It would take forever to build a 24-30 trimarran from a comventional monohull that would be seaworthy and able to cruise anywhere from 7 to 15 knots since those goals are mutally exclusive. Trimarrans get their speed from being very light in weight with hulls that are very narrow compared to their length.
Trimarrans and cats take a longer time to build than monohulls since workmanship has to be very good, and careful to keep weight down, and you have three hulls to build.
Back in the 1970's I designed a 23'6" trimarran for a friend of mine that was designed so he could build it in his apartment diagonally across the living room and dining room, storing the completed parts in a hallway near the kitchen.
If I remember correctly he lofted the hulls, completed the cross beams and two outer hulls, and had the main hull framed and ready to plank including all bulkheads and fixed interior elements, in a little less than a year. Then he fell in love and his girlfriend wanted to move in if he was willing to change the livingroom/dining room furniture so he gave everything away.
The fellow was reasonably dilligent, typically working a couple evenings and roughly one weekend day a week. This was a very simple boat with a forward cabin with a single berth and an aft caccoon like cabin with another single berth. The berths were canvas laced to holes in the frame and poles that passed through the holes. There was to be a boom tent with cooking under the tent in the cockpit from a single burner stove
that stored under the cockpit sole. There was also a storage for a Kohler cooler, an anchor
, and bucket and chuck it head.
The boat had a rotating centerboard that was lowered through a long centerboard trunk that was opened at the top and which allowed the board to be trimmed fore and aft for balance. The centerboard slot served as the cockpit drain. The centerboard could be lowered to a near vertical daggerboard position during which time there was a canvas spray cover that would need to be rigged. I think that the rig
was salvaged from a 24 foot sailboard which I think was a Raven class that had rotted out. I never saw the donor, simply measuring the parts that we had.