Feedback on e-learning

Over the Last few months i have been working with the blogger system and trying out a new way of learning by using the internet and blogs to get the most out of this course. From the word go i found the blogging quite easy to get a grip of, this was probably because i used computers in high school but also because the computer help at the start of the course was a great help and boost to get going. I really enjoyed filling out the questions on my blog after rob had put them up on his blog because i prefer to do it this way compared to filling out a test at the end of each week or month. using the internet has been great to gather info to post on my blog because the information on the internet is all up to date and relevant in today's marine industry.

Great Video on "2 stroke VS 4 stroke"

2 Stroke Engines...continue

Explain how a two stroke engine works?

you can understand a two-stroke engine by watching each part of the cycle in the video below or by looking at these pictures. Start with the point where the spark plug fires. Fuel and air in the cylinder have been compressed and when the spark plug fires the mixture ignites. The resulting explosion drives the piston to the right. Note that as the piston moves to the right, it is compressing the air/fuel mixture in the crankcase. As the piston approaches the bottom of its stroke, the exhaust port is uncovered. The pressure in the cylinder drives most of the exhaust gases out of cylinder, as shown here:

As the piston finally bottoms out, the intake port is uncovered. The piston's movement has pressurized the mixture in the crankcase, so it rushes into the cylinder, displacing the remaining exhaust gases and filling the cylinder with a fresh charge of fuel, as shown here:

Note that in many two-stroke engines the piston is shaped so that the incoming fuel mixture doesn't simply flow right over the top of the piston and out the exhaust port.

Now the momentum in the crankshaft starts driving the piston back toward the spark plug for the compression stroke. As the air/fuel mixture in the piston is compressed, notice that a vacuum is created in the crankcase. This vacuum opens the reed valve and sucks air/fuel/oil in from the carburetor.

Once the piston makes it to the end of the compression stroke, the spark plug fires again to repeat the cycle. It's called a two-stoke engine because there is a compression stroke and then a combustion stroke. In a four-stroke engine there are separate intake, compression, combustion and exhaust strokes.

Explain what is meant, by scavenging when applied to 2 stroke SI engines?

compressed air is sent to the combustion cylinder with the help of blowers etc.,it helps to clean the cylinder of burnt gases, this process is known as scavenging.

Why must roller and ball race bearings be used on 2 stroke SI engine crankshafts?
the caged roller bearings are only use in two stroke engines and where invented before the more modern four stroke method of injecting the oil into the sleeve around the bearing to lubricate it. the roller type is where there are a number of linked balls in the bearing they are joined so that they can not all fall to one side of the cage. the evenly spread balls help by spreading the load all around the circumference of the bearing not just in one spot, this prevents uneven wear. 

Why are rollers caged in crankshaft bearings?
The roller cylinders are all linked to stop uneven spread of the rollers, they are caged to that the rollers all stay in the right place and so that there is not uneven wear on the bearing

Why must ‘split’ type bearings be used on one piece crankshafts?

Why do we have pins between the piston ring gaps on a 2 stroke?

How does a reed valve work on a two stroke?

How do you check a reed valve?

Explain the term ovality and taper and how are they formed?

How does the piston rings seal in the bore?

What is meant by the terms groove depth, side clearance and end gap on the pistons rings?

Explain the difference between a 2 stroke and a 4 stroke engine?

What is meant by each of the following terms:

(a) Mechanical Efficiency(b) Thermal Efficiency(c) Volumetric Efficiency?

List 2 methods of lubricating the internal parts of 2 stroke S.I. engines?

2 Stroke Engines

How does a 2 stroke engine work, explain whats happening below the piston and above the piston?

 when the piston is at the bottom there is no fuel and not much air above the piston head, then as the piston rises again the fuel and air mixture is forced into the bore and up above the piston, as the piston travels up the bore pressure above the piston rises until it is compressed so much it explodes. The piston is forced back down at a rapid rate as the exhaust is sucked out of the cylinder due to a vacuum effect, then it begins all over again...



Why do 2 stroke engines have caged roll bearings?

 Rolling bearing are just two circular rings of metal that are joined together by a series of ball bearings. this means that they can withstand high speeds and are very durable as long as they are cooled while in use. they are used in the two stroke engines to reduce friction and are found around the shaft supporting the pistons.

Why do the  2 stroke piston have pins between the pison gap?

 Will have to ask and fill in later...

Whats the difference between a 2 and 4 stroke engine?

"Stroke" is just referring to the movement of the piston in the engine block. 2 Stroke means one stroke in each direction. A 2 stoke engine will have a compression stroke followed by an explosion made from the mixed fuel and oxygen. On the return stroke new fuel mixture is inserted into the cylinder.

A 4 stroke engine has 1 compression stroke and 1 exhaust stoke. Each is followed by a return stroke. The compression stroke compresses the fuel air mixture prior to the gas explosion. The exhaust stroke simply pushes the burnt gases out the exhaust.

Here is a common list of all the advantages and disadvantages of the two stroke engine:

Advantages of 2 Stroke Engines:
- Two-stroke engines do not have valves, simplifying their construction.
- Two-stroke engines fire once every revolution (four-stroke engines fire once every other revolution). This gives two-stroke engines a significant power boost.
- Two-stroke engines are lighter, and cost less to manufacture.
- Two-stroke engines have the potential for about twice the power in the same size because there are twice as many power strokes per revolution.

Disadvantages of 2 Stroke Engines:
- Two-stroke engines don't live as long as four-stroke engines. The lack of a dedicated lubrication system means that the parts of a two-stroke engine wear-out faster. Two-stroke engines require a mix of oil in with the gas to lubricate the crankshaft, connecting rod and cylinder walls.
- Two-stroke oil can be expensive. Mixing ratio is about 4 ounces per gallon of gas: burning about a gallon of oil every 1,000 miles.
- Two-stroke engines do not use fuel efficiently, yielding fewer miles per gallon.
- Two-stroke engines produce more pollution.
From:
-- The combustion of the oil in the gas. The oil makes all two-stroke engines smoky to some extent, and a badly worn two-stroke engine can emit more oily smoke.
-- Each time a new mix of air/fuel is loaded into the combustion chamber, part of it leaks out through the exhaust port.

 

 www.animatedengines.com/twostroke.shtml

Yamaha DEO30 Strip down

Health and Safety when welding

What colours are these bottles, how are they stored, transport when refilling them
Gas cylinders?

Gas bottles are black, blue or green in most places and are a bottle of a very highly compressed substance, this means they want to be treated with care and are not to be knocked around or tipped over. if the head of one of these bottles where to be knocked off by tipping then it would turn into a very fast missile quickly.  unlike acetylene gas bottles can lye on there sides although it is not recommended all the bottles you use for welding should be kept on a trolley for transport and not rolled or chucked about.

Acetylene?

 Acetylene is the flammable gas which lights the torch, only with the oxygen is the flame from the torch hot enough to weld. acetylene is a gas that will displace oxygen and will catch alight so it must not be left on other than when you light the torch. the bottles must be kept stanting up and on a trolley as the liquid in the bottom of the bottle will settle otherwise and this will come if you use it on its side, this could be very dangerous. these bottles are red or maroon in color and will be the same shape and the gas.

welding hoses?

welding hoses run from the gas bottles to the torch, these are normally the color of each of the bottles and should be hooked up in the correct way. the hoses must never be left on the floor as they cause a tripping hazard and may also become damaged from people stepping on them. they should be coiled up and hung over the bottles or on a hook. if you hear of a leak in any of the hoses you should report it asap. never bend the hose so that it cuts off the circulation, this will cause build up of gas and may put unwanted pressure on the gauges.

Welding torch?

The welding torch is a simple devise that mixed the two gases and gives you your flame. this must always be hung up after use and while having a break when it is on, if not you could bump it and send a extremely hot flame falling out of control. the torch can be held any way that is comfortable for you but it must be always pointed in the general direction of you work and you must never wave it around or talk to someone while holding it.

welding tips?

Welding tips come in many different sizes and are fitted to the end of you torch, these must be cleaned out when using them regularly as molten metal can stick to them and change you welding flame. they must always be screwed on tight otherwise you may get a leak and this will start a second flame from you torch, this could be dangerous also.

Flashback arrestors?

Flashback arrestors are fitted right below the gauges, they serve the purpose of if there is a flashback in the torch and the flame travels up the hose to the bottles this devise will lock down and stop the flow, if this was not fitted the flame could go into the bottle and explode killing you. they must be serviced regularly and if one does go off than you can reset it by pushing the clip back down and you gas will flow again.

What flames are used for different metals?

There are three types of flames that are used for gas welding, the first is the neutral flame. this flame is the most common one and is used for general welding or jointing of two metals, with or without rod. for brazing you will use and slightly colder flame as the braze will melt at a colder temperature, you may also want to change the tip to a larger one if so. The last flame is used for cutting only and will not be very good at all for anything else as it is harsh and powerful and will simply burn right through the metal before you can add rod or melt the two plates together.

Welding in different environments?

There are many work situations which add to the hazards of welding. Each must be assessed carefully, since there may be added hazards such as falls or asphyxiation. This is particularly true of work in confined spaces, where there is a very real risk of death, and the employer should make a critical assessment of the work to be done, and how it may be carried out safely.

Welding in the workshop?

The employer needs to ensure that the lighting conditions are adequate for the work undertaken - giving extra lighting where necessary. Welders stand for long periods of time, since they must keep a very steady hand position, and this means that they can become quite cold if the workshop is not sufficiently well heated. Conversely in hot weather, the environment can become unbearably hot, and the welder has not got the option of removing clothing. Both overheating and underheating can cause fall in comfort, efficiency and productivity.

Housekeeping is extremely important to avoid slips, trips and falls, damage to equipment and fire.

Fumes?

Welding vapourises metals, and anything which is resting on the surface. This gives rise to fume, which is condensed fine particulate material. The fume is mostly oxides of the metals, including any alloying elements, but it also contains gases produced in the arc, such as ozone or oxides of nitrogen, and decomposition products from any paint or coating which was on the metal surface. The nature and quantity of this fume depends critically upon the welding process, the materials and the welding parameters. Some is harmful to health, for instance stainless steel fume contains chromium, and welding galvanised steel produces zinc fume.

WEBSITES

http://www.riegler.net/pages/02druck-temp/schweisstechnik.shop

http://www.osh.dol.govt.nz/order/catalogue/welding.shtml

www.hse.gov.uk/welding/

www.weldinginfocenter.org/health/hs_02.html

www.weldinginfocenter.org/health/index.html  

This is the First page on my 15 meter and a blurb on the boat

15 Meter Power Launch

Barrier 50

The barrier 50 is the latest design to come off the Barrier design drawing board, with its twin Cummins Mercruiser Zeus Drives this slick sports cruiser cruises comfortably at 28 knots. The Barrier 50 supports two Moeller Designed 1000L diesel tanks the cruiser provides a ‘go-anywhere’ approach to your boating experience. Fully loaded with all the latest electronic and mechanical technology this boat is great for a more laid back boat owner who does not want to worry about engine checks and boat maintenance. This streamlined machine is faultless in any sea that can be thrown at it and with its full carbon fiber and alloy constructed hard top you will stay dry while skippering it at the simple but functional helm station. As you step through the center walkway leading out of the cockpit you will notice a tournament sized aft deck on the Barrier 50 which will keep any fisherman or diver happy. Finally when you reach your destination you can feel comfortable when getting in and out of your tender with the hydraulic assisted swimming platform accommodating a boat cradle for your favorite toys. The barrier 50 is any family or couples dream boat who wish for those special moment, whether is hauling in that big fish or exploring the oceans depths, even just relaxing in the sun. It is all made possible with the magnificent craft. 

Engine room layout

The Barrier 50’s engine room is so comfortable that you could even call it a 3rd bedroom if you had to, with a built in stairway and handrail to guide you into the powerhouse of the boat, the two large Cummins engines and drive systems are sure to catch any petrol heads eye. Digital touch display helps in general everyday maintenance.

Engine position: When I decided to power the vessel with the Cummins Zeus Drives I was informed that they were best when fitted in pairs (I will explain further in detail later in doc) this meant that the two engines would have to be fitted side by side and that the engine room layout would have to reflect this decision. The engines and pods where going to be fitted at the very stern of the craft and I would not be placing any items to aft of the engines, this would prove to be easier for engine maintenance and means that all the boats electronics and gen-set equipment is up the front and easy to access.

This is a Riviera 43 offshore and is a great example of a 15 meter power boat

Hi Guys. Here are the websites we were looking at today and a couple more good ones

 Maritimo Power Launchs, with the 360 degree tour of the boats
www.maritimo.com.au

Azimut Yachts is the one with the larger streamlined power vessels
www.azimutyachts.com

Wally boats where the last ones we looked at, made from a heap of carbon fiber
www.wally.com

Riviera also have a good 15 meter to look at
www.rmarine.co.nz/ 

Sea ray have great spec sheets and pictures which give you a good idea
www.searay.com/ 

Riva are very high spec power boats which are amazing to look at and admire
www.riva-yacht.com/visitors/index.php?lang=en

Hope some of this can be helpful 

Engine Cooling

Explain the terms conduction,convection and radiation?

Radiation is when heat is transferred directly through space, for example sunlight is a form of radiation because you can feel the heat from the sun but it can not be seen. Convection is the transfer of heating the water from only movement. when steam is produced the heat flows in the evaporated water and this is how the heat follows the currents. Conduction is the term used to explain the heat transfer from one solid to another. for example when you put a spoon in a cup of hot water the metal partials are rubbed together and that heats up the spoon from the water this is a common way conduction works. heat can also travel from one solid to another.

Indirect cooling?

On a boat the engine is cooled by water because most of the time there is a lack of air flowing fast enough to funnel much, the raw water is sucked from the ocean by a raw water pump and pumped through a series of water jackets around the engine. this cools the main components of the engine and in turn makes for better running conditions

Direct cooling?

Air cooling is an example of direct cooling as the body of the car or boat will scoop up air and force it into the engine compartment, this means the engine will have more fresh air to intake into the turbo or engine through the radiator.

What are the the problems you get with indect and direct cooling?

With direct there is normally not enough air flow to cool the engine by its self as boats operate at much lower speeds than cars most of the time. For indirect, most boats are operated in salt water around the world and with saltwater possessing great corrosion property's it means that the internals of the engine will start to rust and corrode over years of salt sitting in the intake pipes and jackets of the engine.

What is the purpose of a thermostat?

Every common engine has a thermostat that sits between the radiator and the main engine block, it is usually around 5cm in diameter and sits flush in its own housing. its job is to block the flow of coolant to the engine until the system has heated up. by letting the engine warm up faster it reduces engine wear and increases the car or boats fuel efficiency.

Pressure cap?

Basically the pressure cap is just a release valve that will let the pressure inside of the radiator out when it reaches that designated PSI, this is usually around 15 on most car engines. This will increase the boiling point of the coolant inside of the radiator by about 25 degrees Celsius. When the coolant in the radiator heats up the particles expand, this means the pressure cap will release the pressure when it expands and in turn make the boiling point much higher.  

What is the purpose of a core plug and why is it used?

Core or freeze plugs as they are sometimes referred to are small caps near the bottom of the engine block. they are fitted in the manufacture stage when the mold for the engine is made up. they are mainly used more in colder climates when liquid in the engine expands and it has no where to go the plugs will pop out to release the pressure instead of cracking the engine block or doing and damage to the engine.

What is the purpose of a heat exchanger?

A heat exchanger in a specializes device that assists in the transfer of heat from one liquid to another or from one liquid to a solid. In some cases, a solid wall may separate the fluids and prevent them from mixing. In other designs, the fluids may be in direct contact with each other. In the most efficient heat exchangers, the surface area of the wall between the fluids is maximized while simultaneously minimizing the fluid flow resistance.

How does the heat exchanger work?

http://www.ehow.com/video_4973845_a-heat-exchanger-work.html

This video explains well how the common heat exchanger works in a motor vehicle

What is the core of the heat exchanger made of?

The core of a heat exchanger is based on the same idea at a radiator core but is made from a special fibrous paper, which have high moisture permeability, anti-rends, anti-mildew features; with ABS framework,
which is not easy to break, long service time, pro-environment; with galvanized sheet
cover plate and plastic handle. 

How does the centrifugal circulating water pump work?

A circular pump circulates a liquid or gas around in a round piece of pipe, because the pipe is a loop the pump does not need to work as hard and only uses power when necessary. the most common type of circular pump is the centrifugal pump that is powered by a small electric motor in a waterproof housing. the motor drives a small impeller which pushes water past it. 

Why is it important to lubicate the impellor when fitting from new?

When a  new impeller is fitted to a engine or pump the water or lubricant will be drained from the system. this mean when you put the new impeller into the socket there will be no lube and in turn if it way started straight away it would burn out the new impeller very quickly. so when it is fitted you should lube up the new part so it can not be damaged in the initial start up.   

When fitting a impeller what should you check before refitting the housing and why?

That the impeller is offset from the center of the housing. this is because when the impeller turns it scoops the water with the blades and the offset of the center means the water will be picked up easier and there will be no water that can escape from the side of the blades. when an impeller is fitted you must also to a thorough test on all the blades at a small hole or crack a grow very fast when the first start up occurs after servicing.

What is the purpose of a oil cooler and how does it work?

What is the process of a intercooler/aftercooler how does it work?

Hot air from the turbo flows through tubes inside the intercooler. The turbo air transfers heat to the tubes, warming the tubes and cooling the turbo air. Outside air (or water) passes over the tubes and between fins that are attached to the tubes. Heat is transferred from the hot tubes and fins to the cool outside air. This heats the outside air while cooling the tubes. This is how the turbo air is cooled down. Heat goes from the turbo air to the tubes to the outside air.

Why do we have Inhibitors & antifreeze?

It keeps the engine's coolant from freezing in the winter. Ice takes up more space than liquid water, so it would break open the radiator & possibly the engine block. It also has some stuff to slow rusting inside the system, but the main purpose is anti-freeze. You don't want to use pure anti-freeze since it can't cool the engine as well after everything warms up.

How do you test Antifreeze?

 Make sure your car engine is cool. Open the hood of your car and find the coolant reserve container. It is usually a clear plastic tank and if you follow the hoses on your radiator it will connect with the reserve container. It will have lines on it to indicate wether your fluid levels are low or high.

Unscrew the cap to the reserve tank and pour the Antifreeze/Coolant in. You can use a funnel if you need to, so you can avoid spilling. (If your reserve tank is empty you should also add some fluids to the radiator itself.) When you have finished pouring in the correct amount, screw the cap back on.

If your car doesn't have a reserve tank for the Antifreeze/Coolant, pour the fluids directly into your radiator. To check the fluids directly in the radiator, look into it. You should be able to see the fluid.

If you need to pour the fluids directly into the radiator itself, make sure the engine is completely cooled before you unscrew the radiator cap. When the cap is removed, pour a little Antifreeze/Coolant directly into the radiator, being careful not to over flow it.

Make sure you never unscrew the radiator cap on a HOT ENGINE, the fluids and steam could spurt out and burn you. Remember how hot it is in there.

What is cavitation corrosion?

Erosion-corrosion is caused by the relative movement between a corrosive fluid and a metal surface. The mechanical aspect of the movement is important and friction and wear phenomena can be involved. This process leads to the formation of grooves, valleys, wavy surfaces, holes and a worn look.

Describle the terms:

Corrosion Fatigue?

Corrosion-fatigue is the result of the combined action of an alternating or cycling stresses and a corrosive environment. The fatigue process is thought to cause rupture of the protective passive film, upon which corrosion is accelerated. If the metal is simultaneously exposed to a corrosive environment, the failure can take place at even lower loads and after shorter time.

Crevice corrosion?

 This sort of corrosion is only present when there are small cracks or creases in tight areas. the salt sits in these areas and because they are in remote areas the salt is not washed out and it will sit there and end up corroding the metal on which it sits.

What is Electrolysis?

Electrolysis is the separating of a compound into its constituent elements by passing an electrical current through it when in a molten or aqueous state. The word electrolysis means the process of breaking molecules to smaller parts by using an electric current. Positive and negative poles of an electric source, such as a battery, can absorb opposite ions of an electrolyte, causing separation of ions and creation of a new substance.

How do you prevent corrosion?

• Use metals below the water that are as close to each other as possible on the galvanic scale. Don't mix metals.
• Fasteners must always be more noble than the fitting on which they're used.
• Put a zinc on it...!  But don't put too much zinc on it! Weld the zinc on if possible, or bolt the zinc directly to the piece.
• Never paint a zinc anode!
• When bringing AC shore power aboard, it should always first pass through a true marine grade isolation transformer.
• Battery chargers must be a marine quality isolation transformer type.
• Use bonding if necessary, if you have a highly complicated electrical system, in order to reduce the electrical shock hazard.
• Do everything possible to avoid stray currents in the water, and to prevent them aboard

What are sacrifical anode made off?

Anodes are made of Zinc and other very weak metals, they are made of this so that the other stronger metal is not eaten away because the corrosion is focused on the weaker metal. boats have many anodes all over the boats hull and are fitted with a single or two screws through the middle.

Where would you place them in the marine industry?

Anodes are fitted in many places all over the hull, the main points are where the electrical current meets the water and this is normally where the corrosion starts. theses are hull fittings like sea cocks and where the shaft exits the hull. Stern legs are also a large point where corrosion can occur and this means they are fitted with numerous anodes.

WEBSITES
http://ethemes.missouri.edu/themes/1369
http://auto.howstuffworks.com/question248.htm
http://auto.howstuffworks.com/cooling-system7.htm
http://www.ehow.com/how-does_4963320_circulator-pump-work.html
http://blogs.howstuffworks.com/2009/04/15/how-does-a-turbocharger-with-intercooler-work/
http://en.wikipedia.org/wiki/Electrolysis
http://www.waterheaterrescue.com/pages/WHRpages/English/Longevity/water-heater-anodes.html
http://www.thegluepeople.co.uk/v1/html/marine_industry.html
http://www.google.co.nz/imgres?imgurl=http://www.green-planet-solar-energy.com/images/hydrogen-electrolysis.gif&imgrefurl=http://www.green-planet-solar-energy.com/hydrogen-electrolysis.html&usg=__vQyeTEg4MtVmG1HlimazG4dOtKQ=&h=427&w=500&sz=19&hl=en&start=0&zoom=1&tbnid=_sa0wYuXBKrEOM:&tbnh=132&tbnw=156&ei=Zrb_TZOuCcjIrQefpKm-Dw&prev=/search%3Fq%3DWhat%2Bis%2BElectrolysis%26um%3D1%26hl%3Den%26biw%3D1366%26bih%3D552%26tbm%3Disch&um=1&itbs=1&iact=hc&vpx=125&vpy=78&dur=743&hovh=207&hovw=243&tx=142&ty=96&page=1&ndsp=24&ved=1t:429,r:0,s:0&biw=1366&bih=552