TO18 is designed to be a simple, low cost, easy to build, lightweight boat for 2 people to get away. It has much lower performance than proper trimarans like the Farrier 720, Scarab 18 etc, however it should be faster and have more space than similar sized monohulls. Projected weight is 350kg (could well be less). I get this figure from comparison from Farrier Trailertri 18 at 450kg. Note that this design has one less outrigger and two fewer crossbeams and fewer berths, thus saving weight. Interior layout is very simple.
Construction is simplified by having flat bottom, vertical cabin sides, flat straight gunnel and decks. Board is larger than a trailertri because it will sail at lower speeds. Interior layout is very simple, lots of flat spaces. Large comfortable berths are provided. Good sitting headroom for two people facing eachother is also provided. An external leeboard would be simpler than an off-center centreboard but would reduce performance a little. Main hull waterline beam is 97cm at 600kg. The 600kg figure is based on 350kg for the hull, 150kg for 2 crew and 100kg for water, supplies, gear, anchor etc etc.
My main problem with the higher performance excellent trimarans from Farrier, Kurt Hughes, Ray Kendrick etc is that they are overly optimised for high performance, and take a long time to build. Something simple with lots of 90 degree corners would be easier to build. Yes it wont be as fast but should be faster than most monohulls, still have reasonable seaworthiness, plus provide a lot of space to chill out or enjoy the warm sun. Rig is not shown, but could be split as per TO19 LINK or could be conventional second hand bermudan rig, maybe taken from a hobie beach cat
Trailering width is only 7ft. This provides for less stress and worry than traiilering an 8ft wide boat. Boat would only weigh 350kg, thus easily trailered by a 4 cylinder car
Please note that I really like this design, but at present I have no plans to build it. Next project is a 19ft outrigger canoe to start building in March 2013, design for which can be found here LINK
Weight estimate of 350kg is a high figure, my guess is that it could be built for less, perhaps 300kg. A sliding beam configuration is also a very practial configuration, if beam is reduced a little then the amount of crossbeam bury is increased signifcantly. A sliding crossbeam mechanism would have many structural advantages.
Inspiration for this sketch comes from one of my all time favourite boats BIG ZEN, so inspiring LINK
TO18 compared to Matt Layden's Paradox
First I can see you asking why are you bothering to compare these two boats. I guess my answer is that in my eye they are very similar. Both have flat bottoms, no aft cockpit, simple easy to make construction and shoal draught. The outrigger would need a little weight in it for ideal performance, this could be achieved by storing the anchor and chain in the outrigger together with drinking water (both items that need to be carried anyway). TO18 would be a faster boat due to a longer waterline length, narrower waterline beam, lower weight, and greater sail area and not need to reef as early due to greater stability. I would like to think this design is better and here is why
Boat would be much faster than Paradox
Boat would point higher due to large area centerboard vs less efficient chine runners
Boat would be safer due to being unsinkable
Boat has much improved sitting headroom, due to footwell, 51 inches(including footwell) vs 36 inches
Boat has a large flat area to enjoy the sun and space
Boat sails flatter
Boat would weigh less (350kg vs 640kg) (Paradox has 70kg fresh water ballast and 180kg lead ballast)
Boat has more interior space
I have shown a berth forward and a berth aft, but a twin berth is possible (narrow twin berth)
I think readily accessable storage could be extended on each side, as per Paradox