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.
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JollyJack
Fleet Engineer
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Joined: Wed Mar 24, 2010 3:57 am
Currently located: Eastern Canada

Re: Questions?

Postby JollyJack » Fri Nov 15, 2013 7:57 pm

Ratherbeonvacation wrote:
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


There are no Engineer examiners in Cornerbrook, Marystown or Lewisport. The St John's office examiners have other duties as well as exams, which entails a considerable workload. E-mail, .pdf files and telephones are wonderful things, instant communications from Dartmouth, even to the Rock. :)
Discourage incest, ban country "music".

Ratherbeonvacation
Leak Patrol
Posts: 32
Joined: Sun Aug 17, 2008 8:09 pm

Re: Questions?

Postby Ratherbeonvacation » Mon Nov 18, 2013 10:45 am

wow guys!!

Thanks butttt.... I still have a few more "parts" of questions that are kinda stomping me. They are all pretty much the basics but again is there something I am missing and looking over.

1. Thermal efficeincy of a 4 stoke vs 2 stoke. reasons for differences?
2. Advantages and disadvantages of tie bolts?
3. Steps to take when starting up a DIRECT drive engine when tied to the dock
4. Describe 2 systems of supercharging (are they looking for turbocharging and a blower(actual supercharger) or are they looking for something as a rotary blower or gear?)
5. Precautions to take before manouvering with an engine operating on heavy fuel? (change over to diesel?)

EvenKeel
Deck Plate Wanderer
Posts: 25
Joined: Tue Sep 10, 2013 9:47 am

Re: Questions?

Postby EvenKeel » Tue Nov 19, 2013 11:07 am

1. The 2-stroke engine, with a power stroke every revolution will theoretically develop twice the power of a 4-stroke engine of the same swept volume. Inefficient scavenging however and other losses limit the power advantage to about 1.8. However, as far as thermal efficiency the following MAN B&W paper shows that medium speed engines (4-stroke) range from 40-47% efficient while slow speed 2-strokes range from 47-55%. So I would say 2-strokes are about 7-8% more thermally efficient due its longer and slower powers stroke's ability to get more converted energy out of the fuel.

http://www.mandieselturbo.com/files/new ... _speed.pdf

2. Tie bolts hold the bedplate, frames and cylinder beam together in compression and transfer the firing load back to the bedplate. Without tie-bolts, these components would tend to try and separate as the engine fired. What are the alternatives to compare as advantage/disadvantages - maybe opposed piston? One downfall is that you have to keep them properly tightened or misalignment and possible catastrophic damage will occur.

3. Check prop is clear and ensure proper lines are out to secure vessel. Deck department must be made aware (loading, gangway, etc.).

4. In my opinion, anything providing pressurized scavenge air can be considered a super charger, including a turbocharger. There is also under piston scavenging, engine driven blowers, reciprocating scavenge pumps, and electrically driven centrifugal fans for low loads.

5. Timing will depend on size but should be done before maneuvering. Temperature should be allowed to drop about 2 degrees C per minute to prevent gassing up. May take about an hour. Drain diesel tank slightly to ensure no water in it and ensure quick closing valve on tank is open. Ensure return valve to HFO tank is closed to avoid diesel returning there. Load should be reduced on engine to avoid changeover happening too quickly and heating up the diesel causing gassing up due to residual heat in heaters. Changeover the 3-way valve to diesel and monitor viscosity. Shut off trace heating and if fitted with return cooler for diesel, put this online.


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