Questions?

Going through the licensing process ? Have queries, comments, or do you need an answer to that obscure exam question ? This is the place to post.
Ratherbeonvacation
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Questions?

Postby Ratherbeonvacation » Tue Nov 12, 2013 5:53 pm

1.In a straight drive diesel engine, what would you do if a full astern was needed in an emergency when the engine was operated full ahead?[quote][/quote]

2.How would you fit a trammel for future use to find TDC on a large Engine.

3.Why do some engines have tie bolts and some not. (think I might be thinking to hard about this)

4.Steps to take if you found crankshaft deflections out of limits

5. How can clearance volume be changed and corrected?

6. How is clean fuel oil insured on board? (Sampling during bunkering, fuel reports)??

7. How are explosions prevented in Fuel tanks. what gases are found in an empty fuel tank (seems simple enough but maybe I'm missing something.)

8. Temps and pressures for a constant pressure cycle.

If anyone can help with either question it would be a great help. As always thanks and keep the info coming...........

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JollyJack
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Re: Questions?

Postby JollyJack » Wed Nov 13, 2013 9:15 am

1. Think about what will happen if you went EFS when going FAOP.

2. Consult your 1st or 2nd year Apprenticeship notes

3. Think about size. A wee small medium speed vs a 4 story high B&W

4. Why do we take crankshaft deflections? Answer that and your question is answered for you

5. Who asked that question, and why? We don't design engines, we operate and maintain them. (I did it in my pimply youth to "soup up" a Norton 250 twin by taking out the head gaskets and lapping the heads to the barrels. It worked, too! I stopped looking at the speedo and just hung on at 120 mph!)

6. Probably through Lloyds or a P&I club.

7. I think you'd better research this, there's no glib answer. People die in tanks. MOSH Regulations, section 169 et seq.

http://laws-lois.justice.gc.ca/PDF/SOR-2010-120.pdf

PART 14
CONFINED SPACES
GENERAL

169. A person must not enter a confined space without
having been issued a work permit under section 166.

170. Before authorizing a person to enter a confined
space, the employer must ensure that all the requirements
of this Part are met.

(and so on)

8. Reeds Motor EK, Vol 12, p 88
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Ratherbeonvacation
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Re: Questions?

Postby Ratherbeonvacation » Wed Nov 13, 2013 10:40 am

As always thanks for the reply and clarification of some of this.

#1. still is jumping over me. I understand what could happen but if it is needed in an emergency what is to be done

#8. Reeds Motor EK, Vol 12, p 88?? My reeds motor Vol 12 has a sketch of piston ring profile. Is the revision different? mine is 2002.

Same thing with another question I had from a friend "(a) describe/sketch arrangements used to ensure engine cannot be operated in contradicition of the bridge telegraph (b)describe arrangements fitted to prevent engines from oerating in ahead positin after being put in astern position". Someone has put "answer in reed vol 12 pages 112-115 but in mine those pages are Bosh type fuel pumps???? Is this just a revision issue

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Re: Questions?

Postby EvenKeel » Wed Nov 13, 2013 11:26 am

I am scheduled to write Motor in a few weeks - so it looks like we are in the same boat.

I'll just add some text from my notes to what Jolly Jack stated on a few questions.

#1 I think they are looking to see that you know that there is a procedure to stopping the engine first (brakes on intermediate shafting) before reversing otherwise interlocks should prevent starting in the astern direction. Engines may continue to turn after the fuel is cut off due to propeller action. If an engine is reversed and an attempt is made to restart the engine, it can happen that the engine operates in the reverse direction to the control setting. Operation usually causes the cylinder relief valves to lift. Maybe they also want you to explain that you know the interlocks have bypasses that can be used in an emergency so you should be familiar with them? Reed's page 112-115 states the reversing mechanism and interlocks for a Sulzer RD in my edition so maybe they want detail on that.

#2 Info and drawing are found in Sothern's - a trammel can be as simple as a flat bar bent at 90 degrees to form a pointer that rotates on a fixed point.
The rim of a flywheel is usually marked into 360 degrees, showing the top and bottom positions of the various cranks. This is for convenience of setting the various valve timings. A stationary index arrow points at the flywheel
If the flywheel was not marked, the following procedure can be used:
First turn the engine up to near the top for that cylinder and mark the guide and shoe
Then with a trammel fixed on the column and long enough to reach the crank, mark the top of the crank
Now turn the engine over the center until the marks on the crosshead guide and show come together and again mark the crank top with the trammel
Find the center between the two marks on the top of crank and make a center mark
Then turn the engine until this mark comes into line with the trammel point, the engine will now be at top dead center for that cylinder

#3 Also think about an opposed piston engine - no firing loads are transmitted from the cylinders to the bedplates holding the crankshaft bearings
Therefore, they can be constructed to lighter scantlings with no tie bolts - look at Doxfords in Pounders since they still ask about them on exams.
Sketch and describe an opposed piston crosshead engine was a question I was asked for my 3rds - try to do that properly in 35 minutes...

#4 Misalignment of the crankshaft journal bearings will increase the stress range during operation and may cause fatigue failure at one of the points where a stress concentration occurs
Realignment is necessary if the readings are above tolerance - see Lamb's

#5 I think that the question may not be phrased correctly but I think it has to with changing out worn parts to decrease the volumetric clearance
The wear of moving parts (main bearings, rings/liner) will increase volumetric clearance and reduces the volumetric efficiency of the cylinder
Also for an air compressor with a larger clearance volume, the outward travel of the piston will be greater before the pressure is low enough within the cylinder to allow the suction valves to open
In consequence, a large part of the suction stroke is made ineffective and the amount of air taken into the cylinder during each suction stroke is reduced

#6 I think they want a fuel cleaning system described but the question may be again phrased wrongly
This means settling tanks, purifiers, clarifiers, strainers, filters, how heat is used to help, etc. Maybe testing that can be performed aboard.

#7 Lots of info around on tank entry, lots of dangers. Gases = low oxygen, high CO2, hydrogen sulfide from bacteria, methane, flammable vapors from petroleum (upper and lower flammable limits), toxic chemicals

#8 I think that this is in regards to the ideal gas cycle rather than the common manifold turbocharging system - see Reed's Vol 12 page 8. I think my Reed's is the same as Jolly Jacks - 2nd edition 1978. Hard to give actual temps and pressures for an ideal cycle but they do it for the dual (mixed) cycle on page 9 so that can be a reference I guess.

Ratherbeonvacation
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Re: Questions?

Postby Ratherbeonvacation » Wed Nov 13, 2013 11:42 am

Thanks again guys.

Looks like my reeds is different then yours. mine is not even close to those pages.

As for #1. Seems simple enough but can anyone put down a set procedure as such. My experience is mostly with Diesel electric propulsion and medium speed with gearbox/clutches.

The trammel question about finding TDC is clear but it also asks how would you fit a trammel for future use??

#8.....Info is slim

EvenKeel if you dont mind me asking where are you writing the exam. East or West coast is close enough. lol.

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Re: Questions?

Postby EvenKeel » Wed Nov 13, 2013 12:34 pm

The trammel is removable and can be rotated on something as simple as a bolt threaded into the engine frame. That's what is in the drawing anyways - the opposite end of the pointer is bent into a tube to rotate around the bolt. As long as the bolt is in place, the trammel can be fitted and ready for lining up the crank. The flywheel should be marked with help from the trammel to make this process easier for next time.

I also have no experience running direct reversing engines so would have some trouble describing the hydraulic control system with lost motion clutches, etc. Even after reading up on it, I'll put that question to the side if possible.

As far as the ideal gas cycles, more info in Reed's Applied Heat - page 131 in my edition. Has temps and pressures. Is this really something that would be asked on a Motor exam? I am going to put that one to the side too if they want a full numerical explanation.

I am writing in Ontario, yourself?

Ratherbeonvacation
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Re: Questions?

Postby Ratherbeonvacation » Wed Nov 13, 2013 1:03 pm

Thanks again. Anyone else have any input? Especially on question #1.

Depends where I am when I am ready to write the exam. Most Likely Newfoundland. Thanks

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D Winsor
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Re: Questions?

Postby D Winsor » Wed Nov 13, 2013 6:44 pm

I think the answer to question 1 is the use of the air start system as an air brake. The 2 stroke British Polar Engines were fitted with such a system but I can't remember how it is set up.

Question 5 many different engine manufacturers fitted with 2 piece connecting rods including Sulzer have procedures on how to adjust the compression clearance by adding or removing shims between the base of the connecting rod and the bottom end bearing. The thickness of the original shims required for the proper clearance can sometime be found in the original engine fabrication drawings
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JollyJack
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Re: Questions?

Postby JollyJack » Wed Nov 13, 2013 8:45 pm

It is entirely possible that the version of my copy of Reeds, bought in a college book sale in 1984, is arranged differently from yours. Check the index at the back :) Yes, Lambs and Pounders are good reference books..... good point on the Doxford, it's been nearly 40 years since I sailed on the Clan Macporridge. Highest hi-tech instrument on that ship was the voice powered phone to the bridge, all machinery was Juniormatic or Abdulmatic!

To stop a large ship quickly, a procedure was developed by a BP skipper, whose name slips my mind. So you have 300,000 tons traveling at 15 knots in a straight line. No problem, eh? Now you have to stop it as quickly as you can.

His procedure, which is very effective, is to slow the engine to HH, then SH, bringing the helm to hard over. The stern kicks out, which is why you need the power of momentum and HH to keep steerage way and force over the rudder, and the hull acts as a mobile dam to shove water out of the way. The ship stops very quickly by 90 degrees off course, then you go to SH to maintain steerage. If you haven't lost sufficient speed by 60 degrees off course, reverse the helm then drop to SH.

It's similar to the Williamson turn, but you slow the engine down, losing propulsion power. For the Williamson turn, you need power all the way through it.

Both manoevres need sea room, of course, you can't do it in Halifax Harbour, it's ever tighter in St Johns.

If you write in Newfoundland outports, Cornerbrook, Marystown, Louisport etc, ask about writing there and having it marked in Dartmouth, that has been established because of the shortage of Examiners.
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Big Pete
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Re: Questions?

Postby Big Pete » Thu Nov 14, 2013 7:08 am

Hi rather,

Congratulations You have started off a busy thread!
Further to some of the previous answers:-

re:-

1) A lot of research was done years ago into stopping supertankers when they were introduced, if engine speed or pitch was reduced too quickly on large ships the propeller cavitated and lost its grip on the water so you got no breaking affect at all. Generally, the bigger the ship, the lower the power to weight ratio and therefore the bigger the problem with stopping. Hence the idea of reducing engine speed in steps, half ahead, slow ahead etc however, the time / distance at each speed setting would depend on the ship and propeller design as well as the loaded condition. If you have a Torsion meter on the shaft you could attempt to gradually reduce the engine speed settings in a way that keeps the Torque from the propeller, into the engine at a maximum.
On some engines you could select Astern while the engine was being driven ahead by the ship's momentume (but the fuel was off) you could then apply starting air, without fuel, to bring the engine to a stop, so that it could be started astern.
On large ships if you put the directly to full aster you would again have cavitation problems and lose all your thrust so it is better to increase the astern power slowly, again a Torsion meter would be a great help although in practical terms in an emergency situation it might be difficult to be sure if the Torque was reducing because the ship was catching up with the engine or the opposite and cavitation was increasing!
As Jolly Jack says frequent reversal of rudder direction would also slow the ship, although on some ships putting the rudder hard over at Full Sea Speed would probably rip it off! Hoever a steady Port 15, Starboard 15, Port 15 would have a significant braking effect without allowing the ship to go to far off course. This is also used as a measure to prevent pirates boarding from small craft, it increases the bow and stern waves making it harder to get alongside without being swamped, and absorbing lots of power.

2) I have never used a trammel but "even keels" quote from Sotherns appears to be what the examiners will be looking for.


3) Most engines of any size have Tie Bolts. Castings are very poor in tension and require the addittional strength of Tie Rods to support them and prevent them cracking. The Tie rods put a compressive load on the rest of the engine as well as being the shortest and most direct route to connect the force trying to lift the heads off the engine and the force trying to push the main bearings out of the bottom of the engine so that the two forces cancel each other out. They also minimise the Bending moments that would otherwise be placed on other components.
The obvious exception is the opposed piston engine: Doxford, Napier Deltic, Harland and Wolf etc. on these one piston is going up and the other down, both pistons pass the forces on them into their connecting rods and then onto the same crankshaft, neatly cancelling out all the forces with no vertical stresses on anything. That is why a Doxford was much lighter than a Sulzer of the same power output, as well as having much less vibration. The Napier Deltic design started off as a Military aircraft engine at the end of WW II, in spite of its unbeaten power to weight ratio,it was superceded by Jets, so Napier developed the concept for Locomotives, propulsion on minesweepers and Electrical power generation on some warships.

4) If you have excessive crankshaft deflections your main bearings are out of line, so you have to re align them. That means checking and repairing and structural problems in the engine foundations, Double bottoms etc then re chocking the engine.

5) Clearance volume can be changed by shimming the Piston Rod or the cylinder head. Large slow speeds often use shims on the piston rods, smaller engines such as Listers often have soft iron shims under the cylinder line to adjust the bump clearance (and volumetric clearance).

6) How is clean fuel INSURED on board. Is this a misquote? I have never heard of a ship owner taking out an insurance policy on his Bunkers!
I assume it should be "ensured". The answer is what everyone is saying settling & service tanks, Purifiers, clarifiers, and filters, possibly also Homogenisers (not that I have had that misfortune.) Onboard fuel sampling and external sampling for full Lab testing. Using reputable Bunker suppliers.......

7) Fuel Tank explosions SOLAS lays down minimum Flash Points for Marine Fuels and all Settling and Service Tanks should be labelled with a maximum permitted temperature that is below this. Flame Gauzes fitted on all air vents. Possibly signs on the tank sides & Deck forbiding Hot work on the Tank. Usual Tank Entry safety Procedures for enering potentially explosive atmospheres. Gases in an empty tank are usually air and Hydrocarbons.

Hope this helps you and Even keel.

BP
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Re: Questions?

Postby rodrigger » Thu Nov 14, 2013 10:58 am

1) what the examiner would like to know if in an emergency how would you use start air to assist in braking a slow speed reversing engine when going from AHD to AST. HERE IS WHAT YOU DO!

For SULZER :
- telegraph reply is moved immediately to AST
- This will shut off fuel automatically
- lever is moved to START
- this helps to BRAKE ENGINE
-ONCE DIRECTION IS REVERSED, fuel is put back on

For B & W :
- ANSWER telegraph
- Put fuel lever to STOP
- When rev falls to about 40%
- Air is put to assist in breaking
- Once rev is seen in ASTERN DIRECTION
- Fuel is put on

Be aware in both cases consideration is given to the degree of vibration and the amount of AIR being used. I have personally tried it on a B & W engine in my younger days at sea and it works like a charm.

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Re: Questions?

Postby rodrigger » Thu Nov 14, 2013 11:27 am

6) "How is clean fuel oil insured on board? (Sampling during bunkering, fuel reports)??"

I think what the examiner wants is this

- during bunkering fuel sample is drawn from the bunker manifold and is collected by the CE, that sample is sealed, dated and signed by both parties and labeled attached . Two such samples are taken and each parties should retain that sample in a sealed condition for 90 days and if there is any incident onboard re the said supplied fuel i.e excess water in fuel or dirty fuel or bugs etc the company can take the necessary steps to hold the supplier responsible.

- on another note each ship required a "certificate of insurance" for liability issues during fueling ie spills etc.

hope this helps

Ratherbeonvacation
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Re: Questions?

Postby Ratherbeonvacation » Thu Nov 14, 2013 11:31 am

Thanks guys for all the input. Thats what makes this site what it is. Help from all different types of experience that some of us "upcoming" guys will never get to have.

Big Pete, yes that is a mistype on my part. I also think that there is not to much insurance issued with bunkering lol.

Jollyjack if this is wrote in outport newfoundland it cannot be correced there? Can it be sent to St Johns to be corrected? must be quicker that way? Thanks again

EvenKeel
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Re: Questions?

Postby EvenKeel » Fri Nov 15, 2013 10:15 am

Rather - check out this website for more answers on 1rst and 2nd class Motor questions. Since our system is British based, most of the questions carry over. Martin has links to the site in his Machinery section.

http://www.marinediesels.co.uk/

I signed up for a 4 month access to the members section for $15 GBP ($26.16 by Paypal) and it is loaded with applicable info that costs less than a used textbook.

It has simple animations for the large crosshead stuff that I haven't seen much of. Engineers send exam questions that they have received to the webmaster and he answers them complete with drawings for others coming along the system. He has exam questions that go back 15 years.

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JK
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Re: Questions?

Postby JK » Fri Nov 15, 2013 1:06 pm

Jollyjack if this is wrote in outport newfoundland it cannot be correced there? Can it be sent to St Johns to be corrected? must be quicker that way? Thanks again




Dartmouth is the head office for the Atlantic region, and if you are not a PITA to the examiner he will usually get things done as quick as he can.


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