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Topic: Norwegian Crown aground

Ernst
First Class Passenger
Member # 5369

posted 06-08-2006 11:39 AM

Remeber that a ship is moving on the surface of a liquid - even without friction engergy is carried away by the waves generated by the ship.
Generally, this contribution to the resistance gets more important for faster ships.

A bulbousbow should reduce the bow wave and thus reduce the resistance - compared to a ship with the same length at the waterline.

Also, the velocoity distribution on the hull near the bow is changed such that the resistance is reduced. (even at lower speeds where the wave contribution is not yet dominant)

Posts: 9746 | From: Eindhoven | Registered: Jan 2005 | IP: Logged

Globaliser
First Class Passenger
Member # 4153

posted 06-08-2006 12:10 PM

quote:
Originally posted by Frosty 4:
Why do the have a Bulbous Bow instead of just a knife edge bow. Is it Hydro Dynamics or something??

I'm not an expert on this, but I do recall reading something that says that the idea was to reduce the bow wave. The bulbous bow is intended to displace about the same volume of water that would otherwise be thrown up in the bow wave. But it's obviously more energy-efficient to push that water aside horizontally underwater than (in effect) to throw it up into the air. And it does seem to this untrained eye that modern ships generate a pretty small bow wave, even when travelling at speed.

Posts: 1869 | From: UK | Registered: Sep 2003 | IP: Logged

Ernst
First Class Passenger
Member # 5369

posted 06-08-2006 12:24 PM

As said, one tries to cancel out the bow wave.

There are other 'side effects' too - like reducing the friction resistance and also improving the seakeeping abilities.

(One could discuss whether a reduction of resistance could also be achieved by building a longer ship - usually the bulbous bow is (for several reasons) the better solution)

[ 06-08-2006: Message edited by: Ernst ]

Posts: 9746 | From: Eindhoven | Registered: Jan 2005 | IP: Logged

lasuvidaboy
First Class Passenger
Member # 4527

posted 06-08-2006 12:43 PM

Seeing those pics of her w/her bow high out of the water made me think that she will most likely be in a similar position in 20-30 years when she meets her final demise on a scrappers beach.

Posts: 7654 | From: Hollywood Hills/L.A. | Registered: Mar 2004 | IP: Logged

Linerrich
First Class Passenger
Member # 4864

posted 06-08-2006 01:00 PM

Bulbous bows have been on ships in various forms and sizes since the BREMEN of 1929. I've heard it explained, in the simplest of layman's terms, that the bulb "opens a hole in the water for the ship to pass through."

Rich

Posts: 4210 | From: Miami, FL | Registered: Jul 2004 | IP: Logged

lasuvidaboy
First Class Passenger
Member # 4527

posted 06-08-2006 02:42 PM

In regards to bulbous bows, I have read that Mauretania of 1907 wasted incredible amounts of fuel due to her inefficient knife-like bow. The later QM also burned more fuel and needed additional horsepower to match the speed of Normandie which featured a bulbous bow and sleeker hull form. QM at speed had an incredible bow wave (up to the anchor pockets at times) while the more efficient Normandie's was minimal.

Posts: 7654 | From: Hollywood Hills/L.A. | Registered: Mar 2004 | IP: Logged

Ernst
First Class Passenger
Member # 5369

posted 06-08-2006 02:47 PM

Bulbous bows were used well before the Bremen - they were actually inspired by the ram bows of ancient warships.

Posts: 9746 | From: Eindhoven | Registered: Jan 2005 | IP: Logged

lasuvidaboy
First Class Passenger
Member # 4527

posted 06-08-2006 02:57 PM

quote:
Originally posted by Ernst:
Bulbous bows were used well before the Bremen - they were actually inspired by the ram bows of ancient warships.

I recall some naval ships had this feature in the early 20th century.

Posts: 7654 | From: Hollywood Hills/L.A. | Registered: Mar 2004 | IP: Logged

Ernst
First Class Passenger
Member # 5369

posted 06-08-2006 03:10 PM

I would have to look this up - I guess it was in the mid 19th century.(1860ies)

Theories were provided later on. (if I remeber right, extensive investigations have been done in Japan in the 1960ies - there are more or less two types of bublous bows - especially early bulbous bows were not always built in the 'correct' way)

As said, the main effect is to shape the bow wave (in simple words) - but there are many 'details' which also play a role - not only the mentioned lower friction resistance - also the trim of the ship is more favourable. (etc.)

[ 06-08-2006: Message edited by: Ernst ]

Posts: 9746 | From: Eindhoven | Registered: Jan 2005 | IP: Logged

Joe99
First Class Passenger
Member # 3931

posted 06-08-2006 05:53 PM

WOW! Awsome pics. Looks like the water shallow enough to see the rocks from a long way off.

Posts: 51 | From: midwest | Registered: Jun 2003 | IP: Logged

Maasdam
First Class Passenger
Member # 3858

posted 06-08-2006 05:55 PM

quote:
Originally posted by Ernst:
Bulbous bows were used well before the Bremen - they were actually inspired by the ram bows of ancient warships.

Here an example of such warship rambow.
The Royal Netherlands Marine Ram batleship De Buffel of 1868. Shows here elegant rambow.

Greetings Ben.

[ 06-08-2006: Message edited by: Maasdam ]

Posts: 4695 | From: Rotterdam home of the tss. Rotterdam. | Registered: May 2003 | IP: Logged

Frosty 4
First Class Passenger
Member # 5826

posted 06-08-2006 06:24 PM

Didn't the U-boats have a ram on their decks? A saw tooth type device. The Romans and others of that era had rams. Remember the movie Ben Hur, the naval battle.
F4

Posts: 2531 | From: Illinois | Registered: Jul 2005 | IP: Logged

cruiseshipluver
First Class Passenger
Member # 5104

posted 06-08-2006 06:29 PM

Yes Jonno, its called a bulb/bulbousbow, not *thats things that sticks out*......you probably got bulbous bow upset with that comment there...LOL......and yes as some people noted, there seems to be some damage to the bulb......
cruiseshipluver

Posts: 1797 | From: Barbados--cruiseship capital of the Southern Caribbean | Registered: Oct 2004 | IP: Logged

Jonathan
First Class Passenger
Member # 5201

posted 06-08-2006 07:21 PM

It's my namesake. ...and you should mind your language young Jonno.

Sorry bulbousbow, i had no idea that was the name, but thank you for pointing that out and i hope i didnt offend you. Guess i should change my display name to Jonno.

Jonathan

Posts: 559 | From: Ponte Vedra Beach, Florida | Registered: Nov 2004 | IP: Logged

steeplechase
First Class Passenger
Member # 4056

posted 06-08-2006 09:02 PM

How embarrising is this for the Captain his ship stuck on a reef? And next to the tender is that not a bilge pump running off it water?

Posts: 663 | From: elkton maryland | Registered: Aug 2003 | IP: Logged

Ernst
First Class Passenger
Member # 5369

posted 06-08-2006 09:25 PM

So, I just arrived home and could now access my books. I only have the Principles of Naval Architecture and the (rather simple) Introduction to Naval Architecture at hand - which is where I got this information from:

D.W. Taylor was the first one aware of 'the second bow wave that would neutralize the first' explaining the superior performance of the HMS Leviathan - which featured a ram bow. He made experiments in the Washington towing tank resulting in the USS Delaware being the first ship equipped with a speciffically built bulbous bow in 1907. (so it wasn't the mid 19th century as I initally tought - sorry, I don't know everything by heart)

In 1928 Havelock calculated the wave pattern around a sphere - the most important feature being the wave trough behind the sphere (...maybe this is where 'the hole' posted above is coming from) which suggested that positioning a sphere in front of the bow might cancel out the bow wave.

1935/36 Wigley did calculations on the resistance of ships with bulbous bow and came up with suggestions on the shape, position and applicability of such bow shapes. (experiments on that were done by Taylor, Bragg, and Lindblad)

In the 1960ies T. Inui did experiments at the University of Tokyo and came up with some theories resulting in a very efficient bulbous bow shape. (Comparative tests were done with the Murakasi Maru and the Kurenai Maru)

Posts: 9746 | From: Eindhoven | Registered: Jan 2005 | IP: Logged

lasuvidaboy
First Class Passenger
Member # 4527

posted 06-08-2006 09:49 PM

In the late 1980s there was talk at Cunard of modifying QE2's bulbous bow and installing a new more efficent version. After reviewing data, it was determined that her original mid 1960s designed original was as good as a possible 'modern' replacement.

Posts: 7654 | From: Hollywood Hills/L.A. | Registered: Mar 2004 | IP: Logged

bulbousbow
First Class Passenger
Member # 4440

posted 06-08-2006 10:39 PM

quote:
Jonathan wrote:
Sorry bulbousbow, i had no idea that was the name, but thank you for pointing that out and i hope i didnt offend you. Guess i should change my display name to Jonno.

No worries mate. I only did it for laughs. Have a good one.

******

Cheers

Posts: 6866 | From: Adelaide, Australia | Registered: Feb 2004 | IP: Logged

Cambodge
First Class Passenger
Member # 906

posted 06-10-2006 05:24 PM

Frosty4: It is my understanding that the saw-tooth cutter on U-boats was to sever cables which were used to protect harbors, and possibly to cut anchor cables. They were not used later in the war which, I asume, indicated that they were not essential to missions. I do not believe they had anything to do with speed enhancements.

Posts: 2149 | From: St. Michaels MD USA , the town that fooled the British! | Registered: Nov 1999 | IP: Logged

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