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Subject: Trimarans Vs Catamarans, etc as frigates and corvettes
perfectgeneral    4/16/2005 5:56:07 AM
I have heard some doubts as to the hull volume, efficency at high/low speeds, sea-keeping, suvivability and general superiority of the trimaran hull-form for military escort/interdiction/littoral ships. I am throwing down the glove to anyone who can show sources that back these doubts up. Just for openers: 'The trimaran has lower hull resistance at higher speeds, where the narrow, slender main hull results in a saving of about 20 % at high speed. As it is this top speed that determines the size of the machinery fit, a lower power requirement should be reflected in lower machinery costs on build and lower running costs. Scale-model sea-keeping experiments suggest a similar performance to that of a conventional vessel of the same length. A trimaran is typically 20 - 30% longer than the equivalent conventional vessel and gives superior sea-keeping performance. The trimaran is more stable than the monohull. This allows heavy equipment to be fitted more easily and still maintain stability margins.' -http://www.scandoil.com/moxie_issue/issue_7-8/2002_7-8/triton-treat-at-ons-festi.shtml
 
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gf0012-aust    Trimarans Vs Catamarans, etc as frigates and corvettes   4/16/2005 6:53:52 AM
I don't have a web link, but I have a discussion paper in hard copy that discusses issues of slamming and whipping. Thats an issue with the Triton design - and not the current crop of Tri designs such as made by BGV. probably the first lot of real data will be after the LCS decision is made. I don't think you are going to find much in the pub domain until that gets done. OTOH, Beedall points out the following as well: - the very long and wide hull will make a trimaran FSC too large to fit in to existing escort refit facilities and dry docks, necessitating expensive redevelopment of these. - worldwide, there is no experience with designing, building and operating large steel trimaran ships (other than the small RV Triton). - increased and unusual structural stresses may present significant design - challenges and technical risks - possibly higher construction costs. - reduced stealth - radar, noise and wake signatures may actually increase in practice - reduced internal hull volume for a given tonnage, so less room for - accommodation, VLS cells, fuel and stores, etc. - instability if an outrigger is lost or flooded. Knight and Carvers "M-Ship 80" is supposed to get around a lot of the smaller trimaran disadvantage issues.
 
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EW3    RE:Trimarans Vs Catamarans, etc as frigates and corvettes gf   4/17/2005 6:24:36 PM
Isn't the GD version of the LCS based on a commercial design trimaran? There also is the "The Cat" that runs between Bar Harbor ME and Yarmouth NS, it's been a big success, and those waters aren't too gentle. The more I study what literature is available the GD version seems better. The extra beam it has makes for a lot more mission volume and a much bigger flight deck. One of the things that bothered me about the LCS is that it doesn't have any VLS launchers. The extra beam should permit mounting PVLS to give the ship extra sting, and replace those whimpy M2s with Bushmasters. BTW - Do you know if there is an on-line American version of "The Australian Naval Architect"?
 
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blacksmith    RE:Trimarans Vs Catamarans, etc as frigates and corvettes - EW3   4/17/2005 6:37:04 PM
You mentioned commercial trimarans and the "The Cat". The INCAT ferries are catamarans. What appears to be a center hull doesn't actually touch the water at rest. It is a breakwater to reduce pounding when entering big waves.
 
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EW3    RE:Trimarans Vs Catamarans, etc as frigates and corvettes - EW3   4/17/2005 6:51:05 PM
What I was thinking of for the GD LCS is that I read it was a modelled after something from Spain. I could be totally wrong on this, it was one of those things you read in passing, late at night. My reference to the Cat was that cats and tris are ready for the big time.
 
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gf0012-aust    RE:Trimarans Vs Catamarans, etc as frigates and corvettes - EW3   4/17/2005 7:18:06 PM
"BTW - Do you know if there is an on-line American version of "The Australian Naval Architect"?" No I didn't - link??? as a piece of trivia, the Chinese 2208 small Cat is derived from Australian designs from 2000-2001. A chinese company linked up with INCAT to do some "tourist boat" design work, secured some designs and then terminated the partnership.
 
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EW3    RE:Trimarans Vs Catamarans, etc as frigates and corvettes - GF   4/17/2005 7:28:44 PM
I found this link to the Australian Naval Architect http://www.rina.org.uk/rfiles/ANA/anamay2002.pdf (works for several dates) The company I was thinking of was Izar from Spain. They do a lot of multi-hull work are are part of the GD team. "A chinese company linked up with INCAT to do some "tourist boat" design work, secured some designs and then terminated the partnership." Compared to our hero Clintoon, doesn't seem a big deal, but I'd like to see our side be more careful when dealing with the ChiComs. Particularly dual use technology. Can't believe we are going to help them build jet engines and nuclear reactors.
 
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Toy_Boats    RE:Trimarans Vs Catamarans, etc as frigates and corvettes   4/18/2005 9:10:42 AM
The vessel designs suggested for this role (eg triton) are not true trimirans but are infact stabilised monohulls. The outer hulls are barely in the water when the boat is in the upright condition. This allow a long slender hull (lower resistance) without the loss of stability usually associated with it. The stability of a vessel is associated with the maxium breadth of the vessel so the outer sponsons provide the resistance of the long thin centre hull with the stability of the wider vessel. The greater stability of the trimiran allows more hull volume and weight to be placed higher in the vessel. The lower ship resistance allows two options, either the ship can go faster with the same installed power or at the same speed with less power when compared to a similar monohull. The later option is usually chosen as frigates and corvette required speeds havent changed much and the smaller engines are easier and cheeper to install and maintain. The sea keepeing is 'improved' due to the higher stability and the long thin hull. It is not improved as such as seakepping is hard to define, it is more that a trimiran hull form changes the characteristics so it is better in a wider range of scenarios compared to a monohull. They still have problems with wave coming from behind and at angles to the boat. To answer some other points raised if one of the outer hulls is damaged the vessel will actually lean away from the damaged area due to the change in weight distibution. Stealth is comparable to a normal vessel. The Austrailian Naval Architect is the Aus version of the monthly magazine produced by the Royal Institute of Naval Architects. There is no direct US equivelent to the magazine(the US equivelent to RINA is the society of Naval Architects and Marine Engineers ). RINA just had a conference on trimiran vessels (Design and Operation of Trimaran Ships; International Conference, RINA, 29-30 April 2004, London)for the latest research. Hope this helps
 
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gf0012-aust    RE:Trimarans Vs Catamarans, etc as frigates and corvettes   4/18/2005 8:15:54 PM
The primary design opportunity for a trimaran is notionally that of reduced draught. If we ignore the issues of length (taking it to a frigate sized platform), then it becomes ideal for large greenwater ops and some bluewater ops. The requirements definition is always the killer though. A smaller trimaran that isn't dependant on a max transit speed as a fleet asset, could have pods, pumps, jets or gimballed thrusters in the "outriggers" That would give it some remarkable manouvre capability in Fjiords, inlets, brown water/green water ops.
 
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kph    RE:Trimarans Vs Catamarans, etc as frigates and corvettes   4/19/2005 4:26:49 AM
Hi guys, I'm new to this forum and this thread caught my eye as I'm a naval architect. The basic problem with the trimaran (or pentamaran) as platform concepts is that the hull will be rather heavy compared to monohulls. The added weight will be translated into higher resistance requiring either more power to achieve the same speed or alternatively less speed for the same power. Coupled with this weight penalty is the issue of increased cost due to higher steel weight (assuming the hull is made of steel) and heavier propulsion gear, ie more powerful propulsion engines and trains. In terms of seakeeping, for the same displacement, ie total weight, a long and thin monohull is expected to have better characteristics than a short and fat trimaran. Seakeeping issues becomes less significant once the hulls get into the range of aircraft carriers. The above issues have been widely discussed amongst naval architects esp in Britain. However, not withstanding the increased weight and cost and possibly poorer seakeeping associated with the trimaran or pentamaran, there are some applications for which a wide platform may be useful, perhaps a helicopter or even an aircraft carrier. There is also some protective advantage for increased survivability of having the side screens on both sides of the main hull. Just a small contribution to this topic. Cheer!!
 
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Toy_Boats    RE:Trimarans Vs Catamarans, etc as frigates and corvettes   4/19/2005 5:36:01 AM
kph i am curious what type of Naval Architect you are? because for a trimiran and a monohull of the same displacement, the trimiran will have the lower resistance. Weight has very little to do with it.
 
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