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Author Topic: Apparently I misunderstood ballasting.  (Read 5318 times)

kinmel

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Apparently I misunderstood ballasting.
« on: May 13, 2016, 08:10:23 am »

The world's largest cruise ship has been handed over from the shipyard and the Guardian covers the story.

It's description of the ship includes " Harmony of the Seas will produce 20% less CO2 emissions than the two largest ships in its class, partly thanks to air pumped into the hull to lighten its load.

http://www.theguardian.com/travel/2016/may/13/inside-the-worlds-largest-cruise-ship-harmony-of-the-seas
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BarryM

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Re: Apparently I misunderstood ballasting.
« Reply #1 on: May 13, 2016, 08:22:08 am »

That is obviously incorrect. It's not air at all but a helium/hydrogen mix and, under certain circumstances, sufficient can be introduced for the entire ship to take off and thus reduce water drag.

I also hear that the wooden furniture is fully recyclable and may be used to fire the Maccsteam boiler that feeds the quintuple expansion steam engine installation.  Isn't science wonderful?

BM
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Netleyned

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Re: Apparently I misunderstood ballasting.
« Reply #2 on: May 13, 2016, 08:31:02 am »

The passengers will use up all that air as they breathe, but the
Methane they produce will fire the boilers.


Ned
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Umi_Ryuzuki

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Re: Apparently I misunderstood ballasting.
« Reply #3 on: May 13, 2016, 08:48:35 am »

Actually, Stena had some ship proposals a few years back that proposed dual engines and
propellers for reliability and increased maneuverability when transiting canals. These same
ships also had proposals for an air cavity underneath the hulls, like a catamaran.
But the cavity held a layer of air underneath the hull that would reduce hull friction and
therefore fuel consumption. So it produces less pollution.





Some additional concepts call for an air lubrication system, high pressure air is bubbled beneath the
 hull near the bow, which would also create a reduction of hull friction, and gain a 6%  reduction in fuel consumption. Mitsubishi, and NYK have been testing the systems over the last two years.

kinmel

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Re: Apparently I misunderstood ballasting.
« Reply #4 on: May 13, 2016, 09:15:54 am »

Actually, Stena had some ship proposals a few years back that proposed dual engines and
propellers for reliability and increased maneuverability when transiting canals. These same
ships also had proposals for an air cavity underneath the hulls, like a catamaran.
But the cavity held a layer of air underneath the hull that would reduce hull friction and
therefore fuel consumption. So it produces less pollution.

I assumed that some such system was what they were trying to describe, but I wonder what is actually fitted.

That is probably the most interesting part of the design !
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NFMike

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Re: Apparently I misunderstood ballasting.
« Reply #5 on: May 13, 2016, 10:01:45 am »

I just watched an Impossible Engineering programme on tv about the construction of this ship. The system being alluded to is indeed air lubrication of the hull. IIRC micro-bubbles are ejected along the forward 1/3 of the hull.
Propulsion of the ship is by three Azipod drives with four bow thrusters to assist in port.

Sub driver

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Re: Apparently I misunderstood ballasting.
« Reply #6 on: May 13, 2016, 10:10:59 am »

Hi.
Nothing much new here im afraid the concept of air under a hull to ease friction has been around a long time in the 50,s and 60,s the British power boat corporation experimented with it and also Sir Christopher Cockerill too, some power boAts and shovelnose  fast boats have stepped hulls to trap air in the step under the hull to ease friction.
Old idea with new technology.
Regards Sub.
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plastic

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Re: Apparently I misunderstood ballasting.
« Reply #7 on: May 13, 2016, 11:24:12 am »

The world's largest cruise ship has been handed over from the shipyard and the Guardian covers the story.

It's description of the ship includes " Harmony of the Seas will produce 20% less CO2 emissions than the two largest ships in its class, partly thanks to air pumped into the hull to lighten its load.

http://www.theguardian.com/travel/2016/may/13/inside-the-worlds-largest-cruise-ship-harmony-of-the-seas

How big are the pumps? Do they create a vacuum above the ship?
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tigertiger

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Re: Apparently I misunderstood ballasting.
« Reply #8 on: May 13, 2016, 01:36:39 pm »

Nothing new indeed.


I remember some documentary, maybe 10 years or more ago, about Viking ships.
One effect of the hull planking method was that a layer of micro-bubbles formed under the hull and reduced drag.


Interesting question.
Is it still serendipity, if you don't know you have done it? I would guess that all the Vikings knew was that this kind of boat went fast.
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roycv

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Re: Apparently I misunderstood ballasting.
« Reply #9 on: May 13, 2016, 01:47:53 pm »

Hi all, bubbles under boats was being investigated by Lawrence (of Arabia) in the 1930's as a means of making boats faster.
regards Roy
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dreadnought72

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Re: Apparently I misunderstood ballasting.
« Reply #11 on: May 13, 2016, 06:48:53 pm »

Enough bubbles under the hull will eventually make the ship sink.  %)

Andy
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NFMike

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Re: Apparently I misunderstood ballasting.
« Reply #12 on: May 14, 2016, 08:39:11 am »

The Impossible Engineering programme about Harmony of the Seas is on again tonight (Saturday 14 May) at 9pm on Yesterday (Freeview 19, Freesat 163).

nemesis

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Re: Apparently I misunderstood ballasting.
« Reply #13 on: May 14, 2016, 11:37:26 am »

I believe the New Zealanders yacht racing fraternity used this concept on one of their racing yachts after observing seals under water and seeing the bubbles coming out of their fur. It apparently worked to such a degree that it was banned. nemesis
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AlexC

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Re: Apparently I misunderstood ballasting.
« Reply #14 on: May 17, 2016, 11:24:11 pm »

How come they still build these huge ships with so few lifeboats?

8880 total souls on board and only 18 lifeboats + some self inflating rafts... or do they expect all the air/gas under the hull to keep it afloat regardless of mishap? :((

Seems to me they haven't learned much since the Titanic. <:(

Alex
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Colin Bishop

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Re: Apparently I misunderstood ballasting.
« Reply #15 on: May 18, 2016, 09:46:28 am »

The majority of the lifesaving capacity is in the liferafts which can be quickly deployed. The lifeboats themselves hold rather more people that you might expect.  There is probably twice as much lifesaving capacity than is nominally required in case the ship should list and make it difficult to launch boats from one side although they are carried relatively low on the ship to mitigate this.

The big concern is whether you can effectively muster and manage the disembarkation of nearly 8,000 passengers and crew safely and whether the local capacity exists to rescue them - you need more than a few choppers!

When Costa Concordia sank a few years back only some 30 lives were lost, unfortunate for the individuals concerned, but still impressive taking into account the number of people involved and the fact that the ship heeled right over - they are not supposed to do that when holed but designed to settle on a more or less even keel to allow evacuation from both sides. It is possible that with several compartments flooded the ship simply became too top heavy.

Colin
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roycv

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Re: Apparently I misunderstood ballasting.
« Reply #16 on: May 18, 2016, 10:02:03 am »

Hi I was up close to the Queen Victoria a while back, and there are differences with the propellers of the orange lifeboats.  Some have shrouded props I assume for ferrying and others not.  Is that correct?
regards Roy
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Colin Bishop

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Re: Apparently I misunderstood ballasting.
« Reply #17 on: May 18, 2016, 10:12:02 am »

Yes, some of the 'lifeboats' are in fact tenders for use at ports of call where the ship is too large to get alongside or because there are too many other cruise ships clogging up the harbour.

The cruise companies, and many passengers don't like tendering much as it entails a lot of delays in getting people ashore and picking them up again and eats into 'shore time'. There is also more risk of an accident when boarding for elderly passengers who are unsteady on their feet.

That is one reason why modern ships mare built 'high and fat' so that they don't draw too much water and hence limit their ability to berth alongside.

Colin
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MikeK

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Re: Apparently I misunderstood ballasting.
« Reply #18 on: May 18, 2016, 10:30:07 am »

Finnish icebreakers were using this method to ease their way through ice back in the eighties or thereabouts, don't know if they continued with it


MikeK
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