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Shipping Pollution

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Shipping Pollution

Old 23rd Nov 2009, 06:22
  #21 (permalink)  
 
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....and that's the reason why a lot of us like PPRuNe (despite Danny's best efforts to get rid of us). Thanks for your post criticalmass. I learnt something today.
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Old 23rd Nov 2009, 10:53
  #22 (permalink)  
 
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....and that's the reason why a lot of us like PPRuNe (despite Danny's best efforts to get rid of us). Thanks for your post criticalmass. I learnt something today.
Sadly, it also shows the limitations of PPRuNe, when a well written but technically incorrect post is taken as fact.

Sorry critical mass, while correct in some parts (particularly regarding thermal gradient control of the engine), the main thrust of your post is incorrect.

For starters, marine diesels can happily run on higher cal fuels - indeed they routinely switch to MDO (gasoil) when manoevering. (0.5% sulphur MDO has a typical gross specific energy of #~45.7 MJ/Kg; 3.5%S HFO ~42.5MJ/Kg) The sulphur content spec for marine fuels has been reduced over the last few years which has led to an inevitable increase in the cal val of HFO too. However, even if sulphur content of HFO is reduced to say road fuel ULSD levels (10ppm), cal val will only increase by ~5%, and thus still be less than that of current 0.5%S MDO.

Having dismissed cal val as an engineering reason for the use of HFO, its fair to say that its use does have significant benefit, as the lubricity of HFO is excellent - higher distillate products would inevitably have reduced lubricity which would lead to considerably increased wear in an engine.

However, the main reason ships run on HFO is (and will remain) price - HFO is roughly half the price of MDO. (Having said that the reduced sulphur specs for the fuels used in the SECA's {Sulphur dioxide control areas} as mandated under Marpol 73/78 Annex VI adds about $70/ton to the cost of the fuel - still ~$200/ton cheaper than gasoil though!)

Second - modern HFO certainly isn't "purified tar" - its a complex blend of cracked and/or straight run distillate products blended with viscosity cutters such as light cycle oil or gasoil. Ships will indeed continue to run on HFO although the industry expects that SO2 limits will be further reduced in future years.
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Old 23rd Nov 2009, 12:08
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Thank you, Mariner9.
This statement:
Well, if you crack a crankshaft, you may as well scrap the ship
is not entirely correct. Depending on damage crankshafts may be repaired in situ, taken ashore for repairs or replaced by new ones. It is not the end of the world.
Per
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Old 23rd Nov 2009, 12:21
  #24 (permalink)  
 
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Well anyway.......thanks to all those who know something about the subject. I continue to learn
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Old 23rd Nov 2009, 12:27
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Yes I agree Ancient Mariner, a cracked crankshaft rarely lead to a CTL unless the vessel is near the end of its useful commercial life, but thats a side issue.

The main point in critical mass's otherwise excellent post I was disagreeing with is that cal val is the limiting factor for marine fuels - the facts are that current machinery can (and does) run on increased cal val fuels, and the quality of fuel can be considerably improved (albeit at considerable cost) without significantly changing cal val.
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Old 23rd Nov 2009, 12:38
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Mariner9, totally agree, hence my thanks.
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Old 23rd Nov 2009, 13:02
  #27 (permalink)  
 
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LNG

What about gas tankers?Do they run on vapours of the tanks? I think I will buy my great grandchidren shares in a sailcloth business!!
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Old 23rd Nov 2009, 13:10
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oldpax,
If memory serves, boil-off from LNG was/is used as fuel on some vessels. Mothballed my uniform in '85, not up to speed. Never were a tanker person.
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Old 23rd Nov 2009, 14:00
  #29 (permalink)  
 
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CR2
Cargo tanks are washed either when about to load a different grade of oil in the tanks from that carried earlier eg carried gasoil, going to carry kerosene, or on VLCCs or supertankers carrying crude oil washing is normally for tank entry by the crew to carry out repairs or inspections.

The tanks are washed with sea water which is then collected in "slop tanks", after a time the oil will separate out of the water and float on top of the water. The WATER is then pumped into the sea through oil content monitoring equipment. The ship must be more than 50miles away from land and not in a "special area" eg the Meddy. I could go on but I won't bore you.

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Old 23rd Nov 2009, 16:47
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Your brother in law may well be right BAMRA, but Azipods are currently expensive to fit and no more fuel efficient at normal sea speeds than standard propulsion systems. Plus, they increase the draft of the vessel thus reducing flexibility/cargo carrying capability for a vessel of a given displacement. (For example, a typical 270K VLCC draws 20m and if Azipods were fitted, the extra 4 metres or so draft would prevent the vessel going fullly loaded through the English Channel) Accordingly, there's very few cargo vessels so fitted, although they're pretty much standard fit nowadays on modern cruise liners where speed and manoeverability is more important than draft.

No doubt the technology will continue to improve however, and some form of electic propulsion (Nuclear?) may become common.
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Old 24th Nov 2009, 06:04
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I stand corrected about the use of higher cal val fuels in Sulzer-type slow-speed marine diesel engines (sincere thanks to those whose knowledge is greater and more up-to-date than mine). I left the industry in 1992 (I was a Sparks, so what would I know about marine engines anyway) and have had fleeting contact with those few of my ilk who managed to remain.

AFAIR we used to start our main engine on MDO for departure, but switched to HFO once off the wharf and headed for the harbour entrance. I assumed this was to manage heat-flow, but it may simply have reflected the differential in cost between HFO and MDO. The Chief Engineer reckoned the main engine would always start on MDO but he wasn't so sure about HFO for starting. Canny old souls, those grizzled Chiefs.

On one voyage we bunkered with a batch of HFO so poor it wouldn't run the main engine. FOBAS Singapore gave the fuel a thumbs-down (If I recall, FOBAS was a fuel oil bunker analysis service...they analysed a sample of what you had loaded and told you what needed to be added/removed to make it burn) and we soon learned why! As ship's fuel it would have made a great road-base.

The engineers had to cut it with MDO to get the main engine to run, we were at reduced revs for the whole voyage and the alarms went off so regularly in the engine-room it went from being UMS (un-manned machinery space after-hours) to 24-hr engine watchkeeping just to keep the job going. Not a very happy bunch of engineers in "the pit" after that one.

Cost was always and will always be the deciding factor in the shipping industry. As long as HFO is the cheapest fuel that will run an engine, it will be the fuel of choice.
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Old 24th Nov 2009, 07:24
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The main reason for switching from HFO to MDO was that the main engines of the day didn't not have re-circulation of the fuel oil in the high pressure pumps and fuel injectors . When you stopped the engine the fuel oil would then go solid on you since without re-circulation you lost heating of the oil. Not good. The MDO purged the fuel lines, pumps and injectors and facilitated maintenance and re-starts. More modern diesel engines have fuel recirculation and allows you to maneuver on HFO, but most chiefs would still switch to MDO, albeit a bit later.
Smoking diesel engines and boilers, be it white, gray or black is a definite no-no for any proud engineer. That's not to say that the flue gas does not contain soot particles, just not enough for them to be visible.
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Old 24th Nov 2009, 09:54
  #33 (permalink)  

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Smoking diesel engines and boilers, be it white, gray or black is a definite no-no for any proud engineer
THere must be a few losers on the Cross Channel Ferries then
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Old 24th Nov 2009, 10:35
  #34 (permalink)  
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Whilst pollution at sea is a fact and ship's contribute to it,far more pollution enters the sea from the shore. Over the last 25 years regulations and guidelines have been developed that have reduced pollution from ships by amounts that wouldn't have been imagined in the seventies. These regulations have been developed by industry and governments with industry generally taking the lead.If the same level of regulation had been developed and enforced to prevent pollution from the shore the seas would be very clean.

Impressed with your marine knowledge Mariner 9
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Old 24th Nov 2009, 11:08
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Now days on VLCCs at least, HFO is used all the time on the main engine and the generators. MDO is only used for the incinerator, lifeboats, and when the ME and generators are being shut down, eg for Dry Dock, to clear the fuel lines of HFO. A VLCC will only carry about 100mt of MDO, about a day and a half steaming.

Merch

Before I'm corrected, the Emergency Generator also uses MDO

Last edited by merch; 25th Nov 2009 at 11:25.
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Old 24th Nov 2009, 11:19
  #36 (permalink)  
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i was reading somewhere the QE2 got 3 inches to the gallon
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Old 24th Nov 2009, 11:26
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Thanks 1DC , but its my job and my shipping clients wouldn't be impressed if I didn't!
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Old 24th Nov 2009, 11:41
  #38 (permalink)  
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Used to be mine too that's why i am impressed!!
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Old 30th Nov 2009, 15:27
  #39 (permalink)  
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Thread Drift..question for Mariner 9.
Any idea why so many tankers are moored off Southwold/Great Yarmouth??
According to IAS anyway...
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Old 30th Nov 2009, 15:53
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Moored tankers...

...waiting for a propitious rise in crude oil prices again, maybe.
The Ancient Mariner
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