Quote:
Originally Posted by srini1785 This was indeed an eye opener for me. I just have a few questions.
On the topic of engines.
Answers below
On the topic of ships.
Answers below. |
On the topic of engines. 1. What type of fuel is used?. Special grade diesel or the automotive type?.
Marine fuels follow the ISO 8217 Bunker Fuel Standard
For sake of convenience I will only describe Heavy Fuel Oil & Marine Diesel Oil.
Nowadays we have vessels that use the boil-off from LNG which is burnt in the engine.
This is so far restricted to the LNG (Liquified Natural Gas) tankers only.
HFO - Heavy fuel oil is a residual fuel. This is the sludge that remains after oil is fractionated.
Fractionation is the process of distilling various types of oil from the top most grade to the worsening grades and Heavy fuel oil is the last grade.
Instead of dumping it, they blend it and sell it as marine fuel.
It is very cheap source of fuel for the maritime industry.
You could compare it to coal tar that is used on our roads.
MDO / MGO - Marine diesel oil or marine gas oil are blends of distillate oil.
These are expensive to use on a continuous basis as they sometimes can be as high as 8-10 times the cost of HFO per ton.
HFO is stored at 35-45 degrees Celsius in the bunker tank. Heated up to 98 degrees C to purify it in dedicated purifiers and injected into the main engine at roughly 130-140 degrees C depending on the viscosity required.
MDO/MGO does not require any heating and can be injected directly.
2. What type of vibration monitoring systems are used?
Frankly, Vibrations is a vast subject that I have very little knowledge of so will defer to more learned members to answer.
The main engine has dampeners that help in reducing first order and second order vibrations but apart from that I have no knowledge.
3. How are generators coupled to the engines and what power do they produce?.
Most conventional merchant ships will have three auxilliary engines that start on MDO and are changed over to HFO.
B&W Aux engines have special heating arrangements for the fuel valves so they can directly start on HFO.
The Aux Engine is directly coupled to an alternator which supplies power to the MCB & ECB via bus bar and air circuit breaker and this powers the electrical requirements of a ship.
At sea only one Aux Engine is required but at port or anchorage, two are usually in use.
Apart from the Aux Engines, each sea going vessel is mandated to have an Emergency Generator with two kinds of starting procedures and this will power the Emergency Switchboard incase of failure of the Aux engines.
Some ships have a shaft generator that is coupled to the main engine via the flywheel and as soon as the main engine reaches a determined RPM, the shaft generator is engaged and power produced.
The Aux engine is then shut off and kept on standby.
Some super tankers have a Turbo alternators.
Here steam is superheated in a superheater by the main engine exhaust and this steam will propel the Turbo alternator.
The Aux engine is then shut off and kept on standby.
On the topic of ships. 1. If there are no brakes, i guess a large enough anchor would do the job of marooning ( correct word?. ).
Correct term - mooring / anchoring.
The main engine itself is used as a brake on sea going ships.
For an ocean going vessel that has been steaming ahead at 13 knots per hour, even if the engine is stopped, it will still take roughly 3 to 4 nautical miles for a vessel to come to a full stop.
In case the vessel is still not able to stop, an astern (reverse) kick is called for and this behaves as a brake.
Using Ahead and Astern movements, the experienced master will position the vessel in a safe space and use the anchor the moor the vessel.
Anchor is only used to keep a vessel in place. Contrary to popular belief, it is not the anchor that keeps a vessel in place but it is the heavy chain accompanying the anchor and lying safely on the seabed that keeps a vessel in place.
2. Some large ships never get to the harbour i am told, how or what determines the depth of water a harbour should have to accommodate transfer of whatever these giants are carrying.
Every vessel is essentially a cube. Length x Beam (Breadth) x Draught (Height)
Draught is calculated till its keel - the backbone of a ship.
For a vessel in the water, this height is furthur split into air draught and underwater draught which is what is colloquially called draught.
Air draught is the portion of the vessel above the sea line till main deck.
Underwater draught or draught is what is submerged.
A loaded super tanker will have an underwater draught of about 15-18 meters. So the seabed should even at low tide be anything above its maximum underwater draught for a vessel to safely be anchored at a place.
Places like Kandla & Chittagong are notorious because there have been instances when the vessel has sat on the seabed during low tides.
How does the Captain know what is the available draught - He has an instrument that measures the underkeel clearance (UKC). This is logged by deck officers every hour - I may be wrong. This is done so that the vessel does not touch bottom.
So to answer your query, the underwater draught of a vessel informs the master where he can anchor a vessel.
This is one major reason JNPT at Navi Mumbai was made because container vessels did not have sufficient draught to enter Mumbai port.