[Jeroen]

Originally Posted by DrPriyankT

@Gannu1 and @Jeoren..I have a question for you guys.
How do the 7, 9, 11 and other odd numbered engine cylinder combinations maintain their balance on ships? Won't the unequal vibrations produced increase structural wear and tear?

No they don't. Although the basics of engine balancing is exactly the same, it does work out a bit different for marine diesels. Bear in mind that the very large marine diesel, are two stroke and run on maximum maybe 200rpm. So although there are very large masses involved, the (rotation) speeds are relatively small.

These engines get balanced purely by counterweights on the crankshaft.

Originally Posted by Thad E Ginathom

How do they do it in cars? I suspect something like an asymmetrical flywheel might be involved, so that the entire system is balanced even if the sum of the pistons is not.

Also, a really small RPM was mentioned for the propellers. is that geared down from the engines? what RPM do the engines run at? My hunch is it a lot less than the small motors that we are used to. I've notice that with fishing-boat diesels you can sometimes hear the duh duh duh duh individual explosions when the thing is only ticking over.

See above on the balancing. Also medium speed engine get balanced via the crankshaft. On cars, it is actually the same in most case. Atlhough there are engines with special balancing shafts.

On the very large marine diesel the engine, it is coupled through the drive shaft directly to the propellor. So the engine RPM is the propellor RPM. These engine are equipped with a mechanism that allows them to run in both directions. So to go from Ahead to Astern, the engine would be stopped, and then started again into the other direction. These days there might be adjustable propellors, so the engine maintains the same rotations direction, but the pitch of the propellor blade gets adjusted.

These large diesels could run sometimes as low as 20 RPM!

The pictures above show a typical "medium speed diesel engine". RPM would be in the range of 450 - 900 RPM. You would always need a gearbox between the engine and the propellor. Main reason is that (large) propellors start becoming increasingly ineffective at high RPM's

Originally Posted by Gannu_1

Since we mentioned RORO, sharing a few snaps of the Rolldock ships we built before the Biglift one. This ship had a stern ramp just like the ramp of a car carrier over which cars would roll out of the ship.


Smit International is regarded as the pioneer (or as we Indians say, baap meaning father) of the marine salvagers. Their professional reputation precedes them! These guys have salvaged some of the most insane wrecks from the ocean including the Mighty Servant 3, Cougar Ace (refer my previous post for snaps) and the more recent Costa Concordia ocean liner.

I totally understand. Do you have any memorable experiences to share Sir?

Thanks for sharing those pictures. Very nice. Please note how immaculate the engine room looks! That would be the case, not just on new ships, but even on old ships, engineers always try and keep the engine room spotless.

For several reasons. If spotless, its easier to spot if anything goes wrong. Even a small fuel/oil leak is easily visually, detectable. Also, its the first line of defense against fires. Lastly, marine engineers love polishing and cleaning and take great pride in the general state of the engine room!

I worked for Smit (or some of its companies) for several years. Great company, with many remarkable achievements to its name!

All my pictures of those days, are either on paper prints, or on slides. And all of those are either in our home in the Netherlands or in a container in storage in the Netherlands.

I can share a photograph of the first vessel I sailed on though and the route we took; have a look at the top of this web page:

http://www.india.jeroendorrestein.co...Hong_Kong.html

I spent a large part of my career with Smit LLoyd. Here is a link to a very interesting website: http://www.smit-lloyd.com . Unfortunately, it's all in Dutch, but the photographs speak for themselves. If you look closely, you'll see my name there as a number of the photographs are mine. (J. Dorrestein)

Some intesting piccies
http://www.smit-lloyd.com/Foto%20hfd...20(Medium).jpg

Fire Fighting:
http://www.smit-lloyd.com/2.htm

Picking up a pennant wire from an oil rig, somewhere in Scotland.
http://www.smit-lloyd.com/Foto%20hfd...20(Custom).jpg

Towing icebergs, so they don't collide with oil rigs:
http://www.smit-lloyd.com/Foto%20hfd...%20(Small).jpg

Tow out of a huge oil platform from Stavanger:
http://www.smit-lloyd.com/Foto%20hfd...tom)%20(2).jpg

Coming to the rescue:

http://www.smit-lloyd.com/Foto%20hfd...%20(Small).jpg

Getting wet feet whilst anchor handling:
http://www.smit-lloyd.com/Foto%20hfd...%20(Small).jpg

Salvage work:
http://www.smit-lloyd.com/Foto%20hfd...%20(Large).jpg

And if you want to get some idea of how rough it would get, check out the videos:

http://www.youtube.com/watch?v=wcUFfNShH8w

http://www.youtube.com/watch?v=RGdI9x88oTE

The slogan of Smit LLoyd was: Anywhere, Anytime, Anyway

We were very proud of that. The Dutch have always had quite a reputation when it comes to ocean towage, salvage, supply and anchor handling.

In the late 70's early 80s the North Sea oil boom was in full swing. Especially, during winter months, the North Sea can be extremely rough. Continous storms, very rough seas, unpredictable seas. The oil companies would always choose Dutch Tug and AHT to move their rigs during these months over any other. The SmitLLoyd tugs and AHT would move any rig, under any circumstances, anywhere. Where as other tugs would take shelter, or refuse to press on, we just continued. We had superior boats, with exceptional sea keeping characteristics and crews to match.

These boats might look small, they are in fact small, never more than 60-65 meters. But they packed a lot of punch. The last ones I sailed had more than 22.000 horsepower. Extremely sea worthy with outstanding maneuverability. Of course, any ship is only as sea worthy as its crew. These boats had crews of 7-9 persons. During anchor handling it was literally all hands on deck.

Captain on the bridge, Chief engineer handles the various winches, First Officer, Second Engineer and two sailors on deck. Cook kept coffee, sandwiches, soup and snacks going for 24/7, called the engineers if alarms went of in the engine room, and helped out on deck in between.

It wasn't unusual to work for 36 hours, sometime even more straight on. These days, that is probably unheard of, unions, health and safety, but it was what made Smit Special and none of us had any problems with it. We were young, captains, chief engineers in those hey-day were in their late twenties, early thirties. Lots of promotions. Lots of macho driven risk taking behavior, but we were very good at what we did.

Jeroen

[DrPriyankT]

@Jeoren..I have a couple of questions. What exactly does a anchor handling tug do? And why are generally all large diesels going the two stroke way? As far as I know aren't four strokes more efficient?

[Jeroen]

Originally Posted by DrPriyankT

@Jeoren..I have a couple of questions. What exactly does a anchor handling tug do? And why are generally all large diesels going the two stroke way? As far as I know aren't four strokes more efficient?

Anchor handling tugs are tugs that "handle" anchors of oil rigs.

Other than permanent oil facilities, nearly all oil drilling rigs are floating contraptions. The need to be towed into position. Some have legs, that get lowered into the seabed and they raise themselves above the sea. In deeper water than won't work and they are kept in place by a set of anchors.
Could be 10 - 20 huge anchors.

Its impossible for the oil rig to lower and set these anchors themselves. They are spread out evenly around the rig. This is where the AHT comes in. First they tow the rig in position. All AHT are also capable of towing operations.

Then they maneuver close to the rig and a crane will drop the anchor on the deck. Then the Anchor chain will be attached to the towing winch of the AHT. The AHT will steam away from the rig on a predetermined course, whilst the rig pays out the anchor chain. When there is sufficient chain out, the AHT crew will attach the anchor to the chain and lower the anchor with winches onto the sea bed. The wire that is used to lower the anchor is attached to a very large buoy.

When a rig needs to moved into a new position, the AHT will move into position near a buoy, catch the buoy, lift the anchor of the seabed and onto the deck of the AHT. The anchor will be detached from the chain. Then with special winches the chain will be wound in as well. Sometimes the rig might be able to which in the chain, but in most cases that will simply not possible. The AHT needs to winch in the chain, store it in special chain lockers or on deck. Then manoevres close to the rig, who then winches in the chain from the deck and lockers of the AHT.

This will be repeated for as many anchors as the rig needs. Once you start you can't really stop, no matter what the weather and or the sea state is like.

So once you break out the first anchor you have to keep going, no matter what.

Here's a couple of video's that will give you an impression of what goes on:

Excellent video of how to catch the buoy:

http://www.youtube.com/watch?v=tTY3xU5p2EU

Again, catching the buoy, crew goes for a swim!

http://www.youtube.com/watch?v=9yCQC0A3Fl8

Fast forward to 01.00min

http://www.youtube.com/watch?v=vibLDLgCw9I

Good example, how dangerous it can get:

http://www.youtube.com/watch?v=d2ykuwUwT1g

Bringing the anchor on deck, always dangerous and here the sea is pretty calm:

http://www.youtube.com/watch?v=sAWBRPZZcUA

Close quarters maneuvering near the rig, better make sure you know how to swim:

http://www.youtube.com/watch?v=nESXuWJTiHA

http://www.youtube.com/watch?v=MIk6of0bUW0

Not wanting to sound to melodramatic, but this is where the boys get sorted from the men! Not sure if the Discovery series, "the deadliest" catch ever ran on TV in India? This is about the real world adventures of fishermen in the Bering sea during crab sea. Pretty spectacular. Still, anybody that has worked on AHT would call those "tough" fishermen a bunch of pussies. They were out for a few weeks a year in these conditions. AHT men work under these conditions many months of the year.

I did several tours in the North Sea. Food was excellent on board these ships, never the less I sometimes lost 10-15 lbs during these trips. It was very hard and tough physical work.

And of course, once the rig move was completed the normal watch and work routines kicked in. So you could find yourself out on deck, for 36 hours at a stretch, soaking wet, cold. Sleep for a few hours and next you'd pouring over an electronic diagram of the speed control of one of the main engines as it had developed a problem and it needed fixing.

You want a very diverse job; get a job on a AHT, never a dull moment

Jeroen

[Gannu_1]

Originally Posted by Thad E Ginathom

Also, a really small RPM was mentioned for the propellers. is that geared down from the engines? what RPM do the engines run at?

Yes there are gearboxes for reducing the speed of the propeller. Propellers of huge vessels are mostly around the 90-130 rpm mark. The engine's shaft speed could be say 500 rpm, so the gearbox lowers it for the propeller shaft and another bunch of gears within the same gearbox also increases the speed to 1400 rpm, to drive the shaft alternator which powers the electricals in the ship, when the ship is in motion. When she stops, the DGs are started or when additional loads need to be catered to (for instance, when the cranes need to be operated).

Originally Posted by Jeroen

Lots of macho driven risk taking behavior, but we were very good at what we did.

A Dutch superintendent of ours was 70 years young but he used to be the most energetic and enthusiastic among the lot including us, the guys in our late 20s! I mean, the way he used to climb and jump to the scaffolding sends shivers down our spines! He used to access all the hard-to-reach areas with ease, crawling and squeezing through the smallest holes in the ship during its construction phase for weld and paint inspections. Good guy he is. We miss his presence now when the ship has left.

[vibbs]

There are vessels with gear boxes, but most of the bigger ocean going vessels have propeller directly coupled to the engine.

Reason a two stroke, slow speed engine builds up torque from very low rpm. Adding a gearbox, you increase the losses, plus on such huge engines the gear box will need to be big too.

On smaller special purpose vessels you may have a gear box and the same engine doubles up for power generation too at port. However larger vessels will normally have auxiliary engines for power generation and the propeller will be directly coupled to the engine.

[Jeroen]

Just to add what Vibbs already mentioned:

Most seagoing vessels have auxiliary engines to provide electrify and sometimes drive hydraulics etc. How many depends a bit on the exact utility demands and physical lay out. On all our larger tugs we had four auxiliary engine to provide electricity.

Next to that we had separate auxiliary engines that drove dedicated generator that would power the bow and stern thrusters. They take huge loads and the load can vary considerably in a short period, so you don't want them to draw from the main grid.

On the AHT we also carried various bulk cargo, like cement for the oil rigs. Huge tanks that got pressurized and essentially you would blow the cement from the tank into a hose into a tank on the rig. The compressors were sometimes electrically driven, but the larger ones tend to have their individual diesel engine.

So here's an example for a AHT:

2 Main propulsion Diesel 6000HP each
4 Auxiliary diesels for generating electricity 750 HP each
2 Auxiliary diesels for driving bow and stern thruster 1250 each
3 Auxiliary diesels for driving the bulk compressors

Althought the very large two stroke low speed engines are the most efficient diesel around and can be coupled directly to the propellor they have one very notable disadvantage. They are absolutely staggering, monumental BIG.

That's not such a problem for say a tanker, or a container ship. But for a RORO ship, a cruise ship, a tug, an AHT, a dredger, there is simply no room for such large engines. One of the reasons the medium speed four stroke engine made their entry into naval design

Jeroen

[shivshanker]

Dear Maritime Engineers/Experts,

A recent documentary I was watching talked about Multiclyinder Marine Diesel Engines in which the individual cylinder can be switched off or taken off line from the main configuration. Wondering how this technology works, any inputs in educating the rest of us will as usual be highly appreciated.

Lastly, why cannot this technology be adopted to build larger engines for automobiles.. which can be turned on or off based on the load requirements.?

[Jeroen]

Originally Posted by shivshanker

Dear Maritime Engineers/Experts,

A recent documentary I was watching talked about Multiclyinder Marine Diesel Engines in which the individual cylinder can be switched off or taken off line from the main configuration. Wondering how this technology works, any inputs in educating the rest of us will as usual be highly appreciated.

Lastly, why cannot this technology be adopted to build larger engines for automobiles.. which can be turned on or off based on the load requirements.?

Its been done in the autotive industry for some time already!!

See http://en.wikipedia.org/wiki/Active_Fuel_Management

I wasn't aware they were doing it for Marine diesels too

jeroen

[shivshanker]

@jeroen,

Thanks for the update, shows that I need to read up more on TBHP. From the GM technology (the link you provided) I understand that either the Even of the Odd Bank can be turned off!

But the one I have seen was on a Marine Diesel where individual cylinders could be turned off and taken offline. Especially for maintenance work.

I am unable to retrieve from my browser history what I watched, but it is there somewhere for sure.

What is intriguing is how would they handle the mating member to the transmission shaft or the propeller shaft when they want to take the Cylinder offline.

[DrPriyankT]

Is it true that LNG carriers are now shifting towards the steam turbine propulsion as the excess gas which vapourizes from the LNG tanks is more economical to use than to use diesel to power these megaships?

[vibbs]

Originally Posted by shivshanker

@jeroen,


But the one I have seen was on a Marine Diesel where individual cylinders could be turned off and taken offline. Especially for maintenance work.

I am unable to retrieve from my browser history what I watched, but it is there somewhere for sure.

What is intriguing is how would they handle the mating member to the transmission shaft or the propeller shaft when they want to take the Cylinder offline.

Even I am not aware of any such technology being used in Marine diesels. We of course do resort to cutting off a cylinder in case of emergencies and if we are unable to stop the vessel for maintenance.

Originally Posted by DrPriyankT

Is it true that LNG carriers are now shifting towards the steam turbine propulsion as the excess gas which vapourizes from the LNG tanks is more economical to use than to use diesel to power these megaships?

LNG carriers will always have boil off gasses which needs to be re-liquefied or vented off to control the pressure in the tanks. This gas can be burned either in a dual fuel engine or in a boiler and the steam drives the propulsion turbine.

[deutscheafrikar]

Originally Posted by Gannu_1

What happens when the anti-heeling system/ballast system fails? MV Cougar Ace happens!

Attachment 1167372

A sudden instability caused the ship to capsize to the stbd side. A Dutch rescue time was sent in to salvage the ship and they successfully did it,

This ship is listed to Port not starboard as you mention.

[Gannu_1]

Originally Posted by deutscheafrikar

This ship is listed to Port not starboard as you mention.

My bad. I had noticed that after I made that post - apologies! The ship is indeed listed to the port side.

[DrPriyankT]

@Jeoren. ..can normal Gas turbine engines like the GE LM25000 provide enough power for the future aircraft carrier INS Vikrant? The navy plans on having four such GT engines on the INS Vikrant...each producing upto 25k+ HP. Will four of them be enough to power the carrier and its almost 40k hulk along with heavy equipment like aircraft elevators, powerful radars and sonars? The US navy uses 4 GE GTs to power its Alrleigh Burgh class destroyers which weigh around 13k tonnes.

[Jeroen]

Originally Posted by DrPriyankT

@Jeoren. ..can normal Gas turbine engines like the GE LM25000 provide enough power for the future aircraft carrier INS Vikrant? The navy plans on having four such GT engines on the INS Vikrant...each producing upto 25k+ HP. Will four of them be enough to power the carrier and its almost 40k hulk along with heavy equipment like aircraft elevators, powerful radars and sonars? The US navy uses 4 GE GTs to power its Alrleigh Burgh class destroyers which weigh around 13k tonnes.

In all honesty I don't really know. The only way is to try and get some comparisons with other carriers of similar size and weight. Carriers typically have to sail at 30+ knots. This provides extra air speed over the carrier.


I know the US nuclear carriers have somewhere in the range of 250-300K HP, but those are larger and heavier.
Jeroen