Jump to content
Sign in to follow this  
jonno

Ferry Aerodynamics

Recommended Posts

Monty's bow is not too dissimilar to that of WBY in Flensburg. I wonder if they secured blue prints from the defunct Dutch yard?

Share this post


Link to post
Share on other sites
3 hours ago, jonno said:

Monty's bow is not too dissimilar to that of WBY in Flensburg. I wonder if they secured blue prints from the defunct Dutch yard?

I thought BF got the hull design... but above the waterline I can't see what's that special, it's not exactly as if it is mega aerodynamic?!

Share this post


Link to post
Share on other sites
6 hours ago, hf_uk said:

I thought BF got the hull design... but above the waterline I can't see what's that special, it's not exactly as if it is mega aerodynamic?!

I'm not hinting at aerodynamics. It was mentioned on the FSG thread how close WBY's bridge structure is to her bow tip, Monty is very similar with the deflector above the upper vehicle deck access.

Share this post


Link to post
Share on other sites

Do aerodynamics really make that much of a difference to the front of a ferry? I can understand that deflecting spray from the bridge windows would be a priority but in terms of fuel-consumption I can't see the savings would be significant. Further back in the superstructure I guess there is a element of aerodynamics which ensures smoke from the funnel is directed up and away from the outside decks. Ed

Share this post


Link to post
Share on other sites
1 hour ago, Cabin-boy said:

Do aerodynamics really make that much of a difference to the front of a ferry?

You do surprise me sometimes Ed! ūü§£ūüėČ

Share this post


Link to post
Share on other sites

I'm talking purely about the aerodynamics from the first outside deck upwards (not the hydrodynamics from the bow downwards) and whether there are other priorities which are more significant than saving fuel. Given the relatively low speeds, and the constantly changing wind direction, is cutting through the air as cleanly as possible really the first objective or do passenger comfort, engine room and passenger space ventilation and visibility when manoeuvring in port become more important? Ed

Share this post


Link to post
Share on other sites

Thanks, that makes sense in that it's a compromise between fuel consumption and comfort.

I was a little worried when clicking on your link that I'd discover Barfleur to be the most efficient of all the BF fleet and have to make a grovelling apology for any previous comments I might have made about her, but thankfully I'm in the clear. :$

So, given the information gleaned, which ship do we think is the most aerodynamic in the BF fleet, NEX excluded? 

Ed

Share this post


Link to post
Share on other sites
27 minutes ago, Khaines said:

That looks very interesting Brigitte, thanks for posting.

Out of interest the man who pays the fuel bill at Irish Ferries told me a few years back that although Visentnis may not be aesthetically very pleasing (I think we can all agree on that one) whereas Ulysses and Isle of Inishmore got through around ‚ā¨1million of fuel per month, the bill for the Epsilon was only ‚ā¨750,000. I presume that's because they only have 2 engines rather than 4 but that's still a huge saving over a calendar year, can steam at 24 knots if required, and only need a crew of 50 to operate them. One can see the temptation for ferry¬†operators ...

Chris

  • Like 1

Share this post


Link to post
Share on other sites

Aerodynamically, the BF ships - the Cap - her wings had something to do with it, I think.  I don’t think they were decorative, they served an actual purpose.  She would be interesting to know about, before and after her wings were removed - any difference in her performance.  They might have added a quirk to her looks, but how important were they?  I would have said she was with her wings.  

 

The changed funnel shapes as well since the scrubbers, how has that monstrosity on the Pont changed her aerodynamics?  Normandie no different, and Barfleur and Armorique no obvious difference.  Mont is another one with a massive funnel redesign.  Bretagne haschad no changes so probably go for her.

  • Like 1

Share this post


Link to post
Share on other sites

Yes, the pre- and post-scrubber designs might have changed things. Let's go pre-scrubber and take the ships as they were when they left the yards.

My logic tells me it must be Arm as she is the most recent addition and so benefited from the latest design techniques. But one of the single-level loaders might be more aerodynamic in which case Bretagne with her liner-style front end could well be the winner, as you suggested. 

I'm sure Jonno will be able to tell us. With a one-word answer, of course. :D Ed

  • Like 1

Share this post


Link to post
Share on other sites

It's not always just about moving smoothly through the air. Large deck structures can affect a ship's handling as well. The post war Cunarder Caronia (the green one) had an enormous single funnel which acted like a sail and caused docking problems. Likewise, today's cruise ships with their huge appartment blocks and relatively shallow draught can be blown around all over the place in bad conditions, hence all those side thrusters.

On a smaller scale, when the old Isle of Wight Shanklin of 1951 was retired from the Portsmouth/Ryde crossing to take up full time excursion cruising the deck rais were covered in transparent plastic to act as windbreaks but they played havoc with the handling of the ship according to one of her captains.

  • Like 1

Share this post


Link to post
Share on other sites

Large deck structures affecting a ship’s handling, that could be possibly one of the reasons Condor Liberation is not the easiest of ships to handle.  Originally she did not have those massive bridge wings attached to her, they surely affect the flow of air over her, she originally had a cockpit like bridge like NEX, but she was modified with those ugly things.  They have surely had an impact on her performance, she also has an added weight of a stern ramp.  Whatever people’s views on her, she did not start out with all these additions, since then she seems to have had her garage enclosed at the stern.  Used to be curtains there, now appears to be black panels, not sure if they are metal, I presume so, that means more weight.  I think a lot of her problems stem from all the extras put on her.

Share this post


Link to post
Share on other sites
6 hours ago, Cabin-boy said:

I'm sure Jonno will be able to tell us. With a one-word answer, of course. :D Ed

Eh Ed as my roast spuds are about to land and quiver in the knowledge of their impending doom... the bath of skin searing gravy before having their heads bashed in... I'll give you these two...

 
Edited by jonno
  • Thanks 1

Share this post


Link to post
Share on other sites

I think the two links express the form far better than me waffling on.

Something I did notice was that on STX/BF original Pont Aven drawings released she had a bow very similar to that of Bretagne, a classic Atlantic style with high bulwarks (careful!), scuppers and a fo'c'sle sea deflector in keeping to what is seen on naval frigates.

PA was built with none of these, just a flat surface. Though Monty and WBY do have a similar short bow, they do fall away to a shallow prow giving both the same attributes as Bretagne - bulwarks and scuppers, shipped water dissipates rapidly speeding up the recovery from a trough. Their pointy ends also divide the waves far more efficiently, PA just tends to slam into them which no doubt effects her clam shells and the ensuing vibration effects her controllable pitch pods.

The sailors among us will be able to offer a far better description of a wet or dry boat than I ever could.

In terms of efficiency there are now new hull coatings designed to allow a vessel to slip through the sea regardless of season ( thermal dynamics mean a ships hull grips more tightly to cold water increasing drag) and slow the effects of biofouling plus some vessels are now being fitted with the air cavity system meaning the vessel runs on a constant layer of bubbles which again reduces drag and increases fuel efficiency.

Personally i've always felt that a ship's aerodynamic prowess is secondary to everything else.

  • Like 1

Share this post


Link to post
Share on other sites

It's not primarily about aerodynamics in its strictest sense (minimising drag from air resistance) is it?  It's to do with the most efficient way of  deflecting spray and green water shipped up onto the superstructure in a seaway.  Ploughing the bow into a heavy sea has the potential to bring the ship to a halt at best, and cause damage to the weathertightness of the forward superstructure at worst.  One of the goals with forward superstructure and bow design must surely be to maximise the safe speed at which the ship can make way through a head sea, and to that end the hydrodynamics (as opposed to the aerodynamics) of the bow and forward superstructure must be of paramount importance.  (All at the same time as maximising usable space on board).

  • Like 2

Share this post


Link to post
Share on other sites

The bow wave is solely created by the bow shape. Those vessels which are fast with finer, sleeker bows such as Cap finistere generate a rolling wave made up of steady thin sheets of water which continue until they contact the main body of the sea, the free surface. It's then and only then that they become turbulent which the forefoot or bulbous bow is designed to break up.

Slower ships or those faster vessels with a poorly designed blunt bow create turbulent breaking bow waves which are unsteady, add an upturned bulb at the bow and the effect is greater as it can act as a scoop creating greater turbulence.

Aerodynamics are given greater consideration when building cruise ships as you don't want strange airflows passing across the expensive balcony cabins. The more you add to the top of the superstructure the more air turbulence is created... how does that affect an inbound emergency helicopter for instance?.

The more modern design of enclosed inboard lifeboats like we see on MSM, Normandie and Pont Avent have all had the vessels overall aerodynamic properties taken into consideration. Compare them to those on Bretagne and think of the vortices they create. Vortex Induced Vibration (VIV) can be particularly disruptive and in many cases destructive if the resonance created through wind is at an optimal frequency... two different sounds occupying the same space due to say different lifeboat cable tensions are even worse as the amplitudes combine.

Do you alter the tension which may threaten the integrity of the fastenings or do you relocate them during the design phase so reducing aerodynamic interference? 

Sound interference due to wind created by poor aerodynamics on oil tankers is a particular problem to exposed pipe work.

Powered vessels are more dependant on fluid dynamics, vessels under sail rely greater on aerodynamics. If we look at Naval vessels, a radar reflective surface is far more important than airflow above the waterline. Would you say the Type 45 is aerodynamic or hydrodynamic especially when her speed and bow design are considered?

 

Edited by jonno
poor spelling
  • Like 2

Share this post


Link to post
Share on other sites
1 hour ago, jonno said:

Would you say the Type 45 is aerodynamic or hydrodynamic especially when her speed and bow design are considered?

I'd say she is hydrodynamic to reduce the turbulence and therefore the acoustic signature produced, possibly at the expense of fuel consumption. I would also assume that the heat given off by the engines is hidden by clever aerodynamics to reduce the thermal signature. Ed. 

Share this post


Link to post
Share on other sites
10 minutes ago, Cabin-boy said:

I'd say she is hydrodynamic to reduce the turbulence and therefore the acoustic signature produced, possibly at the expense of fuel consumption. I would also assume that the heat given off by the engines is hidden by clever aerodynamics to reduce the thermal signature. Ed. 

Ed, Type 45 WR 21 turbines aren't used for propulsion, they drive electric motors but yes in principle as any exhaust gas has to go somewhere but it can be passed through a cooling process. It's setup similar to a trigeneration system. I have no idea whether the '45's have them but they are available, the Chinese have been playing with them for several years.

Share this post


Link to post
Share on other sites
4 minutes ago, Khaines said:

Yep, you can blame Northrop Grumman for that mishap, the heat exchanger/intercooler didn't like the warm seas of the Middle East. The WR21 was a US turbine with issues until we and the French got our hands on it giving it a total rebuild using the principles of the Trent and derived MT30.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

×