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Subject: Alternative Carrier Concepts
VGNTMH    5/21/2007 3:33:02 AM
**** SINGLE DECK CARRIERS **** Given the very wide beam of catamaran and trimaran craft, has anyone thought of developing a through deck aircraft carrier with the flight and hanger decks on the same level? That is a catamaran or trimaran carrier with a greatly enlarged island incorporating the hanger. With frigate like hanger roller doors out onto the flight deck. The island hanger might take up 30 to 50% of the surface area of the main deck. The general effect might be a bit like the General Dynamics version of the LCS, though more extreme with an even larger flight deck and a through deck. Such a design might have several advantages: • Simplicity, from the removal of the need for lifts. • Strength, as the flight/hanger/main deck would not need to include several large holes for the lifts. • Lower centre of gravity as there could be one fewer decks and the fight deck could closer to the waterline. Though of course the principle disadvantage would be low hanger capacity. Other disadvantages might be: • Possibly narrow flight deck. • Larger wind currents from the larger island interfering with landings, even STOVL landings. • Stability problems due to the large island offset to one side. Does anyone think this idea might have any merit? Has anyone prepared any designs or concepts along these lines? Presumably this concept would relate more to smaller STOVL or helicopter carriers but theoretically a larger angled deck CATOBAR carrier might also be possible. Especially as the angled deck might counter weight the enlarged island. Another possible option might be to have the hanger at the forward end of the flight deck, under and in front of the STOVL ski jump, with a hanger door to starboard and the ski jump to port, with the ski jump maybe a third of the way back from the bow. **** WIND OVER DECK **** Also, as many catamaran or trimaran craft have speeds (at least in calm sea states) of 40, 45, or even 50 knots, is their any possibility of the high wind over deck speeds being used to assist the launching and recovery of STOL aircraft or UAVs? Here I was thinking primarily of using turbo prop light STOL transport type aircraft as carrier based AEW, ASW, or COD aircraft, with the later being used to fly supplies in and casualties out from forward operating amphibious task groups. True, the wide hanger island could greatly restrict the possible wing span of these STOL aircraft, and a STOVL ski jump would interfere with run ups into the wind. But wind speeds of 80km/hr upwards would certainly help! The advantage of this arrangement would be that no catapults would be required, but longer endurance fixed wing aircraft might still be able to be operated.
 
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B.Smitty       5/24/2007 8:50:49 AM
Interesting idea, but I have a feeling designers want to maximize deck area (to the point where islands are growing smaller and smaller, relative to deck area over the years). 

The tri or cat idea is interesting though.  If I were a designer, I'd use the wide beam to permit simultaneous landing and takeoff on runways going down either side of the ship, and still have a hanger deck below. 

I imagine high speed would definitely help both STOVL and CATOBAR aircraft.  

The drawback to a tri or cat would be the relatively low volumetric efficiency vs a monohull (IIRC) and higher weight sensitivity.  

This means less aircraft, munitions, and avgas for a given displacement.  It also means you may have to build significant portions of it out of aluminum or other lightweight materials, which don't tend to stand up to battle damage well.

 
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gf0012-aust       5/24/2007 4:17:50 PM
 
I can't see Cats of any sort being used for conventional carrier aircraft.
 
I saw some of the russian catamaran designs that DERA (now Qinetic) purchased in the late 90's.  Although impressive visually, the DERA maritime enginneers universally regarded them as inefficient when compared to mono hulls.
 
they might/could be useful for UAV (small UAV/UCAV) ops - but the larger F404 (eg) powered UCAVs are more or less a pilotless small fighter, so would invite the same logistic grief attached to fielding them on mono hulls.
 
I've seen some of the Austal and INCAT cat and trimaran designs, and they are very impressive, again, I think their utility will be limited to smaller UCAV/UAV rotor UAV's.
 
 
 
 
 
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french stratege       5/24/2007 7:50:41 PM
I do not agree with Gf0012.Catamaran make sense for a carrier.
However the problem is the beam.With a 80 meter beam for a medium size carrier and above 100 for a large, you have to find a shipyard able to build such a large ship.And also it could bring problem in harbors.
I have a US document (non confidential) on alternative carrier investigating even small carrier with speed of 70 knts which could allow landing of conventional planes on a short track.
I will provide it later.
However and again, cost of planes excess by far the cost of a carrier.
A mdeium siez carrier may cost 3 B $ including mid life refit but 50 planes with ammunitions and midlife refit would cost 5 B$.And add 1,2 B$ for 3 E2C.
So cost of airwing is 6,2 vs 3 for the carrier.
 
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french stratege       5/24/2007 7:51:14 PM
read "a medium size carrier" of course.
 
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B.Smitty       6/12/2007 9:35:54 AM

 
I've seen some of the Austal and INCAT cat and trimaran designs, and they are very impressive, again, I think their utility will be limited to smaller UCAV/UAV rotor UAV's.

I agree.  I think a cat or tri might make a useful littoral VTOL/STOVL carrier, but one still has to ask whether a conventional monohull wouldn't do the job better.  I can definitely see using a JHSV as a small littoral helo/VTUAV carrier though. 

One of the primary benefits of a cat or tri is the potential for high speed, but to be of use operationally, all of the carriers escorts would require similar capabilities.  It's not wise to leave your air defense and ASW escorts behind when you dash off at 45+kts. 




 
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B.Smitty       6/15/2007 9:39:50 AM
Here is a TSSE design for a small SES carrier. 

Sea Archer

 
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Herald1234    Why you don't use a catamaran for a flight deck.   6/15/2007 5:39:46 PM

1. There are transverse forces that affect the Cat hull [flex] in two axes as opposed to a D hull.
2. The flight deck at sea is pitching and rolling bad enough. Now you want to add a pendulum cyclic component to the deck movement?
3. How about hull volume? A Cat loses a lot in that department.

Those are three off the top if my head.

Herald

 
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Herald1234    Why you don't use a catamaran for a flight deck. addendum.   6/15/2007 5:46:21 PM
1. There are transverse forces that affect the Cat hull [flex] in two axes as opposed to a D hull which only has to deal with the loading on one when it hits waves.

Herald

FS, there is a reason why the US didn't build those bird farm plans that enthuse you.

The American naval architects know what they are doing.

Herald


 
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french stratege       6/21/2007 7:18:27 AM
Herald
The main reason is that it make no sense in a economic point of view.
A medium conventional carrier cost 2 B€ to buy.
A single fighter cost about 180 m€ minimum in life cost (initial procurement, annual training, minimum service crew cost)
Either you try to make a very small carrier to save money with reduced capacity in plane to be less than those 2 B€ but considering that for the same displacement a catamaran cost more, it would be difficult to save more than few hundred million € so the equivalent of few planes, and this for an umproven design with few planes.
There is no place for a less than a conventional 35 000 tons carrier.It makes no sense considering fighter cost.
Now a very big navy which have already conventional carrier, could find the need of a cheap "escort carrier" in number I mean a carrier which would carry maximum a single fighter squadron (about 8/10 conventional fighters) to be used mainly  as an air defense ship as well as a LPH and would be in the 20 000 tons class.Then a trimaran:or catamaran hull could make sense with a single catapult or a skijump.Indeed the saving would make sense if we consider to get 20/30 small escort carrier.However this requirement do not exist since WW2.Even the danger of tactical nukes did not pushed US navy to egt this sort of ships in cold war so today, it would be quite unlikely.A big ship make more sense for volumetric efficiency and ship cost/plane.
BTW you need always a landing track about 190 m mimimum and requirement of having a ship capable of air operations in sea state 5 at least.
 
 
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french stratege       6/21/2007 7:58:08 AM
In fact people do not understand that small carrier (like in RN or Italian navy) exist because Harrier exist.
And Harrier existance is due to history and was not driven by navy requirements.
Harriers exist because in the sixties some people in Europe thought that conventional aircrafts will be destroyed by attack of Warsaw pact and likely with nukes.
At the same time in Britain, staff thought that air superiotiy fighters would be obsolete due to air defense missiles.Fighters were not needed anymore and only bomber were still needed mainly for CAS.
So Royal air force asked for a VTOL fighters.French and German considered that also so developement of prototypes in both countries.
Only RAF when to get a VTOL aircraft , the Harrier.Swedish who had a similar requirement went to STOL aircraft (Viggen).Indeed penalty in cost in weight (and cost so) is 30% for VTOL and 10% for STOL.
Sweden choose dispersion on road network.
Navy market alone is too small to justify the R&D cost of a VTOL fighter which cost today more than 12 B $ alone (only R&D) so the cost of building 6 medium conventional carrier to give an idea.
AT this time RN tought that nuclear threat at sea justify more numerous but smaller ship to reduce vilnearibility to nukes so they purchase also the Harrier.
RAF AND RN got the Harrier and no other fighter was developped in UK
It got success because US Marines bought it also SINCE it was available.
Today nobody would build a STOVL planes due to cost.Only Marines and UK would like to replace the harrier and only a joint procurement would justify it if you could reduce the cost with communality of a conventional fighter so they drop in JSF program.
However the joint USmarine/RN/RAF requirement increase difficulties and cost in JSF program so this version is fought by USAF and US navy.
If RN OR US marine cancell JSF STOVL version, this version is dead since its developement would be too costly for a single customer.End of small carrier when Harrier will become totally obsolete (in 2020 max) as no plane would be available.
Navies would go CTOBAR or STOBAR only so with carrier likely bigger than 35 000 tons for the economic reasons I mentionned above.
 
 
 
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