Welcome kph Since I am not in my primary field of expertise (and yes, some question if I have any field of expertise) let's discuss this. A trimaran with a long slender hull will have a poor volumetric efficiency. Limited volume. Small payload fraction. However, the long slender hull greatly reduces the principle drag on a frigate or destroyer at speed, namely wave drag. I would agree with your position if the vessel in question was a trawler, freighter or any other type of slow application. But when your talking about trying to run a moderate sized vessel (100m or so) at 30-40 knots, you need to reduce the wave drag or all you end up with is a floating engine room. Hence the move to multi-hulls.

We meet again Goldfinger, errr I mean blacksmith ;) No I'm not haunting you. But "A trimaran with a long slender hull will have a poor volumetric efficiency" is not necessarily true. The extra width of a trimaran (2-3x of a slim hull) provides stabilty, which means you can put more systems higher up in the ship. The GF design for the LCS is a good example. It has much more volume than the Lockheed monohull. It is about 2x+ the width, and can carry much more weight up high due to the design. Also the outboards provide volume. It also can do 50+kts steady state for about 30hrs. I think it needs some tweaking, but it's a great starting point. http://www.naval-technology.com/projects/littoral/

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. As a matter of fact, I happen not to be the type of naval architect who designs toy boats....lol. Sorry, couldn't resist it. More to the point, suffice it to say that a multihull vessel would have lower resistance only at rather high froude numbers, or in other words, at high speeds for particular lengths. This would be true of the likes of racing catamarans, for instance. At lower speed length ratios that are applicable for the likes of frigates, a multihull vessel would be more resistful due to the greater wetted surface area. Therefore, although concepts have been promoted for multihull frigates and destroyers, none have actually materialized. Further, weight has absolutely everything to do with resistance and power. A lot of effort is made to control weight in modern frigates. For racers, weight is downright critical. However, gf does have a point about lower drafts of multihull platforms, assuming comparable displacements. This may be an advantage especially when pump jets are used in place of conventional propellers. Pump jets have been used successfully on the Swedish Visby class of patrol vessels and the Singaporean 56m patrol vessels. With their low drafts, these vessels are ideal for hiding or otherwise pursuing suspects into shallow waters. EW3 also has a valid point about the ability to place equipment higher up in multihull platforms due to their better stability characteristics. However IIRC, the only significant use of multihull vessels in the military is for troop transport using aluminium catamarans by the Australians. There is some interest in the US but I am not aware of any firm commitment there.

The USN is heavily committed. http://www.naval-technology.com/projects/littoral/ First one gets built next year (proably already started), the 2nd and 3rd in 2006, then #4 in 2007. Then #5-7 in 2008, then #8-13 in 2009 and beyond.

Thanks for the informative link on the LCS. It's interesting to note that the LM version is a steel monohull with aluminium superstructure. The link does not state the materials used on the GD trimaran version; I guess both the hull and the superstructure may be made of aluminium. Would be grateful for any information to confirm.

Info is thin on these ships right now. I just try to use google every so often and look for anything new.

The trimaran does not have the stability or the volumetric efficiency of a catamaran where fully 50% of the displacement is offset to either side. A trimaran hull with almost equal sized hulls would be less efficient than a cat and still not exhibit similar stability. The Navy has used catamarans for years. The navy built its first SWATH vessel in '91.

I'm not a naval architect. I understand displacement hulls very well, as I race sailboats, but anything else is something I have to learn. As you've seen we are down to two candidates for LCS. Can you give me an indsiders view which is better and why?

Monohulls have to be shorter, at the same weight, than Trimarans for stability (they roll over). Catamarans have to be shorter because all the hull is on the outside. Trimarans can have a long inner hull and short outriggers. Catamarans have it in the speed stakes, but trimarans have better seakeeping (good for a long voyage). The same 50% weight distribution per edge that was sited as an advantage makes Cats poor at surviving damage (they sink when you damage one side). The rules about wet surface only apply to suface in the water. Lower draft brings lower resistance. A hemisphere has the minimum wetted surface by volume, wanna sail in one? The thin hull profiles, stability (even after damage) and long hull for good seakeeping make Tri-hulls the best option. If you want to bump up the speed and go for surface effects you could replace the straight V of each hull with a triple liker this vVv--vVv--vVv. The outriggers would be smaller, but I ran out of typeface.

Thanks - I can see how I will be spending my morning. "Trimarans can have a long inner hull and short outriggers." That is essentially what the General Dynamics LCS design is like. The outriggers are about 2/3 the length of the inner hull. In a displacement hull the maximum speed is determined by 1.34(sqrt(length at waterline)). Is there any such formula for CATs and TRIs? The GD version of the LCS is supposed to be able to do 50+kts for 1500NM.