Have you checked out Magic's butt lift?

yes, what I was saying is that my organization also tried many of the 'sure to improve fuel consumption AND increase speed' improvements. We'd do the modification and then measure the results on one ship of the class. IME in the vast majority of cases the cost of the modification did not win out over actual fuel savings.

 

So I suspect - no proof, just my opinion - that DCL has done an 'experiment' on Magic and will run it for a time and see if there ARE savings.

 

I'll reference again the bulbous bow ... when a ship is designed with it from the get go, it is a winner. Retro fits ... not so much and not EVERY ship hull form benefits . . . ever seen a destroyer with a bulbous bow?

 

here's a brain teaser: Almost every new sizable ship IS built with a bulbous bow - they improve fuel consumption and ride. If the ducktail provides similar savings, why are ships still built without them?

 

Ship design is not an EXACT science IMO . . . there are still MANY mistakes made. (If you want a horrible example research what the USCG spent to stretch 110' patrol boats to 123' to accommodate extra equipment. Some engineers said it would work while others said no it won't. The work was done to 6(?) hulls and they cracked; re-enforcements were added to the hulls, and they cracked again. The boats the work was done do are now JUNK ... waiting to be artificial reefs)

Bingo Captain!

AKK

Indeed, the duck tail has been in use for years. Here is a cruise line that has been using it for a while.

Indeed, the duck tail has been in use for years. Here is a cruise line that has been using it for a while.

 

but(t) look at the fleet ... do ALL their ships have this? Just waiting for a dry dock visit? Or subjective results?

So does anyone know why the Freedom class were built with the ducktail already installed, and yet the Dream and Fantasy not, if they WILL require them later in life?

ex techie

edit to add: it looks like the designers of the Royal Princess decided to pre-install one too?

but(t) look at the fleet ... do ALL their ships have this? Just waiting for a dry dock visit? Or subjective results?

I believe the ship that have them (RCL ones) were already built with a duck tail. Having said that, not all RCL ships have a duck tail.

Older ship:

Newer ship (although it may be built in with a different design):

Newest ship:

Other cruise lines that also use the ducktail design.

Definitely looks like most new ships are built at the yard with a duck tail of sorts already installed and have taken advantage of the space above to create more deck/staterooms.

I wonder why DCL didn't do the same for the Dream and Fantasy if that is the norm now?

ex techie

[sNIP] from anything I've SEEN, NO THIS IS not THE design of the D and F [sNIP]

After looking at the old stern of the Magic vs. the Fantasy, I think you maybe wrong there Capt_BJ?

The Dream and Fantasy might have cleverly concealed stern flaps built in and disguised?

The Fantasy certainly has a higher aft part of her stern than the Magic and a lot of space between the waterline?

What do you think? Also Skipper?

Magic:

Fantasy:

ex techie

We were on the Magic this weekend and interviewed Lysa Migliorati, the Disney Imagineer who was fielding technical questions during a media session, and she addressed the issue of the "duck tail".

It was a necessary addition not for experimental purposes but (among other things) because the weight on the upper deck has changed due to the expansion of Cabana's buffet restaurant and the addition of the Aqua Dunk. These changes created stability issues that were corrected with added weight at the bottom of the ship. So it wasn't 'experimental', it was a necessary counterbalance for the changes made to the top of the ship.

much less expensive ways to add ballast to a ship

I throw the BS flag at this one

but what do I know, I only depended on my knowledge for the safety of my crew and ship . . .

[sNIP] . . . ever seen a destroyer with a bulbous bow? [sNIP]

much less expensive ways to add ballast to a ship

 

I throw the BS flag at this one

 

but what do I know, I only depended on my knowledge for the safety of my crew and ship . . .

I know the Magic had to undertake stabilization testing after dry dock '03 due to Off Beat being changed into Diversions. We were all confined to our cabins for the night as the ship did a number of rolls port to starboard.

Nothing else much changed during that dry dock but that was necessary.

I would have thought the additional weight of the steel structure to support the AquaDunk, let alone the additional water tanks and pumps (has anyone spotted where they have concealed those yet?!?) and being only on the starboard side would make stability an issue without extra ballasting capability on the port side?

ex techie

much less expensive ways to add ballast to a ship

 

I throw the BS flag at this one

 

but what do I know, I only depended on my knowledge for the safety of my crew and ship . . .

I don't know anything at all about cruise ship design. But she does, and she's got intimate knowledge of what's been done and why when it comes to the Magic, so..... :D

That's interesting that the bulbous bow/sonar dome extends significantly below the keel. I understood that the purpose of the bulbous bow was to falsify the apparent LBP giving the hull a longer hydrodynamic profile. I wouldn't think that this would work so far below but then I only have a test tank 5 feet long in my bathroom.

ex techie

The British and Australian Navy think it works

From another website:

mariner31 answered 5 years ago

The first respondent hit it RIGHT on the head... it reduces drag, improves the ride regarding pitching, and increases speed efficiency.

 

Those bulbous bows are the result of naval engineers NOTICING that effect on destroyers and frigates. As a result, they appear on carriers, tankers, and containerships that have NO sonar.

 

The person who said there was no such CLASS as the "Fletcher" is completely wrong: the "Fletcher"-class were 175 USN destroyers built between 1942-1944.

Source(s):

US Naval Aircrewman / Limited Duty Officer 1985-1999

Sailed aboard Spruance-class, Oliver H. Perry-class, Knox-class, Kidd-class, Burke-class and Ticonderoga-class Tin-cans as well as the USS Kitty Hawk, Midway, Lincoln, Ranger, Independence, Enterprise, and Stennis.

ex techie

I'm sure that it is a benefit as well! lol!

DESCRIPTION

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefore.

 

BACKGROUND OF THE INVENTION

1. Field of the Invention

 

This invention relates to a hullform configuration to improve efficiency and power of vessels or the like. In particular, the invention relates to improved performance for a Naval destroyer with a sonar dome positioned below the baseline of the hull.

http://www.google.com/patents/US5280761

ex techie

Capt_BJ, Skipper, Host Mick.

I was always taught to question knowledge. Never Authority.

I hope you all appreciate my curiosity. It is not meant in any malicious way.

Just genuine curiosity.

ex techie

Capt_BJ, Skipper, Host Mick.

 

I was always taught to question knowledge. Never Authority.

I hope you all appreciate my curiosity. It is not meant in any malicious way.

 

Just genuine curiosity.

 

ex techie

No problem, I can only tell you want I know!

Capt. BJ really hit is on the head, every ship is different and all new ship design is experimental , until proven.

AKK

Cheers Skipper!

They must pre test these modifications in a wave tank though right?

What do you think about the shape of the Magic vs the Fantasy hull design I posted above?

It looks to me as they might have incorporated the duck butt into the design?

ex techie

I was under the impression that the ducktail improved stability but it seems that very little of it is submerged. Searching around, I found this that indicates the efficiency improvement with the ducktail:

"A ducktail is basically a lengthening of the aft ship. It is usually 3-6 meter long. The basic idea is to lengthen the effective waterline and make the wetted transom smaller. This has a positive effect on the resistance of the ship. In some cases the best results are achieved when a ducktail is used together with an interceptor.

4-10% lower propulsion power demand. Corresponding improvement of 3-7% in total energy consumption for a typical ferry."

Wartsila did the presentation.

http://gcaptain.com/part-design-efficient-ship/

I was under the impression that the ducktail improved stability but it seems that very little of it is submerged. Searching around, I found this that indicates the efficiency improvement with the ducktail:

 

"A ducktail is basically a lengthening of the aft ship. It is usually 3-6 meter long. The basic idea is to lengthen the effective waterline and make the wetted transom smaller. This has a positive effect on the resistance of the ship. In some cases the best results are achieved when a ducktail is used together with an interceptor.

4-10% lower propulsion power demand. Corresponding improvement of 3-7% in total energy consumption for a typical ferry."

 

 

Wartsila did the presentation.

 

http://gcaptain.com/part-design-efficient-ship/

Sounds like the upward flow of the wake by the props being directed back down again helps improve the forward propulsion of the ship?

ex techie

Sounds like the upward flow of the wake by the props being directed back down again helps improve the forward propulsion of the ship?

 

ex techie

That would be accomplished by the interceptor trim plane shown in that article by Wartsila.

I'm guessing that the duck tail reduces the churning of the wake that follows the flat transom. Sailboats have been doing it for a while: http://www.yachtcouncil.com/media/images/yachts/1523/111401/BasicInfoSize-Cruising-Sailboat-Other-111401-Transom-view.jpg

it was a trick question

modern destroyers have a large sonar dome at the bow .... this has come over time to result in the bulbous bow which the US Navy does use on some ships.. aircraft carriers and refuelers built today FOR SURE have these hull features. Other hull forms? {why don't patrol boats or the most recent Coast Guard Cutter builds have B' bows?}

and one might note that the pretty picture does not show a traditional bulbous bow but a sonar shape AND no duck tail . . . .

it was a trick question

 

modern destroyers have a large sonar dome at the bow .... this has come over time to result in the bulbous bow which the US Navy does use on some ships.. aircraft carriers and refuelers built today FOR SURE have these hull features. Other hull forms? {why don't patrol boats or the most recent Coast Guard Cutter builds have B' bows?}

 

 

and one might note that the pretty picture does not show a traditional bulbous bow but a sonar shape AND no duck tail . . . .

Why don't they have them Capt-BJ?

ex techie