

A Case Study in Research I

Presented by:

E/Cdt Bepitel, Breylle L.

E/Cdt Veloso, Ryan P.

Crankshaft-III

Presented to:

C/E Denise C. Valdez

Instructor

January 2013


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TABLE OF CONTENTS PAGES

Appendix

List of Figures

Synopsis

Glossary

3

4

5

Chapter 1 - Introduction

1.1 Background of the Study 6

1.2 Parts of a Rudder 7

1.3 Types of Rudders 8

1.4 Types of Rudder Failures 9

Chapter 2 - Narrative

2.1 Causes of Rudder Failure

2.1.1 Stock failure 10-11

2.1.2 Delamination 12

2.1.3 Cavitation 13-15

Chapter 3Analysis of Data

3.1 Rudder Failure Repairs

3.1.1 Rudder Stock Repair 16-18

3.1.2 Delamination Repair 18-23

3.1.3 Cavitation Repair 24-29

Chapter 4Conclusion 30

Chapter 5Recommendations 31

5.1 Actions to be taken during MOB in the berth

Sources 32


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APPENDIX

List of Figures

FIGURE PAGES

Fig. 1 Damaged Rudder Stock 10

Fig. 2 Delaminated Rudder Skin/Coating 12

Fig. 3 Cavitation of a Rudder 13

Fig. 4 Rudder Stock Repair 16-17

Fig. 5 Drilling and Filling of Delaminated Area 19

Fig. 6 Removing the Skin and Repairing the Core 21

Fig. 7 Grid 2 Ft By 2 Ft Squares in Indexed Locations of Cavitated Rudder 24

Fig. 8 Critical Repairs to a Rudder that has Suffered Cavitation 24


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SYNOPSIS

Ships rudder breakdown is a constant expense and interruption to ship

owners and operators.

A great deal of effort goes into the design and manufacture of rudders

because they are such an important part of a vessel. As any ship owner

knows, a ships rudder is particularly prone to damage. The problem features

more prominently in high speed container carriers and other fast ships, which

are more seriously affected than slower vessels. However, it is a potentialproblem and hazard for all ships and boats.

If a rudder is not given the proper protection against different rudder failures

such as rudder stock failure, delamination and cavitation, these result in

frequent, costly repairs to or replacement of this vital part of the ships

underwater equipment. The financial consequences can be substantial for

the owner. So far, the bulk of efforts to relieve this problem are quite effective

somehow.


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GLOSSARY

Cathodic Protection(CP)- is a technique used to control the corrosion

of a metal surface by making it the cathode of an electrochemical cell

Epoxy - has a wide range of applications, including metal coatings,

use in electronics / electrical components, high tension electrical

insulators.

Erosion corrosion -is a degradation of material surface due tomechanical action, often by impinging liquid, abrasion by a slurry,

particles suspended in fast flowing liquid or gas, bubbles or droplets,

cavitation.

Fiberglass - is a fiber reinforced polymer made of a plastic matrix

reinforced by fine fibers of glass.

Fouling -is the accumulation of unwanted material on solid surfaces to

the detriment of function.

Oxidation -is defined as the interaction between oxygen molecules

and all the different substances they may contact, from metal to living

tissue.

Shipowner -is the owner of a merchant vessel (commercial ship).

Turbulence- is a flow regime characterized by chaotic and stochastic

property changes.


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1. CHAPTER I

INTRODUCTION

1.1 Background of the Study

A rudder is a device used to steer a ship, boat, submarine, hovercraft,

aircraft or other conveyance that moves through a medium (generally

air or water). A rudder operates by redirecting the fluid past the hull.

In basic form, a rudder is a flat plane or sheet of material attached with

hinges to the ships after end. Often rudders are shaped so as to

minimize hydrodynamic drag. On simple watercraft, a tilleressentially,

a stick or pole acting as a lever armmay be attached to the top of

the rudder to allow it to be turned by a helmsman. In larger vessels,

cables, pushrods, or hydraulics may be used to link rudders to steering

wheel.

Through normal use, rudders go through a lot of stress. With every turn,

the skin on each side is subject 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 may have

been under-engineered all contribute to rudder failure. Of all the parts

of a ship, rudder is one of the most important parts in a vessel for it is

use in maneuvering. After hull integrity, rudder integrity is the most vital

component of a seaworthy vessel.

Maintaining rudder integrity is quite hard because of its situated

position. It requires dry docking before proceeding to its maintenance.

As a result, there are already many reported cases of breakdown of

ships rudders.


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These caught the attention of the seafaring industry to solve this issue

because of the damages caused by ships rudder breakdown like

collision, grounding and worst, loss of lives. As a result, the researchers

have come up with the following cases of rudder failures but before

that, parts of the rudder, types of rudders and kinds of rudder will be

discussed first.

1.2 Parts of a Rudder

1.2.1 Rudder Stock

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.

1.2.2 Rudder Framework

Rudder framework is made out of stainless steel, rather than mild steel,

and is firmly attached to the stock with long, strong welds.

1.2.3 Rudder Bearings

Rudder bearing is used to support rotating shaft against either

transverse or thrusts loads.

1.2.4 Rudder Shaft

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.

1.2.5 Rudder Brace

Rudder brace is the system of aligned gudgeons and pintles which

form a pivot for the rudder.


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1.3 Types of Rudders

The choice of the rudder type will depend on factors such as ship or

boat type and size, the shape of the stern, size of the rudder required

and whether there is a propeller upstream of the rudder.

1.3.1 Balanced Rudder

Open stern frame with a bottom pintle, which is a support bolt or pin

with a bearing. The upper bearing is inside the hull. It has been applied

to vessels such as tugs and trawler sand extensively to single-screw

merchant ships.

1.3.2 Spade Rudder

A balanced rudder. Both bearings are inside the hull. Bending moments

as well as torque are carried by the stock, leading to larger stock

diameters and rudder thickness. Applied extensively to single and twin-

screw vessel, including small power craft, yachts, ferries, warship and

some large merchant ship.

1.3.3 Full skeg rudder

An unbalanced rudder. The rudder is supported by a fix skeg with a

pintle at the bottom. Applied mainly to large sailing yathcts, but also

applied as hydroplanes on the underwater vehicles.

1.3.4 Semi-balanced skeg rudder

Also known as horn rudder or mariner rudder. The movable part of the

rudder is supported by a fixed skeg with a pintle at the bottom of the

skeg.


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1.3.5 Semi-balanced rudder, aft of skeg or deadwood

Typically applied to the twin-screw ship with the single rudder. Tends to

have been suspended by the use of twin rudder or type.

1.4 Types of Rudder Failures

There are many different causes of rudder breakdown. It has its own

unique characteristics which differ from the other. One can causedamage to the ship instantly and others can affect in a long duration

of time.

These damages require careful investigation for it will occur anytime if

neglected to be solved. Examples of rudder breakdown are as follows:

1.4.1 Stock Failure

Stocks can fail in several ways, all related to inadequate strength.

However, a rudder stock should not be so strong that it pries open the

bottom of a boat rather than bending in a collision or grounding.

1.4.2 Delamination

It is the separation of the layers of coating caused by stress and

dissolution of the adhesives.

1.4.3 Cavitation

Cavitation is caused by the flows from the motion of the propeller, the

cavities imploding on the propeller blades or being transported rapidly

back to implode on the rudder surface. The cavitation can also be

caused by the turbulence around the rudder itself, and the collapse of

the cavities can occur almost immediately after the cavity is created.


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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.

Most rudders are constructed around a solid or hollow stainless steel or

aluminum stock. This tube or bar connects the rudder to the boats

steering mechanism.

Stocks can fail in several ways, all related to inadequate strength.

However, a rudder stock should not be so strong that it pries open the

bottom of a boat rather than bending in a collision or grounding. This

makes spade rudders on lightly built boats unavoidably more

vulnerable to a bent stockthe rudder is sacrificed to save the hull.

A bent metal stock can result in a rudder being jammed off-center,

which will stop any efforts to steer a boat with sails, a jury rudder or by

towing lines. Composite rudder stocks, meanwhile, will break rather

than bend.

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.

Stainless steel, in particular, suffers when deprived of oxygen, which is

exactly what happens up inside a rudder tube full of stagnant

seawater. This effect is worsened when 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

compromised enough that an impact or strong twist snaps it like a

pretzel, and the rudder falls away.


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2.1.2 Delamination

Fig. 2 Delaminated Rudder Skin/Coating

Delamination 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.

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.


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2.1.3 Cavitation

Fig. 3 Cavitation of a Rudder

A 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 vapor-

filled 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.


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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.

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.


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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.


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3. CHAPTER III

CASE ANALYSIS

As any ship owner knows, a ships rudder is particularly prone to

damage caused by many factors such as erosion, corrosion, possible

near grounding incident and many more. These factors result in

frequent, costly repairs to or replacement of this vital part of the ships

underwater equipment.

So far, the bulk of efforts to relieve this problem have not been fully

effective. Symptoms of rudder failure are not easily detected, but the

ship can lower the risk of failure with a proper program of rudder care

and maintenance. The researchers have come up with the following

repairs taken from reliable sources.

3.1 Rudder Failure Repairs

3.1.1 Rudder Stock Repair


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Fig. 4 Rudder Stock Repair

According 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 fewinches 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.


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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.

3.1.2 Delamination Repair

Accumulated stresses can lead to cracks in other locations on the

rudder. A common skin failure on an aging rudder occurs in the area

where the metal mandrel inside the rudder ends.

These stress cracks show up on the sides of the rudder about two thirds

of the length down from the top. The damage may be isolated to the

cracks in the fiberglass skin or problems may go deeper.

When delamination is discovered, drill a few small holes to drain any

water that may have accumulated inside the void. Tap on the outside

of the rudder to identify the extent of damage.

Delaminated areas will have a distinct dull sound compared to

undamaged sections. Use a pencil or permanent marker to identify the

boundaries of damage.

The researchers have come up with the following procedures for

repairing delamination of rudders:


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There are two approaches one can take to restore strength to the

delaminated area.

1. The first and easiest option is the drill and fillapproach.

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.

Drilling and Filling Approach

Fig. 5 Drilling and Filling of Delaminated Area

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.


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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.

1. Drill a series of 1/8" to 3/16" holes on a one inch grid pattern over

the debonded area. Drill deep enough to get to the center of the

core. You may hit the metal mandrel.

2. Dry the core. Wet cores can take weeks or months to dry even ifa multitude of holes have been drilled. Force drying with heaters or

heat lamps is recommended for speeding the process. A small fan

blowing over the surface will help.

Locate any heat source carefully to minimize the risks of fire. I have

been surprised to find how hot a surface can get after leaving a heat

lamp unattended for several hours.

3. Verify that the core is dry by drilling a few more holes when you

think the rudder has dried out. Squeeze the core drillings to see if they

are dry.

4. Inject a slow curing epoxy such as 105 Resin and 206 Hardener or

105 Resin with 209 Extra Slow Hardener. Use syringes to force the epoxy

into the delaminated areas. Lay the rudder on its side with the drilled

side facing up, so gravity works in your favor.

5. Refill the holes as necessary with unthicken epoxy until the holes

are filled flush with the surface. A light layer of fiberglass cloth can be

applied over the area to strengthen the area if desired.


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Removing the Skin and Repairing the Core Approach

Fig. 6 Removing the Skin and Repairing the Core

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.

1. Cut through the fiberglass skin using the marked boundary of the

delaminated area as a guide. Use a rotary tool or a circular saw

with the blade set to cut just below the surface of the fiberglass.

2. Carefully pry off the fiberglass skin to expose the delaminated

core. Removing the skin may be difficult if the delamination is

within the core rather than between the skin and core.


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8. Press the fiberglass skin into the thickened epoxy and hold it in

position (flush with the surrounding skin), with weights, duct tape

or bungee cord.

9. Prepare the cuts in the fiberglass skin for repair by grinding a 12:1

bevel in both directions from the cut. An 1/8" thick fiberglass skin

will require a 1/2" wide bevel on either side of the cut.

10. Apply several layers of fiberglass tape over the joint. Use enough

layers to equal the thickness of the skin. (Several layers of 731 or732, 9 oz. fiberglass tape equals about 1/8".

11. Prepare the surface of the cured epoxy by washing with water

and an abrasive pad, and sanding thoroughly (or wet sanding).

Fair the fiberglass buildup with 407 Low-Density filled epoxy.


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3.1.3 Cavitation Repair

Fig. 7 Grid 2 Ft by 2 Ft Squares in Indexed Locations of Cavitated Rudder

Fig. 8 Critical Repairs to a Rudder that has Suffered Cavitation

Rudder cavitation damage is a well-known and extensively

documented phenomenon. There is a vast amount of literature on the

subject. High speed video has been used to capture the process of

cavitation in action so that it can be studied.


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Computer programs have been developed to model the effects of

cavitation and predict where the most damage will occur, depending

on the construction and shape of the rudder. Many scientists have

investigated the phenomenon and scientific papers on the subject

abound.

There have been many attempts to prevent the damage caused by

cavitation. In the main these attempts fall into the following categories:

1. Change the position of the rudder so that it is not behind the

propeller. This reduces cavitation on the rudder, but is

impractical since the ship loses its maneuverability. The ideal

placement of the rudder so that it provides maximum control of

the ship is directly behind and in the wake of the propeller. The

more rapidly moving water makes the rudder more effective.

In other words, positioning the rudder so that it carries out its

function in the best possible way renders it most liable to

cavitation damage.

2. Redesign the rudder so that it is less affected by the flows and

turbulence. Some inventors have developed a twisted rudder

which is marketed and in use.

The twist is an attempt to reduce the turbulence caused by the

flow of the water from the rotation of the propeller by changing

its angle of attack on the rudder. This has met with some success

but has not eliminated the problem.


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3. Strengthen the surface of the rudder to increase its resistance to

cavitation erosion, often with some other metal. This has only

partially relieved the problem, and can in fact be

counterproductive if the combination of metals increases the

electro-chemical/corrosion factor. The difference in potential

between metals can cause very rapid corrosion to occur.

Historically, the most dramatic example of this was perhaps the

attempt to put copper sheathing on steel hulls to protect them

from fouling. The proximity of the two metals resulted in very

rapid corrosion of the steel. There have been attempts to

reinforce the rudder with a stainless steel plate over the steel,

only to have the welds or fasteners holding the plates in place

corrode completely so that the plates simply dropped off.

4. Use cathodic protection systems to reduce the electro-

chemical/corrosive effects. Since the corrosion only sets in after

the protective coating has been eroded by cavitation, this is like

putting a lock on the barn door after the horse has been stolen.

It may reduce the corrosion, but it does not address the primary

cause, which is the erosion damage caused by the cavitation.

5. Develop better coatings and rudder protection.

Current Practices

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.


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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 dry dock.

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.

There have been many attempts to devise a better protection system

for the hull. Most of these have been ineffective but not all of them. 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 ship owner/operator.

Dry docking is expensive in many ways, not the least of which is the off-

hire time it entails.


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Successful Approach

One particular coating, a specially formulated glass flake vinylester

surface treated composite (STC) has been found to be extremely

effective in completely preventing rudder cavitation erosion from

occurring in the first place, thus breaking this vicious circle.

This was an entirely practical solution, stumbled upon almost by

accident by the manufacturer, since the coating system was designed

for protection of the underwater ship hull and fouling control, notdeveloped specifically for rudder protection. Observation of the

coating system in action demonstrated that hull areas which are

normally prone to cavitation erosion were successfully protected with

this STC. There was no cavitation erosion where it normally would be

expected to occur. This then led to its experimental application to

rudders.

So far in the eight years that this system has been in use on many

different rudders not one has suffered any cavitation erosion damage.

The rudders so treated have not even needed to be recoated with the

STC, let alone repaired or replaced. The STC not only offers protection

against rudder cavitation damage, it has also been used to repair

rudder damage where it has occurred due to an ineffective paint

scheme. In cases where the steel was pitted but not completely wornaway, the STC was used to build up and repair the pitting, before

being applied to entire rudder to protect it against future damage. This

has also proved to be 100% effective.

Due to its high glass content, this coating is extremely tough and

resilient and has the added advantage of being an electrical insulator

which successfully prevents electro-chemical corrosion from taking

place.


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While the experiment with the STC has not yet been attempted on

every type of vesselsrudder, and it remains to be tried on some of the

really high speed ships, results to date show a potential final solution to

all rudder cavitation problems.


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4. CHAPTER IV

CONCLUSION

During the duration of the case study the researchers had able to

come up with the following conclusions:

1. Rudder breakdown is a constant expense and interruption to

ship owners and operators. Increasing numbers of high speedcontainer carriers and other vessels have magnified the problem

since they suffer from different rudder failures more than lower

rev, slower ships.

2. Most attempts to solve the problem have proved unsuccessful,

as evidenced by the continuing need for frequent repair or

replacement of rudders. Rudder design has mitigated the

problem somewhat but far from solved it.

3. For rudder stock, failure usually occurs because of repeated and

reversing torsional stress or even corrosion.

4. For delamination, the failure is due to crack formations in the

rudder. These cracks serve as a pathway for fluid to enter the

coating down the core/substrate. As a result, the rudder coating

tends to debond from the core.

5. For cavitation, most coatings generally fail to provide adequate

protection and usually erode. Cavitation usually occurs

electrochemical processes and even hydrodynamic drag.


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5. CHAPTER V

RECOMMENDATIONS

After analyzing the case, the researchers had come up with the

following recommendations:

1.

To avoid further accident caused by ships rudder breakdown,

scheduled dry docking maintenance must be observed.

2. Ships should also choose the right type of rudder that would suit the

ships speed and even the route itself.

3. For rudder stock, repair and maintenance should be observed at

any cost. Checking the alignment and ensuring it free of cavitation

could also help.

4. For delaminated area, the second approach stated in the Chapter

III, removing the skin and repairing the core approachis the best

way to repair a delaminated rudder area. It is a more reliable repair

because one can see what he is bonding to. Surfaces can be dried

quickly and thoroughly, and damaged core can be removed and

replaced with new core.

5. For cavitation, cathodic protection is not really a solution for this. It

will only slower down the process. To maintain rudder for cavitation,

dry docking must be observed. Choosing the right paint coating,

choice of rudder material and type of rudder are big factors that

should be observed by ship owners.


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SOURCES:

http://sailmagazine.com/boatworks/know-your-rudder

http://www.google.com.ph/imgres?imgurl=http://www.shf.org.au/JO-

photos/JO-engineering-post2007/JO-rudder-stock-

repaired.jpg&imgrefurl=http://www.shf.org.au/JO-photos/JO-

engineering-images-from-2008.html&usg=__IgG0HzO4U-

5LkA5r3JnlKb2NS5M=&h=750&w=1004&sz=35&hl=fil&start=40&zoom=1&t

bnid=vwMNrkjRR5q85M:&tbnh=111&tbnw=149&ei=UIjFUPPNLKnAiQek_oD4Cg&prev=/search%3Fq%3Drudder%2Bstock%26start%3D20%26um%3

D1%26hl%3Dfil%26sa%3DN%26gbv%3D2%26tbm%3Disch&um=1&itbs=1

SILJA EUROPA (FIN), Breaking of the Starboard RudderM/S SILJA

EUROPA (FIN), Breaking of the Starboard Rudder Shaft in Aland

Archipelago on 22 November 2009

www. Marketendia.com

1 Jae-Moon Han et al., Analysis of the cavitating flow around the

horn-type rudder in the race of a propeller,CAV2001:sessionB9.005
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ship's hull damage

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