Ventura & Azura differences

[Aim1]

Apologies if this has already been covered, but has anyone noticed the differences between the sterns of the two ships?

 

Ventura:

 

Azura:

 

How come Azura has got a ducks tail but Ventura hasn't? I'm guessing something to do with stability?

[LEESRE]

I noticed this on the sail out of Azura, must be the stability.

[Johnthed0g]

This was discussed somewhere else, I think it was stability.

[BrianI]

Its not to do with stability. It reduces the resistance of the ship through water and thus improves fuel efficiency.

See p 7 of this link

http://www.wartsila.com/Wartsila/global/docs/en/ship_power/energy-efficiency/energy-efficiency-ship-design.pdf

Brian

[tom_uk]

Its not to do with stability. It reduces the resistance of the ship through water and thus improves fuel efficiency.

See p 7 of this link

http://www.wartsila.com/Wartsila/global/docs/en/ship_power/energy-efficiency/energy-efficiency-ship-design.pdf

Brian

 

That's an interesting document, Brian, and I shall study it properly later. But what I can't help wondering is, why hasn't there been one on any previous 'Grand' class ship? - Azura is the 11th, and none of the previous 10 have a ducktail. What's different about this one?

 

One thing that's different is the regs under which she was built. Solas 2009 applies to Azura, and it didn't apply to any of the previous Grand class ships. Here's a link to a paper about 'probabilistic stability determination'. Para 4.2.1 of this paper says that "This could have major influence on the design of such ships as the principles for assessing the level of safety by means of a damage stability calculation are fundamentally changed"; which could explain the diffeences between this Grand-class ship and her predecessors.

 

It's quite possible, of course, that both arguments (possible increased efficiency & 'probabilistic stability determination' calculations) have been factors in this change to Azura.

[Johnthed0g]

May be wrong but I seem to recall a ducktail being retrofitted on another grand class??

[tom_uk]

May be wrong but I seem to recall a ducktail being retrofitted on another grand class??

 

I don't think so, unless it's happened in very recent months. I've been through the 'Ship Alphabet' section of Bart de Boer's excellent ShipParade site, and the pictures of the Grand class ships are all ducktail-less. Also I haven't noticed any mention of it on the Princess forum.

[Stackerman]

The Ventura and Azura are 2 of the new builds having the old propulsion sytems, i.e. Shafts and rear facing Props. I have often wondered why they have not incorporated the newer Azipod system which has been common on new builds for over 10 years. I know that there were initial Design problems with the pods., but most of these have been rectified in recent builds.

[Druke I]

One of the most obvious "duck tail" on a new-build is Celebrity's Solstice.

[tom_uk]

The Ventura and Azura are 2 of the new builds having the old propulsion sytems, i.e. Shafts and rear facing Props. I have often wondered why they have not incorporated the newer Azipod system which has been common on new builds for over 10 years. I know that there were initial Design problems with the pods., but most of these have been rectified in recent builds.

 

Grand Princess, the first of the class, was built in 1998 and must therefore have been designed even earlier. It's not surprising that traditional propulsion was chosen at that time. I don't think it would be easy to change the design in such a fundamental area without an enormous amount of work and cost.

 

And is it a problem? The Grand class seem maneuverable-enough, I haven't read any real complaints about vibration, and of course they have completely avoided the problems with pods. Not that I think pods necessarily have a worse track record that conventional systems, btw, it's just that major work on the podded propulsion unit requires time in dry dock and this generally isn't the case with conventional systems.

[tom_uk]

One of the most obvious "duck tail" on a new-build is Celebrity's Solstice.

 

Yes, and I think it looks very good indeed, possibly a result of being designed with the rest of the ship. It's also bigger than you think, and there's plenty of room for someone to stand on the ducktail. (Not when she's at sea, of course.)

 

I've also always rather liked the little ducktail on the Norwegian Star class, and of course this is also an aspect of the differences between Oriana and Aurora.

[voicebox]

one theory that i have to why a conventional propulsion system has been used on Azura and all the other grand class ships is the stability and the weight distribution. from looking at ships that use Azipods and ships that don't i have noticed that ships with Azipods generally have less of a super structure at the stern of a ship compared to ships that use conventional propulsion systems

 

 

 

I will explain

 

 

(Copywrite: Mike Taplin 2007)

 

 

 

The Queen Victoria is a modified vista class vessel that is propelled by two Azipods. As you can tell by looking at the stern of the ship there is not as much weight over the stern so that it isn't top heavy. This means that the center of gravity is low in the hull and not over the Azipods.

 

 

 

 

 

 

(copywriter: Luis Filipe Jardim 2008)

 

 

 

But as you can see from looking at the photo above of Ventura there is an awful lot of weight above the propellers. this makes the ship top heavy above the propellers. This feature combined with the ships relatively small draft causes this and all other ships of the same design the have trouble heeling when turning and i have this on good authority from an officer that worked on the Ventura. this could also be one of the reasons that the ductail was added to the Azura.

[tom_uk]

But as you can see from looking at the photo above of Ventura there is an awful lot of weight above the propellers. this makes the ship top heavy above the propellers. This feature combined with the ships relatively small draft causes this and all other ships of the same design the have trouble heeling when turning and i have this on good authority from an officer that worked on the Ventura. this could also be one of the reasons that the ductail was added to the Azura.

 

You could be right. But the point I keep coming back to is this: why hasn't a ducktail been necessary on any of the previous ten Grand Princess class ships? They're basically the same ships, and Azura, Ventura, Crown Princess, Emerald Princess and Ruby Princess are almost exactly the same ships. What's changed that might require one on Azura? Well, the most obvious change is the regulations. The new 'probabilistic assessment of stability' requirements could result in exactly this change in design.

[BrianI]

As I understand the primary reason for a ducktail is to increase efficiency and thus reduce fuel costs. When oil was cheap, it was not considered necessary. See this link

http://www.wartsila.com/Wartsila/global/docs/en/ship_power/energy-efficiency/energy-efficiency-ship-design.pdf

Brian

[BrianI]

 

But as you can see from looking at the photo above of Ventura there is an awful lot of weight above the propellers. this makes the ship top heavy above the propellers.

The ship cant be any heavier over the propellors. If it was the rear end would be lower in the water than the front. The centre of gravity of the ship has to be somewhere near the geometric centre for the ship to sit level in the water.

Brian

[voicebox]

as a reply to brians post. the point that i was making is that relitivley there is more weight above the propellers on excludingthe ventura and all of the other grand class ships the over the propellers of most vista class ships ( except the M/S Eurodam) this would make the ship unstable when manovering due to the pure fact that Aipods pull the ship rather that a rudder that gentally pushes the ship using the thrust from the propeller.

 

I would think that the duckatial was added to the Azura because of the new stricter regulations.

 

Robert

[Brayman]

Just because the prop pushes water against the rudder to alter course doesn't mean to say it is any more unstable. Just slightly less manoeuverable(?), that's why they install bow and stern thrusters.