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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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blacksmith    RE:Trimarans Vs Catamarans Vs Monohull- kph,etc.   4/21/2005 7:55:43 PM
But the waterline speed will affect all three hulls, although less on the outrigger hulls due to their lower displacement.
 
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gf0012-aust    RE:Trimarans Vs Catamarans Vs Monohull- kph,etc.   4/21/2005 8:49:53 PM
"The outriggers are about 2/3 the length of the inner hull." Have a look at some of the BVG designs. They're basically following this "outrigger to centre hull" ratio. Very slick designs.
 
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EW3    RE:Trimarans Vs Catamarans Vs Monohull- gf   4/21/2005 8:57:13 PM
In a word - WOW. http://www.bgv-international.com/ One interesting byproduct of a trimaran is that the extra beam permits the sides of the ship to lean inwards (to reduce RCS) without a huge volume penalty.
 
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kph    RE:Trimarans Vs Catamarans, etc as frigates and corvettes   4/21/2005 10:54:31 PM
These BVG designs sure looks slick?.guess it?s the outriggers contributing to stability thus enabling the center hull to be long and thin which is good for speed and also seakeeping. This config translates to reduced residuary resistance at high speeds and less skin friction resistance by use of spray strakes close to the waterline. It?s also interesting to note that they claim some ground-effect contribution from the winglets. The max speed for a particular hull IIRC is roughly inversely proportional to 2/3 root of the weight and directly proportional to cube root of the power available. Hope that helps... Nonetheless this concept is IMO feasible only for high speed applications ala coastal patrol or maximum upto the size of the LCS. Incidentally, I saw a web page alluding to an aluminium hull construction for the GD version of the LCS. This would reduce weight considerably, perhaps half its equivalent weight in steel. As mentioned earlier, the LM version has a steel hull and alum superstructure. Without trying to discourage lateral thinking, I think the prospect of a trimaran frigate materialising is still rather slim. The reason is basically still the same; ie for the speed at which frigates are likely to operate, a trimaran hull is simply not efficient. Plus there are other practical nuisance factors such as berthing and docking (for refits) an unorthodox vessel in existing facilities.
 
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gf0012-aust    RE:Trimarans Vs Catamarans, etc as frigates and corvettes   4/22/2005 12:24:01 AM
"Incidentally, I saw a web page alluding to an aluminium hull construction for the GD version of the LCS. This would reduce weight considerably, perhaps half its equivalent weight in steel. As mentioned earlier, the LM version has a steel hull and alum superstructure." the australian input is wrt to an aluminium build. One of the clear benefits is that INCAT blast the decks so that they provide a natural non slip finish.. another words, no requirement for painting chemical non slip surfaces etc... Certainly the USN people I know who've gone for a walk on such decks have been impressed. Saves weight, cuts back on chemicals, is environmentally friendly, is cheaper, emables a faster slip to launch build rate, and saves on lifecycle maint costs.
 
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EW3    RE:Trimarans Vs Catamarans, etc as frigates and corvettes   4/22/2005 12:31:14 AM
No facts to back this up, but I bet "INCAT blast the decks so that they provide a natural non slip finish", but it also reduces radar reflection.
 
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gf0012-aust    RE:Trimarans Vs Catamarans, etc as frigates and corvettes   4/22/2005 12:47:34 AM
"No facts to back this up, but I bet "INCAT blast the decks so that they provide a natural non slip finish", but it also reduces radar reflection. " dimpled decks would also effect the final "reynolds number" - maybe not significantly - but nonetheless.
 
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EW3    RE:Trimarans Vs Catamarans, etc as frigates and corvettes   4/22/2005 12:58:24 AM
Never associated a "reynolds number" with radar. Just with respect to an object moving through a viscous material at a given speed. But I have to admit my only knowledge of it is from University and not any practical experience.
 
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gf0012-aust    RE:Trimarans Vs Catamarans, etc as frigates and corvettes   4/22/2005 1:28:06 AM
"Never associated a "reynolds number" with radar." my bad ;) I was using it as an example of having a slippery body in an airstream. More appropriate when looking at inlet manifolds rather than a big blob trying to break the grip of surface tension..
 
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EW3    RE:Trimarans Vs Catamarans, etc as frigates and corvettes   4/22/2005 1:36:41 AM
Got it. But I have to admit, while I'm not in a position to even experiment on the idea, a "granulated surface" might make a bad radar target. Speaking of inlet manifolds, you didn't mess with cars did you? We used to glass bead certain parts of our race cars. It weas meant to reduce internal stresses and clean them up, before magnafluxing them.
 
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